Establishing a Holocene Tephrochronology for Western Samoa and Its Implication for the Re-Evaluation of Volcanic Hazards

ESTABLISHING A HOLOCENE TEPHROCHRONOLOGY FOR WESTERN SAMOA AND ITS IMPLICATION FOR THE RE-EVALUATION OF VOLCANIC HAZARDS

Aleni Fepuleai

A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy

School of Geography, Earth Science and Environment Faculty of Science, Technology and Environment The University of the South Pacific

August 2016

DECLARATION

Statement by Author I, Aleni Fepuleai, declare that this thesis is my own work and that, to the best of my knowledge, it contains no material previously published, or substantially overlapping with material submitted for the award of any other degree at any institution, except where due acknowledge is made in the next.

Signature: Date: 01/07/15

Name: Aleni Fepuleai

Student ID: s11075361

Statement by Supervisor The research in this thesis was performed under my supervision and to my knowledge is the sole work of Mr Aleni Fepuleai.

Signature Date: 01/07/15

Name: Dr Eleanor John

Designation: Principal Supervisor ABSTRACT

Samoan volcanism is tectonically controlled and is generated by tension-stress activities associated with the sharp bend in the Pacific Plate (Northern Terminus) at the Tonga Trench. The Samoan island chain dominated by a mixture of shield and post-erosional volcanism activities. The closed basin structures of volcanoes such as the Crater Lake Lanoto enable the entrapment and retention of a near-complete sedimentary record, itself recording its eruptive history. Crater Lanoto is characterised as a compound monogenetic and short-term volcano. A high proportion of primary tephra components were found in a core extracted from Crater Lake Lanoto show that Crater Lanoto erupted four times (tephra bed-1, 2, 3, and 4). The four major episodes generated via the western slide motion mechanism (WSMM), correspond with the western movement of the Pacific Plate. The WSMM also triggered simultaneous activities along the easternmost part of Upolu, as shown by the presence of contaminant tephra components throughout the core and the westward shifts in the locus of volcanism. In addition, the WSMM influenced the westward progression in volcanic age of the Samoan hotspot. This suggests that it occurred before the development of Savai’i and Upolu. The similarity in radiometric ages of shield volcanoes and post-erosional activities along the islands chain indicates that the hotspot volcanism and the WSMM process activated simultaneously. Vesicularities in tephra sand indicate explosive activities during the four major episodes. The new radiometric ages of lava and tephra indicate that the Crater Lanoto volcano was activated between 200 ka (corresponding to the Salani Formation, Pleistocene) and 3.4 ka (Lefaga Formation, Holocene). In addition, the new radiometric age viewed with respect to the distance from the current hotspot (Vailuluu) show that Crater Lanoto volcano is a part of more widerspread post-erosional volcanism. There is no long term consistency in the eruption interval among the six volcanic formations in Samoa; due to the lack of radiometric dating and the fact that stratigraphic sampling needs to be higher resolution. The high content of organic material associated with the primary tephra deposit of the tephra bed- 2 episode suggests a cone collapse event (CCE). This CCE is a part of Salani volcanism cut-off, at least 22.3 kyrs ago, associated with the Fagaloa-Falealili Fault and Manase-Gataivai Fault on Upolu and Savai’i, respectively. The similarities of the compound monogenetic features of the Crater Lanoto volcano with other cones along the main fissure enable, to re-evaluate the potential vent scenario on the main islands, for future volcanic prediction.

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ACKNOWLEDGMENT

First and foremost is to give the glory to the Almighty God for His unconditional support, protection and love, providing me with wisdom, understanding and physical strength to fulfil the requirement for the successful completion of this research. The culmination of this work has not been merely an individual effort, as it could not have been made possible without all the people and organizations that deserve a special mention and recognition for their invaluable contributions in terms of financial, scientific, logistic, motivational and moral support.

I am greatly thankful to my supervisors, Professor Stephen Gale and Professor Brent Alloway for their enormous help throughout field works, laboratory works, advice, humour and logistical support. I am also grateful to my “late comer” supervisors Dr Eleanor John and Professor Michael Petterson (SOPAC director) for their advice and perseverance in editing of my first and second draft, given time constraints. I am grateful to acknowledge Dr Holger Sommer for sharing his knowledge and his expertise in Geochemistry principle and analysis. In addition I am greatly thankful to Dr Stephen Galvin and Dr Eberhard for their time, advice and effort to goes through the second final version of this thesis. I am grateful to acknowledge the help and sharing of knowledges amongst my fellow PhD students, Robson S Tigona and Elina Bloomfield. I am also grateful to Dr Shaun Williams (Specialist-Hazard & Disaster Management GEOL, Christchurch NZ) in sharing some of his recent publications and valuable geology information. Through their invaluable knowledge and expertise, I was able to put the pieces of the thesis together and to successfully submit it before the due date. In my own native language, I can only say “Malo le fai o le faiva, ua ae ma le manuia” (great work everyone).

To the School of Geography, Earth Science and Environment and it’s academic staff, thank you all so much for giving me the opportunity and the professional support to carry out such high level research at the University of the South Pacific (USP). On a personal level, I have been able to foster friendship and improved on my networking skills with the school in the past three years. iv

Many thanks and appreciations extend to Professor Brent Alloway and the Geology Department of the Victoria University, Wellington for their technical support and assistance during my EMP analysis work. I am greatly thankful to Professor Ian Smith and the University of Auckland for special quotes on my XRF analysis and volcanology geology advice. I am grateful to acknowledge the Geoscience Nuclear Science (GNS) Taupo, NZ during my short visit and provide some volcano modelling information. I would like to acknowledge Dr Russell Howorth (former SOPAC director), Professor Michael Petterson and people of the South Pacific Commission, for offering me return airfares to Samoa (fieldwork area) and New Zealand, together with the arrangement of my visit to the GNS. I would also like to express my gratitude to Dr Anthony Koppers (College of Oceanic & Atmospheric, USA), Dr Stanley Hart, Dr Rhea Workman, and Dr Mathew Jackson (Woods Hole Oceanographic, USA) and Dr Jasper Konter (Oceanography, University of California, USA) for sharing their radiometric dating and geochemistry data of the Samoa island chain. I am greatly thankful to laboratory technicians for providing data and references for radiometric age and geochemistry: Dr Anthony Koppers (Oceanic & Atmospheric), Atun Zawadzki and Fiona Bertuch (Australia Nuclear Science and Technology Organisation), Tom Savage (School of Geosciences, University of Sydney), Tracy Howe (School of Geosciences, University of Auckland) and Roger Briggs (Waikato University). In addition, I acknowledge Mr Radesh Lal (School of Engineering, USP) for setting up the new Magnetics Susceptibility equipment. I am greatly thankful to Semi Qamese (Fiji) and Peni Hausia Havea two of my PhD colleague for helping me in my thesis setting and sharing other technical valuable information.

The fieldwork component of the thesis was long and laborious which could not have been completed without the open permit approved by the Ministry of Natural Resources and Environment (MNRE) in Samoa. I am greatly thankful to the Weather Service (colleagues and friends) for initial thoughts and advices about the fieldwork; Mulipola Ausetalia, Lameko Talia, Filomena Nelson and their team. Thank you so much MNRE for your kind gesture.

I would like to personally acknowledge the Palea Vea’s family (Saleapaga) for accommodated us in the field at the easternmost part of Upolu. I am greatly thankful to the Director of the Youth With A Mission Organisation (YWAM) in Samoa, Fepuleai Usufono Fepuleai and his team for their tremendous helps in the field and great hospitality during our two times visits. I am also grateful to J Keil for the six empty drums (size: 44 gallons) that used to construct our coring platform.

For more than three years spent away from loved ones and family overseas was not easy but the distance that separated us only strengthened and fuelled in me the desire to successfully complete my thesis. I am indebted to my wife Tamaitia and my lovely children, Christine-Ferila & Ankaramy-Toalele-Tolova, for their unconditional support, understanding and tolerance during my educational quest with USP and my university career. It is to them that I owe this thesis. A special mention also goes to my siblings, family and friends (Fiji, Samoa and New Zealand) for their continual support and encouragement making this research possible. Finally, another triumphs to the Almighty Lord Jesus Christ, for all His blessings on me, and my family during this long and rough journey in my entire educational career.

…………FAAFETAI TELE LAVA and VINAKA VAKA LEVU………..

TABLE OF CONTENTS

ABSTRACT ...... III

ACKNOWLEDGMENT ...... IV

TABLE OF CONTENTS ...... VI

LIST OF FIGURES ...... XII

LIST OF TABLES ...... XXIII

LIST OF ACRONYMS ...... XXIV

CHAPTER 1 ...... 1

INTRODUCTION ...... 1

1.1 Background ...... 1 1.2 Rationale ...... 5 1.3 Aims and Objectives ...... 6 1.4 Introduction to Methodologies ...... 10 1.5 Reasons for the Selected Site ...... 10 CHAPTER 2 ...... 13

TECTONIC SETTING AND STUDY SITE ...... 13

2.1 Overview ...... 13 PART 1: GEO-TECTONIC SETTING AND VOLCANOLOGICAL EVOLUTION ...... 13

2.2 Tectonic Setting and Process ...... 13 2.3 Samoa Volcanic Field ...... 17 2.3.1 Outline ...... 17

2.3.2 The Samoan Plume ...... 21

2.3.3 Isotopic Composition of Lavas of Samoa ...... 22

2.3.3.1 Samoan island chain ...... 23 2.3.4 Regional Geology ...... 28

2.3.4.1 Volcanic Formations ...... 28 2.3.4.2 Common mineral phases in the lava of Western Samoa ...... 34 2.3.4.3 Physiography of the main islands ...... 36 2.3.4.4 Structural geology of the region ...... 38 2.3.4.5 Age of the Volcanism ...... 41 2.3.4.6 Volcanic hazards in Western Samoa ...... 45 2.3.4.8 Human Occupation ...... 50 2.3.4.9 Previous works in the volcanology of Samoa ...... 51

PART 2: THE STUDY AREA ...... 54

2.4 Volcanic Heritage Sideline of the Study Area ...... 54 2.5 The Crater Lake Area ...... 55 2.6 Structural Geology of the Eastern upolu ...... 58 2.7 Geology of the Crater Lanoto ...... 62 2.7.1 Lava flow ...... 67

2.7.2 Tephra depositS within the Crater Lake Lanoto basin ...... 70 CHAPTER 3 ...... 72

METHODS ...... 72

3.1 Overview ...... 72 3.2 Field work methods ...... 72 3.2.1 Coring Gear ...... 73

3.2.3 Coring Procedure ...... 73

3.2.3 Total station device ...... 75 3.3 Laboratory Methods...... 76 3.3.1 Separation of Sediment from the Coring barrel Shell ...... 76

3.3.2 Magnetic susceptibility techniques ...... 78

3.3.2.1 First version of the magnetic susceptibility ...... 79 3.3.2.2 The second version of the magnetic susceptibility ...... 80 3.3.3 Radiocarbon dating ...... 83

3.3.4 LEAD-210 (210Pb) ...... 87

3.3.5 Argon-argon dating ...... 91

3.3.6 X-ray Fluorescence technique ...... 94

3.3.7 Electron probe microanalysis (EPMA) ...... 96

3.3.8 Inductively coupled plasma MASS spectrometry (ICPMS) for trace element digestion procedure ...... 100 CHAPTER 4 ...... 103

RESULTS AND DISCUSSION ...... 103

4.1 Results ...... 103 4.2 The Coring Site Procedure ...... 103 4.3 Magnetic Susceptibility (MS) of lake sediments ...... 105 4.3.1 Selection of The Master Core Using First Version ...... 105

4.3.1.1 Dry bulk density of the master core D3 ...... 106 4.3.2 Magnetic Susceptibility (MS) – Master Core “D3” ...... 109

4.3.1.2 Volume-specific magnetic susceptibility (VSMS) versus depth...... 110 4.3.1.3 Mass-specific magnetic susceptibility (MSMS) versus depth...... 111 4.3.1.4 Frequency-dependent magnetic susceptibility (FDMS) versus depth ...... 112

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4.3.1.5 Mass-specific magnetic susceptibility (MSMS) versus frequency-dependent magnetic susceptibility (FDMS) ...... 116 4.3.1.6 Summary of critical points from the magnetic susceptibility sediment ...... 118 4.4 Stratigraphic Column of the Master Core D3 ...... 119 4.4.1 The Stratigraphic column of the Crater Lake Lanoto ...... 119

4.4.2 Morphology of Pyroclasts of the tephra deposit ...... 128

4.4.3 Optical Microscopy Minerals – Crater Lanoto ...... 130

4.4.2.1 Olivine ...... 131 4.4.2.2 Pyroxene ...... 132 4.4.2.3 Plagioclase ...... 132 4.4.2.4 Groundmass ...... 133 4.4.2.5 Summary of critical points from the stratigraphic column ...... 133 4.5 Geochemistry ...... 134 4.5.1 X-ray Fluorescence (XRF) of the inner rim lava ...... 134

4.5.1.1 Results: Major and trace element of the Crater Lanoto lava ...... 135 4.5.1.2 Summary of critical points from major and trace elements ...... 141 4.5.2 EPMA and XRF Analysis – Tephra Component ...... 141

4.5.2.1 EPMA: Results for tephra component ...... 141 4.5.2.2 XRF: Results for tephra sand ...... 144 4.5.2.3 Summary of critical points from EPMA and XRF ...... 144 4.5.3 Inductively coupled plasma mass spectrometry (ICPMS) for trace element analysis .... 144

4.5.3.1 Results ...... 144 4.5.3.2 Summary of critical points from ICPMS technique ...... 153 4.6 Dating of Lake Sediment ...... 155 4.6.1 Argon-argon Dating ...... 155

4.6.1.1 Results ...... 155 4.6.1.2 Summary of the critical points from the Argon-Argon dating ...... 162 4.6.2 Radiocarbon Dating ...... 162

4.6.2.1 Result ...... 163 4.6.2.2 Summary of critical points from Radiocarbon dating ...... 164 4.6.3 Lead-210 Dating ...... 165

4.6.3.1 Results ...... 165 4.6.3.2 Summary of critical points from Lead-210 dating...... 167 4.7 Discussion ...... 168 4.7.1 Part 1: Interpretation of Results ...... 168

4.7.1.1 Interpretation of magnetic susceptibility ...... 169 4.7.1.2 Interpretation of the stratigraphic column ...... 174 4.7.1.3 Geochemical Interpretation ...... 178 viii

4.7.1.4 Interpretation of tephra component from EPMA and XRF procedure ...... 185 4.7.1.5 Interpretation of ICPMS data and AIR ...... 186 4.7.1.6 Interpretation of the Argon-Argon dating ...... 190 4.7.1.7 Interpretation of the Radiocarbon age ...... 193 4.7.1.8 Interpretation of Lead-210 activity ...... 195 4.7.2 Part 2: The age of the Crater Lanoto Volcanic Events ...... 197

4.7.2.1 MS curve – Lake Lanoto versus the marine sediment oxygen isotope (MSOI) ...... 197 4.7.2.2 Chronology construction of the Crater Lake Lanoto ...... 201 4.7.2.3 Crater Lanoto radiometric age relative to the hotspot and isotopic signature ...... 212 4.7.2.4 Summary of critical points from the age of Crater Lanoto events ...... 218 4.7.3 Part 3: Volcanic Hazards of Crater Lanoto ...... 219

4.7.3.1 Evidence of human occupation and indigineous knowledge ...... 220 4.7.3.2 Intervals of Lanoto volcano in contrast with other Samoan eruptions ...... 223 4.7.3.3 Eruption style of the Crater Lanoto volcano ...... 228 4.7.3.4 Holocene bush fire hazards on the easternmost part of Upolu ...... 235 4.7.3.5 Summary of critical points from volcanic hazards of the Crater Lanoto ...... 236 4.7.4 Part 4: Monogenetic Process of the Lanoto Volcano ...... 237

4.7.4.1 What is the monogenetic and polygenetic volcano? ...... 237 4.7.4.2 Distribution of the monogenetic volcanoes in Samoa ...... 240 4.7.4.3 Tectonic movement along the Crater Lanoto volcanic line ...... 242 4.7.4.4 Feeder dyke model of the Crater Lanoto Volcano ...... 249 4.7.4.5 The similarities of Lanoto Volcano with other monogenetic eruptions ...... 261 4.7.5 Geological history – Lanoto Volcano ...... 265 CHAPTER 5 ...... 271

CONCLUSION AND RECOMMENDATIONS ...... 271 5.1 Overview ...... 271 5.2 Deposition Basin Components ...... 271 5.3 Geochemistry – lava and tephra Component ...... 272 5.4 Reliable age of the Crater Lanoto Volcano ...... 273 5.5 Monogenetic process – Lanoto Volcano ...... 274 5.6 Eruptive Scenario – Lanoto Volcano ...... 275 5.7 Volcanism Age Progression ...... 279 5.8 Additional Features – geological Map ...... 279 5.9 Summary of the Research Findings ...... 280 5.10 Recommendations for future work ...... 282 REFERENCES ...... 286

APPENDICES ...... 306

Appendix 1: First Veersion of the MS-Technique ...... 306 Appendix 2: Master Core D3 Subsmapled – Petril Dishes ...... 317

Appendix 3: Second Version – MS Technique ...... 325 Appendix 4: Core Description ...... 330 Appendix 5: Argon-argon Dating ...... 364

x LIST OF FIGURES

FIGURE 1.1 Modified from Hart et al. (2004) (a) Shows the eastern part of the Samoan island chain, also indicating the two political divisions with their main islands, Western Samoa (Savai’i and Upolu) and American Samoa (Tutuila and Manua). (b) Map showing the western part of the chain, with seamounts to the west of Savai’i aligned parallel to the trend of the Vitiaz Lineament. Both (a) and (b) show water depth around the Samoan group of islands...... 2

FIGURE 1. 2 Flow diagram of the fieldwork and laboratory methodology overview used in the project...... 10

FIGURE 1.3 Crater Lake Lanoto location together with other crater lakes on Upolu and Savai’i. All these lakes are a part of the Samoa Nation Park and are fully under the management of the Ministry of Natural Resource and Environment...... 12

FIGURE 2.1 Google Earth image showing the location of the Samoan group of islands, with respect to the Kermadec-Tonga Trench. Number “1” indicates the approximate position of the Kermadec-Tonga Trench, during earlier volcano activity on Savai’i about 10 million years ago (Jackson et al., 2010), number “2” represents the footprint structure of the Kermadec-Tonga Trench as shifts east due to roll-back processes at 5-6 million years (Hart et al., 2004; Koppers et al., 2008), and number “3” represents the present position of the Kermadec-Tonga Trench...... 14

FIGURE 2. 2 Flow diagram of the Samoan Volcanic Field, where it originates as shield volcanism and then shifts to post-erosional volcanism due to the influence of tectonic processes. The post- erosional activities may be split into short and long-term eruption...... 20

FIGURE 2.3 Plot showing isotopic relationship of 206Pb/204Pb versus 87Sr/86Sr in lavas of the Samoa Volcanic Field with respect to other hotspot. Two trends (A & B) represent shield and post-erosional volcanism respectively. Data extracted form GEOROCK, Hart et al. (2004); Jackson et al. (2007); Workman et al., (2004; 2009). (Modified from Workman et al., 2004)...... 25

FIGURE 2.4 Plot describing the isotopic signature of lava of Samoan island chain (a) 206Pb/204Pb versus distance from Vailulu’u hotspot (b) 87Sr/86Sr versus the distance from Vailulu’u hotspot. Data extracted from Hart et al (2004), Workman et al (2004), Sims & Hart (2006) and Jackson et al (2007)...... 26

FIGURE 2.5 Show isotopic signature of lava of Samoan island chain (a) 143Nd/144Nd versus distance from Vailulu’u hotspot (b) 3He/4He versus the distance from Vailulu’u hotspot. Data extracted from Hart et al (2004), Workman et al (2004), Sims & Hart (2006) and Jackson et al (2007)...... 27

FIGURE 2.6 Age relationship between sea level and volcanic formations of Samoa. The black dashed-line plots from previous data whilst the red dashed line is not to scale. The x-axis is not to scale. This sketch modified from Kear and Wood (1959)...... 30

FIGURE 2.7 Geological map of Savaii Island showing the six formations of Western Samoa. Also shown is a series of faults which dissect the island. The blue solid line represents an inferred fissure system located along the crest of the island in a form of chain over a broad convex plain or fan-like structure (modified from Kear and Wood, 1959)...... 32

FIGURE 2.8 Geological map of Upolu Island showing the six formations of Western Samoa. Also shown is a series of faults that deeply dissect the island. The blue solid line represents an inferred fissure system located along the centre ridge of the island (modified from Kear and Wood, (1959))...... 33

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FIGURE 2.9 Cross sections and geology of Savai’i Island (a) Section A-A” shows a section from Asau harbour on the western end of Savai’i to Apolima Island in the east. (b) Section B-B” shows a section from the village of Salailua on the southwest of Savai’i to Saleaula village in the northeast (Modified from Kear and Wood, (1959)). The colour of rock unit corresponds with the geological map of Savaii (Figure 2.8)...... 37

FIGURE 2.10 Cross sections and geology of Upolu Island (a) Section C-C” shows a section from Apolima Island on the west of Upolu Island to Nu’utele Island and Namu’a Island in the east. (b) Section D-D” shows a section from Magia on the northwest of Upolu to Salamumu village in the southwest of Upolu. Section E-E” shows a section from the village of Solosolo on northeast Upolu to Lepa village in the southeast (Modified from Kear and Wood, 1959). Each unit colour coincides with the geological map of Upolu (Figure 2.8)...... 38

FIGURE 2.11 Map showing radiometric dates previously retrieved from subaerial deposits on Upolu and Savai’i. Most dated lavas on the main islands were from the Fagaloa Formation on the northeast Upolu and north part of Savai’i. Holocene dates were mostly from the central part of Savai’i...... 42

FIGURE 2.12 Bathymetric map of the Crater Lanoto maar. Contour interval is 1 metre...... 56

FIGURE 2.13 View of the inner part of the Crater Lake Lanoto (a) Looking from the top of the crater to the lake area toward the western part. Indicates the thick forest surround the lake, along the crater wall. Low lying area to the west of the lake is the broad swamp, estimated to be covered the three quarter of the crater. (b) Shows a section of the broad swamp area to the eastern part, with batches of deep pools. (c) Indicates two water pumps installed on the jetty, to distribute the water to the nearby village to the south east. (d) Indicates a section of the deepest part of the lake, where in the background is the flattop volcano of Lano-o-lepa...... 57

FIGURE 2.14 Geological map of the easternmost part of Upolu. The Crater Lake Lanoto together with Crater Lake Olomaga and Crater Lake Lano’omoa lie along the Upolu Major Fissure System, which bounded by Tiavea Fault to the north and Sinoi Fault to the south. It also shows that, the easternmost part of the island is dominated by Salani Formation, and only small portion of the Fagaloa Formation outcropped to the north. The Sinoi Fault dissected the Lepa Fault between Aufaga and Saleapaga village. The sizes of volcanic craters are not to scale (Modified from the geological map of Kear and Wood, 1959)...... 58

FIGURE 2.15 Cartoon showing the four stages model (crater formation, scoria cone growth, lava outpouring and crater floor subsidence to form pit-crater) of the re-eruption scenario of Western Samoa volcanoes...... 61

FIGURE 2.16 Cross section along the Crater Lake Lanoto from Crater Lake Lano’omoa on the southeast toward Crater Seuga on the northwest. This figure also shows the east and the west limb of the Sinoi Fault, presumably downthrows deep underneath the Crater Lanoto volcano. The boundaries between volcanic units are not to scale...... 63

FIGURE 2.17 Aerial photograph shows the ukulele-like shape of the Crater Lake Lanoto, to the east of the Crater Lano-o-lepa volcano, or the south of Maimoaga vents. Pyroclastic deposit occurs on the western and the eastern parts of Lanoto and arrows show the direction of flow during eruption or a collapse. Several strips of unconsolidated materials produced by mini- avalanche events overlie the pyroclastic deposit. A tongue of lava flow extends parallel to the Sinoi valley, while the other stretch south to the east of Crater Fili. Large slump of more than 300 m in length occurred at the southern part, partly covered some portion of lava flow. The western limb of Sinoi Fault extends north-south direction, to the west of Lano-o-lepa, where the east limb stretches to the south of Lanoto crater. Stream channels radial from Crater Lano-o-lepa and

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Crater Lanoto to the south, where link to the east of the Sinoi valley, in other words run parallel with the Sinoi Fault. The original aerial photo is a property of the National Mapping Section, of the Ministry of Natural Resources and Environment of the 2011 version...... 64

FIGURE 2.18 Photograph showing the top of the south eastern part of the Crater Lanoto wall, dominated by thin sheet pahoehoe lavas intercalated with very thin scoria flow which are reddish brown in colour. The outcrop is about 8-10 m high...... 68

FIGURE 2.19 Highly weathered thin-sheeted lava flow of the outer rim wall on the south eastern part of the crater. The onion skin like weathering structure of about 1.5 m diameter at the base of the outcrop. The outcrop is about 7.12 m high...... 69

FIGURE 3.1 The coring gear; 50 mm hammer (11 kg), 50 mm PVC semi-handle clamps (8 kg), 90 mm hammer (18 kg) and 90 mm PVC semi-handle clamps (13 kg)...... 73

FIGURE 3.2 Coring operation carried out at the deepest parts of the lake. The glued-barrel insert penetrated perpendicular to the lake floor before hammering it down to a certain depth...... 74

FIGURE 3.3 Coring procedure used to extract core D3 (a) The insertion of the longest core (master core) at site D3 at the central part of the lake. (b) The 90 mm coring barrel penetrating, almost 5 m into the lake sediment. (c) The tripod and block-and-tackle used to extract core D3. 75

FIGURE 3.4 The two halves of the 90 mm diameter core barrel (master core D3) after being cut open vertically...... 77

FIGURE 3.5 First version of the magnetic susceptibility technique was set-up, where each core was scanning through the core scanning board device, which connects to the MS meter...... 80

FIGURE 3.6 The second version of the magnetic susceptibility method set up where Dual Frequency sensor (MS2B) connects to the MS meter...... 82

FIGURE 3.7 Plot of time in years versus the fraction of 14C atom present...... 84

FIGURE 3.8 Schematic diagram shows the major pathways of 210Pb components, into the Crater Lake Lanoto sediment, through either directly wash of the isotope component of 226 Ra into the lake, or the rapid decay of diffusion 222Rn gas. The unsupported components perhaps, fall either directly from the atmosphere into the lake, or settle in sediment around the crater rim, before in- wash activities occur, where fusion them with top lake sediments (Modified from Oldfield and Appleby, 1984)...... 88

FIGURE 3.9 Black 1050 Degree Vulcan muffle furnace, for mineral ignition and the cooling station. (b) Black Eagon 2 Electronic Furnace for fusing the samples...... 96

FIGURE 3.10 Schematic sketch of the Electron Probe Microanalysis components produce as the electron beam bombard the specimen...... 97

FIGURE 3.11 The JEOL 733 EPMA set up of Victoria University. The equipment connects to two computers, where record activities and direct the probe to the most detail part volcanic shard component...... 98

FIGURE 3.12 Three polished mounted multiple samples of 1 cm thick. Glass shards were all sealed with carbon coating glass. Each six holes glass shard contains small portion of rim tephra deposit, top, middle and lower part of the four tephra beds...... 99

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FIGURE 3.13 (a) Set up fume cardboard for the dissolving of samples in test tubes on the dri- block before heating up. (b) Samples transfer into measuring flask and dilute with ultrapure water before settle for several hours within the fume cupboard...... 101

FIGURE 3.14 Schematic sketch of the ICPMS set up procedure (Modified from Wolf, 2005). ... 102

FIGURE 4.1 Aerial photograph showing the grid of cores and the catchment reference samples taken from the depositional basin. Rock samples (green dots) were taken from several lava flow boulders at the inner part of the crater rim to the northern part. The boulder features dominate the inner lava is a part of the contract and extension of the lava flow as it cooled down. Soil samples (pink dot) were taken from around the crater rim...... 104

FIGURE 4.2 Plots of VPMS versus depth from the three cores aligned core sets alignment (B, C & D) using downcore measurements of the first version of the MS. These cores were considered for the selection for the master core; B2, B3, B4, C2, C3, C4, D2 and D3 of the Crater Lake Lanoto. Core D3 was chosen as the master core because of its completeness and the fact that it shows the highest resolution...... 106

FIGURE 4.3 Graphs showing the dry bulk density and saturation moisture content properties downcore in core D3; (a) Downcore variations in dry bulk density of the Crater Lake Lanoto master core D3. (b) Downcore variations in the saturation moisture content of the master core D3...... 107

FIGURE 4.4 The above figure showing the dry bulk density of the master core D3 sediments plotted against saturation moisture content. The gap (blue arrow) in the sediment lineation, represents a progressively changed in both dry bulk density, and saturation moisture content with depth...... 108

FIGURE 4.5 Plot showing VSMS versus depth for core D3. This plot supports that idea that core D3 has the longest, most complete and highest resolution records of all 21 cores extracted from the Crater Lanoto. Low MS (troughs) values indicate a diamagnetic behaviour of the sediments with high organic content and low mineral content. High MS values (peaks) show high concentrations of magnetite mineral. The blue and green circles show four major eruption sources of the Crater Lake Lanoto represented by tephra bed-1, tephra bed-2, tephra bed-3 and tephra bed-4. Notice that the size of the spheres does not correspond to the volume of the eruption materials...... 111

FIGURE 4.6 Mass-specific magnetic susceptibility versus depth from the second version procedure. These dry samples of the core D3 show the similar features, display from the first version plot shown by Figure 4.4...... 112

FIGURE 4.7 Frequency dependent magnetic susceptibility versus core D3 depth, characterised by three diagonal zones. Dashed lines indicate the range of values suitable for classification as lake sediments. Blue arrows indicate the position of the four tephra beds downcore (tephra bed-1, tephra bed-2, tephra bed-3 and tephra bed-4)...... 114

FIGURE 4.8 The FDMS versus depth plot shows unusual high and low values of the paramagnetic and diamagnetic respectively. A majority of the 219 samples scattered mostly at the range between 1 and 10 FDMS percentage...... 115

FIGURE 4.9 The logarithim scale plot between the MSMS versus the FDMS of the lake sediment, inner volcanic rim soils, inner rim and outer rim lava. These four components plotted at three significant regions; diamagnetic, paramagnetic and ferromagnetic. The arrow shows the direction xv of the shift in the MS strength from low to very high value. Sediment surrounded by red circles are label as isolated group...... 117

FIGURE 4.10 The 12 units of the Crater Lake Lanoto stratigraphic column which divided based on physical characteristics such as colour, common mineral phenocryst, percentage of organic content and the abundance of tephra sand. Four samples (tephra bed-1, base of tephra bed-3, top of tephra bed-3 and base of tephra bed-4) were radiocarbon dated. An image (not to scale) shows physical characteristics of the top part of the core...... 120

FIGURE 4.11 The image shows primary tephra sand deposit of the tephra bed-1 with their size range from 0.5 mm to 10 mm. The tephra sands are highly vesicular, scoriaceous smooth tubulous in form. Iddingsite mineral dominates olive greenish yellow tephra sand. Those with greyish green colour sand associate with reddish brown hematite. Scale bar (yellow) is 2 mm. 121

FIGURE 4.12 Photograph showing broken fragment of tephra bed-2 with fine to medium grained (1-7 mm) in size. Tephra sands are commonly dark greenish to brownish yellow in colour, with vesicular scoriaceous and irregular to tabular form. Few tephra sand comprise of olive brownish yellow colour of iddingsite mineral. Yellow brownish red hematite is commonly occurred along cavities and vesicles of tephra sand. Scale bar (yellow) is 2 mm...... 124

FIGURE 4.13 The image shows primary tephra sand deposit of the tephra bed-3 with their size range from 0.5 mm to 20 mm. Tephra sand are highly vesicular, scoriaceous, smooth and tubulous in form with yellow greyish green colour. Wide head with narrow tail feature of “Pele’s tear” is commonly occurred in the Lano-9 Unit tephra sand. Scale bar (yellow) is 4 mm...... 126

FIGURE 4.14 Image showing tephra sand deposits of the primary tephra bed-4. Tephra bed-4 is mostly fine to coarse grained (0.5-15 mm) in size. Greenish yellow tephra sand comprises of iddingsite. Reddish brown hematite starts fill in cavities and vesicles of the tephra sand. Like those of Lano-9 Unit tephra sands, Lano-11 Unit airfall are highly vesicular, scoriaceous, smooth and tubulous in form. Scale bar (yellow) is 4 mm...... 127

FIGURE 4.15 Dark green to grey or brownish red lapilli tuff deposits with their size range from 0.5 to 1 mm. Vesicles geometry ranges from spherical to elliptical in shape. Tubulous, scoriaceous smooth pyroclasts are commonly range from 0.1 to 0.8 cm in length. Pyroclast fragments shows a mixed of “thin-wall” and “thick-wall” feature. Scale bar (red) is 5 mm...... 128

FIGURE 4.16 Scoriaceous, tubulous, dark green to grey lake deposit of tephra bed-4. They are highly vesicular tephra of soft and smooth surface with their size ranges from 0.6 to 1.2 mm. Vesicles are commonly filled with very fine sediment, with poorly spherical, well ellipse to poor ellipse in geometry. Lack of interconnection mechanism amongst bubble could be the resulted of “thick-wall” feature. Scale bar (red) is 6 mm...... 129

FIGURE 4.17 Olivine phenocryst in cross and plane extinction (a) Shows oblique extinction of embayed olivine phenocryst, sits in a groundmass of plagioclase titanaugite and micro-magnetite of rock (LLRH1), under cross polarised light. (b) Indicates coarse and fine cracks on the olivine phenocryst. Scale bar is 0.125 mm...... 131

FIGURE 4.18 Augite phenocryst shows cross and plane polarised view (a) Shows simple twinning and zoning in the augite phenocryst of the rock (LLRH2). (b) View under plane polarise light show, irregulars cracks dominate the augite phenocryst. Scale bar is 0.125 mm...... 132

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FIGURE 4.19 Groundmass under plane polarised light (a) Shows rare medium sizes of opaque minerals in the groundmass of rock (LLRH2). (b) Very fine opaque groundmass surround the olivine phenocryst. Scale bar is 0.125 mm...... 133

FIGURE 4.20 Total Alkali Silica plot shows that lava of the Crater Lanoto scatter heavily in the central part of the Samoan Volcanic Field (SVF). The SVF (yellow) boundary was determined from previous work of; Fepuleai (1997), Cibik (1998), Workman et al (2004), Jackson et al (2007) and Konter & Jackson (2012) (Modified from Le Bas et al., 1986 and Konter & Jackson, 2012)...... 137

FIGURE 4.21 Major element variation diagram of Crater Lanoto lava (a) SiO2 versus MgO shows lava scattered into three distinct groups along a wide steep negative correlation (b) SiO2 versus Al2O3 also displays that lava samples also form into three groups along wide steep positive correlation...... 138

FIGURE 4.22 Trace element plot of lava flows from the Crater Lanoto (a) Yttrium versus Zirconium shows lavas scatter into three groups along narrow steep positively correlation. (b) Zirconium versus Nickel indicates a narrow shallow negative correlation where lava also scattered into three distinct groups...... 139

FIGURE 4.23 Major versus trace elements plot of Crater Lanoto lava of (a) SiO2 versus Cr shows the three distinct groups form along a wide steep negative correlation. (b) MgO versus Ba generates the three distinct groups scatter along a steep narrow negative correlation...... 140

FIGURE 4.24 Major versus trace elements plot of (a) MgO versus Cr relationship shows lavas form three distinct groups along a narrow steep positive correlation. (b) MgO versus Ni plot also generates three distinct groups along a narrow positive correlation...... 140

FIGURE 4.25 (a) Microlitic texture of the volcanic glass shard of the tephra bed-1, under (x 370) dominates by desiccation cracks and weathering halo’s features. (b) A closer view of the tephra sand grain, under (x 800) shows the microlitic volcanic glass shard, with desiccation cracks and weathering halo’s features, of the tephra bed-1 deposit...... 142

FIGURE 4.26 Basaltic tephra glass shards from Mount Gambier, southeast, South Australia use to compare with those of the Crater Lanoto (a) Volcanic glass show prismatic microlites mainly titanaugite. (b) Volcanic glass showing its curves and microlites of prismatic titanaugite. (Images from Lowe, 2011)...... 143

FIGURE 4.27 ICPMS trace element plots (a) Ca versus Mg shows a positive correlation. (b) Sr versus Ni also shows a positive correlation...... 149

FIGURE 4.28 ICPS trace element plots (a) P versus Copper Cu shows a broad positive correlation. (b) Cr versus V shows wide positive correlations...... 150

FIGURE 4.29 ICPMS trace element plot (a) K versus Co shows a broad positive correlation. (b) Ca versus Mn shows a wide positive correlation...... 151

FIGURE 4.30 ICPS trace element plot (a) Ni versus Al shows a broad positive correlation. (b) Al versus Fe shows a wide positive correlation...... 152

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FIGURE 4.31 Acid-insoluble residue of silicate primary and second mineral shows dominated downcore. Oval represents distinct tephra group...... 153

FIGURE 4.32 Cumulative of Argon released versus calculated age of the groundmass high- resolution incremental heating procedure yields the weighted plateau age spectra of 143.9 Ka...... 156

FIGURE 4.33 Cumulative of Argon released versus K-Ca ratio of high-resolution incremental heating steps procedure of groundmass...... 158

FIGURE 4.34 High resolution of the normal isochron for the groundmass, where values seems to spread widely along the atmospheric reference line (dark grey) and the normal isochron line (pink) of the Crater Lake Lanoto. Reference lines have atmospheric intercept of 299.8 ± 4.1 of plateau age of 39Ar/40Ar (x-axis) and 36Ar/40Ar (y-axis). The reference line construct very tightly with the calculated normal isochron line. The heating steps are represented by green squares. Total fusion point indicates by the red circle and blue squares, represent the groundmass components...... 159

FIGURE 4.35 Inverse isochron, where values are mostly scatter toward lowering value of the 39Ar/40Ar at 45%. Reference lines (dark grey) has an atmospheric intercept value of 300 ± 4.1 on the plateau age between 39Ar/40Ar (x-axis) and 36Ar/40Ar (y-axis). The reference line constructs very tightly with the calculated isochron line (pink). The heating steps represent by green square. Total fusion indicates, by red the circle (not included in the calculations), blue squares represent the groundmass components...... 160

FIGURE 4.36 (a) Argon released versus calculated age of the plagioclase phenocryst. (b) Argon released versus K/Ca ratio of the plagioclase phenocryst...... 161

FIGURE 4.37 (a) Normal isochron plot of the plagioclase phenocryst components (blue), where very few scatter close to the total fusion point (red), while the majority disperse further away. (b) Show a positive trench of the inverse isochron of the plagioclase phenocrysts...... 162

FIGURE 4.38 Plot of new radiocarbon age versus depth of core D3. Sample LLD3/49 and LLD3/219 from greater depth seem younger than of those of LLD3/34 and LLD3/73 respectively...... 164

FIGURE 4.39 The total activity of 210Pb versus depth of the core D3...... 166

FIGURE 4.40 Supported activity, unsupported activity and CIC ages versus depth of the core D3...... 167

FIGURE 4.41 Secondary minerals (“a” to “d” about1-8 mm in size) occur in the catchment soil and tephra bed-4 (a) Pyroclastic deposit associated with thin soil comprise of hematite mineral and magnetite. In rim deposit hematite is commonly occurred in two forms yellowish red, reddish brown. (b) Thin pyroclastic deposit associated with soil contains halloysite mineral but not as common as hematite. (c) Pyroclastic deposit associated with thin soil comprise of maghemite. Maghemite also occurs in two form greyish red and yellow brownish red. (d) Olivine mineral is commonly altered to iddingsite. Tephra components from tephra bed-4 show yellowish olive of iddingsite minerals...... 172

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FIGURE 4.42 Flow diagram models of the Crater Lake Lanoto sediment of how the weak MS of the primary minerals transform into strong MS of the late secondary mineral. The diagram construct based on several previous studies; Morrison & Asghar (1992), Naidu et al. (1997) Fepuleai (1997) and Cibik (1999). Yellow arrow indicates intense of weathering progression coincide with the MS strength (weak MS to strong MS) of sediment. (The diagram modified from Dam et al., 2005; 2008)...... 173

FIGURE 4.43 Major plots of the Crater Lanoto with lava from the SVF (a) SiO2 versus MgO shows negative correlation. (b) SiO2 versus Al2O3 shows positive correlation...... 182

FIGURE 4.44 Major and trace element plots of the Crater Lanoto with lava from the WSVF (a) Magnesium Number versus SiO2 shows a negative correlation. (b) Y versus Zr shows a wide positive correlation...... 183

FIGURE 4.45 Major and trace element plot of lava from the western and eastern part of the island chain (a) Magnesium number versus Na2O plot shows a wide linear correlation. Lava split into trend A and B. (b) Magnesium number versus Y plot also shows broad negative correlation. Trend A and B dominate with lava from the western and eastern part of the chain...... 184

FIGURE 4.46 MSWD of inverse isochron of the groundmass versus groundmass age. The Crater Lanoto plots together with subaerial and submarine other volcanoes along the Samoan island chain...... 192

FIGURE 4.47 Radiocarbon age of the Crater Lanoto plots with radiocarbon ages of other Holocene formation from Upolu and Savai’i. Horizontal scale is not to scale...... 195 FIGURE 4.48 (a) Magnetic susceptibility oscillation records, of the Crater Lake Lanoto master core D3. Yellow arrows (MS curve) indicate radiocarbon dated samples position with respect to depth. (b) Sea level fluctuate based on the marine sediment oxygen isotope data (Bintanja et al, 2005). Green arrows (MSOI curve) represent reliable radiometric age of the Crater Lanoto. Dashed red arrow represents the new age position of the tephra bed-3 (top) and tephra bed-1. Numbers on the MSOI represent stage...... 199

FIGURE 4.49 Chronology of the Crater Lanoto volcano. This chronology construct based on the new radiometric age and geological formations from Kear and Wood (1959)...... 202

FIGURE 4.50 The sea floor structure and heavy debris surrounding Western Samoa (Modified from Hill & Tiffin, 1989). Slump block to the northeast between Upolu and Savai’i is the part of the volcanic shoal exposes between Apolima and Savai’i...... 210

FIGURE 4.51 The age-distance relationship of shield and post-erosional volcanism, of the subaerial and submarine lava of Samoa volcanic province (Modified from Koppers et al, 2011). All ages plotted above, were from previous studies Mcdougall (1985), Keating & Tarling (1985), Natland & Turner (1985), Johnson et al (1986), Goodwin and Grossman (2003), Workman et al (2003), Natland (2003), Jackson et al (2009), Hart et al (2004), Gudge & Hawkins (2004), Koppers et al (2008), Nemeth & Cronin (2009), McDougall (2010) and Koppers et al (2011). ... 213

FIGURE 4.52 Google Earth image shows, an approximately subdivisions of the Samoan island chain base on the two significant processes, sequential and synchronous, where influence the volcano age progression. Both west and the east end of the chain, suggested to be dominated by sequential process, while those in the middle label as generate from the mixed of the two. As the Pacific Plate move toward west, it is expected to correspond with the volcano age progression, of the Samoan island chain (Google Earth Map)...... 215

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FIGURE 4.53 Previous dated lava suites of the six formations included those of the Crater Lanoto volcano. The volcanic intervals calculated from McDougall (1985), Keating & Tarling (1985), Natland & Turner (1985), Johnson et al (1986), Goodwin and Grossman (2003), Workman et al (2003), Natland (2003), Jackson et al (2009), Hart et al (2004), Gudge & Hawkins (2004), Koppers et al (2008), Nemeth & Cronin (2009), McDougall (2010) and Koppers et al (2011). ... 225

FIGURE 4.54 Google Earth image (2013 version) indicating the volcanic ash dispersed (red and yellow circle), during the Crater Lanoto eruption episodes, based on the volcanic hazard evaluation of Western Samoa (Cronin et al. 2006). Yellow circle represents low explosive episode while violent activities indicates by red circle. Wide yellow arrow (not to scale) shows, lava flow heading south, along the Sinoi valley toward Saleapaga village...... 234

FIGURE 4.55 Flow diagram simplifies the monogenetic and polygenetic eruption activities in Upolu and Savai’i...... 239

FIGURE 4.56 Monogenetic and polygenetic eruption centres on Upolu Island, based on the aerial photograph interpretation and the geological map by Kear & Wood (1959). Green (with star sign) and pink circles represent the long term monogenetic centre. Blue, yellow, green and pink stars imply short term monogenetic cone. The size of the stars and circles are not to scale...... 241

FIGURE 4.57 Monogenetic eruption centres on Savai’i Island, based on the aerial photograph interpretation and the geological map by Kear & Wood 1959. Green (with star sign) and pink circles represent the long term monogenetic centre. Blue, yellow, green and pink stars imply short term monogenetic cone. The size of the stars and circles are not to scale...... 242

FIGURE 4.58 Google Earth image shows the western-slide motion mechanism (yellow arrow) trail, expose along the Crater Lake Lanoto, Crater Olomauga, Crater Lanotai, Crater Lano’omoa, Crater Lano-o-lepa and Crater Lake Olomaga. Crater Fili, Crater Tialata and Crater Mauga-o- savaii are single cones, which all part of the monogenetic-polygenetic process...... 243

FIGURE 4.59 Early monogenetic phase of the easternmost part of Upolu. The single injection ignites single cone eruption. Arrested dyke network develops during the early monogenetic phase. Storage magma batch of low and large volume monogenetic correspond with the side of the eruptive cone. The model is not to scale...... 247

FIGURE 4.60 Late monogenetic phase of the easternmost part of Upolu associates with an increase in tectonic activities. Feeder and arrested dyke network is increased at this late stage of monogenetic phase. Dashed straight lines refer to inactive feeder dyke and dashed oval represents inactive magma batch. The model is not to scale...... 249

FIGURE 4.61 A plan view of half-elliptical shaped with half length (2b) and half width (2w) of the geometry propagation upward of a dyke, from deep down the lithosphere, under buoyancy fluid regime of density (pm) with viscosity (n), advance through host rock of elastic modulus (m) (from Lister, 1990; Lister and Kerr, 1991, figure 1 & figure 11 respectively)...... 252

FIGURE 4.62 Laterally spread model of the magma at the level of neutral buoyancy (LNB), where the magma descend if the density (pm) is greater than the density p) of overlying rock (but accent if less than those of the underlying (Modified from Lister, 1990, figure 1; Lister and Kerr, 1991, figure 11)...... 253

FIGURE 4.63 The distance above the source versus the dyke dimension (width and length), speed, flow-rates and time (days). Fagaloa Formation dykes (red, green, dark blue, light blue and purple) plot with those of Crater Lanoto in oval (Modified from Blake et al, 2006)...... 256

FIGURE 4.64 The total dyke widths versus flow rate of the Crater Lanoto and Fagaloa Formation dykes (blue and green). (Modified from Blake et al, 2006)...... 258

FIGURE 4.65 The total dyke width versus time plot of the feeder dyke of Crater Lanoto. The plot based on the three depths, 7 km (from oceanic Moho), 25 km(from Auckland Moho) and (some depths deeper in the lithosphere) 100 km. Fagaloa Formation dykes (brown, green and yellow) were also plotted for comparison. (Modified from Blake et al, 2006)...... 259

FIGURE 4.66 Potential vent zone of Upolu Island, constructs based on volcanic hazard map of Samoa by Cronin et al (2006)...... 262

FIGURE 4.67 Potential vent zone on Savai’i Island, where links to Upolu through the Inter-island Fissure System. This map based on the volcanic hazard map of Samoa by Cronin et al (2006)...... 264

FIGURE 4.68 Schematic of the narrow graben-like eruption model of the Crater Lanoto volcano before and during the tephra bed-1 activities. The monogenetic activity of the Lanoto volcano initiated at Crater Fili location before moved to the west. Thin and thick dashed and solid lines are referred to low and large volume monogenetic activities repectively. The above figure is not to scale...... 266

FIGURE 4.69 Pit-crater eruption episode of the Crater Lake Lanoto formed after the volcanic locus shifted to the west. Dashed oval and lines represent inactive sources and feeder dykes respectively. Thin and thick dashed and solid lines are referred to low and large volume monogenetic activities repectively. The above figure is not to scale...... 268

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LIST OF TABLES

TABLE 2.1 Distinguishing features of monogenetic and polygenetic volcanoes...... 19

TABLE 2.2 The six volcanic units of the Western Samoa sequence and their distinguishing features based on the classification of Kear and Wood in 1959, with their estimated ages (modified from Fepuleai, 1997)...... 29

TABLE 4.1 XRF raw major and trace elements of the Crater Lanoto inner rim lava flow with their grid references...... 136

TABLE 4.2 Raw data of the ICPMS trace elements...... 146

TABLE 4.3 The four dated samples; LLD3/34, LLD3/49, LLD3/73 and LLD3/219. Sample LLD3/210 was based on only 10ug carbon hence the large error...... 163

TABLE 4.4 The total, supported and unsupported 210Pb activities downcore, at the top part of the master core D3...... 165

TABLE 4.5 Summary of the radiometric age of the Crater Lanoto. Notice: There was no radiocarbon dated for tephra bed-2, but instead the inner lava flow suggests is the product of the tephra bed-2 episode selected to be argon-argon dated...... 198

TABLE 4.6 Summary of features and events in the Crater Lanoto and Samoan region could associate with the cone collapse event...... 205

TABLE 4.7 List shows some of the impact the CCE scarred the geomorphology of the main islands...... 212

TABLE 4.8 Summary of the radiometric age, MSOI age and with their estimated intervals of the Crater Lanoto volcano. Note: The MSOI ages were determined from the comparison of the magnetic susceptibility and the MSOI curve...... 224

TABLE 4.9 Eruption style of the Crater Lanoto volcano and associated hazards...... 230

TABLE 5.1 An appropriate analogous predict to be associated with short term compound monogenetic type eruption like Crater Lanoto. (Modified from Cronin et al., 2006) ...... 277

TABLE 5.2 Various tasks and methods to benefit future research and improve understanding in the volcanic field of Samoa...... 283

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LIST OF ACRONYMS

Acronym Description AIR Acid Insoluble Residue AlF Alaoa Fault ApFS Aleipata Fissure System AFS Asaga Fissure System ANSTO Australian Nuclear Science and Technology Organisation AMS Accelerator Mass Spectrometry CCE Cone Collapse Event CCEPC Composition Chart for Estimating Percentage Composition COE Cut Off Event DZ Dominated Zone EPMA Electron Probe Microanalysis FFF Fagaloa Falealili Fault FgF Fagatoloa Fault FFs Falealupo Fault FFu Fanuatapu Fault FtF Fito Fault FDMS Frequency Dependent Magnetic Susceptibility HFZ High Frequency Zone HPVZ High Potential Vent Zone IIFS Inter-Island Fissure System ICPMS Inductively Coupled Plasma Mass Spectrometry KTT Kermadec Tonga Trench LlF Lalomauga Fault LfF Lefaga Fault LpF Lepa Fault LPVZ Low Potential Vent Zone LRI Long Range Interval MgF Ma’agi’agi Fault

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MS Magnetic Susceptibility MFS Matavanu Fissure System MGF Manase Gataivai Fault MSOI Marine Sediment Oxygen Isotope MSMS Mass Specific Magnetic Susceptibility MPVZ Medium Potential Vent Zone MRI Medium Range Interval MSWD Mean Sum Weighted Deviates MF Moa’moa Fault NFs Neiafu Fault NT North Terminus NFu Nu’usuatia Fault OF Ologogo Fault PFS Papalaulelei Fissure System SfF Safune Fault SIFs Salailua Fault SlFu Salani Fault SF Saluafata Fault SVF Samoa Volcanic Field SvFS Salelavalu Fissure System StF Sataua Fault SOAF Sataua Ologogo Arc Fault SRI Short Range Interval SMFS Savaii Major Fissure System SnF Sinoi Fault SfF Siufaga Fault SFS Solomea Fissure System TfF Taelefaga Fault TFS Tafua Fissure System TgFS Taga Fissure System TF Tiavea Fault

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UMFS Upolu Major Fissure System VF Vaisigano Fault VLFZ Very Low Frequency Zone VSMS Volume Specific Magnetic Susceptibility WSMM Western Slide Motion Mechanism XRF X-ray Fluorescence

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CHAPTER 1 INTRODUCTION

1.1 BACKGROUND

Samoa consists of two political parts: a western group of islands known as Western Samoa and an eastern group called American Samoa. Upolu and Savai’i are the two main islands of the western group, whilst the Tutuila and the Manua Group (Ofu Island, Tau Island and Olosega) are the main islands of the eastern part. Figure 1.1a shows the alignment of islands on the western and the eastern group of Samoa.

The Samoa group of the islands seem to be aligned, with parallel long and short trenches orientated roughly northwest-to-southeast. Long trenches include those of Savai’i, Upolu and Tutuila, whereas the short trenches contain the Manua group and Rose Island (Figure 1.1).

The western group were the first South Pacific islands to become independent in 1962, whilst the eastern group is still administered by the United State of America. The two governments recently agreed to rename the western and the eastern groups “Samoa”. However, the older names “Western Samoa” and “American Samoa” are still used in this study to avoid confusion among readers. Because German administrated Western Samoa in the early 1900s many early geological studies were published in German magazine (Zeitschrift der Gesellschaft fur Erdkunde zu berlin), including the eruption descriptions of the 1905-1911 eruption on Savai’i (Wegener. 1902). Details of these early geological works are discussed in Section 2.10 of this thesis.

Western Samoa is made up of nine islands with a total land area of 2831 km2. Savai‘i and Upolu have landmasses spanning 1709 km2 and 1114 km2 respectively. The total population of Western Samoa was estimated to be 183,081 in the 2010 census, with the largest proportion of the population living on Upolu Island. American Samoa comprises of five main islands with a total population of 55,519 during 2010 census. A total land area is about 197.1 km2.

The Samoan islands are located between latitudes 13o to 15oS and longitudes 168o to 171oW and ride on approximately 110 million year old oceanic crust (Workman et al., 2004). The islands, atolls, submerged reef banks and seamounts, form a chain with a total length of 1400 km, which extends from Rose Island in the east to the seamounts on the western end of Savai’i Island. Figure 1.1b shows the seamounts in the western part of the island chain where a width of the chain varies from 130 to 220 km (Gudge & Hawkins, 1991; Hawkins, 1987). Away from the chain, water depths of up to 5000 metres increase to 7000-9000 metres to the south in Kermadec Tonga Trench (Figure 1.1a & b).

The island chain of Samoa has been dominated by alkalic volcanic activities (Fepuleai, 1997; Cibik, 1999). The geochemical nature of lavas from deep submarine and subaerial volcanoes, of the Samoan island chain, reveals a combination of “shield” (or plume) and “post-erosional” volcanism.

The two different volcanism types were mostly responsible for building up this volcanic island chain, known as “Samoa Volcanic Field” (SVF) in this study. Detailed descriptions of the two types of volcanism are found in Section 2.3. Shield and post-erosional volcanism are distinct due to the structurally control mechanisms of formation. Chemical distinctions of the two volcanisms are detailed in Section 2.3.3. Kear and Wood (1959) used term “post-erosional” to define young activities (Middle Pleistocene to Present) on both main islands.

The island of Samoa is interesting when compared with the island of Hawaii. The volcanism of Hawaii generates from several eruption phases such as pre-shield, shield, post-shield and post-erosional (Frey et al., 1991; Kennedy et al., 1991). The pre-shield stage is represented by alkalic and tholeiitic suites, whilst the main shield building stage is dominated by tholeiitic suites. The post-shield phase is associated with differentiation processes that are followed by the caldera collapse (Clague, 1987). Stearns (1946) was the first to recognise the term “shield volcano stage” during his work in many sites on the island of Hawaii.

The evolution of the Samoan volcanism could be very similar to that of Hawaii. Fepuleai (1997) subdivided the oldest volcanism (Pliocene-Pleistocene), Fagaloa Formation into

3 two parts: Lower Fagaloa and Upper Fagaloa. Cibik (1999) stated that the Lower Fagaloa represents the pre-shield stage whereas the Upper Fagaloa evolves from the major shield building phase. Kear and Wood (1959) suggested that major erosion occurred as the major shield activities ceased. This represents a major unconformity between older formation (Pliocene-early Pleistocene) and post-erosional suites expose on the main islands. Post-erosional volcanism generate along the major rift axis where similar new volcanoes erupted following some structural elements with unknown eruption frequency.

Samoa is a classic example (like Hawaii) of plume-related volcanism. As the Pacific Plate moves west, the plume produces a trail of oceanic volcanic islands that become younger as you move east. However, the presence of later post-erosional activities along the island chain has triggered controversy amongst researchers, as the island chain contains young volcanoes on both ends. This is described in more detail in Section 2.3.2. The shield activity is originated from a plume hotspot and represents an earlier phase of volcanism along the Samoan island chain (Hart et al, 2004). An active underwater volcano named Vailulu’u (Figure 1.1a) to the east of Manua (eastern end of the Samoa island chain) represents the present hotspot position of Samoa (Hart et al., 2004).

Hart et al (2004) use the term “rejuvenated” to describe post-erosional activities dominated the later (young) subaerial and submarine volcanic cone. Rejuvenated eruption is the stage where a volcano “refuels” after a long period of dormancy and erosion. It is suggested that Holocene activities of the post-erosional stage spread along the island chain of Samoa (Kear and Wood, 1959; Natland, 1980; 2003. A plumbing system of the volcanic ocean island like Samoa could associate with fractures along the lithosphere. These could trigger a series of spatter eruptions, cinder cone eruptions, submarine volcano and re-eruption of subaerial and submarine craters. This would generate an eruption gap in time and space that lead to degradation of edifices with all the consequences of sedimentary basin evolution around. A new magma emplacement to the crust that fed a new post-erosional volcanism with may have different chemical characteristics and eruption style. The Samoa Volcanic Field is believed to have been active as the fracturing Samoan lithosphere moved west along a deep mantel underneath the Samoan Islands (Natland, 2003).

The two main islands (Savai’i and Upolu) are considered to be potentially volcanically active (Cronin et al, 2006). Several written descriptions of recent eruptions (1902-1911), on the northern part of Savai’i provide some indication of volcanic activity on historical timescales (Weber, 1902; Wegner, 1902; Angenheister, 1909; Anderson, 1910; Friedlander, 1910; Thomson, 1921). The volcanic hazard in Western Samoa have been recently documented by several authors including Taylor and Talia (1999), Cronin et al. (2001), Cronin et al. (2006) and Nemeth & Cronin (2009).

1.2 RATIONALE

There are many reasons why this study is important for the Samoan community, future research, implications for the economy and volcanic prediction scenario on the island.

Volcanic hazards are a challenge for Samoa and we can learn much about the current volcanic hazards by learning about the nature and frequency of past volcanic activity. In order to make predictions about future eruptions, a robust record of past eruption (chronology) is needed to better understand the behaviour of Samoa volcanoes and mechanisms behind them. Such information is lacking for this area, partly due to rare opportunities for gaining access to get long continuous sections of tephra deposits due to erosion and blanketing by later volcanic material.

The tectonic setting of Samoa islands is associated with many uncertainties from previous research in relation to a process of lithospheric fracturing and plume activities. High resolution records of the time, space, stratigraphic, chemistry, mineralogy and petrography of Samoan volcanics are lacking. Such information would aid our understanding in nature of eruption style and the other more recent processes operating around Samoa.

The islands of Western Samoa possess several volcanic crater lakes, situated along the central ridges of the two main islands, Upolu and Savai’i. These are believed to be the product of Holocene volcanism (Kear and Wood, 1959), which is likely to be continuing to the present. Such sites elsewhere in the world have been shown to preserve detailed

5 sedimentary records of volcanic ash and other tephra fallout (Oldfield et al., 1980; Guilizzoni & Oldfield 1996; Cronin et al, 2006; Nemeth & Cronin, 2009a; 2009b). A similar record in Samoa could help us learn more about long term patterns of volcanism in the area thus informing us about present volcanic hazards. In addition, lake sediments would provide significant clues of structural events based on information such as bedding structure, grain size, thickness and fracturing/jointing/faulting regimes. This information would help to better construct of an overview of tectonic processes associated with volcanism in Samoa.

The tephra records preserved in the crater lakes sediments of Western Samoa offers significant opportunity for hazard assessment. Such sediments would contain signatures of past explosive activities that may not be fingerprints from exposed surface deposits (Molloy et al, 2009). These records may be used to reconstruct the high-resolution chronologies, providing a record of the frequency location type of volcanic activity in the region (Gale, 2009). Because the volcanic ash from each eruption episode is likely to be chemically and mineralogically distinct, each tephra layer should have a unique chemical and mineralogical fingerprint, providing potential for them to be used as event markers. This would allow correlation across a broad area as airfall deposits are often widespread (Lowe, 2011). Tephra beds would be used as volcanic time marker tools in the broad affected area once the volcanic events have been independently dated.

However, the volcanic nature of Western Samoa is characterised as a homogeneous source and unchanged over many millions of years (Fepuleai, 1997). Hence tephra deposits from various volcanic activities would be difficult to distinguish in this sense and is a major challenge for this study.

1.3 AIMS AND OBJECTIVES

This project aims to address issues and significant questions, associated with the volcanism process of Samoa as listed below:

The main aim and objective of this thesis, is to establish a reliable event chronology for Western Samoa during the Holocene epoch, based on tephra stratigraphy in closed lake basins of Savai’i and Upolu. This chronology will be used to inform us about the nature, and pattern of volcanism in the islands, during the last several thousand years as well as identifying important event markers for regional correlation.

This baseline data will be of value both to government organizations and to scholarly research. Reconstruction of reliable records of the timing and source of these Holocene eruption activities should result, in an improved understanding of volcanic hazards in the Samoan islands chain. This understanding will inform volcanic risk management on the two main islands, Upolu and Savai’i. In addition, the data presented in this thesis will improve the capacity of official organizations to respond to and manage natural disasters.

It was expected that such data could provide much information. For example the tephra record could tell us something on about the eruption styles (magmatic versus phreatomagmatic explosive), general eruption intensity (thickness), eruption duration source regions (single and multisource tephra beside a narrow stratigraphy interval of the lacustrine records) and to identify some syn-eruption sedimentary processes associated with the sedimentation in the closed lake basins. In addition, the tephra deposit age would contribute to refine the eruption frequency along the volcanic fissure of the main islands.

Furthermore, chemical, mineralogical and petrographic analysis of tephra layers from the lake cores may; for example, help to improve our understanding of volcanism processes of Samoa and the tectonic processes in relation to the geological setting of the island chain.

This study can be roughly divided into two components with different, but not independent aims and objectives. The study design will be based on the availability of valuable lake sediments in the depositional basin.

(i) This first component involves the reconstruction of a high-resolution chronology of volcanism in Western Samoa, by determining the radiometric age of tephra layer in the crater lake cores. Lava (inner rim and outer rim suite) will be also dated and used as

the base radiometric age of the crater. Inner rim lava occurs within the crater whilst the outer lava surrounds the outer part of the crater rim. The two lava suites suggest that they may have been erupted from different volcanic episode and time. (ii) The second component involves the determination of the chemical, mineralogical and sedimentological characteristics of each layer deposit. This information should allow us to address the following hypothetical questions for this study: - Has volcanism in Samoa changed through time? If so, how? The change in the volcanism could be associated with tectonic activities in the region. - What was the duration of each eruption interval? Were they long or short-lived? The eruption interval would provide valuable information for predictions of future eruptions. Combination of long and short-lived volcanism could also reflect the continuation of tectonic process in the Samoan region. - Was each episode explosive or effusive? What sedimentary features fingerprint these volcanic behaviours? Samoan volcanism has low silica content (Fepuleai, 1997) hence explosiveness of volcanic activities could be associated with other factors such as groundwater/surface water and elevated gas content within the magma chamber. - Can we see evidence of contaminated tephra components in the sediment? Contaminated tephra is referred to components from other volcanic eruptions in the area. The presence of contaminant tephra in a crater lake basin would indicate that the entire volcanic fissure along the main islands may have been active. - Can we see evidence of simultaneous activities in the lake sediment? Simultaneous eruptions are characterised as by volcanoes that erupt at the same time, as Natland (2003) described was a common behaviour of post-erosional activities. A mix of contaminant tephra within tephra layer of the study crater lake would also reflects an active central rift. - How does the information gathered from the study crater lake core inform us about mechanisms associated with Samoan volcanism? How could this information relate to regional tectonics? A combination of radiometric age (lava/tephra), chemistry of tephra components and physical geology of the area would provide valuable information to determine the mechanism.

- How can we extrapolate this information gathered from the crater lake core to inform us about volcanic hazards in the region? Does it help us predict the nature and timing of volcanism in the near future? - Can we see evidence of “cone collapse” and “major erosion” event in the sediment, briefly described in Kear and Wood (1959)? How can these events relate to other evidence of volcanism on the island? Cone collapse event (CCE) in this study refers to a series of tectonic activities that occurred in the region in the past. Kear and Wood (1959) suggested that the erosion event is represented by a major unconformity between the older and younger volcanism (shield and post-erosional respectively). This CCE could cause a cessation of early post-erosional activities, the caldera collapse (Keating, 1992; Natland & Turner, 1985) on the northeast Upolu and the uplift of several portions of the main islands described in Kear and Wood (1959). - Can we see evidence of bush fire during each eruption episode? Charcoal present in the crater lake sediment would shows another volcanic hazard associated with the Samoan volcanic activities. - What is the variation in magnetic susceptibility of lake sediments over time interval? How can these results fit into the volcanic history of Samoa? Magnetic susceptibility (MS) strength of the crater lake sediment is controlled by the presence of magnetite mineral. Details of the MS technique used in this study are found in Section 3.2.5 of this thesis. Variation in MS would identify different type of sediment deposit and the presence of contaminant tephra component. - Can we see evidence of human occupation in the sediment? How would these occupants respond to the volcano hazard in the past? Human occupation may be associated with erosion and charcoal in the sediment. Williams et al (2014) referred to charcoal deposit along the northeast coast of Upolu (Fagali’i village) as human occupation evidence which makes these assumptions more challenge for this study. - What elements in the indigenous knowledge in the study area are related to the volcanism nature? Indigenous knowledge relate to the volcanism could be hidden in culture activities (dance/song) and language in the region.

1.4 INTRODUCTION TO METHODOLOGIES

Figure 1.2 shows a flow diagram of the methodologies involved in the project, which includes a variety of field and laboratory components. A thorough literature review serves as a platform for understanding the current state of knowledge about Samoan volcanism. It also serves to inform about the most up to date laboratory techniques of radiometric dating methods for tephra, geochemical analyses and relevant field descriptions. A reconnaissance trip to the main islands was then carried out to identify different aspects of the volcanism from a field perspective and to enable us to select the best coring site for the study. Radiometric dating and geochemistry analysis are the main methods used in reconstructing the high-resolution chronologies.

FIGURE 1. 2 Flow diagram of the fieldwork and laboratory methodology overview used in the project

1.5 REASONS FOR THE SELECTED SITE

Out of seven volcanic crater lakes on Upolu and Savai’i, Crater Lake Lanoto was chosen as the best site for this study (Figure 1.3). All seven low relief volcanic crater lakes are classified as maar in this study however, six were difficult to access or too deep to core using our available coring equipment. Crater Lake Matulano and Crater Lake Mafane locate about 600-1000 m above sea level in the eastern central part of Savai’i were 10 difficult to access, despite being otherwise perfect sites for coring. Similarly, Crater Lake Lanoto, Crater Lake Lanonea and Crater Lake Lanoata’ata in the central western Upolu, were also not appropriate for coring as they were either more than 20 m (Lanoto) or difficulty to access. Crater Lake Lano’omoa and Crater Lake Olomaga on the easternmost part of Upolu were also difficult to access and core.

Crater Lake Lanoto is a broad elongate maar located along the central ridge to the easternmost end of Upolu Island. The Lanoto maar formed from a series of eruptions that excavated the pre-existing topography and generated a hole in the ground, breaking the the groundwater table lying along the central rift of the island. The lake is located between 171o31’54 East and 14o00’51 South and is 400 m above sea level. Note that throughout this thesis, the term “Crater Lanoto” refers to the volcano and “Crater Lake Lanoto” is the water-filled volcanic crater lake, acts as a closed sedimentary basin and captures inter-eruptive and syn-eruptive sediments.

The Crater Lake Lanoto is distinct in that it is an entirely closed basin with no drainage outlet. This close-basin structure contributes in the entrapment, and retention of a near- complete record of undisturbed depositional products, including information about every volcanic event during different eruption episodes in the form of tephra. In addition, Lanoto basin would also trap volcanic ash from other volcano activities in the region. A more detailed description of Lanoto volcano architecture is found in Section 2.4. Other critical factors that favoured the selection of the Crater Lake Lanoto included; (1) relatively easy access and (2) ability to core lake sediment with the coring equipment available to the research team.

CHAPTER 2 TECTONIC SETTING AND STUDY SITE

2.1 OVERVIEW

This chapter is presented in two parts, Part-1 and Part-2:

(i) Part 1 – describes the tectonic setting and processes, the Samoa Volcanic Field and regional geology. (ii) Part 2 – describes the study area in terms of its volcanic heritage, crater lake area, structural geology of the eastern Upolu and geology of the Crater Lake Lanoto.

PART 1: Geo-tectonic setting and volcanological evolution

2.2 TECTONIC SETTING AND PROCESS

The Kermadec-Tonga Trench (KTT) represents a boundary between two major plates that extend from the northeast of New Zealand to the southwest of Samoa (Figure 2.1). The boundary marks the subduction of the southern part of the Pacific Plate beneath the northeast corner of the Australian Plate (Hawkins & Natland, 1974; Hawkins, 1975; Natland, 1980; Natland & Turner 1985; Wright et al, 2000). Figure 2.1 shows the geological setting of the Samoan island chain to the northeast of the KTT. Immediately to the south of Samoa, the northern end of the KTT bends sharply to the west, to become part of the east-west aligned Vitiaz Lineament, to the north of the Fiji group. The sharp bend in the Tonga Trench is known as the “Northern Terminus” (NT) (Hart et al., 2004) (Figure 2.1). The NT is thought to be moving east at a rate of approximately 170 mm per years due to roll-back in the Pacific Plate (Bevis et al, 1995; Natland, 2003, Hart et al, 2004; Koppers et al, 2008; Price et al, 2014). Number “1” (Figure 2.1) represents that the KTT has shifted toward the east, about 10-12 million years ago (Jackson et al, 2010). The

13 boundary continued move to the east with its position around 5-6 million years ago denoted by the number “2” with its current position by the number “3” (Hart et al., 2004; Koppers et al., 2008).

Hawkins and Natland (1974) described the Samoan islands chain as almost parallel to a vector of the Pacific Plate motion and to the Vitiaz Lineament. The island chain of Samoa is located along the axis of flexure and is believed to be associated with a magma leakage mechanism (Hawkins and Natland, 1974). Magma leakage of Samoa occurs at the sharp bend in the Vitiaz Lineament (Hawkins & Natland, 1974; Hawkins, 1975; Jackson et al., 2010). A structural weakness resulted of tectonic elevation at the tearing portion of the Pacific Plate could generate the “mantle leaking” (Workman et al., 2004). Price et al

(2014) described the leaking of the Samoan mantle toward northwest Lau Basin (Fiji) as being associated with an adiabatic upwelling process. This adiabatic upwelling process drains out from the thick Pacific lithosphere, toward the thin Northern Fiji Basin lithosphere. The Vitiaz Lineament (Figure 2.1) formed due to the downward drag subduction of the Pacific Plate (Natland, 1980). This allows the Samoan mantle plume, to seep through the northern Lau Basin (Jackson et al, 2010). Jackson et al. (2010) stated that the Manatu seamount, Rochambeau seamount and the Futuna Island within the Fijian volcanic region, (Figure 1.1b) fingerprint isotopic signatures (high helium content) of the Samoan volcanism.

Natland (2003) proposed that the propagation of fractures perpendicular to the principal stress, or the motion of the Pacific Plate, is shown by the alignment of volcanoes and subordinates vents along the Samoan island chain. As such, Samoan volcanism has been characterised by Turner and Hawkesworth (1998) as result of magma that has spread in narrow finger-like intrusions along the island chain.

The Australia Plate is moving north at about 66.2 mm per year, while the Pacific Plate is advancing west north at about 71 mm per year (Hawkins, 1987; Hart et al., 2004). The highly oblique nature of the Vitiaz Lineament generates a range of transpressional phenomena from Papua New Guinea through the Solomon Islands to Samoa (Coleman, 1966; 1991; Petterson et al., 1997; 1999). In Papua New Guinea and the Solomon Islands a large number of rhombohedra shaped basins have been produced with faults parallel to the basins forming throughout the arcs. In the Samoa region, the Vitiaz Lineament to the west of Samoa represents the torn lithospheric part of the Pacific Plate (Hawkins, 1987; Hart et al, 2004). As the Australian Plate continues to advance north it is dragging the tearing section of the Pacific Plate in a mechanism known as “down-drag subduction” (Natland, 1980; Natland & Turner, 1985; Hawkins, 1987).

It is believed that the tearing of the Pacific Plate is the product of tectonic stresses. Based on geochemistry and tectonic processes in the region from previous studies, this is thought to have generated numerous of Holocene volcanic activities along the island chain. This is claimed to be an earlier model of the Samoan Volcanic Field (SVF)

(Hawkins & Natland, 1974; Natland, 1980; Natland & Turner, 1985; Hawkins, 1987). However later studies have suggested that SVF is resulted of an upwelling plume mechanism. The argument is based on the fact that hardly any evidence of seismic activities occurs along the tearing portion compared to the subducting part of the Pacific Plate. However, it is suggested that the Pacific Plate seems not to be subducted into the trench, but continues to advance in a westward direction (Millen & Hamburger, 1998; Govers & Wortel, 2005; Price et al, 2014). Although the Vitiaz Lineament is not currently a subduction zone however, it was a subduction zone until the collision between the Solomon Island-Papua New Guinea arcs and the Ontong Java Plateau at 20-15 Ma (Petterson et al., 1997; 1999).

The Uo Mamae seamount at a depth of about 1380 m, to the south of Upolu represents clear evidence of the down-drag effect (Hawkins, 1974; Gudge & Hawkins, 1991 and Hawkins, 1987). Potassium-argon dates of 940,000 ± 20,000 years from both coral and volcanic fragments indicated that, around one million years ago the seamount formed an island, which has since been submerging, at an average rate of 1.5 mm/yr (Hawkins, 1987; Gudge & Hawkins, 1991).

Shaw (1973) and Natland (1980) proposed that the shear melting results from vertical and horizontal motions in the asthenosphere. This provides the principal dilatancy, which allows the molten lava to percolate to the surface at the North Terminus of the Tonga Trench. Koppers et al., (2008) described a similar hypothesis with their “lithospheric cracking” concept also known as the “tapping mechanism” (Natland, 1980; 2003). Shallow magma melts enable the production of multiple volcanic centres through tapping or lithospheric cracking processes along the Samoan island chain (Hawkins & Natland, 1975; Natland, 1980; Hawkins, 1987; Natland, 2003).

2.3 SAMOA VOLCANIC FIELD

2.3.1 OUTLINE

Post-erosional volcanism in Samoa is widely spread along the central rift of the main islands and commonly erupts in two styles: 1) monogenetic and 2) polygenetic. The monogenetic type is a small volcano generated from a small volume of eruptive magma defined as a “one-off” eruption (Cronin et al., 2006; Nemeth and Kereszturi, 2015). Such a small volcano also corresponds with a small eruptive volume of ≤ 1 km3 and relatively short-lived eruption duration of ≤ 10 years (Nemeth and Kerezturi 2015). Monogentic volcanic field like Samoa may create a wide variety of volcanoes such as spatter cone, scoria cone, maar-diatremen and tuff ring (Nemeth and Kereszturi, 2015). Polygenetic eruptions occur repeatedly over hundreds or thousands of years (Natland, 1980; Takada, 1994; Cronin et al., 2006; Nemeth & Cronin, 2009, Kaulfuss et al., 2012). However, a lack of radiometric dates of individual craters means that it is hard to classify the polygenetic eruptions as rare activities on the main islands.

The two eruption types are very difficult to distinguish in the field, especially when they have similar ages and a lack of tephra layer outcrop, indicates a series of eruption episodes. A similar problem is encountered elsewhere in the world particularly when they are closely associated in the same volcanic field (Sheth and Canon-Tapia, 2014; Nemeth and Kereszturi, 2015).

Western Samoa contains small-volume potentially monogenetic volcanoes sitting on the dorsal ridge, in the central part known as a rift axis of the island. These small vents could be fed up by dykelets and hence build very short-lived volcanoes. Whereas those in the zone associate with melt source of more stable volcanic plumbling and conduit system, we could expect a long lived poly-phase volcano, more similar to a sensu stricto polygenetic eruption (Nemeth and Kereszturi, 2015).

In this study several cones from Upolu and Savai’i were classified as monogenetic and polygenetic volcano based mainly on volume of lava flow and pyroclastic deposit (Table

2.1). This would reflect some ideas about the size of eruptive volume in monogentic and polygenetic activity in Samoa. Most of these small volcanoes in Upolu and Savai’i erupted from a single or multiple vents known as “compound monogemtic” (Nemeth and Kerezturi, 2015) during Pleistocene to Holocene period (Kear & Wood, 1959). The Table 2.1 indicates that monogenetic of Samoa seem fit in the classification of few cones from North Island of New Zealand, based on volume ejectas of < 1 km3 of dense rock equivalent eruption deposits (Nemeth et al., 2012; Kerezturi and Nemeth, 2013; Nemeth and Kerezturi, 2015).

The Crater Lanoto is a compound monogenetic volcano with a small eruptive volume of 0.003 km3 in comparison with other eruptions in the Table 2.1. Mauga Afi volcano on the eastern part of Savai’i erupted simultaneously from two separate compound vents (2.2 km) during 1902 (Anderson, 1910; Kear and Wood, 1959). This simultaneous volcanic behaviour could be commonly occurred along the Samoa Volcanic Field. Tafua-i-savai’i and Matavanu volcano comprise of large eruptive volume of 0.647 and 0.629 km3 respectively. This may classify the two volcanoes as polygenetic activity or a “large volume monogenetic volcano” described in a theorectical model of Nemeth and Kerezturi (2015). A more discussion in monogenetic activity is found in Section 4.7.4.1 as follows

TABLE 2.1 Distinguishing features of monogenetic and polygenetic volcanoes of Upolu and Savai’i in comparison with those from the North Island of New Zealand (Nemeth and Kerezturi, 2015).

Edifice

Volcano name and Volcano Width Length Height (m) Lava flow Estimate Age of the location type (m) (m) extend eruptive Samoan from the volume Volcanism vent (m) (km3) (Kear and Wood, 1959) Crater Lanoto monogenetic 100- 320 69 2 x 103 0.003240 Pleistocene to (eastern part of (compound 180 Holocene Upolu) scoria cone) Crater Olomauga monogenetic 750 820 68 >800 0.003575 Pleistocene to (eastern part of (compound Holocene Upolu) scoria cone)

Crater Tialata monogenetic 220 250 61 >200 0.000090 Pleistocene to (eastern part of (scoria cone) Holocene Upolu) Lanoanea (central monogenetic 300 400 8 >250 0.000050 Pleistocene to east Upolu) tuff ring Holocene (maar crater) Lanoata’ata (central monogenetic 200 270 9 >100 0.000044 Pleistocene to east Upolu) tuff ring Holocene (maar crater)

Tafua-upolu (western monogenetic 420 500 130 >150 0.001000 Holocene part of Upolu) (scoria cone) Mauga Fito (central monogentic 600 1100 140 9 x 103 0.227918 Holocene Upolu) (compound cinder cone) Seu’seu (western part monogenetic 30 50 35 120 0.000010 Pleistocene to of Savai’i) (spatter Holocene cone) Tafua-savai’i polygenetic 500 700 120 5 x 103 0.647494 Holocene (southeast part of (compound Savai’i) scoria cone) Matavanu (northeast polygenetic 200 300 15 8 x 103 0.629364 Historical Savai’i) (scoria cone) Mauga Mu (western Monogenetic 180 300 12 2 km 0.003885 Historical Savai’i) (compound scoria cone) Mata-ole-afi (western Monogenetic 400 600 9 1.5 x 103 0.041439 Historical part of Savai’i) compound (scoria cone) Mauga Afi (western monogenetic West West 13 36 x 103 1.097114 Historical part of Savai’i) (2.2 km (80) (120) separate East East compound (110) (180) scoria cones) Pukeiti (NZ) monogenetic 70 60 15 unavailable 0.0037 114 Ka Maungataketake (NZ) monogenetic 1100 1300 25 unavailable 0.0330 41-140 Ka Rangitoto (NZ) monogenetic 1000 600 120 unavailable 0.7000 0.5 (Ka)

Cronin et al (2006) addressed this by introducing the term short- and long-term eruptions. Therefore, it seems most appropriate to refer to the volcanic activities as “short” and “long term monogenetic” or “short” and “long term polygenetic”. Figure 2.2 displays a

19 flow diagram of the Samoa Volcanic Field (SVF). It shows that shield and post-erosional volcanism processes are currently active. Koppers et al. (2011) stated that the volcanism has erupted in form of “sequential” and “synchronous” processes. Sequential activity is referred to volcanoes that erupt in a good sequence whilst synchronous are those formed in simultaneous activities. In other words, shield volcanism associates with sequential process whereas the synchronous dominates the post-erosional activity.

The volcanism in Samoa is thought to have originated from shield activities and then shifted to the post-erosional due to the influence of tectonic processes (Natland, 1980; 2003; Natland & Turner, 1985; Hawkins, 1987; Hart et al., 2004; Koppers et al., 2008; 2011). Both stages of volcanism classified as short or long term monogenetic and polygenetic. Radiometric dating of lava in the region shows that monogenetic and polygenetic eruptions have occurred simultaneously (Goodwin and Grossman, 2003; Workman et al., 2004; Nemeth and Cronin, 2009; Koppers et al., 2008; McDougall, 2010).

A more detailed discussion of the nature, history and the characteristics of monogenetic and polygenetic activities of the SVF can be found in Section 4.7.4.1 and Section 4.7.4.2.

FIGURE 2. 2 Flow diagram of the Samoan Volcanic Field, where it originates as shield volcanism and then shifts to post-erosional volcanism due to the influence of tectonic processes. The post-erosional activities may be split into short and long-term eruption.

Natland (2003) outlined a parallel scenario known as “simultaneous post-erosional volcanism”, where activities on the islands of Western Samoan match geochemically and in age. In other words, lava from post-erosional volcanism erupted from multiple centres. It is thought that the sharp bending of the down-going Pacific Plate provided extra stress, resulting in rupturing and deep extensional structures in the Samoan lithosphere. The subsequent cracks and fractures allowed the post-erosional volcanism magmas to resurface on the main islands (Hawkins, 1975; Natland, 1980; Natland and Turner, 1985; Hawkins, 1987; Natland, 2003; Hart et al., 2004; Koppers et al., 2011). This assumption has also supported from crack interaction theory of Takada (1994) stated that, the monogenetic volcanism occurs in regions where stress field is more tensional associates with large or small differential stress. Conversely Cibik (1999) believed that flexural bending cannot account by the formation of post-erosional activities, but it is the result of conduit networks where melts ascend from an underlying plume.

In addition, a reconditioning of ocean lithosphere after the generation of older seamount trails to the west of Savai’i, resulted in a lithospheric contraction, as it cool down over time (Koppers et al., 2011). Multiple cracks along the oceanic lithosphere of Samoa, not only ejected fertile upper mantle materials but also low volume decompression melts, where the production of numerous short term volcanoes on the lithosphere of Samoa and its surroundings occurred (Natland, 2003; Garcia, et al., 2010; Koppers et al., 2011).

2.3.2 THE SAMOAN PLUME

Post-erosional volcanism has produced young eruption activities on the western end of the island chain, which, if the chain was formed solely by a plume-related mechanism, should contain the oldest islands. As result, the Samoa Volcanic Field has been the subject of much debate for decades. Several studies have proposed that the eruption activities in the Samoa Volcanic Field are driven by thermo-mechanical processes, related to the tearing portion of the Pacific Plate (Hawkins and Natland, 1974; Hawkins, 1975; Natland, 1980; Natland and Turner, 1985; Brocher, 1985; Hawkins, 1987). This was the general view until the 5 Ma age of the deep submarine flank of Savai’i was confirmed during the 2005 Alia Expedition (Koppers et al., 2008). Argon-Argon dating

(40Ar/39Ar) of the deep submarine flank, part of the shield-building lava stages of Savai’i Island, reveals a plume origin for Samoa (Hart et al., 2004; Koppers et al., 2008).

There are three significant types of activity hotspot: primary, secondary and tertiary (Courtillot et al 2003). Koppers & Watts (2010) also proposed a similar assumption. This classification is based on their duration (short-lived and long-lived), the age progression of the seamounts and the volume of mantle plume. Anomalies in seismic shear wave velocity studies reflect that Hawaii is a “primary hotspot”. In addition, it has a long-lived, strong mantle plume as deep as 1,500 km and, several kilometres wide (Koppers & Watts, 2010).

It is suggested that the Samoan plume-driven hotspot can be referred to as a “secondary hotspot” process, consisting of short-lived magmatism linked to a less voluminous mantle plume. This particular hotspot is characterised by a weak mantle plume, which implies to represent an off-shoot from so-called super-plumes (Courtillot et al, 2003; Koppers et al., 2008; Koppers and Watts, 2010). The volcanic nature of the tertiary hotspot remains unclear (Courtillot et al., 2003; Koppers and Watts, 2010). A nonlinear age progression of volcano produced by primary and secondary hotspots could be the work of the three plate processes such as plate extension, lithosphere cracking and small-scale shallow mantle convection (Koppers and Watts, 2010).

2.3.3 ISOTOPIC COMPOSITION OF LAVAS OF SAMOA

Most previous studies have not clearly distinguished the two volcanic activities (shield and post-erosional) along the Samoan island chain in term of major and trace elements. However, isotopic composition from previous works have been recalled in this study, to identify the characteristic nature of the two volcanism types. These data included those from a series of seamounts, submarine flanks of the main islands and subaerial lava along the broad volcanic chain. Samples collected from lava suites to the northwest of the Crater Lanoto volcano (2-3 km) would give some significant information, whether the study area is a part of the hotspot or post-erosional activities.

This section outlines the isotopic characteristic of lava samples from SVF (1, 2 and 3) and also plots them with the other volcanic setting lava suites (4) for comparison:

1. Western province volcanoes (submarine and subaerial) 2. Eastern province volcanoes (submarine and subaerial) 3. Volcanic region of the Crater Lanoto (2-3 km) north west of the study area 4. Other volcanic settings (Cook-Austral, Pitcaim, Hawaii and Marquesas)

2.3.3.1 Samoan island chain

The SVF is chemically and isotopically heterogeneous (Jackson et al., 2007). Lavas from SVF classified into three isotopic end members: EM2 (enriched mantle 2), EM1 (enriched mantle 1) and HIMU (high μ [μ = U + Th] / Pb (Jackson and Dasgupta, 2008). It has been suggested that EM1 and EM2 should have a close chemical connection with many oceanic island chains like Samoa. This would be based on volcanism signature in term of isotopic compositions of elements such as strontium (Sr), neodymium (Nd), lead (Pb), helium (He) and osmium (Os) content (Hart et al., 1992).

The isotopic EM2 reservoir components are of (87Sr/ r86Sr), (143Nd/144Nd), (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb,), (3He/4He) and (187Os/188Os) (Hofmann, 2003). These constituents enable the determination of end members, the evolution of mantle composition, magma source and heterogeneities present in the volcanism of Samoa (Workman et al., 2004; Sims & Hart, 2006; Jackson et al., 2007; Koppers et al 2008; Jackson, et al., 2009; Jackson et al, 2010). Other isotopic arrays reported by Jackson and Hart (2006) that have been poorly characterised within the lavas of Samoa include those of the DMM (Depleted MORB Mantle: with low 3He/4He and low 87Sr/Sr86), FOZO (Focus Zone: with high 3He/4He and low 87Sr/Sr86) and PHEM (Primitive Helium Mantle: with high 3He/4He and middle-range 87Sr/Sr86).

The isotopic EM2 of the SVF should be lower in 3He/4He and have high 87Sr/Sr86. However, both the radiogenic isotopes of 3He/4He and 87Sr/Sr86 are associated with high levels of uncertainties, in Samoan lavas (Jackson and Hart, 2006). The isotopic end member EM2 and PHEM/FOZO are suggested to be associated with a deep plume 23 environment whilst the HIMU and DMM components are expected to have a shallow source (Workman et al., 2004).

Figure 2.3 shows the isotopic relationship between 206Pb/204Pb versus 87Sr/ r86Sr of lavas from the SVF with respect to other hotspots (Cook-Austral, Pitcairn, Hawaii and Marquesas). Lavas are plotted into four isotopic fields; EM1, EM2, HIMU and DMM based on Workman et al (2004)’s isotopic mantle classification. Deep submarine flanked lava from Savai’i is enriched in 87Sr/ r86Sr whilst depleted in other Samoan volcanic region. Lavas from the SVF scatter heavily in the EM2 field whilst very few eastern province sample plots in the EM1 region with those from Pitcairn. A few lavas from the eastern volcanic province and western seamount overlap with the Hawaiian samples in the DMM region. Similarly, lavas from western seamount and eastern volcanic province overlap with those from Cook-Austral hotspot in the field of HIMU. Marquesas lavas overlap with the Pitcairn toward the DMM region.

In addition, the plot in Figure 2.3 displays the two trends, “A” and “B”, which represent shield and post-erosional volcanism respectively. The shield trend “A” is dominated by lava from the deep submarine flanked of Savai’i, the eastern volcanic province and the Vailulu’u hotspot. The post-erosional volcanism trend is associated with lavas from Upolu, Savai’i, western seamount, eastern volcanic province and Marquesas hotspot. In addition, post-erosional samples from Upolu include those from the Crater Lanoto volcanic region, and are plotted along the trend B, within the EM2 isotopic field (Figure 2.3). This indicates that these lavas are a part of post-erosional volcanic origin.

In terms of the relationship between 206Pb/204Pb ratios and distance from the Vailulu’u hotspot, the ratios are relatively high in the eastern province volcanism, lower toward the western province with further increases through the western (Figure 2.4a). The submarine flanked lava of Savai’i is classified as part of the plume volcanism which has high 206Pb/204Pb. The post-erosional lava suites from Upolu (northwest of the Crater Lanoto) and Savai’i plot along trend “B” in the field of low 206Pb/204Pb ratio.

High 206Pb/204Pb values in western province volcanism, is evidenced in mixing of EM2 component and those of the HIMU (Workman, 2004). The HIMU component is a product of an under-plate process occurring deep in the Samoan lithosphere (Workman, 2004).

Figure 2.4b shows a plot of 87Sr/ Sr86 ratios versus distance from the Vailulu’u hotspot. The 87Sr/ r86S ratios are high in the submarine flanked-lava of Savai’i, with lower values in the eastern province volcanism, western province post-erosional lavas and the western seamounts. The post-erosional lava from Upolu (northwest of the Crater Lanoto) plots at the low 87Sr/86Sr zone. 25

High 87Sr/86Sr ratios of the deep submarine lava suggest the presence of recycled components derived from the upper continental crust (Wright and White, 1986; Hauri and Hart, 1993; Farley, 1995; Jackson et al., 2007; Koppers et al, 2008; Jackson, et al., 2009). Low 87Sr/86Sr ratios show mixing of EM2 components with those of HIMU.

The post-erosional lavas of Upolu (northwest of the Crater Lanoto) and the eastern province contain relatively high in 143Nd/144Nd ratio, whereas these values are lower toward Savai’i, and higher values further toward the west of the island chain (Figure 2.5). Low 143Nd/144Nd ratios of the submarine flank-lava also show evidence of recycling of sedimentary components (Wright and White, 1986; Hauri and Hart, 1994; Farley, 1995; Jackson et al., 2007; Koppers et al, 2008; Jackson et al., 2009).

Figure 2.5b shows that eastern province volcanism has higher 3He/4He ratios than the west. The post-erosional lava from Upolu (northwest of the Crater Lanoto) and Savai’i have plotted in the low 3He/4He zone with several samples from eastern province.

Ofu Island to the west of Tau (Figure 1.1) has the highest ratio along the island chain; this value is recorded as the highest in comparison with those of the northern hemisphere hotspot (Hawaii, Iceland, Galapagos, Cape Verde and Azores) (Jackson et al., 2007; 2009).

The high helium ratio of Ofu Island is one of the most controversial topics in the literature at this part of the Pacific. High 3He/4He ratios suggests that the mantle underneath Ofu Island has a large primitive reservoir, and only hosts a small portion of recycled material (Jackson et al., 2007; 2009). Farley (1992; 1995) suggested that this is a product of undegassed reservoir from the deep-rooted plume and not the result of subduction process. Meibom et al (2003) suggests that this anomalously high helium ratio is due to mixing between radiogenic and unradiogenic components. Anderson (1993; 1995) suggested that the mantle underneath Ofu is associated with interplanetary dust particles on the ocean floor. However Jackson and Hart (2006) proposed that the melt inclusions and whole rock samples from Ofu Island are isotopically homogeneous. This indicates that high 3He/4He ratio scenario in lava of Ofu Island, has no evidence of mixing throughout the volcanism process.

In conclusion, it seems that, lava along the SVF includes post-erosional volcanism of Upolu and Savai’i, with significant variation in isotopic ratio composition with respect to

27 their distance from the Vailulu’u hotspot. Hence, a question is addressed at this point: “Is this isotopic variation is a part of the “tectonically controlled volcanism process?” Kereszuri and Nemeth (2013) stated that, the low magma supply in monogenetic volcanoes corresponds with the tectonically controlled volcanism results from an “externally magma generation process”. This typical monogentic activity is commonly associated with a passive by-product of tectonic shear that forces the melt to be extracted from the partially molten aggregate (Kereszuri and Nemeth, 2013).

2.3.4 REGIONAL GEOLOGY

2.3.4.1 Volcanic Formations

Kear and Wood (1959) divided the products of volcanic activity in Western Samoa into six geological formations based on several criteria such as mineral composition, texture, physical appearance, extent of soil profiles, the presence of a reef, degree of weathering and erosional features. From oldest to youngest, the volcanic formations are termed: the Fagaloa Volcanics Formation; the Salani Volcanics Formation; the Mulifanua Volcanic Formation; the Puapua Volcanic Formation; the Lefaga Volcanic Formation and the Aopo Volcanic Formation. The Fagaloa Formation is a deeply eroded unit and unconformably overlain by the Salani, Mulifanua, Puapua, Lefaga and Aopo Formations.

The latter five volcanic units (Salani, Mulifanua, Lefaga, Puapua and Aopo) are referred as “post-Fagaloa” or “post-erosional” in many old and recent publications. The term “post-Fagaloa” is also used in this study. In addition, the term “this-study” will be placed beside a name of a new volcano cone, fault, fissure, tephra sand and tectonic feature on the eastern most part of Upolu. The naming of these volcanic-geology features will be of value to future research activities in the region. The term “tephra sand” use in this study is referred to the size of tephra grain deposit.

Table 2.2 shows the classification outline of the six rock formations of Western Samoa after Kear and Woods (1959). Sea level changes, geomorphology and geology features were the main tools by which the six formations were classified.

AGE FORMATION FEATURES

Historical AOPO VOLCANICS Fresh or slightly weathered, no to very thin soil pahoehoe and aa flows fill up older valleys and spill out over the coasts, lagoons and cover barrier reefs. The unit outcrops only to the north of Savai’i, medium to fine crystal of olivine present. The lava flow commonly form dome structures known as tumulus.

Middle to Late PUAPUA Slightly weathered with thin soil, lava offshore and form Holocene (Post VOLCANICS rocky (ironbound) coasts, ubiquitous aa, pahoehoe Glacial) structure form domes, mineral olivine is a common phenocryst which range from fine to coarse grained.

Early Holocene (Post LEFAGA Intermediated weathered, thin soil, only narrow fringing Glacial) VOLCANICS reefs present offshore of these outcrops, like the Puapua phenocryst olivine dominate with fine to coarse grained.

Late Pleistocene MULIFANUA Intermediate weathered, thin soil, the existence of wide (Last Glaciations) VOLCANICS barrier reef existing offshore, highly jointed and highly vesicular unit and abundant of mineral olivine.

Middle to Late SALANI Thick soil and deeply weathered, reef is quite far Pleistocene(Last VOLCANICS offshore, gorges cut in flanks, abundant of mineral Interglacial) olivine

Middle Pleistocene FAGALOA Consist of a very thick soil, deeply weathered, abundant to VOLCANICS of mineral olivine, feldspar and pyroxene, reef is closed Pliocene(Penultimate to the inshore or none in some part of the islands, deeply Glaciation) eroded and dissected volcanic terrains and lava associated the thick unit intruded by series of dykes.

Figure 2.6 shows the sketch (from Kear and Wood, 1959) of the age relationship between sea level fluctuations and volcanic eruptions in Samoa. From the Pliocene to the Middle Pleistocene, the activities producing the Fagaloa Formation occurred at the lowest sea level during the Penultimate Glaciation stage. Large degrees of erosion and weathering occurred as the Fagaloa volcanism ceased. Middle Pleistocene to Late Pleistocene activities associated with the Salani Formation occurred, as the Quaternary sea level rise during the Last Interglacial time. The Vini Tuff member of the Salani Formation was 29 formed by an eruption that coincides with the highest Quaternary sea levels. Another episode of massive erosion and weathering occurred as the Quaternary sea level decreased. Throughout the Late Pleistocene, the Mulifanua Formation activities occurred as the sea level dropped during the Last Glaciation stage. Lefaga Formation volcanism was active during the transgression event of Flandrian (Holocene) at the Post Glacial stage in the Early Holocene. The volcanoes that formed the lithologies of the Puapua Formation and Aopo Formations erupted at the peak of the Late Holocene to Present sea level.

Flandrian transgression during Holocene time corresponds with the subsidence of the paleoshoreline at Maninoa (south of Upolu) at a rate of 0.52-0.12 mm per year (Goodwin and Grossman, 2003). Subsidence of the northwest of Upolu in the Holocene calculated

30 at the rate of 1.25 ±0.15 mm per year. This subsidence on northwest Upolu could possibly be due to volcano edifice-loading (Dickinson and Green 1998; Dickinson, 2007).

Fepuleai (1997) subdivided the Fagaloa Formation into the Upper Fagaloa Formation and the Lower Fagaloa Formation. This division is based on stratigraphical position, mineral content, thickness of lava flows, vesicularity, density, geochemistry and other physical characteristics.

A series of dykes intrude the thick sequence of lava flows of the Fagaloa Formation; these are referred to as the Fagaloa Intrusions (this study) and are classified as part of the Upper Fagaloa Formation. In most locations, these intrusive bodies range from several centimetres to a few metres in thickness and mostly dip vertically. They are very well exposed on the eastern part of Upolu Island. A massive dyke called the Lemafa Intrusion (this-study) extends from Falevao along Fagaloa Bay and east towards Uafato village and Ti’avea village. The Lemafa Intrusion has a width of 15 m to 100 m and is more than 10 km in length. Commonly the dykes are fine to coarse grained, dark green to dark grey in colour of fresh surface with porphyritic texture (Fepuleai, 1997). Common mineralogy includes those of olivine, plagioclase and pyroxene.

The six formations are predominantly composed of olivine-rich basalt. In most locations, the volcanic rocks are thick pahoehoe flows (smooth lava), intercalated with aa flows (volcanic breccia or irregular flow). Figure 2.7 shows a geological map of Savai’i. A narrow strip of the Fagaloa Formation crops out on the south and north-eastern part of Savai’i. The Salani Formation and Puapua Formation dominate the eastern part while Mulifanua Formation is extensive on the western. The Aopo Formation occurs only on the northern part of Savai’i Island. Volcanic cones are widely spread in the central toward east and narrower to the west, represented by solid blue. The island is dissected by series of faults and will be discussed in more detail in the Structural Geology of the Regional (Section 2.3.3.7).

As shown in Figure 2.8 the Fagaloa Formation dominates the northeast part where only a small portion crops-out in the southwest. The Salani Formation is wide spread in the central and extends toward the southeast. The Mulifanua Formation and Lefaga Formation dominate the western end of the island. A small portion of the Puapua Formation crops out at the south central coast of Upolu. Volcanic cones align in the central part represent by the solid blue line. Like Savai’i, the island is deeply dissected by series of faults and is discussed in more details in the Section 2.3.3.7.

Lavas of the six formations are porphyritic with coarse phenocryst phases of olivine, plagioclase feldspar and pyroxene, which are set within a fine-grained micro-crystallised matrix. However, lavas of the Lower Fagaloa Formation in several locations (and particularly Cape Papaloa and Cape Utumau’u on the northeast part of Upolu) display a holocrystalline texture (Fepuleai, 1997). Generally, the phenocrysts range from 0.5 mm to 2 cm in diameter. However, in several locations on both Upolu and Savaii Island, coarse phenocrysts are rare in the lavas of the Salani Formation, Mulifanua Formation, Lefaga Formation, Puapua Formation and Aopo Formation.

The thickness of each unit varies widely and is very difficult to determine in the field. Generally, the lavas of the six Western Samoa formations are dark grey to almost black in appearance, although several lava flows of the Upper Fagaloa Formation and Salani Formation, are light grey in colour and referred to as “differentiated lava” (Fepuleai, 1997). These lavas are often distinguishable because of their mineral content and their blacker, duskier appearance in the field. Lavas of this kind crop-out at a few locations on

33 both eastern Savai’i (Manase-Safotu), north-eastern Upolu Island (Afulilo) and Alaoa to the south of Apia.

Soils in several parts of the islands are stony and relatively shallow especially in the areas dominated by young volcanism. A good example is between the villages of Puapua and Samalaeulu, to the northeast of Savai’i Island (Figure 2.7). Holocene deposits known as Lalomauga Alluvium (Kear & Wood, 1959), cover most of the exposed terraces of the older lavas along the east and northeast of Upolu ranging from 1.5 m to 8 m or more in thickness (Fepuleai, 1997). These deposits are mainly talus of older volcanic units. Presumably, other locations in Upolu and Savai’i have a thin deposit of this type particularly in zones dominated by younger volcanism (Fepuleai, 1997). Calcareous volcanic pocket deposits of Nu’utele Sand and Tafagamanu Sand units (Kear & Wood, 1959) crop-out along the southwest coast of Upolu and the south of Savai’i (Fepuleai, 1997). Colluvium deposits are common situated within the Fagaloa Formation and Salani Formation in Savai’i and Upolu, especially those associated with scarp faults and joint networks.

2.3.4.2 Common mineral phases in the lava of Western Samoa

Common mineral phase from shield eruption and post-erosional activity of Upolu and Savai’i had been recalled as base information for this study. This will determine whether the tephra deposit of the Crater Lanoto has a similar composition. The information will help to identify the tephra and link to some potential stratigraphic horizon of the Crater Lake Lanoto depositional basin.

Fepuleai (1997) stated that olivine is the most abundant mineral phase in the lavas of Western Samoa, followed, in order of decreasing abundance by plagioclase, pyroxene and iron-titanium oxide. Dykes and lava flows of Upolu and Savai’i are strongly porphyritic (Fepuleai, 1997 & Cibik, 1999). The most common coarse phenocrysts are olivine, plagioclase and clinopyroxene with a groundmass dominated by titan-augite, needle feldspar and iron-titanium (Fepuleai, 1997 & Cibik, 1999).

(i) Olivine

Olivine makes up approximately 47 % by volume of the lavas of Western Samoa (Fepuleai, 1997). The olivine in the lavas of the Fagaloa Formation and post-Fagaloa on the main islands is predominantly forsteritic in composition (Fepuleai, 1997; Cibik, 1999). Olivine is commonly altered to reddish-brown iddingsite. Iddingsite develops coherently within the olivine crystal giving of staining on most road-cut outcrops in Samoa (Fepuleai, 1997). The rock locally consists of a mixture of clay minerals, iron oxide and ferrihydrite. A lack of anisotropy in olivine means that alteration spreads evenly across the olivine crystal. This alteration process involves the addition of iron and water and the loss of magnesium. A few dykes from Samemea (northeast Upolu) observed showed further alteration of olivine into clay minerals in the presence of a strong oriented calcite crystal structure (Fepuleai, 1997).

(ii) Plagioclase

Plagioclase phenocrysts in Fagaloa and post-Fagaloa are commonly euhedral in shape range from 0.5 mm to 3 mm in size (Fepuleai, 1997). The second most abundant mineral phase, in lavas of Western Samoa makes up about 18 % of the rock volume. Several thin sections of “differentiated lava” from Manase-Safotu (north Savai’i) and Afulilo (northeast Upolu) contain abundant plagioclase feldspar phenocrysts, a few percent of opaque mineral and rare olivine phenocrysts (Fepuleai, 1997). Samples from the Upper Fagaloa Formation, northeast Upolu and post-Fagaloa from Savai’i, display interlocking plagioclase feldspar phenocrysts within a groundmass containing subhedral twinned laths to untwinned crystalline masses. Plagioclase has a predominantly labradorite-bytownite composition within both the Fagaloa Formation and post-Fagaloa suites.

The groundmass plagioclase feldspars are usually in the form of euhedral to subhedral laths of less than 0.5 mm in length. Zoning observed under cross polar is apparent in several of the coarser phenocryst microscope occur in several coarse phenocrysts and is normal or occasionally oscillatory (Fepuleai, 1997; Cibik, 1999). However, alteration has obscured zoning trends in other samples from Fagaloa lavas.

(iii) Pyroxene

On average, pyroxene makes up 7 % of the lava volume. The pyroxene phenocrysts are not as dominant as those of olivine within the Fagaloa and post-Fagaloa lava suites in Upolu and Savai’i. Pyroxene is commonly euhedral in form with irregular cracks. The presence of these irregular cracks is very unusual in pyroxene. Mega-phenocrysts observed at Cape Utumau’u, Cape Papaloa and Afulilo range from 0.9 cm to 2.5 cm in size. Some thin sections of lavas from northeast Upolu show a reaction relationship between olivine and pyroxene, where olivine phenocryst are enclosed by a rim of pyroxene. Alteration is observed in pyroxene phenocrysts from northeast Upolu (Fepuleai, 1999) and very few places in Savai’i (Cibik, 1999). Certain lavas of the Fagaloa suite contain brown titan-augite in the groundmass (Fepuleai, 1997). Pyroxene of Fagaloa Formation and post-Fagaloa on Upolu and Savaii has diopside-augite in composition (Fepuleai, 1997; Cibik, 1999). Zoning is present with high chromium cores.

(iv) Opaque minerals

Very fine phenocrysts of the minerals ilmenite, spinel and magnetite are occasionally present in Fagaloa and post-Fagaloa units from Upolu and Savai’i (Fepuleai, 1997; Cibik, 1999). Commonly, the phenocrysts are anhedral and range in size between 0.04 mm to 0.2 mm. Very fine needle or hair magnetite and ilmenite commonly occur as inclusion in mega phenocryst of plagioclase feldspar, olivine and pyroxene.

2.3.4.3 Physiography of the main islands

This section presents a cross section of Western Samoa island group included in the study area in Figure 2.10a (cross section C-C”). It would give us some ideas how widely these post-erosional lava suites and the elevation of the study area with respect to other part of the island group.

The shape of Upolu and Savai’i is determined by the distribution of volcanic eruptions along the main fissure systems. Thus, Upolu Island has a narrow shape because the volcanic cones are aligned and concentrated along the central fissure system (Figure 2.8). 36

The island of Savai’i has volcanic cones aligned along its fissure system structure resulting in a long broad shape of the island (Figure 2.7).

On both main islands, the central ridge rises to between 300 and 1800 metres above sea level. Figure 2.9 shows two cross sections of Savaii island (A-A” & B-B”). Mauga Sili’sili in central Savai’i is the highest summit in Western Samoa with an elevation of 1858 metres above sea level. The Savai’i Island has high relief topography in the west, which flattens toward the east. High relief topography in the island coincides with the high Holocene to Present eruption activities. In section A-A” the island seems gently slope toward north-west and southeast. The island is steep on both northern and southern part displays by section A-B”.

Figure 2.10 shows two cross sections of Upolu Island (C-C”, D-D” & E-E”). In section C-C” the high relief topography is found on the eastern side with a reduction in relief to

37 the west. Mauga Fito volcano in the central part (southeast of Apia) is Upolu’s highest point with an elevation of 1093 metres. Tafua-upolu volcano is exposed as an outlier on the westernmost part of Upolu in section D-D”. The eastern part of Upolu at Section E-E” shows peaks of the Fagaloa Formation from Solosolo to Lemafa. Deeply weathered associated with heavy erosion of Fagaloa Formation, has resulted in deeply incised relief, particularly northeast Upolu. These erosional processes have resulted in the formation of great amphitheatre-headed canyons, which merge to produce sharp peaks and steep rugged terrain of narrow razor-backed ridges (Kear and Wood, 1959).

2.3.4.4 Structural geology of the region

Series of faults deeply dissect both main islands. The faults are in part, believed to be associated with a succession of slope failures (Kear & Wood, 1959; Fepuleai, 1997). Both the Manase-Gataivai Fault (this-study) on Savai’i and the Fagaloa-Faleali’li Fault

(this-study) on Upolu are oriented in a northeast-southwest direction. These two strike slip faults offset the alignment of Salani craters on Savai’i (Figure 2.7) and Upolu (Figure 2.8). The Fagaloa-Faleali’li Fault could trigger the cessation of Salani Formation activities, on the north eastern part of Upolu Island (Hawkins, 1987). Hawkins (1987) suggested that the Fagaloa-Faleali’li Fault might be the product of the downward-drag due to the subduction of the northern part of the Pacific Plate.

The Sataua Fault to the east of Asau village (northwest Savai’i) strikes northwest- southeast and links with the Ologogo Fault on the east (Figure 2.7). This forms a concave structure known as “major arc fault” which is, open and downthrown to the northwest (Taylor and Talia; Butcher et al, 2000; Cronin et al., 2006). The Sataua-Ologogo Arc Fault (this-study) is located along the zone of most active tectonic movement on Savai’i. The zone is also the location of all the historic eruptions from 1760 to 1911 and is located where new vents are most like to develop (Taylor and Talia, 1999; Cronin et al., 2006; Nemeth & Cronin, 2009).

The volcanic cones of Savai’i Island take the form of a chain over a broad convex plain and those in Upolu are distributed along a topographic crest known as “the rift zone”. Savai’i Major Fissure System (this-study) and the Upolu Major Fissure System (this- study) extend parallel to the central rift of the main islands. The Savai’i Major Fissure System (SMFS) forms a fan-like structure while the Upolu Major Fissure System (UMFS) has a single rift zone. The SMFS branches out to the mid-eastern part of the island, to form the Matavanu Fissure System (this-study), the Solomea Fissure System (this-study), the Papalaulelei Fissure System (this-study), the Asaga Fissure System (this- study), the Salelavalu Fissure System (this-study), the Tafua Fissure System (this-study) and the Taga Fissure System (this-study). These branches of the fissure systems are generally aligned northeast-southwest.

An Inter-islands Fissure System (this-study) links the SMFS and UMFS. The extension of the Fanuatapu Fault (this-study) north-south, is almost perpendicular to the Upolu Major Fissure System, and presumably parallel to the Aleipata Fissure System (this- study) (Figure 2.8).

The Fagaloa Intrusions on the north eastern part of Upolu have variable orientations, with dips from gentle to vertical (Fepuleai, 1997). The overall orientations of these intrusive bodies are commonly northwest-southeast direction, similar to that of the volcanic cones along the UMFS.

Columnar joints dominate lavas suite of the Fagaloa Formation and post-Fagaloa Formation on Upolu and Savai’i. These columns range from many centimetres up to many metres in length. In many hilly parts of the main islands, scarp faults are associated with networks of joints have in the triggered failures (for instance Mauga o Vaea south of Apia, Mauga o Fao & the Fagaloa Bay).

Onion skin-like textures are a common product of physical weathering occurring mainly in lavas of the Salani Formation. Kear and Wood (1959) used this feature to distinguish the Salani Formation from the Upper Fagaloa Formation and other younger units. The development of onion skin weathering known as “sheeting” occurred in lavas of the Upper Fagaloa and Salani, on Upolu and Savai’i is believed to be a resulted of the unloading of overburden by erosion. This unloading via erosion releases pressure on the underlying rocks and causes the rising rock to expand. These particular rocks are difficult to break through the middle rather than thin sheets. The sheeting features are a good example of “mechanical weathering” within the lavas of Western Samoa. Joint and fracture indicate that these rocks went under enormous stresses associated with structural deformation when they are deeply buried.

Spheroidal weathering causes physical changes in many outcrops of the Fagaloa Formation on the northeast Upolu. This type of weathering commonly occurs, where joints intersecting on rock surface associated with surface water. These features are very well exposed in many roads cutting on the main islands.

Most post-Fagaloa lava flowed from the central part of the main islands, drained to the coast via lava tunnel, and are up to many kilometres in length. For instance, the Puapua lava flow from the Mauga-o-Fito eruption (Figure 2.8) advances toward the central north coast of Upolu (Lauli’i village and along the Alaoa stream) via lava tunnels at least 12 km long. Other lava flows from the same eruption, flowed toward the central south coast

40 via lava tunnel of approximately 9-11 km. Collapsed lava tunnels form circular valleys on the main islands, and several have become popular tourist sites on Upolu Island. A good example of largescale collapsed lava tunnels is located at Tiavi waterfall (southwest of Mauga-o-Fito) (Figure 2.8) which has a depth of 110 m with diameter of up to 800 m. The Tiavi is a part of Fagaloa Formation which is overlain by lava of the Salani Formation. To-le-sua (less water tunnel) and To-sua (deep-water tunnel) sites (small scale tunnel) locate at Lotofaga village, south east Upolu with 20 to 40 m depth and diameter of 25 to 50 m. The To-le-sua and To-sua formed during the re-eruption of the Fogalepulu (central east), shown by the narrow strip of the Lefaga Formation advance to the south coast in Figure 2.8.

2.3.4.5 Age of the Volcanism

Published dates for volcanic events in Western Samoa are limited (Cronin et al., 2006). One of the major aims of this study is to establish accurate dates with the aim of constructing a reliable chronology of the Samoa Volcanic Field (SVF). Kear and Wood (1959) presented the first chronology with their six volcanic formations ranging in age from Pliocene to Historical.

Figure 2.11 shows a map with the distribution of published radiometric dates in Upolu and Savai’i. Pliocene dates mainly derived from potassium-argon and argon-argon dating methods (K-Ar and Ar-Ar), dominate the northern part of Upolu and Savai’i. Only very few Middle to Early Pleistocene (K-Ar) dates have been retrieved in either of the main islands. Several Late Pleistocene radiocarbons (14C) dated lavas and volcanic ash obtained from the north and western part of Savai’i. Holocene 14C dates dominate the central part of Savai’i and only very few, have been reported on the south coast of Upolu.

Natland and Turner (1985) used K-Ar whole rock methods to date thick pahoehoe flows of the Fagaloa Formation from northeast Upolu yielding ages from 1.5 to 2.8 Ma. McDougall (2010) generated K-Ar dates from Fagaloa Formation lavas in Upolu (pahoehoe flow from the northeast, Mount Vaea to the south of Apia, Lefaga Bay on the southeast and Samai village to the northeast of Lefaga Bay), obtaining dates ranging from 1.38 to 2.78 Ma. McDougall extended his K-Ar dating to the northern part of Savai’i yielding ages between 0.32 and 0.42 Ma. A trachyte cobble of pahoehoe at Vanua (north of Satupaitea village) in the southern central part of Savai’i produced a40Ar/39Ar date of 2.05 Ma (Workman et al., 2004). A sample from the narrow strip of the Fagaloa Formation on northern Savai’i at Vaipouli (from a road section outcrop) showed Ar-Ar date of 0.236 ± 0.052 Ma whilst sample from Manase were argon dated at 0.386 Ma. The Fagaloa lavas (road section outcrop) on the southwest of Upolu at Fagalei Bay (west of Falese’ela) were dated at 0.933 ± 0.10 Ma and those of the Matafa’a (west of Falese’ela) were dated to 2.65 ± 0.02 Ma, also using Ar-Ar methodologies (Workman et al., 2004).

The deep submarine flanked lava of Savai’i was dated at 5.0 Ma (Koppers et al., 2009) using Ar-Ar methods. This age confirmed the island was a part of the plume-driven hotspot (Koppers et al., 2008) during the Pliocene time.

Paleomagnetic studies by Keating and Tarling (1985) revealed that some road section outcrops of the Fagaloa Formation on Upolu are reversely magnetised. However elsewhere, all lava flows possess normal magnetization, including the whole island of Savai’i. Mixed polarity (both normal and reversed polarity present) is observed in both lava flows and dykes of the Fagaloa Formation at several locations on the northeastern part of Upolu. Transitional polarity of Upolu outcrops (Vavau village, southeast, Vaipu and Sopoaga, northeast) yield a paleomagnetic age of 0.7 Ma. Keating and Tarling suggested that the transition polarity represents an episode when the reversal polarity shifts to normal polarity. This age is fitted at the stage as the waning of the Fagaloa Formation volcanism but waxing of the Salani Formation.

A thick outcrop of the Salani Formation which is exposed along the Malio’lio the biggest non-perennial river to the north east of Savai’i at Samalaeulu village (Figure 2.7), has yielded K-Ar dates of 0.21 Ma (McDougall, 2010). Two lava samples of the Salani Formation from Vaiola village and along the western coast of Savai’i were also K-Ar dated to 0.11 to 0.09 Ma. Lavas of the Mulifanua Formation from Sataua village, at the western end of Foailuga village (Figure 2.7) on the southwest of Savai’i, have K-Ar dates of 0.03 to 0.22 Ma.

The post-Fagaloa lavas of the Lefaga and Puapua Formation on the Upolu Island have not been dated as yet. However, coral clasts from the Mavaega reef (southwest coast of Upolu), were radiocarbon dated at 2767 ± 68 and 3075 ± 125 cal yr BP (Goodwin and Grossman, 2003). The reef is elongated parallel to the coastal plain of Mavaega, where it is found overlying by the broad strip of Lefaga Formation in several locations. This relationship between the reef and lava flow provides a reasonable estimation of the Lefaga volcanism perhaps, occurred sometimes between 2767 and 3075 yr BP.

Kear and Wood (1959) suggested that the Apolima Island (between Savai’i and Upolu) together with the islands to the eastern end of Upolu (Nu’utele, Fanuatapu, Nu’ulua, and Namu’a) are of the same age. They proposed that calcareous volcanic sediment known as the “Vini Tuff” (Vini is a local name for the Nu’utele Island) cropped-out on these islands and formed during the Middle Pleistocene. In addition, Kear and Wood (1959)

43 also classified the Vini Tuff, as pre-Lefaga and probably lower Salani Formation means that, the volcanoes forming these islands re-erupted several times. However, Stern (1944) observed Apolima Island from the air and suggested that it was the product of recent volcanic activity. The eastern islands have wide reefs whereas Apolima Island has no sign of a reef. This suggests that the eastern islands are much older. However, we cannot rule out the explanation that Apolima has a very steep submarine terrain, where it may be difficult for any coral to grow. In fact, the presence of the calcareous volcanic ash of Vini Tuff in all the islands (included Apolima) is suggestive of a similar age. Grant-Taylor and Rafter (1962) yielded the radiocarbon age of this particular calcareous volcanic of 1915 ± 65 yrs BP (Nemeth and Cronin, 2009), showing that these islands had been simultaneously active during Salani and Lefaga volcanism.

Radiocarbon dates from coral clasts in coastal plains and fringing reefs of the Maninoa area (southern part of Upolu) yielded ages of 959 ± 86 and 681 ± 75 cal yr BP (Goodwin and Grossman, 2003). Maninoa reef overlies by the broad lavas of the Puapua Formation at this part of the island, providing some clue about the age of this Holocene eruption. The headland lava of the “O le Pupu” is part of Puapua Formation (from Maninoa to Mulivai village) on the south coast Upolu suggested to have occurred at 959 to 681 cal yr BP (Goodwin and Grossman, 2003). Therefore the volcanic activities of Puapua Formation on Upolu perhaps could have been ignited less than 1000 yr BP corresponding to those on Savai’i which have been radiocarbon dated between 230 ± 70 to 1850 ± 80 yr BP (Nemeth & Cronin, 2009). This clearly suggests that both volcanism of Lefaga and Puapua were active continuously from Middle to Late Holocene respectively.

Recent radiocarbon dates for lavas and volcanic ash on Savai’i (230 ± 70 to 1850 ± 80 years BP) (Nemeth and Cronin, 2009) together with the age of Vini Tuff suggest that Samoa volcanism was active in Holocene times. There are discrepancies in dating techniques with time. For instance, lavas from Falealupo (western end of Savai’i) were radiocarbon dated at 2920 ± 180 years BP (Nemeth and Cronin, 2009), show these lavas belong to Mulifanua rather than the Puapua Formation. The extent of the area allocated to the Puapua and the Mulifanua Formations on the geological map (Kear and Wood, 1959) should therefore be reconsidered.

The physical appearance of the Lefaga Formation is much fresher than might be expected given the Early Holocene age determined by Kear and Wood (1959). Geochemical similarities of the Puapua and Lefaga Formation (Fepuleai, 1997) do not rule out the possibility that the two units are contemporaneous.

2.3.4.6 Volcanic hazards in Western Samoa

Volcanic cones are wide spread in the islands of Western Samoa, with an estimated the at least 425 (Kear and Wood, 1959; Taylor and Talia, 1999). These volcanic cones have different shapes and sizes, the majority being characterised by a wide base with relatively flat morphology reflecting quiet effusive volcanism (Kear and Wood, 1959; Taylor and Talia, 1999). However, several scoria and cinder cones scattered along the central ridges of the main islands have steep slopes of up to 35-46o.

Cronin et al. (2006) identified five main types of volcanic hazard occurred during Holocene to Present and predicted they could be repeated in the near future on the main islands, Savai’i and Upolu. These are; (i) Long term activities (volcano emits greater volume of lava), (ii) Short term activities (volcano emits small volume of lava), (iii) Explosive phreatomagmaticactivities (hydro-volcano), (iv) Explosive scoria-cone and (v) Downthrown of the Sataua-Ologogo Arc Fault to the northwest of Savai’i (submarine flank collapse).

The five volcanic hazards scenarios were determined from several criteria such as; exposed volcanic features (geological/geomorphology); information from older people (indigenous knowledge); comparison to other volcanic activities elsewhere in the world and remote sensing information (Cronin et al, 2006; Nemeth & Cronin, 2009).

(i) Long-term activities

Evidence of long-term eruptions activities may recognised in the five post-Fagaloa units on both main islands. The duration of such eruption-types may be up to twenty years (Cronin et al., 2006; Nemeth & Cronin, 2009). During the eruptions of Mauga Mauga Afi in 1760, Mauga Mu in 1902, Mata o le Afi in 1902 and Matavanu between 1905 and 45

1911, lava outpouring from these historical eruptions blanket at least 200 km2 of the northern part of Savai’i Island.

An example of the impact of such long-term eruption may be seen at the village of Saleaula to the northeast of Savai’i where a broad strip of lava, erupted between 1905 and 1911, almost buries the entire village. It estimated that this lava flow travelled about 40- 50 km from its source. The melting of iron roofs and the presence of tumulus (lava blister) structures in the area implies that the lava flow was still fluid and very hot when it reached the village. Tumuli are dome-shaped structures, thought to result from flow beneath a solidified crust meeting an obstruction, causing the molten stream below the crust to push up the overlying crust and form a dome-like feature (Ollier, 1964).

(ii) Short-term activities

Short-term eruption activities tend to be smaller, shorter-lived and confined to a single outlet. They have occurred in many parts of Savai’i and Upolu (Kear & Wood, 1959; Cronin et al., 2006). Eruptions of this sort typically only last for a few days or even a week and the area of associated damage may affect areas of 2 km2 to 50 km2 (Cronin et al., 2006).

The road construction at Seuseu village of Falealupo district (western end of Savai’i Island), provides a perfect site to view a road section of a short-term spatter cone of a monogenetic type eruption. It may be recognised in the field by a very thick layer of volcanic ash associated with a reddish brown scoria breccia unit and thin lava flows. The spatter cone eruption may be explosive, depending on the dissolve gas content in the magma. Vesicles in the lava of many volcanic cones range from millimetre to several centimetres in diameter.

(iii) Explosive phreatomagmatic activities

Phreatomagmatic eruptions, which are those associated with the interaction of hot magma and water are one of the most explosive volcanic eruption types that have occurred in Western Samoa (Taylor, 1999; Cronin et al., 2006; Nemeth & Cronin, 2009). A typical 46 eruption can last for weeks to months and may destroy areas of 10-100 km2 (Cronin, et al., 2006). They commonly occur along the end of the Savai’i Major Fissure System and Upolu Major Fissure System. The problem with this type of eruption is that they are fast and hardly have any precursor events. They however can gradually transition to more magmatic explosive eruptions over time if the external water source is exhausted. Therefore the hazard aspects and the eruption scenario of such eruptions are valuable information to assess and communicate with the local community.

Cronin et al (2006) reported explosive phreatomagmatic activity elements of the Tafua- savai’i volcano, located at the end of the Tafua Fissure System occurred in the Late Holocene. Apolima Island (located along the Inter-Island Fissure System), Cape Tapaga, (located at the eastern end of the Upolu Major Fissure System), Fanuatapu and Namua Island (along the Aleipata Fissure System) are all characterised by explosive phreatomagmatic eruptions. As previously mentioned the age classification of Kear and Wood (1959) and radiometric dates shows that, these volcanoes ignited in early Salani and re-erupted during Holocene times.

(iv) Explosive scoria-cone activities

Evidence of explosive scoria-cone eruptions is common in the Puapua Formation and is perhaps present in the Mulifanua Formation. The products of these eruptions are recognised in the field by their flat-top cones (Cronin et al, 2006). In addition, these volcanoes are commonly comprised of double or triple craters like those of Apolima Island, Tafua-savai’i and islands on the easternmost part of Upolu. The typical duration of such eruptions activity can be in the region of weeks or even years. Flat-top feature denotes that the upper parts of these cones had been blown away.

Tafua-i-upolu crater, located along the Upolu Major Fissure System (south of Satapuala village) on the westernmost end of Upolu (Figure 2.8), is a perfect example of this typical eruption. The volcano produced more than 4 m thick of fine to coarse volcanic ash of reddish yellow colour exposes to the southern part of the crater.

(v) Submarine flank collapse

The seafloor image of Western Samoa indicates a considerable mass movement on the seafloor area surrounding the western group of the island (Hill and Tiffin, 1993). This seems to be associated with the failure of thick sequences of lava and sediment along the flanks of both islands. A massive slump block on the northern flanks of the islands between Savai’i and Upolu is indicative of large-scale collapse of the northern margin (Hill and Tiffin, 1993). The two main islands rise steeply from a depth of 4000 to 5000 m (Hill & Tiffin, 1993; Hart et al., 2004), and are less than 200 km from the Kermadec Tonga Trench thought to be the major focus of earthquakes in the region. The Sataua- Ologogo Arc Fault (Figure 2.7) to the northwest of Savai’i is downthrown to the northwest, possibly due to instability along the submarine flank of Savai’i. Failures of this sort often generate devastate tsunami. Coastal villages at this part of the island with less than 10 m above sea level would suffer potentially serious consequences in the near future (Cronin et al., 2006). There is no evidence of palaeotsunamis deposit in the area (Williams, 2009; 2013), which implies that the northern flank failure of Savai’i must be older than expected. Palaeotsunami deposits along the older coast line could have been buried by the broad lavas of the Mulifanua Formation and Puapua Formation in the northern part of Savaii. More discussion of the submarine flank collapsed of Savai’i found in Section 4.7.2.2 of Chapter 4.

2.3.4.7 Climate

Samoa has a tropical climate with two distinct seasons, the wet season (October to April) and the dry season (May to September) (Saifaleupolu, 1998). A uniform temperature, elevated rainfall, high relative humidity and predominantly south easterly trade winds dominate weather patterns (Saifaleupolu, 1998). Tropical cyclones are occasionally present during the southern hemisphere summer.

The highest rainfall on both Upolu and Savai’i occurs in the highlands area, with an average of 6000 mm per annum, whereas rainfall in the coastal area ranges from 2200 to 5000 mm per year (Saifaleupolu, 1985; 1998). The central high relief features of the main

48 islands are believed to be the main factor controlling the distribution of the rainfall, in relation to the southeast trade wind (Saifaleupolu, 1985; 1998). It is estimated that the trade winds occurs about 82.6% of the time from October to April, and 54% from May to November (Saifaleupolu, 1985; 1998; International Climate Change Adaptation Initiative, 2011).

The El Nino and La Nina events, known collectively as the El Nino Southern Oscillation (ENSO), are associated with changes in the relative ocean temperatures and air pressures between the west Pacific “warm pool” and the east Pacific (west coast of South America), affect Samoa (International Climate Change Adaptation Initiative, 2011). Normal conditions are associated with high air pressure in the eastern Pacific, strong southeast trade winds (SETW) and a west Pacific “warm pool” (Philander, 1983; 1985; McPhaden & Picaut, 1990; Tigona, 2011; de Freitas & Tigona, 2012). However, under El Nino conditions a reduction in air pressure in the eastern Pacific leads to a weakened SETW, allowing the relatively stronger western trade wind to push the warm pool toward eastwards. As a result, higher rainfall generates toward the east in area including Samoa. Under La Nina conditions, the west Pacific warm pool leads to higher rainfall in areas such as Vanuatu, Fiji, Solomon, Papua and Australia. This corresponds with a strong upwelling of cold ocean (cooler than normal) along the west coast of South America (Philander, 1983; 1985; McPhaden & Picaut, 1990; Tigona, 2011; de Freitas & Tigona, 2012).

A series of flooding and drought events that have occurred on the main islands are considered to be related to the ENSO (Saifaleupolu, 1985; 1998; International Climate Change Adaptation Initiative, 2011). The Samoa Meteorology Division records (1950- 2005) indicated that under the El Nino phase, the islands experience wetter seasons than normal, whereas under La Nina conditions they experience wetter and cooler wet seasons than normal (International Climate Change Adaptation Initiative, 2011). Tropical cyclones in Samoa normally occur during El Nino phases (Saifaleupolu, 1985; 1998).

Temperature variations within Samoa are relatively small with a highest mean recorded temperature between December and March of 27oC and a lowest mean temperature

49 between July and September of 26oC (Saifaleupolu 1985; 1998). It has been suggested that temperatures are increasing at a rate of 0.2oC per decade since 1950 (International Climate Change Adaptation Initiative, 2011).

2.3.4.8 Human Occupation

As previously mentioned the human occupation in the Samoan region, is a significant component of this study. The aim of this section is to contribute towards determining the impact and style of eruption during the Holocene.

Archaeological evidence reveals that, human occupation in Samoa started about 3500 years BP (Petchey, 2001; Martinsson Wallin, 2007). This indicates that the Lapita civilisation stretched from the Bismarck Archipelago of north eastern Papua New Guinea to Samoa (Petchey, 2001; Martinsson Wallin, 2007). Turtle bone and collagen in the Lapita pottery assemblages were discovered in the lagoon of Mulifanua village (northwest of Upolu). Pottery was dated by radiocarbon methods at around 2800 years BP (Green, 1974; Petchey, 1995; Dickson & Green, 1998; Petchey, 2001).

Radiocarbon ages of the pottery suggest that the first occupants witnessed the eruption activities associated with the Lefaga Formation and the Puapua Formation on the main islands. This could partly explain why occupants settled along the coast, to distance themselves from the eruption activities in the central ridge of Upolu. In addition, there is a lack of literature relating to how the first occupants responded during Holocene volcanicity in Samoa. In spite of this, the Samoa indigenous knowledge could fingerprint some clues, and is discussed in details in Section 4.7.3.1.

This is an interesting scenario: Samoan islands are big and high and most of the known young volcanoes are not more than a small spatter or scoria cone. Such volcanoes are likely to have been produced eruption plumes that were not particularly high, and the areas they affected were fairly limited consequently, we can imagine that many of the event were observed.

2.3.4.9 Previous works in the volcanology of Samoa

The literature review of the project area provides a solid platform for this study, enabling the filling-in of many gaps in our knowledge about the geology and volcanology of Samoa. For example, it: (1) provides detailed geochemical/isotopic and physical volcanic geology of the island chain (2) provides the radiometric age of the Samoan volcanic formations (3) provides information about Holocene to present activities (4) provides information on tectonic activities associated with the island chain (5) outlines volcanic hazards associated with Samoa from Holocene to present and (6) provides valuable information to direct us how to carry out the field work and laboratory analyses.

Geologic and tectonic studies of the Samoan island chain included those of Dana (1849); Thomson (1921); Stern (1944); Kear and Wood (1959); Stice (1968); Shaw and Jackson (1973); Hawkins and Natland (1975); Hawkins (1975); Peterson & Tiling (1980); Natland (1980); Natland and Turner (1985); Okland et al. (1986); McDougall (1987); Hawkins (1987); Brocher (1985); Gudge and Hawkins (1988; 1991); Hill and Tiffin (1993); Fepuleai (1997); Cibik (1999); Natland (2003); Workman et al (2004); Hart et al (2004); Jackson et al (2007); Koppers et al (2008); Jackson (2009); Jackson et al. (2010); Jackson and Shirey (2011) and Konter and Jackson (2012). Geophysical studies include those of by Tarling (1962; 1965); Keating and Tarling (1985) and Keating (1985). Tectonic movement influences on the hydrogeology, of the northwest Savai’i area as described by Keating (1992) and Butcher et al (2000). Koppers and Watts (2010) and Konter and Jackson (2012) discussed the geology and tectonism of the island chain in more detail, shedding light on some areas about the volcanism origin of Samoa.

Several German authors reported recent eruptions, in the early 19th century on the island of Savai’i, including Wegner (1902); Weber (1902); Angenheister (1909) and Friedlander (1910). Anderson (1910) translated the early eruption activities into English, which became the first document focusing on the geology of Western Samoa. The active plume- driven hot spot of Vailuluu, described by Hart et al (2004) and Staudigel et al. (2006).

Kear and Wood (1959) estimated the age of the six volcanic formations, in relation to several geomorphologic features. This first detailed geology study, of Western Samoa

51 contains the most valuable base information for any future scientific research on the island. The potassium-argon ages of the earlier volcanism were reported by Natland and Turner (1985) and Workman et al (2004). The only radiometric dating of the Holocene volcanism so far was undertaken by Grant-Taylor and Rafter (1962) and Nemeth and Cronin (2009). The radiocarbon dating, from Nemeth & Cronin (2009) was one of the main components, of the volcanic hazard assessment on the island. However, several coral clasts from Goodwin and Grossman (2003) dated to the Middle to Late Holocene coastal evolution of Upolu, produce some indication of Holocene-age activities in the southern part of the island.

Volcanic hazard assessments of Savai’i and Upolu were originally carried out by Taylor & Talia (1999), under the United Nations Development Programme, through the South Pacific Disaster Reduction Programme of the South Pacific Applied Geoscience Commission (SOPAC). Cronin et al. (2006) reviewed the volcanic hazards of the two main islands, in conjunction with the Massey University Institutional Repository, European Union, SOPAC and the Government of Western Samoa. In addition Nemeth and Cronin (2009) investigated if there was any link between the oral traditional of Samoa, in relation to the broad spreading eruption activities, from the Holocene to the present.

Isotopic, geochemical and petrographic studies of the basaltic lava flows of the six volcanic units (Fagaloa Formation, Salani Formation, Mulifanua Formation, Lefaga Formation, Puapua Formation and Aopo Formation) of Western Samoa have been reported by Hedge et al. (1972); Hawkins and Natland (1974; 1975); Hawkins (1975); Peterson and Tiling (1980); Natland (1980); Natland & Turner (1985); Palacz and Sauders (1986); Wright and White (1986); Johnson (1986), Wright (1987), Hawkins (1987); Pored and Farley (1992); Hauri et al. (1993); Hauri and Hart (1993); Fepuleai (1997); Cibik (1999); Natland (2003); Workman et al (2004); Hart et al (2004); Jackson et al (2007); Koppers et al (2008); Jackson (2009); Koppers and Watts (2010); Jackson and Shirey (2011) and Konter and Jackson (2012).

Jackson et al. (2010) used the isotope signature tools, to determine the origin of several seamounts and islands along the Samoan island chain, where their geochemistry signatures distinguished them from the Samoan volcanism. The outcome of the study facilitates the reconstruction of an interloping process, where the Austral hotspots (Rarotonga, Rurutu and Macdonald) to the southeast, were sailed from the west, through the Samoan volcanic zone as the hotspot highway. In addition Jackson et al. (2010) used the same approach in examining the isotopes signature to trace the Samoan mantle leaking mechanism toward the Fiji Basin. More comprehensive studies of the same scenario, reported by Price et al (2014), reveal the wide extent of the Samoa mantle leaking, to the noth eastern part of Fiji.

The human occupation in Samoa commenced during the period of heavy Holocene volcanic activity, with studies including those from Green (1974); Petchey (1995): Dickinson and Green (1998); Petchey (2001); Goodwin and Grossman (2003); Martinsson-Wallin (2007) and Nemeth and Cronin (2009).

Argon-Argon dates flank submarine lava of Savai’i reaffirmed the idea that the Samoa island chain was the part of the hotspot process, of the last 5 Ma as reported by Koppers et al. (2008). This new age, together with more recent dating by Koppers et al (2011), reveals that the eastern end of the island chain facilitated the reconstruction of the two young sub-parallel en echelon trenches, based on isotopic components and their geographic position.

PART 2: The study area

2.4 VOLCANIC HERITAGE SIDELINE OF THE STUDY AREA

Like many other parts of Samoa, the eastern end of Upolu has mythology that relates to Tagaloalagi, a god of rock (Figure 2.8). The volcano legend at this part of Upolu is an amalgamation tale from people who grew up in the Aleipata district, and other parts of Samoa. The mythology of Samoa describes that, Tagaloalagi was the chief of all gods (aitu – ghost spirit), the creator of the universe who rules the eastern and western part of Samoa.

According to the volcanic heritage story of Aleipata district, the eastern end of Upolu was ruled by one female and four male giant gods (aitu) meaning volcanoes. These are all the siblings of the Tagaloa’alagi; four brothers Lano-o-lepa, Lanoto, Lanotai and Lano’omoa with one sister Olomauga. The five gods bestow the honour known as “O ao o Atua” (Goliath of gods). Lano-o-lepa was the eldest, had three children, a boy (Tialata) a girl (Olomaga) and a son (Mauga-o-savai’i) from the Savai’i Island’s queen. Lano’omoa the second oldest, had two children (boy and a girl), Lua-o-tane and Lua-o-fafine. Lanoto and Lanotai were still single at the time. The four male giants were possessive, and fully protective of their sister, reason that she settled in the centre among them.

The word “ao” means “cloud” suggesting that these edifices were eventually in or above the fog line. However, these volcanoes have become the highest elevation at this part of the island. A prefix “Lano” has an extension “Lanomau” in the Samoan language means “permanent place”. This refers to the central eastern most part of the island, now claimed as their forever burial location. The term “Lano” on the other hand is a “mavaega” or “feagaiga” means “promise” or “bravery award” from the Tagaloa’alagi for wellbeing of his people.

Mythology states that the five gods settled in the high central ridge as giants, so that they could be seen by the rest of the island. From high central ridge the five gods would be

54 able to communicate as far as Manua Island (American Samoa) the residential of the Tagaloalagi. As they became older the gods had pledged to their people. “If we die our hot bloody tears (meaning lava) would become a thick solid foundation of the territory, our ashes would be developed into fertile environment, and our cold tears (meaning lakes) would be the part of our memory forever. In addition our tears would signify peace and love, so anyone would have a washed would be revived”. This referred to cold lakes (include the Crater Lake Lanoto), harbouring within the Aleipata mountain range, at the eastern most end of Upolu.

2.5 THE CRATER LAKE AREA

Under the Western Samoa Land and Environment Act 1989, the Crater Lake Lanoto was declared as part of the Samoa National Park, even though the lake area is under a customary ownership (Schuster, 1993). This declaration allows the government to manage, and protect sites like the Crater Lake Lanoto for conservation purposes. For instance non-drinkable water sources from the lake have been distributed to the nearby villages for domestic uses. This small water scheme is currently administrated by the Samoa Water Authority with supports from a council of chiefs (matai) of the Aleipata district. The water scheme project was installed in September 2009 to help the drought at this part of Upolu Island.

Lanoto maar has a length of 225 metres and a width of 180 metres. A bathymetric map shows that the depth of the lake is up to 5 metres or more in the central part (Figure 2.12). The maar has steep on the eastern and western but shallow toward northern part. It surrounding by a broad swamp area and it estimates to cover almost half of the crater floor.

FIGURE 2.12 Bathymetric map of the Crater Lanoto maar. Contour interval is 1 metre.

Figure 2.13a shows the broad swamp area surrounded the deep part of the lake and Figure 2.13b indicates several deep pools up to 7 metres depth scattered within the swamp areas. Figure 2.13c shows the jetty located near the central part of the lake where it was used as the coring platform. Two water pumps have been installed on the jetty to pump the water to the nearby villages. Figure 2.13d shows the deepest part of the lake of more than 5 metres. The Crater Lake Lanoto is shallowed by the flat-top volcano of Crater Lano-o- lepa on the western side.

The crater wall of Lanoto volcano is heavily vegetated with mixed species of primary lowland and montane rain forest. Vegetation local names are in bracket beside the botanical taxonomy. Tree ferns include the species Cyatheaceae (oli’ol’i), Cyclosorus interruptus (laugasese launinii), Acrostichum (lauauta or alofilima), Paspalum orbiculare (vaolima) and Mikania micrantha (fuesaina). Wetland areas are dominated by a few patches of Pandanus turritus (fasa or lau kokolo) and herbaceous marsh. These include Rhizophora samoensis (togo), Barringtonia samoensis (fuku), Erythrina fusca (gatae), Inocarpus fagifer (ifi), Hibiscus tiliaceus (fau), Kleinhovia hospital (fua’fua), Bruguiera gymnorrhiza (apulupulua), and Xylocarpus moluccensis (akone vao). Eleocharis dulcis (utu) carpeted almost every part of the swamp with batches of Macropiper puberulum (ava’ava’aitu), Carex graeffeana (vao tolo or fiso), Paspalum orbiculare and Pandanus turritus).

2.6 STRUCTURAL GEOLOGY OF THE EASTERN UPOLU

Like many parts of Upolu the easternmost end of the island, is deeply carved by many valleys that radiated out toward the coast. Figure 2.14 shows the geological map of the eastern most part of Upolu with the Crater Lake Lanoto situated in the Aleipata region bordered by four major faults: the Fagaloa-Faleali’li Fault (Figure 2.9) to the west, the Tiavea Fault (this-study) on the north, the Lepa Fault (this-study) on the south and the Fanuatapu Fault (this-study) to the east. At the eastern part of Upolu Island, the alignment of volcanic cones along the Upolu Major Fissure System interrupted by the Fagaloa- Faleali’li Fault system at the south of Lemafa.

The Upolu Major Fissure System (UMFS) continues from the west of the island, toward Nu’ulua Island on the eastern end of Upolu. At the eastern end, the UMFS branches out in northeast-southwest direction, to form the Aleipata Fissure System (ApFS). The ApFS seems to run parallel with the Fanuatapu Fault (Figure 2.7). The Lepa Fault strike continues along the coast to the Cape Tapaga on the eastern end of the island. The fault apparently elongated parallel with the UMFS toward the easternmost end of the island (Figure 2.7).

Collapsed Fanuatapu, Nu’ulua and Nu’utele craters are presumably associated with the down-thrown of the Fanuatapu Fault toward east direction (Figure 2.8). The fault running at an acute angle offsets the parallel orientation of both the Upolu Major Fissure System and the Lepa Fault. The Fanuatapu Fault seems to continue to the south of Nu’ulua Island. This could relate to the major interruption in the continuity of the volcanism further east, along the deep ocean runs parallel with the UMFS. The ApFS generates a short string of explosive phreatomagmatic eruption, including those of Nu’utele, Nu’ulua, Fanuatapu, Namua and Cape Tapaga (Cronin et al., 2006).

A major limb of the Sinoi Fault (this-study) extends in a southerly direction and dissects the Lepa Fault between Aufaga and Saleapaga village (Figure 2.14). This cross cutting relationship shows that the Lepa Fault is much older than the Sinoi Fault. The Sinoi Fault branches out in a northeast direction where east and west limbs are parallel to a major stream running from the central part of the island. The two limbs stretch out to the north and slice up the Upolu Major Fissure System, on the west of the Crater Lake Lanoto and the east of Crater Lake Lano-lepa (Figure 2.14).

Highly jointed, fractured, eroded and weathered lavas of the Lower Fagaloa Formation (Fepuleai, 1997), dominate the northern portion of the eastern part of Upolu Island (Figure 2.14). The broad Salani lavas advance toward the coastal area to the northern part, through lava tunnels and valleys and almost overlying the rest of the older formation. Like the Fagaloa Formation, the Salani Formation is highly fractured, highly jointed, highly eroded and highly weathered, and dominates the east most part of Upolu. The Salani lava outpours from several vents, along the Upolu Major Fissure System

59 including those of Crater Lano-o-lepa, Crater Afulilo, Crater Lanotai, Crater Lano’omoa, Crater Lua-o-fafine and Crater Lua-o-tane (Figure 2.14).

In many locations, the Salani lavas are dark-grey pahoehoe-flows, with a thicknesses of 20 cm to 1 m or even more, intercalated with thin reddish-brown scoria breccia. Along the coast at some places, the scoria breccia and pahoehoe flow almost have the same thickness. It is estimated that the thick Salani unit is upthrown at least some 60 m northwards along the Lepa Fault, at a very steep angle (almost vertical), striking in an east to west direction. The upthrow of the Lepa fault to the north east generates a narrow coastal platform from the east of Aufaga village, to the west of Cape Tapaga (Figure 2.14).

Kear and Wood (1959) suggested that lavas of the Fagaloa Formation and post-Fagaloa suites on the main islands outpoured from the same rift zone put simply, the re-eruption of older volcanic craters is a common characteristic of Samoan volcanism. Re-eruption of the older craters has occurred since Fagaloa Formation was deposited and continues to the present. This could be the major reason for the scarcity of craters of the Fagaloa Formation exposed on the main islands (Fepuleai, 1997; Cibik, 1999). A good example is the exposure of the young Mulifanua cones as outlier along the older Salani Formation on the easternmost part of Upolu (Figure 2.14). This assumption emphasises the fact that older craters, thought to be ceased, have a tendency to re-erupt. In other words, the Salani and Mulifanua craters that are widespread in the centre rift, of the eastern Upolu could cover the older craters of the Fagaloa Formation.

Three stages model cartoons (crater formation, scoria cone growth, lava outpouring and crater floor subsidence to form pit-crater) demonstrate the cone evolutionary feature of the eruption scenario in Western Samoa. The three cones evolutionary stages are very difficult to distinguish in the field. Figure 2.15a shows the first stage of a newborn vent known as “crater formation” along the central major fissure system zone. This initial stage it can in form of a cone or an elongated fissure. Figure 2.15b displays the second stage of the cone evolutionary known as “scoria cone growth”. This second stage associates with multiple activities results in cone morphology change. Figure 2.15c

60 indicates the third stage of the cone evolutionary process known as “lava outpouring - phase”. Lava outpouring occurs as the scoria cone growth activities frequently continue. The evolutionary final phase is referred to a stage that the volcanic crater subsidence and forms the pit-crater (Figure 2.15d). This can be a resulted of volcano crater floor collapse and later forms maar-lake in many cases. Most of the post-erosional cones observed along the major fissures of Upolu and Savai’i are either stage (b), (c) or (d). Commonly, they recognised in the field as a towering steep slope cones, in many parts of the main islands (Figure 2.15d).

Crater Lanoto is characterised as the growth scoria cone which outpoured lava from double craters contemporaneous of the Mulifanua Formation age (Kear and Wood, 1959). In similar case, the re-eruption of the Crater Lano-o-lepa (west of Crater Lanoto) of the Salani Formation displays a combination of stage (b) and (c) of the evolutionary model.

This resulted in the formation of the Crater Lake Olomaga and Crater Tialata during the Mulifanua Formation episodes (Figure 2.13). Similarly, the Fogalepulu volcano of the Salani Formation (not on the map) northwest of Seuga crater (Figure 2.14) also exhibits a parallel eruption style. Based on the geological map (Kear and Wood, 1959) the broad elongate crater of Salani Formation comprises of three scoria vents of Mulifanua Formation could represent a re-eruption activities of the Fogalepulu volcano.

2.7 GEOLOGY OF THE CRATER LANOTO

A combination of the short and long term eruptions associated with the post-Fagaloa Formation are peppered along the Upolu Major Fissure System at the easternmost end of the island. Kear and Wood (1959) stated that the Crater Lanoto includes Crater Olomauga, Crater Olomaga, Crater Tialata, Crater Mauga-o-Savai’i and Crater Seuga, are all of the short-term eruption type associated with the Mulifanua Formation. This classification was based on the small volume of emitted lava flow. A scatter of short-term activities of the Mulifanua Formation, at the eastern end of Upolu represents simultaneous eruption behaviour of the post-Fagaloa volcanism.

Figure 2.16 shows a cross section from Crate Lanomoa (southeast) to Crater Seuga (north-west). Crater Lake Lanoto is located at approximately 400 m above sea level, where it is shadowed by Crater Lano-o-lepa to the northwest and Crater Olomauga to the southeast. The two limbs of the Sinoi Fault, elongated in a northeast to southwest direction deeply dissect the thick Fagaloa and Salani Formations. A downthrown section of the Sinoi Fault is approximately located between the Crater Lanoto and Crater Tialata.

A thicker Lalomauga Alluvium unit blankets most terraces on the eastern and western part of the Crater Lanoto. Lalomauga Alluvium mainly consists of the weathered materials of the Mulifanua Formation and dominated by mixed assemblage of old and younger volcanic units. Reddish brown soil predominates the area and it believed to be a product of rapidly weathered scoria breccia. Colluvium deposits are very thick around several craters and scarp faults and mainly host organic and inorganic materials. Soil erosion appears to be high in steep locations, and also areas close to a network of radial drainage.

Figure 2.17 shows aerial photographs of the Crater Lanoto. Crater Lanoto is a ukulele- shapes feature, elongated northwest to southeast. The rim has a flat top cone structure which is characterised by Cronin et al., (2006), as an explosive scoria cone volcanic feature. In addition, Crater Lanoto is a double-cratered volcano, which may have erupted from two activities, “narrow graben-like crater” and bowl-like feature known as “pit- crater”.

The volcano could be initially erupted from the narrow graben-like crater on the eastern side and pit-crater in the western at the final stage, hence its shape. The pit-crater could be a product of tension along the major fissure system associates with local faults. The narrow graben-like crater is a similar description to define the Matavanu eruption in 1905-1911 on the central western part of Savai’i. This volcano has a chain of pit-craters, which suggested to be initially erupted from three vents but following the crater floor collapse and formed a single elongate crater of 200 m wide and 300m long (Taylor and Talia, 1999). The Crater Lanoto could also have the chain of pit-craters but lack of evidence to claim such a feature.

FIGURE 2.17 Aerial photograph showsing the ukulele-like shape of the Crater Lake Lanoto, to the east of the Crater Lano-o-lepa volcano, or the south of Maimoaga vents. Pyroclastic deposit occurs on the western and the eastern parts of Lanoto. Several strips of unconsolidated materials produced by mini-avalanche events overlie the pyroclastic deposit. A tongue of lava flow extends parallel to the Sinoi valley, while the other stretch south to the east of Crater Fili. Large slump of more than 300 m in length occurred at the southern part, partly covered some portion of lava flow. The western limb of Sinoi Fault extends north- south direction, to the west of Lano-o-lepa, where the east limb stretches to the south of Lanoto crater. Stream channels radial from Crater Lano-o-lepa and Crater Lanoto to the south, where link to the east of the Sinoi valley, in other words run parallel with the Sinoi Fault. The original aerial photo is a property of the National Mapping Section, of the Ministry of Natural Resources and Environment of the 2011 version.

The pit-crater formation could be a product of a ring of normal fault generated from tension fractures and normal fault at shallow depths rather than related to magma

64 chamber as most caldera collapses affect much greater depths (several kilometres) (Gudmundsson, 2008). Ring fault mechanism for basaltic volcanism is still poorly understood (Gudmundsson & Nilsen, 2006; Gudmundsson, 2008). However, this ring fault could be associated with a surface subsidence of the pit-crater to the western part of Lanoto volcano at a shallow depth of approximately 5-7 m or even more. The ring fault may be indicated in the bathymetric map (Figure 2.12), where the subsidence part forms a kind of funnel shaped. The contact between the pit-crater and the pre-volcanic country rock support the subsidence.

This subsidence scenario together with erosion may cause the maar-diatreme of the Crater Lake Lanoto to expose on several sections. Maar-diatreme is associated with fragmented country rock, brown-yellowish juvenile lapilli tuff and volcanic bombs revealing, an architecture of phreatomagmatic volcano (Nemeth & McGee, 2010; Kaulfuss et al., 2012). Additionally, few volcanic bombs of up to 6-12 cm long with 3-5 cm wide are, well-welded with the brownish yellow lapilli tuff occurred on the western and northern section of the pit-crater. Several of these volcanic bombs together with ballistic (10-30 cm) are commonly composed of irregular cracks, described as cauliflower bomb/ballistic in Nemeth and McGee (2010). The cauliflower bomb/ballistic implies the magma/groundwater interaction of explosive activity.

Several sections of the outer part of the Crater Lanoto rim walls are associated with cone rafting, whilst the southern part has a large slump more than 300 m in length. This could be product of weathering and erosion process in the area. Crater Lano-o-lepa to the west is a flat top volcano which is parasitically overlying by double craters of later activities of the Crater Lake Olomaga (Figure 2.17). The Crater Lano-o-lepa also shows the same eruption style, where older eruption starts from the east and younger activities occur on the west. The explosive scoria-cone eruption style could dominate the Lano-ole-lepa and Olomaga activities. A detailed description of the geological mechanism behind the formation of this distinct volcanic feature is found in Section 4.7.4.3 (Chapter 4).

The lower elevation of the western part of the crater wall implies collapsed and eroded. This generated a broad pyroclastic deposit, which extended north to south down-slope toward the foot of the Crater Lano-o-lepa (Figure 2.17). The growth and destruction of 65 the Crater Lanoto edifice may produces a complex facies architecture, that could fit in a description of a long term monogenetic volcano known as “polycyclic monogenetic”, as stated in the Nemeth and Kerezturi (2015).

The crater wall on the eastern is much steeper almost vertical in slope and higher compared to the western part. Despite the collapse at the western section however, it is still had evidence of the steep slope as well. The hard rock environment of the short-lived eruption like Crater Lanoto volcano, has a limited likehood of an explosion event. Based on the concept model of the integration in crater and edifice growth (Kerezturi and Nemeth, 2013), the Crater Lanoto volcano is estimated to have been up to ≥ 69 metres in height.

The eastern part of the crater is covered with broad unconsolidated to lithified materials which indicates that some of these materials were still very hot as they deposited. A well- welded portion of the pyroclastic deposit (30 m wide) coated the western part of the crater implying that is may have collapsed during eruption. Strips of unconsolidated material overlie the broad pyroclastic deposit, representing a later mini-avalanche event and it could be associated with erosion or may be a part of a cone collapse. There are series of stream channels that radiate out from the Crater Lanoto and Crater Lano-o-lepa toward the northern and southern zones.

Generally, the Crater Lanoto eruption is associated with a thick scoria breccia unit, and possibly with reddish brown weathered volcanic ash with a small volume of associated lava. Crater Fili (this-study) is located 30 metres from the main outlet divided the lava stream into two directions, along the Sinoi Fault and to the south-western part (Figure 2.17). The narrow tongues of V-shaped lava flow extend down slope along the Sinoi Fault whilst the other stretches out toward south direction to the east of Crater Fili. This is to suggest that, the Crater Fili could be older than the Crater Lanoto. Crater Fili is adjacent to the Crater Lanoto and suggests they are both part of a same magmatic activity. The Crater Fili could represent the initial eruption stage before the volcanism locus shifted to the west, as a result of some kind of mechanism and erupted as a narrow graben-like crater activity of the Crater Lanoto. This “western shift in volcanism locus” is

66 discussed in more details in Section 4.7.4.3. Maimoaga vents (this-study) of the Mulifanua Formation to the north of the Crater Lanoto (Figure 2.17) are dominated by scoria breccia, though they look fresher than those of Crater Lanoto. The vents are also adjacent to the Crater Lanoto implies they are part of the same magmatic activity.

There is no published information in relation to the age of the Sinoi Fault. However, the narrow tongue of lava flow extends down-slope of the Sinoi valley, runs parallel with the eastern limb suggesting that the fault is much older than the Crater Lake Lanoto. On the other hand the Sinoi Fault could also have triggered the cessation of activities in the Crater Fili, before activities started again in the west at the narrow-graben like crater of Lanoto volcano.

2.7.1 LAVA FLOW

The outer part of the crater rim wall of Lanoto volcano is flanked by thin-sheeted pahoehoe and scoria flow. Figure 2.18 shows an outcrop of the outer rim wall on the eastern portion of the crater. Highly weathered and fractured pahoehoe flow of light to dark grey with 5-12 cm thick, intercalated with very thin-sheeted of brownish red scoria flow. Both pahoehoe and scoria flow, consist of highly vesicular with porphyritic texture of coarse olivine phenocryst associated with a medium to fine matrix grained. The outer rim pahoehoe lava consists of thin lustre band of fine to coarse olivine and pyroxene phenocryst. Coarse olivine and pyroxene phenocrysts of 5-12 mm in size are commonly occurred in the outer rim lava suites. At the upper part of the rim wall it seems more vesicular and scoriaceous in comparison with those at the lower section. The rim wall slope ranges between 45o to 65o or almost vertical in several section.

Thin-sheeted pahoehoe flows indicate that the lavas are very fluid and could be moved rapidly down-slope during earlier eruption episodes. This implies that the thin-sheeted pahoehoe lavas were produced by very high temperature eruptions, associated with very low magmatic viscosity. The thin-sheeted flow is characterised by highly vesicular lava indicating a fair amount of gas was trapped within the flow as it cooled down.

Boulders dominate the inner and outer part of the crater rim wall on the western part of the crater. Most of these boulders are in situ while others seem disturbed by erosion. This implies that these typical lava flows are deeply dissected by a series of joints intersecting at different angle. Kear and Wood (1959) use the boulder characteristic as a unique feature to distinguish the Mulifanua Formation, from other volcanic units of Western Samoa. These boulders are believed to be due to shrinking hot lava flows as they cooled and broke up. Unstable shrinkage lava flow suggested was the major factor associated with the collapse of the western part of the crater wall.

Lavas exposed at the inner part of the crater are less vesicular and scoriaceous than those at the outer part of the rim wall. Olivine and pyroxene phenocrysts in the inner rim lava approximately are less abundant in comparison with those of the outer rim lava. The

68 inner rim lava may refer to as a “solidified lava-lake” described in a maar-distreme volcano model of Kereszturi and Nemeth (2013) and Nemeth & Kereszturi (2015). In addition, the outer rim flows are highly weathered in comparison with those of the inner rim hence, the outer rim lava suites are much older.

Figure 2.19 shows the onion-skin like structure feature of about 1.5 metres in diameter on the south eastern portion of the outer rim wall. This distinct form of mechanical weathering is common in lava of Salani Formation, and the Upper Fagaloa Formation (Kear and Wood, 1959). This is also supports the idea that the outer rim lava is much older than the inner suites.

Spheroidal weathering also occurs in the outer rim lava. The intersection of joints and fractures associate with the intensity of weathering at the outer rim lavas. The spherical weathering feature is very rare in lava suites of the inner part of the crater in comparison with those of the outer part.

2.7.2 TEPHRA DEPOSITS WITHIN THE CRATER LAKE LANOTO BASIN

Primary tephra deposits around the Crater Lake Lanoto rim and nearby areas are very limited. This is common where there are very steep and heavily vegetated slopes, and high rate of erosion. Furthermore on the eastern part of of Upolu, the area is blanketed with a broad lava flow. However, tephra deposit within the Crater Lake Lanoto basin could contain relatively continuous records of the past activities in the region. Lake sediments are expected to contain a mixture of primary, secondary, epiclastic, cryptotephra (microscopic airfall) and contaminated tephra components.

Based on the geological map (Kear and Wood, 1959) the Crater Lanoto and other volcanoes nearby are products of Mulifanua activities. This corresponds with the fact that these volcanoes could have erupted simultaneously. Hence airborne deposits within the lake basin may not only have originated from the Crater Lanoto eruption activities, but also contain tephra components from other volcanoes in the area. Contaminated airborne deposits could be mainly transported, via the prevailing southeast trade wind. The predominantly southeasterly trade wind is parallel to the chain of volcanoes to the eastern end of the island. This is possibly why there may be more contaminant tephra associate with lake sediment deposits and the coring operation would intercept these volcanic components within the depositional basin of the Crater Lanoto. In addition, Natland (2003) proposed that heterogeneous source lying along the island chain of Samoa and it expects the post-erosional volcanism could have similar chemical signature. Hence the geochemistry of Crater Lanoto tephra deposit and contaminant airborne would be a challenged to distinguish in this study.

Thin soil deposits on the inner rim wall platform some 6-12 cm in depth show evidence of pyroclastic deposits. These deposits are highly weathered, uniformly scoriaceous, brittle and dark grey to brownish red in colour. Perhaps, the majority of these deposits, along the rim wall, could be eroded and transported into the lake as secondary or epiclastic deposits, and mixed with a high content of organic materials in the lake sediment. At this stage, most of the in-washed primary tephra component will have completely changed its original morphology. Tephra deposits extracted from the lake

70 core are highly weathered, uniformly scoriaceous, tubular and yellowish brown colour. The morphology of tephra deposits from the inner rim platform, and the lake basin is discussed in more detail in Section 4.4.2 and Appendix 3 of this thesis.

A very few thin layers of strongly-welded brownish yellow fine to coarse volcanic tuff, expose on the southeastern part of the crater, and several sections along the pit-crater rim, display features that are suggestive of deposition of airborne materials. These include lapilli deposits of 0.5 to 3.5 cm and volcanic bombs of up to 12 cm in length. This indicates that the Crater Lanoto activities could behave differently, that sometimes erupted quietly or in an explosive style.

CHAPTER 3 METHODS

3.1 OVERVIEW

This chapter is divided into two main sections: fieldwork methods and laboratory techniques. The fieldwork section includes coring gear, coring procedure and the total station mapping device procedure. Laboratory methods include the following: method of separation of the sediment from the coring barrel and 2 cm subsampling, magnetic susceptibility (MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), inductively coupled plasma mass spectrometry (ICPMS) for trace element, argon-argon (40Ar/39Ar) dating, radiocarbon (14C) dates and lead-210 (210Pb) dating.

3.2 FIELD WORK METHODS

The fieldwork was carried out in two parts. Firstly, a reconnaissance trip to obtain overview of the volcanism was carried out on both main islands. The focus included volcanic lakes, the overall volcanology-geology and structural geology features dominating the two main islands. Faults and fissures on the main islands were determined from field observations, satellite images and aerial photographs. The main purpose of this was to identify how the structure geology influences the nature of volcanism in Samoa. All faults and fissures were named and plotted on the geological maps (Figure 2.7 & 2.8). In addition, several locations within the 5 km in radius from the selective site were visited, to locate primary tephra deposits. Unfortunately, the extension of these volcanic components is very limited due to erosion, thick vegetation, later lava flow and human activities.

The next phase was the coring of the selected site; the Crater Lake Lanoto. It was relatively easily to gain access to the lake interior sediments with the coring equipment, which was one of the main reasons for choosing this particular site. The crater lake

72 sediments of Lanoto were cored by hand, following the methods of Gale, 1995. The fieldwork methods and coring procedures are outline below.

3.2.1 CORING GEAR

All coring gear was designed for use in remote areas like Crater Lake Lanoto. The coring equipment was built from scratch using the designs of Gale (1995). The materials required to construct the gear, for these particular coring operations are available in Samoa, and repairs could have been carried out on the island if necessary. Figure 3.1 shows several coring devices used in the operation. The coring apparatus include those of 50 mm and 90 mm PVC, semi-handle clamp, 50 mm and 90 mm PVC cylindrical hammer, and 7 m of 50 mm and 90 mm waste PVC. A flexible waste PVC was selected as coring barrel due to it toughness and resistance to cracking.

FIGURE 3.1 The coring gear; 50 mm hammer (11 kg), 50 mm PVC semi-handle clamps (8 kg), 90 mm hammer (18 kg) and 90 mm PVC semi-handle clamps (13 kg).

3.2.3 CORING PROCEDURE

There were twenty one cores were extracted from a 50 m by 50 m grid covering almost the entire deposit basin. Most cores were inserted by hand using a percussion technique. This involved sliding the cylindrical hammer, down onto clamps tightly fastened around the core barrel. The depth of insertion was measured and prior to

73 extraction, the top of the barrel was capped to increase suction, and to minimise the risk of losing the core, from the bottom of the barrel.

Because of the water depths involved (up to 5 m) within the coring grid zone, we occasionally increased the length of the core barrels by partially inserting the first barrel into the sediment, and then gluing a second barrel in place on top of the first. After leaving the two barrels strapped in position overnight, coring and extraction proceeded in the usual way. This procedure was remarkably successful.

Each core barrel was chopped down to the top of the sediment column to minimise disturbance during the transportation. The cores were carefully transported vertically avoiding disturbance from the coring site to the vehicle and the laboratory, in order to avoid any mixing at the mud-water interface.

Figure 3.2 displays the coring procedure in the deeper part of the lake area where a raft was used as the coring platform. The glued-barrel of 50 mm PVC was, clamped on both sides before it was hammered down to a certain depth. Extraction was normally undertaken by hand. This involved twisting the barrel out of the sediment using clamps tightly fastened around the barrel walls.

FIGURE 3.2 Coring operation carried out at the deepest parts of the lake. The glued-barrel insert penetrated perpendicular to the lake floor before hammering it down to a certain depth.

Figure 3.3 shows the coring of the master core on the jetty platform. The glued-barrel hammered down to 7 m water depth and extracted a sediment core of almost 5 m. A

74 custom-built tripod was set up over the core, and a block-and-tackle set-up was used to extract the core barrel.

3.2.3 TOTAL STATION DEVICE

A depositional basin map of the Crater Lake Lanoto created using an electronic measuring device known as electronic theodolite of a “total station” procedure. This employed to create a map of the Crater Lake Lanoto. A beam sent by a modulated, near-infrared light diode in the theodolite to a prism on a target. The prism stationed at several spots at the edge of the crater rim basin, where it reflects the beam back to the instrument, which installed on the jetty platform at almost the centre of the Crater Lanoto volcano. The distance between the instrument and the edge of the lake calculated from the difference between the departure and the arrival time of the wavelength beam. Total station measurements uploaded to computer application software and generate the deposition basin map of the crater. The map of the Crater

Lanoto depositional basin produced from the total station device procedure found in Chapter 4 section 4.1.

3.3 LABORATORY METHODS

Magnetic susceptibility techniques were deployed in both the field and laboratory. The three dating methods (Argon-Argon, Radiocarbon and Lead-210) were chosen so that, the earliest and the latest volcanic event of the Crater Lanoto were captured. Both Lead-210 and Radiocarbon dating of samples were, carried out at the Institute for Environment Research, Lucas Heights, New South Wales, of the Australian Nuclear Science and Technology Organisation (ANSTO). Argon-Argon dating of sample was performed, at the College of Oceanic and Atmospheric Sciences (Oregon State University, USA).

Electron probe microanalysis carried out, at Victoria University in Wellington, New Zealand, whilst XRF analyses on tephra and rock samples were, performed at the Waikato University and University of Auckland respectively. ICPMS analyses for trace element, Part 1 and Part 2, were conducted at the University of the South Pacific, Fiji and the University of Sydney, Australia respectively.

3.3.1 SEPARATION OF SEDIMENT FROM THE CORING BARREL SHELL

A separation of sediment from the core barrel was carried out cautiously. Figure 3.4 shows the two halves of the core barrel. The master core (D3) was cut open along its long axis and the two halves of the barrel were carefully separated to expose the sediment without disturbance.

FIGURE 3.4 The two halves of the 90 mm diameter core barrel (master core D3) after being cut open vertically.

The core was subsampled into a series of contiguous 20 mm thick slices. Each slice was placed onto a pre-weighed and labelled petri dish and weighed in its saturated state. The petri dishes and samples were then placed in an oven at 90°C, for 48 hours before being transferred to a desiccator, to cool prior to reweighing. Dry bulk density and moisture content of the master core were determined from 219 sub-samples. Raw data for the dry bulk density and moisture content of the 219 samples is found in the Appendix Section 2.

The dry bulk density and saturation moisture content of the 219 samples sample were calculated using the following equations (Gale & Hoare, 2011):

ρdb = M / V

-3 Where “ρdb” represents a dry bulk of the density (kg m ), “M” represents a dry mass (kg) of the sample volume “V” (m3).

Smc = W – D / D

Where the saturation moisture content “Smc” of a sample defined as the original mass of the sample “W”, subtract from the mass “D” of the dried sample.

Each dry slice on a petri-dish was carefully trimmed to about 2 mm of the outer shell, to remove any potential contaminants, for example that had been smeared downcore along the inner walls of the core barrel during the coring operation.

3.3.2 MAGNETIC SUSCEPTIBILITY TECHNIQUES

Magnetic susceptibility (MS) is a quantitative measure of the “magnetisability” of a material which has largely controlled by the concentration of magnetite in the sediment (Appleby, 1985; Oldfield, 1988; Dearing, 1999; Gale & Hoare, 2011). Reliable MS techniques have been used by scientists since the 1970s and 80s, which such techniques classifying and interpreting all aspects of the environmental materials (Dearing, 1999). In many cases, MS technique is a valuable tool for identifying different sediment units and their sources. In addition, MS measurements determine concentrations of Fe-bearing minerals and other different types of materials (Dearing, 1999).

In mathematical terms, volume magnetic susceptibility (x) is defined as the ratio, of the magnetisation induced within the substance (M), to the strength of the applied magnetic field (H) (Lascu, 1999; Dearing 1999; Gale & Hoare, 2011):

x = M / H, where

x = volume magnetic susceptibility

M = magnetisation induced of measure sample (Am-1)

H = field strength (T)

The MS technique was deployed for this study in two ways: the “first version” and the “second version”. The first version involves scanning a sedimentary core through a core logging sensor. The second version involves the drying of sediment from a selected core and transferring it into small vial to determine its low and high frequency, through dual frequency sensor device.

3.3.2.1 First version of the magnetic susceptibility

The first version of the magnetic susceptibility technique was carried out in the field to allow rapid non-destructive correlation of multiple cores within the sediment basin. This would link data to field observations enabling us to establish a detailed stratigraphy for the Crater Lake Lanoto. Magnetic susceptibility, also offers a rapid means of identifying tephra deposits (Oldfield et al., 1980; Appleby et al., 1985). The first version procedure of the MS technique was carried out for all 21 cores, in the field. Low frequencies reading were recorded at every 2 cm downcore. This was to assure that the 21 cores are consistent in the integrity of the sedimentary sequence.

Several procedures were implemented during measurement to ensure and maintain the accuracy and precision of the results. Before making any measurements, the 50 mm and 90 mm core-scanning sensors, were calibrated by using commercial calibration specimens, with susceptibilities of (x = 1490 x 10-6 CGS) and (x = 720 x 10-6 CGS) respectively. A magnetic susceptibility working station must be free of ferrous materials, and spurious magnetic fields, to minimise magnetic interference.

Figure 3.5 shows a set-up of the first version of the Magnetic Susceptibility (MS) technique. Each core was scanned through the core scanning board device where it connects to a MS meter. Measurements were made at 20 mm increments along every 21 cores. Low and high frequency MS were recorded for every increment. Those readings made at the start of each session, tended to be rather erratic, so recording began only once the equipment had stabilised, and consistent readings were obtained. At least three readings were made at every increment down the core. If these were inconsistent, however, further readings were made until consistent values were obtained.

FIGURE 3.5 First version of the magnetic susceptibility technique was set-up, where each core was scanning through the core scanning board device, which connects to the MS meter.

A mass specific susceptibility of each incremental measurement is represented by the following equation (Dearing, 1999):

Xlf = k / p

3 -1 where “Xlf” represents the low frequency of the mass specific suceptibility (m kg ), variable “k”refers to the volume susceptibility and variable ‘p” is represents the sample bulk density of kg m-3.

Mass-specific MS with respect to depth would identify horizons of high and low magnetite concentration within the sediment core. High magnetite content is represented by peaks and low contents are displayed by troughs. Volcanic sediments are associated with peaks whilst organic material tends to produce troughs.

3.3.2.2 The second version of the magnetic susceptibility

A second version of the MS procedures included measurements using small vial (length = 3.2 cm & diameter = 2.2 cm) of dry soil (inner volcanic rim deposit), basaltic lava chips (mini-core) and lake sediment. The method was utilized, to determine the relationship between the mass-specific magnetic susceptibility, against the frequency-dependent magnetic susceptibility, of dry lake sediments, catchment soils and catchment basaltic

80 lava. This would enable us to determine the actual processes associated with the lake deposition, base on variations in the concentration of magnetite distributed in soil, basaltic lava and straigraphic lake sediment.

In sample preparation, each catchment soil was sifted through a sieve pan of 2.0 mm mesh size. Coarse pebbles were crushed using fingers or a pestle and mortar before being subjected to a riffling process. The riffling procedure was use to separate bulk sediment sample into fine and coarse size. This riffling stage involves a lot of dust and all equipment were scrupulosly clean after every sample session to avoid contamination.

Figure 3.6 shows the set-up for the second version apparatus where the Dual Frequency Sensor (MS2B) connects to the MS meter. The catchment soils, lake sediments and rock chips were transferred into pre-weighed small vials, and weighed before insertion into the Bartington Dual Frequency sensor type MS2B device. A 2.1 cm minicore from each inner rim lava hand specimen was directly inserted into the MS2B apparatus. At least 25 readings were obtained from every sample (sediment & lava) to ensure it indicates a long consistent reading. Low and high frequency susceptibility values were recorded for every sample. These tests were carried out in a location where equipment had stablised and produce consistent readings.

FIGURE 3.6 The second version of the magnetic susceptibility method set up where Dual Frequency sensor (MS2B) connects to the MS meter.

Each sample measurement defined by an equation as follows (Dearing, 1999):

k (corrected reading) = sample k – (first air k + second air k) / 2

Where “k” is a volume magnetic susceptibility. (Note: “corrected reading” is the average of the 25 readings for low and high frequency MS for every sample of the 219 in total).

The frequency dependent susceptibility percentage measuremeant involves two “k” readings (low and high frequency MS) expressed by the following equation (Dearing, 1999);

(Klf – Khf / Klf) x 100,

At low frequency magnetic susceptibility “Klf” is the corrected readings and “Khf” is the corrected readings athigh frequency magnetic suceptibility.

Frequency-dependent susceptibility measurement downcore would identify high and low values imply the present of contaminate tephra component. A relationship between the mass-specific MS and the frequency-dependent MS would help classify different

sediment units and their sources. This classification would base on the strength and nature of the MS components within the sediment.

3.3.3 RADIOCARBON DATING

Scientists commonly use three terms: “radiocarbon dating”, “carbon dating and “carbon- 14 dating” to describe the same dating technique. The dating method, involves measuring the relative concentration of the naturally occurring radiometric isotope carbon-14 (14C) to determine the age of carbon-bearing components occurring in rock and sediment.

Carbon naturally occurs in three principal isotopic forms; carbon-12 (12C), carbon-13 (13C) and carbon-14 (14C). The 12C and 13C isotopes are stable and nonradioactive, whereas 14C (radiocarbon) is unstable and radioactive. Radiocarbon is constantly being produced in the atmosphere as cosmic rays interact with nitrogen molecules. This

radiocarbon then reacts with atmospheric oxygen to produce atmospheric CO2 which can then be converted to organic matter in plants via photosynthesis. The radiocarbon in plant matter can further be transferred to organic tissues in heterotrophs as they consume the plant matter. As an animal or plant dies the 14C isotope starts to decrease in concentration as it radioactive decays to produce nitrogen. Therefore, the older the tissues, the less radiocarbon it contains. The age of the plant or animal tissue can be reliably determined because this radioactive decay is predictable. The half-life of radiocarbon (the time it takes for half of its atoms to have decayed to produce nitrogen) was initially estimated to be 5568 years (Libby, 1946) but more recent estimates place it at 5730 years (Godwin, 1962) and this value used by scientists today to determine the age of plant and animal tissues.

Figure 3.7 shows the plot of time versus the fraction of 14C present. After an animal or plant dies its 12C isotope concentration remains the same through time. However, as stated above, every 5730 years, the concentration of the 14C isotope drops to half its original level. Once another half-life has been experience (i.e. after 11,460 years) the tissues will now contain about ¼ of the original 14C atoms (11,460 years). After the

17,190 and 22,920 years, the tissues would contain only 1/8 and 1/16 of the original number of isotopes 14C isotope respectively. As a consequence, by measuring the ratio of the 14C isotope to the 12C isotope, we can calculate how many thousands of years have passed since the animal or plant died. We use this procedure to determine the age of the tephra deposits in Crater Lanoto for several reasons: 1) depositional basin contains organic materials and 2) the lake is a part of Mulifanua Formation has an age of approximately between late Pleistocene and early Holocene (Kear and Wood, 1959).

FIGURE 3.7 Plot of time in years versus the fraction of 14C atom present.

Samples carefully selected from the four different depths intervals to obtain a broad view of the age of the four main volcanic episodes of the Crater Lanoto. The four dated samples (LL/D3-219, LL/D3-73, LL/D3-49, & LL/D3-34) were taken from Lano-1 Unit, Lano-7, Lano-9 Unit and Lano-10 Unit, respectively.

Two different methods were employed in this study to establish radiocarbon concentrations and convert them into age. Early methods included the “beta counting” technique where one literally counts the number of beta particles emitted by the decaying 14C atoms. This method was used for smaller sized samples (LLD3-49 & LLD3-73) in

84 this study. For the larger samples (LLD3-34 & LLD3-219) the acceleration mass spectrometry had been used.

The Accelerator Mass Spectrometry (AMS) of the Radiocarbon technique was performed at ANSTO to date tephra deposits of the Crater Lake Lanoto. Wide distributions of plant type in the sedimentary records provided valuable information in relation to climate and environmental changes during the Holocene time. Plant components chosen for the radiocarbon dating from the Crater Lake Lanoto sediments had to be selected with caution due to the presence of roots and stems that were not contemporaneous with the sediment they were ultimately preserved in.

Firstly, the dated sediment was sieved through 100um mesh. The <100um carbon fraction was retained then chemically treated, before it was dried for several hours. The carbon fraction of each sample was soaked, and washed in 10% hydrochloric acid (HCl), at a temperature of 60oC for at least half an hour. This was to ensure that all carbonates and fulvic acid contents had been removed. Hydrofluoric acid (HF) of 40% was added at room temperature overnight to ensure that, silica was removed for heavy liquid separation. Each sample fraction was placed in 10% sodium hydroxide (NaOH) at 60oC for 1 hour. This procedure was repeated several times, to ensure every sample fraction was free of humic acid and contamination.

A heavy liquid separation (LST) process was performed at 1.8 g/m and 2.0 g/ml, to separate inorganic matter from the lighter organic components. Unfortunately insufficient material could be isolated for dating so all material was dated. Again, the samples were placed in 10% HCl, at room temperature, to ensure all the atmospheric carbon mono-oxide (CO), contamination contents were fully removed, before being placed in combustion tubes, at set up temperature of 60oC to dry up. Samples (LLD3/34, and LLD3/73), with sufficient quantity for dating, went through sulphuric acid (H2SO4) treatment. This coincides with the fact that the two samples extracted from Lano-10 Unit and Lano-7 Unit. The two units comprise of 20 and 10 percentages of organic materials respectively, which were deemed adequate for the process.

Stuiver and Polach (1977) reviewed the counting rate methodology used to transform 14C concentrations into age expressed in the following equations (RC1, RC2, RC3, RC4 and RC6). The count rate procedure was one of the main features of the Lucas Heights radiocarbon dating technique employed to determine the age of tephra deposit within the Crater Lake Lanoto. This included the international standard of the radiocarbon activity widely used in most laboratories is defined by equation (RC1).

13 Equation – RC1: AON = 0.95AOX [1 – 2(19 + δ C) / 1000], where “AON” represents activity value and “AOX” refers to the 95% of the measure net oxalic acid activity (count rate).

The oxalic acid activity was normalised for 13C fractionation where measurements of δ13C are 13C/12C ratios expressed as a deviation from Pee Dee Belemnite (PDB) standard. Stuiver and Polach 1977 also outline that “absolute international standard” (abs) activity is defined by equation (RC2);

λ(y-1950) -1 Equation – RC2: Aabs = AON e , where “λ” represents 1/8267 yr (based on hypothetical half-life of 5730 years by Godwin, 1962).

14 14 Where “AON” represents the C activity of oxalic acid, normalised for C fractionation, which depends on the year of measurement (y). The radiocarbon proportion of the sample at this point in time is defined as a ratio between the activities of the present, in the year 1950 AD, and decay components normalised activity in the sample.

In order to determine the isotopic fractionation in all samples, the δ13C activity need to normalise into -25 per mil, with respect to the PDB standard, based on the terrestrial wood values express by the equation (RC3).

13 Equation - RC3: ASN = AS [1 – 2(25 + δ C) / 1000], where “ASN” represents normalised sample activity and “AS” represents a measure sample activity.

Based on Libby half-life hypothesis measured in 1950 AD, to calculate the age of a sample before 1950, is given by equation (RC4), where time is a function of nature logarithm, is also known as the “conventional radiocarbon ages”.

Equation - RC4: t = -8033 ln [ASN (in 1950) / AON (in 1950)], where variable “t” represents age of a sample before 1950 AD.

Percentage modern component “pM”, of the radiocarbon dating is a significant measure to determine, if the years of collection and measurement are not identical. This would

include the read just of the ASN for decay occurred, between collection and measurement procedure, at these particular times express by the equation (RC5).

λ(y-1950) Equation - RC5: pM = ASN / Aabs x 100% = ASN / AON e x 100%, where “pM” represents a percentage modern component.

3.3.4 LEAD-210 (210Pb)

Lead-210 (210Pb) dating was employed in this research, to date the events between 150 and 200 years ago at high resolution. Twelves samples (D3/1, D3/2, D3/3, D3/4, D3/5, D3/6, D3/7, D3/8, D3/9, D3/10, D3/11 & D3/12) from the top part of the master core (D3) were selected for 210Pb dating.

Lead-210 is a naturally radioactive isotope, produced from the decay through series of parental nuclei isotopes, like those of Uranium-238 (238U), Thorium-230 (230Th), Radium-226 (226Ra) and Radon-222 (222Rn). 210Pb components are absorbed into Crater Lake Lanoto sediments, through two significant paths, which are referred to as supported and unsupported 210Pb activity (Oldfield & Appleby, 1984; Oldfield 1988; Appleby, 1990; Appleby 2001).

Figure 3.8 shows the schematic sketch of the two pathways of the unsupported 210Pb and supported 210Pb into the Crater Lanoto deposit basin. Firstly, the supported 210Pb activity, derived from in situ decay of a fraction of 226Ra isotope, is directly washed into the lake through erosional processes. The activities of parental 226Ra were measured, to determine the nature of the supported 210Pb activity (Hollins et al, 2011; Harrison et al, 2003). Secondly, the decay portion of the isotope 226Ra, might be diffuses through the atmosphere, as the radioactive isotope gas Radon-222 (222Rn). These diffusion gas components, possibly resulting in rapid decay to unsupported 210Pb, where it became

87 atmospheric fallout through precipitation and dry deposition processes (Oldfield & Appleby, 1984; Appleby, 1990; Appleby, 2001; Harrison et al, 2003; Hollins et al, 2011).

FIGURE 3.8 Schematic diagram shows the major pathways of 210Pb components, into the Crater Lake Lanoto sediment, through either directly wash of the isotope component of 226 Ra into the lake, or the rapid decay of diffusion 222Rn gas. The unsupported components perhaps, fall either directly from the atmosphere into the lake, or settle in sediment around the crater rim, before in-wash activities occur, where fusion them with top lake sediments (Modified from Oldfield and Appleby, 1984).

Sample D3/1, D3/2, D3/3, D3/4, D3/5, D3/6, D3/7, D3/8, D3/9, D3/10, D3/11 and D3/12 from the upper part of the sequence (Lano-12 Unit), had been investigated for the Lead 210 method. Lano-12 Unit is the top part of the master core D3, and it describes in more detail in Section 4.4.1, Chapter 4. The 12 lake sediment samples were grinded into very fine powder, using the tungsten carbide apparatus (Rocklab Shaker Unit), of the University of the South Pacific. The apparatus was scrupulosly cleaned, and sand acid wash between every sample session. This was to ensure there would be no contamination, associated with the dating analysis procedure. Ethanol (95%) was been used to speed up the drying process, and avoid the stickiness of the sediment within the tungsten pot and rings. About 5 grams of every sample required for210Pb dating at the Institute for Environment Research, Lucas Heights, New South Wales (ANSTO).

The main feature of the Lead-210 dating is determining the vertical distribution of the two components, supported and unsupported 210Pb within lake sediment (Hollins et al, 2011). Supported component is the in situ decay of the parental Radium 226Ra isotope. Some fraction of the 226Ra diffuses into the atmosphere and become radioactive isotope gaseous Radon 222Rn. Radon gaseous rapidly decays into 210Pb and become atmosphere fallout through precipitation.

The granddaughter polonium (210Po) activity was used to determine the total unsupported 210Pb activity. The ANSTO of the Lead-210 procedures describe by Harrison et al (2003) and Hollins et al (2011). The procedure followed the first Lead-210 method by Goldberg (1963) and lake sediment application with Krishnaswamy et al (1971). Samples were dried in the oven at 105oC for several hours before spiked with 209Po and 133Ba tracers.

Each sample leached with hot concentrated sulphuric acid (H2SO4) for several hours. This was to make sure to release the polonium and radium. The two elements yielded into silver disk and barium sulphate (BaSO4) precipitate respectively. Silver disks of Polonium were analysed using High Resolution Spectrometry. Precipitated radium was determined through High-purity Germanium gamma detector (HPGe) using artificial tracer 133Ba.

Noller (2000) explained that, the concentration of 210Pb activity at depth, under ideal conditions, where the sedimentation is constant and undisturbed, noticeably represented by the Equation (L1);

Equation-L1: P(x) = Po exp (-λx / V), where

210 “Po” represents the concentration of Pb activity on the surface during the time(t = 0), “λ” represents the decay constant for the 210Pb that is (0.03114 y-1) and volume is the velocity of the sedimentation based on an exponential fit to the measure 210Pb.

In order to determine the concentration of integrate activity, of unsupported 210Pb isotope, in relation to a “constant rate of supply” (CRS) concept at such depth, is expressed by Equation (L2) (Appleby & Oldfield, 1978; Noller, 2000). It also suggested that, at any certain depth, the CRS is determined in related to the law of radioactive decay. This is

89 defined as the initial concentration of the unsupported 210Pb isotope, is the function of the constant rate supply, expressed by the Equation (L2).

Equation-L2: Co (t) r (t) = constant, where Co (t) is defined as the initial concentration of unsupported 210Pb in sediment of time taken (t) and the r (t) represents the rate of the dry- mass sediment of g cm-2 yr-1

The two geochronology models are CRS and the constant initial concentration (CIC) by Goldberg et al (1963) and Appleby & Oldfield (1978). The two models also referred recently as the Constant Flux and Constant Specific Activity (Noller, 2000). They are all related in the law of radioactive decay. At any depth (x) the 210Pb activity both model expressed as Equation (L3).

-λt 210 Equation-L3: Cx = Coe , where λ = is the decay constant for Pb, then the Equation - L3 rearranged few time to yield Equation L4). From the Equation (L3) the age of sediment at depth (x) can be defined as Equation (L4).

Equation-L4: t = 1 / λ Log (Ao / Ax)

210 Where “Ao” represent the total unsupported Pb activity at the top sediment of the core 210 D3 and “Ax” represents the total of unsupported Pb activity at the sediment beneath depth x of top part of the core D3.

The Equation (L4) has to be rearranged at depth (x), in order to yield a “constant initial concentration” (CIC) model, for sedimentation rate of the unsupported 210Pb isotope activities, defines by Equation (L5) as follows. The sedimentation rate of unsupported 210Pb activity was determined using the “constant rate of supply” (CRS). This concept is also known as constant initial concentration (CIC) in many literatures. Both concepts (CRS and CIC) are related to the law of radioactive at certain depth (Goldberg et al 1963; Appleby & Oldfield, 1978; Noller, 2000).

Equation-L5:t = 1 / λ Ln (Co / Cx) by Noller (2000) “OR” t = 1 / λ Ln (Ao / Ax) by (Goldberg et al 1963; Appleby & Oldfield, 1978).

Where variable “t” represents a difference in age between sediment at the top part of the Lano-12 Unit and sediment below the unit in years, “λ” represents the decay constant for 210 -1 the Pb that is (0.03114 y ), “Co” represents the initial concentration of unsupported 210 210 Pb activity at top of Lano-12 Unit and “Cx” refers to a total unsupported Pb activity in sediment below the Lano-12 Unit “x”.

3.3.5 ARGON-ARGON DATING

Potassium (K) atom has three natural occurring isotopes: potassium-39 (39K), potassium- 41 (41K) and potassium-40 (40K). The two stable isotopes are potassium-39 (39K), classified as the most abundant naturally occurring potassium isotope on earth, and followed by potassium-41 (41K). The least abundant isotope is radioactive 40K refers, has been commonly used in the dating of old volcanic mineral.

Potassium-40 (40K) has a half-life of 1250 million years, where a small portion decays to Argon-40 (40Ar) and the rest into calcium-40 (40Ca). Potassium (and therefore a component of 40K) is present in lava. The K-Ar dating method typically assumes that lava, and the rocks formed from that lava contained no argon and that radiogenic argon- 40 produced by the radioactive decay of 40K is retained in the volcanic rock. Because we know the decay constant for the reaction 40K → 40Ar, we can measure the relative concentrations of each isotope and, assuming that all argon-40 was generated from the radioactive decay of potassium-40, we can calculate the age of the lava.

The potassium-argon (K-Ar) dating technique has been used to date volcanic minerals on the two main islands, Upolu and Savai’i (Natland & Turner, 1985; McDougall, 2010). K- Ar dating requires the analysis of split samples for separate potassium and argon isotope analysis. Argon-argon dating (or 40Ar/39Ar dating) was introduced as a radiometric dating method to advance on K-Ar dating in terms of accuracy (Kelly, 2002). In addition, this method only requires one single analysis of a single mineral grain.

For 40Ar/39Ar dating, a mineral or rock fragment is crushed and then neutron irradiation from a nuclear reactor is used to convert potassium-39, (39K) into the radioactive argon- 39 (39Ar). A sample of known age is simultaneously exposed to neutron irradiation. 91

Trapped gases are then released from the mineral via heating and the isotopic composition of its component argon measured in a high-vacuum mass spectrometer. The isotopic measurements of argon can be used to calculate the 40K/40Ar ratio and after a correction for argon present that did not come from the decay of 40K (either from adsorption of atmosphere argon or inherited via diffusion), we can calculate the age of unknown sample in the same way as K-Ar dating, outline above.

Argon-argon has been successful used in Samoa in numerous of studies in both subaerial and submarine setting (Koppers et al, 2009; 2011). The 40Ar/39Ar was employed in this study, to determine the age of the inner part of the crater wall. The lava crop out at the outer part of the crater wall (outer rim lava suite) seem much older however, deeply weathered, fractured and highly altered, were the major reasons to avoid these suites for the argon-argon dating. Rocks selected for dating were carefully taken from the fresh flow at the inner crater rim lava flow. The alteration portion of the sample sawed out before the preparation procedure process. This was done in order to meet all the requirement steps, to satisfy and maintain an appropriate and reliable result.

Plagioclase in the groundmass and plagioclase phenocrysts from the fresh and unaltered inner crater rim lava used, for argon-argon dating. Raw data for the groundmass and plagioclase phenocryst found in the Appendix Section 5. Use of groundmass is highly recommended for argon-argon dating (Koppers et al., 2011). This conclusion based on a successful of the groundmass analyses from previous work. The study involved the radiometric dated of lava from the eastern part of the Samoan island chain. This project was targeted lava suites along the two young en echelon volcanic chains named, Vai and Malu (Koppers et al, 2011).

The sample preparation for argon-argon dating Crater Lanoto lava was followed the method of Koppers et al (2000; 2011). Rock samples were ground into three grain size 500-300, 210-300 and <210 µm. Each sample went through the sieving process. Sieved sample rinsed with 18 (Megaohm) MΩ water and acid leaching before dried overnight at 40oC.

At different amperages input all samples were carefully run through several procedures in the Frantz magnetic separator. Both groundmass and plagioclase phenocryst sample, rinsed with acid leaching and then 18 MΩ water, in the ultrasonic bath at a set up temperature of 50oC. Handpicking on the sample fraction was carried out to remove, any remaining alteration in both phenocryst and microcrystal. However the acid leaching procedure can be repeated, in case of any more severe alteration still present in sample.

Samples were irradiated for approximately 6–7 hours in the nuclear reactor after samples enfolded in aluminum foil (Koppers et al., 2000; 2011).The low and high temperature increments process, releases the argon gaseous on the surface, and the inner part of the mineral phase. This would be done through heating step of the irradiation technique. Each sample went through different heating intensity procedure. Low temperature scenario ensures that any remaining alteration and atmospheric signature would completely confiscated (Koppers, 2011).

The 39Ar/40Ar incremental step heating technique, allows the argon gas components to release gradually including those of submicroscopic mineral phases, as the temperature increase in a stepwise manner scenario (Koppers et al., 2011). This heating increment procedure, removes gas from mineral phases in all dimensions and deep within the mineral (Koppers et al., 2011). At least 33 incremental heating steps performed, to ensure a completed outgassing of argon gas from analyse of dating samples.

In addition heating step procedure is a significant method, to analyse mineral phases, in relation to their different break down temperature (Kelly, 2002). Lower temperature heating method using laser intensities unit (below 0.05 W), was the last stage of the heating step. Hence, all the remaining alteration and atmospheric signature were expected to be completely removed from the analysis groundmass and phenocryst components.

Kelly (2002) mathematically defined (Equation 3.1 and 3.2) the K-Ar dating method, as where the natural logarithm of the total decay factor of the 40K, and partial decay of the constant 40Ar are functions of time expressed by the equation (3.1);

Equation-3.1

Where variable “t” represents the time since closure, “λ” represents the total decay of potassium-40 (40K) and (λe + λ’e) is referred to the partial decay constant for argon-40 (40Ar).

Thus the Equation (3.1) rearranged few times to yield, the natural logarithm of the 40Ar and 39Ar ratio, with the total decay factor of 40K all becomes a function of time. This represented by the Equation (3.2), which was the main tool to determine argon-argon age of the groundmass and phenocryst procedure of Crater Lanoto inner rim lava suite.

Equation-3.2

Where variable “t” represents a time, “λ” represents a total decay factor of potassium-40 (40K) and “J” is referred to a dimensionless irradiation-related parameter of the heating steps procedure.

3.3.6 X-RAY FLUORESCENCE TECHNIQUE

The XRF technique was first discovered in 1845-1923 by Wilhem K Rontgen, a German physicist (Shackley, 2011). In 1950 the X-ray Spectroscopy became a commercial elemental analysis.

X-ray fluorescence (XRF) is a non-destructive analytical technique which involves the measurement of secondary X-rays emitted from a material which has been bombarded with high energy X-rays. The radiation emitted has energy characteristic of the elements present. Therefore, the XRF signature can be used to characterise major and trace elements present in rock or mineral in a non-destructive way.

94 Rock samples were analysed through a triplicate set up using a Panalytical Axios (1kw) wavelength disperse XRF, at the University of Auckland, New Zealand. The major and trace elements obtained from Rh tube, with a triplicate operation, follows the 28 international standards procedure calibration. Matrix corrections were made using theoretical alphas, and appropriate line overlap corrections for all elements.

Seven fresh inner volcanic rim lavas and six tephra samples (2 volcanic rim deposits and 4 lake tephra deposits) were selected for the XRF analysis. Rocks and tephras were ground to a very fine powder, using tungsten carbide apparatus and Rock-Labs Shaker Unit of the University of the South Pacific, Suva. In the basic XRF procedure, the powdered form enables the x-ray radiation to pass through every atom enabling an accurate signature i.e. fingerprint of the specific major and trace elements present.

Seven rock powder samples were weighed before being placed in an oven overnight at a temperature of 105oC to remove any remaining moisture within the samples. The samples were allowed to cool down for at least 30 minutes and reweighed before being ignited in the Black 1050 Degree Vulcan Muffle Furnace for at least 8 hours over night (Figure 3.9a). The Vulcan Muffle Furnace procedure allows all minerals in the samples to be ignited before allowing them to cool down and be reweighed. The samples were transferred into platinum wares, ready for the Eagon 2 Electronic Furnace procedure.

Figure 3.9b shows the Eagon 2 Electronic Furnace for samples fusing activity. The platinum placed in the Eagon 2 Electronic Furnace apparatus at 1050oC for 12 minutes, to ensure that all samples fused. The resultant fused disc to be used for XRF should be free from common notable problems, such as cracking, bubbles, recrystallization and insufficient materials. Where these problems were encountered, additional fused discs would be produced until perfect discs were attained.

FIGURE 3.9 Black 1050 Degree Vulcan muffle furnace, for mineral ignition and the cooling station. (b) Black Eagon 2 Electronic Furnace for fusing the samples.

Six tephra sand samples were analysed for XRF at Waikato University. Like inner rim lava suites a six representative tephra samples were also analysed through fuse disc

procedure. Weighted tephra powders were mixed with lithium metaborate (LiBO2) before transfer to Pt-Au crucible. This technique involves mixing of 0.3 gram of tephra powder, with lithium metaborate then transfer of the mixture to a Pt-Au crucible. Crucibles were placed in the muffle furnace at 1050oC for 6 hours. Samples were reweighed before being placed in the electronic furnace for 14-15 in minutes in the fused disc procedure. Glass discs must be homogenous to reduce effects associated with matrix and mineralogy size.

3.3.7 ELECTRON PROBE MICROANALYSIS (EPMA)

EPMA is a non-destructive technique used to determine chemical composition in tephra deposits of the Crater Lake Lanoto. Four tephra layer samples (LLD3/34, LLD3/49, LLD3/73 and LLD3/219) were selected for EPMA and each tephra layer sample went through the three analyses procedures: top of the layer, middle part of the layer and base of the layer.

EPMA was first introduced in 1950 by Raimond Castaing regarded as the father of the EPMA procedure (Mulvey, 1983). In his PhD in 1951 he constructed the fundamental 96 principles of the EPMA procedure which still use in the modern day. The EPMA improve through time and became commercially viable in the 1960s (Mulvey, 1983).

The EPMA technique involves the scanning of the sample surface by an electron beam. Figure 3.10 shows a schematic of the EPMA as the electron beam bombards the sample. This reflects a series of signals from backscattered electrons, secondary electrons, cathodoluminescence or X-RAY (Chatterjee, 2012). Backscattered electrons are high- energy electrons which produce an image from a relatively smooth surfaced volcanic shard. Secondary electrons are detected by a low-energy detector which produces images of volcanic shards with rough surfaces. Cathodoluminescence is a characteristic X-ray light use to determine a qualitative and the quantitative of element composition in the sample. All these characteristics combine to produce high resolution scanning electron image and complete quantitative and qualitative chemical analysis of volcanic tephra sample. Increasing precision of the EPMA techniques, has allowed subtle distinctions in major element concentration to be identified (Lowe, 1988a).

FIGURE 3.10 Schematic sketch of the Electron Probe Microanalysis components produce as the electron beam bombard the specimen.

EPMA of the Crater Lanoto tephra samples was carried out at Vitoria University, Wellington, using the JEOL 733 Scanning Electron Microprobe (Figure 3.11). The JEOL 733 microprobe is equipped with three wavelengths and dispersive X-ray spectrometer

97 for bombard the analysis sample. This special designed cornerstone technique is used primary for elemental analysis of polished mount surface volcanic glass shard and mineral. JEOL 733 beam is generated from heated tungsten filament of thermionic emission unit between 10 and 30 kV. In addition the beam also produce image of 40,000-36,000X magnification (Chatterjee, 2012).

FIGURE 3.11 The JEOL 733 EPMA set up of Victoria University. The equipment connects to two computers, where record activities and direct the probe to the most detail part volcanic shard component.

The aim of this EPMA analysis was to scan fresh individual volcanic glass shards for their major element composition. This could help fingerprints various behaviour in the Crater Lanoto activities during the four volcanic episodes.

There are some concerns about using the tephra bulk samples in the EPMA based on the fact that their composition can be disrupted, from other phenocrysts that are unrelated magmatically (Shane, 2000; Alloway et al., 2007 and Lowe, 2011). The bulk samples are very likely to contain fair amounts of accidental juvenile ejecta materials, from nearby volcanoes (Pearce et al., 2004). Bulk samples may also be contaminated by erosion and weathering process products of the surrounding lake material.

In samples preparation procedure the rim deposit, upper, middle and lower part of the four tephra layers, were wet sieved to retain the 250 µm to 63 µm size fraction. The

98 sieved sample was then diluted with 10% hydrochloric acid for at least 2 hours. This was to make sure iron component and organic matter were removed. The diluted sample was then rinsed thoroughly with distilled water, and then acetone was added before drying it in the oven at 50oC for 2 to 3 hours. The dry sieving procedure was carried out for all samples to extract the 125 µm, 250 µm from the 250 µm and 63 µm size fraction. The coarser grains collected through 125 µm to 250 µm sieving pan, were selected for probing.

A very tiny portion (0.5 g) of selected samples was poured in a six holed glass shard, with the bottom part sealed with clear sticky tape. Figure 3.12 shows three six holed glass shards containing fragments of tephra sands. The sieved tephra grains were sandwiched by a mixture of an epoxy resin/hardener mounting of 3 to 1 ratio respectively. The three mounted glass shards placed on the hot plate, at a temperature of 50oC for 18-19 hours. Glass shards were ground down to 1 cm before polished in order to expose internal surface. All samples were coated with carbon coating glass before being bombarded with three wavelengths X-ray spectrometer of the JEOL 733 microprobe.

3.3.8 INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY (ICPMS) FOR TRACE ELEMENT DIGESTION PROCEDURE

Inductively Coupled Mass Spectrometry (ICPMS) is an elemental determination analytical technique first commercially introduced in 1983 (Ammann, 2007) and used in many fields as diverse as the food industry, geochemistry, environment, forensic science and archaeology (Wolf, 2005).

The ICPMS for trace element analysis was employed in Part 1 and Part 2 for this study to determine the nature and history of eruption deposition within the Crater Lake Lanoto. Analysis for Part 1 was carried out at the USP whilst that for the Part 2 was carried out at the University of Sydney.

(i) Part 1

Rock and sediment samples were ground into very fine powder, before being run through the digestion procedure. All powered samples were weighed and placed in the oven for 24 hours at 40oC, before being cooled down for 3 to 4 hours and reweighed. The samples were dissolved in concentrated hydrochloric acid (aqua regia) at a temperature of about 120oC following those of Gale et al (2006). Figure 3.13a & b shows the fume cardboard set up for aqua regia digestion.

Approximately about 5 gram of a sample portion is added to the digestion tube and mixed with aqua regia of 9 ml of nitric acid pure (69-72%) (Figure 3.13a). The mixture was placed on the techne dri-block at 120oC for 4 hours. About 10 ml of hydrochloric acid (sp.gr.1.1B) solution (37%) was pipetted into all samples and continually heating, until 1.5 hrs before cooling down for several hours.

Each cooled acidity sample was transferred into a measuring flask via filter papers and then diluted with ultrapure water before allowed to settle for several hours (Figure 3.13b). Pure mixed pour into vial, and keep in the fridge before determining their trace elemental chemistry process, through Inductively Couple Plasma Spectrometry analysis (ICPS).

100

Filter papers with acid-insoluble residue (AIR) were placed in the oven at 40oC for 24 hour before being reweighed. The first engagement of the AIR was to determine whether the procedure would need to be repeated for those which gave too low values. Secondly, the AIR was also offers a rapid mean to determine a widespread of tephra components downcore. The AIR contents are mainly silicate minerals mainly of olivine, pyroxene and plagioclase phenocryst dominate the tephra deposit. Silicate minerals within the Crater Lanoto are good tephra indicator components of the master core D3.

Three blanks and fifteen sediment samples were analysed together at every session. Blank samples used to monitor contamination during the process and also to test reagent purity during the digestion method.

FIGURE 3.13 (a) Set up fume cardboard for the dissolving of samples in test tubes on the dri-block before heating up. (b) Samples transfer into measuring flask and dilute with ultrapure water before settle for several hours within the fume cupboard.

Unfortunately, Inductively Coupled Plasma Mass Spectrometry for major elements could not be performed at the University of the South Pacific (USP). Aqua regia (a cocktail of nitric and hydrochloric acids) is good at digesting metals and most of the more mobile elements, but is not capable of taking the most resistant silicates (particularly quartz) into solution. The only way to dissolve these is to use hydrofluoric acid (often in combination with other hazardous chemicals such as perchloric acid). USP does not have facilities for handling HF (in particular, special fume cupboards are required), so it was not possible to perform such analyses.

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(ii) Part 2

Part 2 of the ICPMS analysis for Part 1 samples was carried out at the University of Sydney, Australia. Samples went through series of calibrations using the Australian ICPMS standard procedures for trace element (Gale et al., 2006). Part 2 of the ICPMS comprises two components, high temperature sources (ICP) and mass spectrometer (Figure 3.14). At first the atoms in the sample are ionized using inductively coupled plasma (ICP) that is an electrically conductive gas with high concentration of ions. Argon gas flows inside the ICP torch unit transporting the sample ions to the mass spectrometer through a sampler cone and skimmer cone (from a high pressure to a low pressure system). Ions are then separated by their “mass to charge” ratio and a detector receives and measures an ion signal related to the concentration of that ion/atom. The number of ions is then translated into number of atoms of that element using a calibration standard (Wolf, 2005).

FIGURE 3.14 Schematic sketch of the ICPMS set up procedure (Modified from Wolf, 2005).

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CHAPTER 4 RESULTS AND DISCUSSION

4.1 RESULTS

This section presents the outcome of the fieldwork and laboratory analyses, which include: the coring site procedure; magnetic susceptibility of the lake sediments; stratigraphic column of the master core; geochemistry and dating of lava and lake sediments.

4.2 THE CORING SITE PROCEDURE

The electronic theodolite procedure was used to produce the detailed depositional basin map of the Crater Lake Lanoto (Figure 4.1) as discussed in Section 3.2.3. The 21 cores extracted from50 m grid intersections along the long axis of the lake basin. The coring procedure covered the central part of the deposition basin where the most detailed cores thought to obtain. Cores were taken in 6 m long, 50 mm and 90 mm diameter PVC barrels. Using this multiple coring sampling procedure allowed to rapid characterisation of stratigraphy of the lake sediment deposit. The multiple coring sampling procedures corresponded with the selection of the longest, most detailed and most complete core for further analysis.

Several cores were extracted from the deep part of the lake (C3, B3, C4, B4 and D4) to the south east of George Island. In order to obtain these cores, a raft designed as a coring platform. The raft paddled out to the surveyed coring site, and anchored in position before coring, and extraction proceeded in the normal fashion.

A series of soil samples was collected around the crater rim, to obtain a reference collection of catchment materials. The materials included those of volcanic sediment and organic litter from the upper part, about at least 150 mm depth of the catchment surface. This was done to obtain comparative material, to aid in determining the provenance of the lake sediments.

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Rock samples were taken from several fresh boulders at three particular locations from the inner crater rim. These boulders are in-placed at stratigraphical position to the north eastern portion of the crater. Global positioning system (GPS) coordinates of the locations from which soil and rock samples were taken are also plotted on the map in Figure 4.1.

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4.3 MAGNETIC SUSCEPTIBILITY (MS) OF LAKE SEDIMENTS

The magnetic susceptibility (MS) section presents into four main parts as follows:

1. An outline of the selection procedures for the master core. 2. An outline of the dry bulk density and moisture content of the master core. 3. Investigation of the master core in more detail through the first and second version of the MS technique.

4.3.1 SELECTION OF THE MASTER CORE USING FIRST VERSION

The most detailed core was rapidly identified from plotting volume-specific magnetic susceptibility (VSMS) with depth. Figure 4.2 shows plots of the VSMS versus depth for 8 out of 21 cores that were most appropriated for further study. The eight cores that were considered in the selection of the master core: B2, B3, B4, C2, C3, C4, D2 and D3. This selection was based on peak and trough features, of how they deepen and widen spread downcore. Raw data from some of the eight cores is found in the Appendix Section 1.

All cores indicate the divergent nature of the Crater Lake Lanoto sediment: diamagnetism is represented by troughs and paramagnetism together with ferrimagnetism corresponds to peaks. Several well-defined peaks are strongly indicative of the presence of volcanic tephra (which may contain paramagnetic and ferrimagnetic minerals). These peaks can signify either macroscopic (coarse tephra) or microscopic cryptotephra (very fine tephra).

The cores B2, B4, C2, C3 and C4 all indicate peaks. However the VSMS measurement of these sediments, are very low indicating the presence of organic material. In terms of cores from B, C and D within the central part of the lake, core D3 show the most complete record, compared with those of the other seven cores B2, B3, B4, C2, C3, C4 and D2 (Figure 4.1). High VSMS values in cores B3, D2 and the deepest core B4 were omitted from the master core selection as these three cores lacked of continuity and detail downcore. The 90 mm diameter core at site D3 was selected as the master core for this study. This particular core located very close to the central part of the lake (Figure 4.1), with a sediment depth of 4.6 m.

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At a depth of up to 1.8 metres, cores B2, B3, B4, C2, C3, C4, D2 show a lot of missing records, whist D3 has a wide range of valuable data at the same depth. Similarly, between depths of 0.5 and 4.6 m, core D3 also shows changes in sediment deposition, represents by the three major peaks. A significant disturbance, of sedimentation within the Crater Lake Lanoto is signified from the middle peak of the core D3. This disturbance feature occurs between 2 and 3 m depth, where other cores have data sets. This major sedimentation feature seems to have occurred in the eight cores at varying depths. This suggests that the floor of the Crater Lake Lanoto is rough and structurally wavy.

4.3.1.1 Dry bulk density of the master core D3

Dry bulk density of sediments helps us estimate changes in porosity in sediments as they accumulation through time. Figure 4.3a displays the relationship between dry bulk

106 density versus depth from core D3 based on measurement of 219 lake sediment samples. The plot shows three major peaks corresponding with the high bulk density of material with a low organic material. Troughs coincided with material with low bulk density and rich in organic material. Zones of high and low bulk density correspond with those of high and low MS values respectively within core D3. Concentrations of organic matter in Crater Lake Lanoto sediment appear to decrease downcore, based on the saturation moisture content with respect to depth.

Compactness and permeability properties of the entire sediment core (D3) were determine through the “saturation moisture content” procedure. Figure 4.3b is a plot of saturation moisture content versus depth for the 219 lake sediment samples. The peaks and troughs in Figure 4.3b correspond to troughs and peaks, respectively in Figure 4.3a which shows downcore variations in dry bulk density. The dry bulk density of the lake sediment is inversely proportional to its moisture content, as would be expected: lower bulk density might indicate high porosity enabling more moisture to fill the voids. Peaks in saturation moisture content represent zones of high void space, while the troughs are indicate zones of low permeability. Saturation moisture decreases downcore, as shown the reduction in peak values in other words deeper sediments are drier and more compacted.

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When saturation moisture content is plotted against dry bulk density of the lake sediment for 219 samples, the datapoints plotted tightly along a negative linear slope with a gap at the lower end indicate by an arrow (Figure 4.4). Both properties have progressively changed with depth. The gap is approximately associated with sediment from between 36 and 40 cm depth. Within this depth range the saturation moisture rapidly dropped while those of dry bulk density suddenly elevated.

As stated, the inversely proportional relationship between dry bulk density and moisture content shows, intuitively that, denser sediments that are more compacted display lower permeability characteristics. The close relationship between these two properties over the entire depth of the master core D3 suggests that, sediments derived from a single source display consistent textures and grain shapes. More importantly, the linear relationship between saturation moisture content and dry bulk density indicates that, no part of the sedimentary column has experienced disturbance or reworking (Figure 4.4). Considering this, it is probable that these sediments displayed low mobility behaviour during deposition. For example, the mid-depth peak of core D3 (shown in Figure 4.2) indicates a thick layer of mixed, organic and greenish yellow

108 tephra sediment. If these sediments are characteristic of low mobility deposits then the mixture could be a product of a “collapse cone” or major erosion process. Detail discussion of the cone collapse and major erosion found in Section 4.7.1.2 (i) & (ii) and 4.7.2.2 (ii).

4.3.2 MAGNETIC SUSCEPTIBILITY (MS) – MASTER CORE “D3”

The Crater Lake Lanoto sediment deposits behave in three distinct fashions, known as diamagnetic, paramagnetic and ferrimagnetic. Diamagnetic materials generate an induced magnetic field in a direction opposite an external magnetic field, applied to the material. The opposite effect occurs in paramagnetic materials, which create an induced magnetic field in the same direction to the externally applied magnetic field and are therefore attracted to it. Ferrimagnetism mainly occurs in magnetic oxides, namely magnetite, and refers to a type of permanent magnetism where atoms have magnetic moments that are opposing but unequal allowing spontaneous magnetisation.

Low MS values imply a low magnetite concentration in the sediment. Such sediments are likely to be dominated by diamagnetic plant organic matter with a low mineral input and a high organic accumulation. In contrast, paramagnetic behaviour of sediment gives high MS values. However, ferrimagnetic sediment gives the highest MS values, and indicates the presence magnetite and/or other iron oxide components. High concentrations of magnetite suggest derivation from basalt and volcanic fallout materials. These accumulated sediment deposits included those that fell back into the crater as well as fallout components from nearby eruption activity. These deposits are referred as primary contributors to a high volume of magnetite concentration in the lake sediment. Raw data for the MS second version of the 219 samples is found in the Appendix Section 3 of this thesis.

This remainder of this section presents a more detailed overview of MS measurements in the master core when compared to the first MS version displayed in Figure 4.2. The first and the second version producer will demonstrate valuable clues about Crater Lake Lanoto sediment depositional basin. These parameters are included:

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(a) Volume-specific magnetic susceptibity (VSMS) versus depth

(b) Mass-specific magnetic susceptibility (MSMS) versus depth (c) Frequency-dependent magnetic susceptibility (FDMS) versus depth (d) Mass-specific magnetic susceptibility (MSMS) versus frequency-dependent magnetic susceptibility (FDMS).

4.3.1.2 Volume-specific magnetic susceptibility (VSMS) versus depth

Volume-specific magnetic susceptibility (x) is expressed as the ratio of magnetisation induced in a measure sample (M) over the field strength (H) following equation-MS1;

(Equation-MS1): X = M / H (Lascu, 1999; Gale & Hoare, 2011):

Let us recall the first version of the MS curve (Figure 4.2) and determine different features of the oscillating pattern in more detail. Figure 4.5 displays the VSMS versus the core depth showing four major peaks in core D3 at depth intervals of (0.5 – 0.6 m, 0.6 – 1.2 m, 2.0 – 2.8 m and 4.1 – 4.5 m). The intervals therefore almost have equal trough volume, regardless of having differences in VSMS values. In addition, the four major peaks represent major eruption sources are known as tephra bed-1, tephra bed-2, tephra bed-3 and tephra bed-4.

These four eruption sources are corresponded with the abundance of tephra sand components at these particular depths. The minimal peak of the tephra bed-4 source signifies the latest post-erosional eruption of the Crater Lanoto. Tephra bed-2 (mid-peak) between 2 and 3 m depth interval shows a “shortening” of peak i.e. it appears as though the “tip” of the peak is missing. This shortening of the tephra bed-2 peak, may be associated with an erosional or a cone collapse event. Three minor peaks associated with the tephra bed-2, yield high MS readings implying high magnetite concentration, even though they are associated with high organic content. This shows that tephra bed-2 layer has still dominated by tephra components, despite the fact that the entire layer is a mixture of organic and volcanic components.

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4.3.1.3 Mass-specific magnetic susceptibility (MSMS) versus depth

The MSMS was determined from the MS second version of the 219 dry samples. Mass- specific magnetic susceptibility (Xlf) is defined as the ratio of the volume susceptibility of dry sample (k) over the sample bulk density (p). The relationship is defined in equation MS2;

3 -1 (Equation-MS2): Xlf (m kg ) = k / p (Dearing, 1999)

Figure 4.6 shows the MSMS of dry samples versus core depth with troughs and peaks denoting low and high concentrations of magnetite, respectively. This profile is similar to that shown in Figure 4.5.

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The tephra bed-2 is shown as a missing portion at the top of the peak, so at this early stage may be classified as the eroded/broken tephra layer. This particular part of the tephra bed-2 is represented by three mini-spikes in Figure 4.5, corresponding to high MS readings. Tephra bed-1, tephra bed-3 and tephra bed-4, settled at high MSMS values are similar with those of the first version displayed in Figure 4.5. High frequency susceptibility values of the tephra bed-2 are close with tephra bed-3 and tephra bed-4. This verifies that the dry sample of the tephra bed-2 still comprises of high concentration of magnetite minerals.

4.3.1.4 Frequency-dependent magnetic susceptibility (FDMS) versus depth

The FDMS was determined from the MS second version of the 219 dry samples. Frequency-dependent magnetic susceptibility (K) is the percentage measure express as the ratio of the difference between the low frequency magnetic susceptibility (Klf) and

112 high frequency susceptibility (Khf) over the low frequency magnetic susceptibility (Klf) following equation MS3;

(Equation-MS3): K (%) = (Klf – Khf / Klf) x 100 (Dearing, 1999)

Figure 4.7 shows plot of FDMS versus depth for core D3 and display an apparently wide distribution of diamagnetic, paramagnetic and ferrimagnetic sediment at various depths. The plot has been divided into three diagonal zones (dashed lines) referred to as, very low frequency zone (VLFZ), dominated zone (DZ) and high frequency zone (HFZ). Dashed lines were constructed just to show the dominated area of the plot.

At the four tephra layer depths, it seems the majority of samples start to scatter away from each other at the DZ whilst move furthermore at HFSZ and VLFZ. Samples with paramagnetic properties are mostly scattered at the four particular depths interval (0.5 m, 0.6 m, 2.0 m and 4.1 m), associated with the four well-defined peaks of the first magnetic susceptibility version in Figure 4.5. Hence at this very early stage, it still not clear whether the high values could represent errors made during the analytical process, the present of ferrimagnetic material or it may be the result of contaminated tephra components.

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Figure 4.8 shows a logarithm scale relationship between the FDMS versus depth. This particular plot shows the similar activities of dry sediments indicated in Figure 4.6 where obviously shows the four tephra layers at certain depths.

Low and high MS values sediments (also scatter in VLFZ & HFSZ of Figure 4.7) are strongly considered as errors during the process. They are known as isolated group component in this plot. These particular samples present in troughs and peaks of MS curve (Figure 4.5), which seems behave differently from the rest. Diamagnetic and paramagnetic sediment can be changed their behaviour may be due to natural causes or technical error.

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Commonly the FDMS produces several unusually high background readings, due to the presence of a high magnetism interference substance, in the surrounding area where the analysis took place. However, background readings of low and high magnetic susceptibility of these particular sediments, were low and normal like the rest of the other samples.

Like Figure 4.7, the Figure 4.8 has also shown the similar approach, that samples are scattered away from each other. If this is the case then most of these deposits have no connection to the Lanoto volcano and may be much younger then the Crater Lanoto itself. This assumption would not rule out the fact that, the Crater Lanoto volcano may be active simultaneous with several nearby volcanoes however, there is something else triggers the behaviour of these tephra components. Weathering of sediment can be also contributing, to the increase in the magnetic susceptibility strength of lake sediments. A detail discussion of this topic is found in Section 4.7.1.1 (iii).

A majority of 219 samples are mostly scattered at the range between 1 and 10% of FDMS downcore. Several depths intervals are characterised as diamagnetic zones shown in

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Figure 4.5 and 4.6. However, Figure 4.8 shows the same intervals contain high FDMS values like those of tephra beds deposits. Hence, troughs and peaks in this particular plot are both show high and low magnetite accumulation in the lake deposit. This is to consider may be the trough and peak of the MS curves could be control by some mechanism.

4.3.1.5 Mass-specific magnetic susceptibility (MSMS) versus frequency-dependent magnetic susceptibility (FDMS)

Few catchment soil samples, rock (mini core & chips) and 219 dry lake sediment samples, the relationship, of FDMS and MSMS was determined. In mathematically term, if the MS Equation-2 (Section 4.3.2.2) is substituted into Equation-3 (Section 4.3.2.3) then the relationship between the MSMS versus FDMS of the three components (soil, rock & lake sediment) is expressed as;

K = [k/p – (Khf / k/p)] x 100

Where (K) is the percentage measure of the frequency-dependent magnetic susceptibility,

(k) is the volume susceptibility of dry sample, (p) is the sample bulk density and (Khf) is the high frequency magnetic susceptibility.

Figure 4.9 shows logarithm scale plot of MSMS versus FDMS of the lake sediment, rim soils, inner and outer rim lava. The relationship between the two parameters, allows the sediment and lava suite within Crater Lake Lanoto, to be classified into three significant zones; diamagnetic, paramagnetic and ferromagnetic. Dearing (1999) described diamagnetic zone as weak negative susceptibility, labelled paramagnetic material as weak positive susceptibility and strong positive susceptibility referred to ferrimagnetic. This classification is based on a transformation state, of the low MS strength, from diamagnetic phase to ferrimagnetic characteristic.

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FIGURE 4.9 The logarithim scale plot between the MSMS versus the FDMS of the lake sediment, inner volcanic rim soils, inner rim and outer rim lava. These four components plotted at three significant regions; diamagnetic, paramagnetic and ferromagnetic. The arrow shows the direction of the shift in the MS strength from low to very high value. Sediment surrounded by red circles are label as isolated group.

Inner lava and lake sediment overlap at paramagnetic zone while those of the rim soil and outer lava scatter in the ferrimagnetic zone (Figure 4.9). Lake sediment, lava flows and soil all display an extraordinary relationship. The majority of lake sediments and inner lava are dominated the MSMS field between 6 and 100 interval, whilst those of the soil and outer rim lava plotted higher. This indicates a discrepancy in MS strength among the rim soil, outer rim and inner rim lava components where seem isolated, implies originated from a difference sources. In addition, the isolation of the three components could be driven by the intense weathering nature of the materials.

The magnetic susceptibility of the soil could be influenced by many factors, discussed in more detail in Section 4.7.1.1 (iii). The plot is also indicated that the inner and outer rim lava flow could have been generated from difference magmatic sources. This is also reflected from the physical characteristics of the outer rim lava, which contains great abundance of olivine and pyroxene in comparison with those of the inner suites. In other

117 word it seems that the ferrimagnetic outer rim lava derives from olivine-pyroxene enriched magma whist paramagnetic inner rim lava is a part of olivine--pyroxene depleted source.

Some of the sediments initially characterised as diamagnetic in nature, appear to be scattered across toward paramagnetic zone. This signifies that the MS strength of lake sediments can change throughout time, from diamagnetic into ferrimagnetic stage (Figure 4.9). A shift in MS strength from diamagnetic region to ferrimagnetic suggested is due to the intense of weathering. The soil could be either derived from parental source, the outer rim lava or from diamagnetic and paramagnetic materials (inner rim lava). Diamagnetic and paramagnetic component transforms into ferrimagnetic ones through intense weathering processes (Dam et al., 2005; 2008). The present of the lake soil component, within the ferrimagnetic zone, is a good example of the transformation scenario, which discussed in more detail in Section 4.7.1.1 (iii).

Several groups isolated from the values of the rest of the lake sediment are also identified within the mixeture. These particular sediments were identified from Figure 4.7 and Figure 4.8, and are characterised as having low and high frequency susceptibility values. The majority of these sediments fell in the paramagnetic field whilst a very few components scattered in the diamagnetic and ferrimagnetic field. The isolated sediment groups at this stage are strong considered they are not part of the Crater Lake Lanoto sediment deposit but components of other eruption activities. This indicated that these contaminated components are commonly occurred throughout core D3.

4.3.1.6 Summary of critical points from the magnetic susceptibility sediment

(i) Many peaks represent the tephra accumulation and troughs represent sediments rich in organic matters.

(ii) Several troughs still correspond to layers comprising tephra components.

(iii) Troughs and peaks could be controlled by some other mechanisms.

(iv) Sediments comprise of low and high percentage of FDMS and form small isolated groups, imply the presence of the contaminated tephra components.

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(v) The outer rim lava and soil plot in ferrimagnetic zone whilst the inner lava and the lake deposits dominate the diamagnetic zone.

(vi) The inner and outer rim lava plot in separated region suggesting that the two lava suites could be generated from two different sources (olivine-pyroxene enriched and olivine-pyroxene depleted).

4.4 STRATIGRAPHIC COLUMN OF THE MASTER CORE D3

The stratigraphic column section is divided into four main parts:

1. Identification of the 12 units downcore based on their physical characteristic and abundance of certain components. 2. Variation in sand morphology at various depths. 3. Optical microscopy of mineral phase occurring in the inner rim lavas facilitating correlation with phenocrysts occur in the master core D3.

4.4.1 THE STRATIGRAPHIC COLUMN OF THE CRATER LAKE LANOTO

The master core D3 was described microscopically and logged according to several criteria such as colour, texture, organic content, mineral content and abundance of tephra. The core was then divided into twelve units shown in Figure 4.10 from oldest to youngest (Lano-1 Unit to Lano-12 Unit). An image from the top part of the core shows most common physical characteristics which are used to distinguish the organic and the volcanic material (Figure 4.10). Dark colour indicates high content of organic materials and that of olive-green is sediment dominated by volcanic components.

A more detailed description of each unit, down to every 2 cm of the total core length of 440 cm, is found in Appendix Section 4 of this thesis. A chart for estimating percentage composition (CCEPC) was used, to determine the content of organic and volcanic materials downcore. Several sediment samples (tephra bed-1, top of tephra bed-2, top & base of tephra bed-3 and tephra bed-4) were radiocarbon dated. The radiocarbon age and

119 high content of organic present in tephra bed-2 is discussed in more detail in the following Sections 4.7.1.2.

Lano-1 Unit

Lano-1 Unit occurs between depths of 396 and 440 cm and is composed of primary tephra bed-1 deposits (Figure 4.11). Primary tephras in this deposit are those grains that still have their original shape (elongate/round-subrounded) with unfilled/partly-filled vesicles. The tephra sand ranges from very fine to very coarse in size (0.5 mm–10 mm), and commonly brownish to pinkish grey colour. It is generally soft, poorly to well sorted,

120 highly vesicular, scoriaceous, smooth and tubulous in form. A few fine grained and highly weathered silicate minerals are present in the unit. Olive greenish yellow tephra sands contain brownish yellow iddingsite: those with more greyish green colour associate with reddish brown of hematite mineral. Hematite mineral commonly dominates cavities and vesicles of the tephra sand. The Lano-1 Unit contains three forms of hematite, yellowish red, reddish brown and vitreous greasy lustre. A few grains of goethite, halloysite gibbsite are also occurred in this lower unit.

A high concentration of charcoal fragments, mostly from tree wood, dark grey in their physical appearance, range in size from fine to very coarse in size and are common throughout the whole unit. The charcoal fragments consist mainly of big tree branches. Organic content estimated about an average of 20% determined from CCEPC, while the volcanic materials dominate.

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Lano-2 Unit

Lano-2 Unit overlies the Lano-1Unit, which is some 24 cm in thickness. Lano-2 Unit has a hydrothermal alteration component between 372 and 392 cm depth, representing the dying stage of the tephra bed-1 eruption. Highly weathered tephra occurs throughout the whole unit, associated with brownish yellow iddingsite. Iddingsite mineral often occurs together with fine and poorly sorted materials, of greenish yellow to reddish brown hematite. Halloysite, goethite and gibbsite also present in Lano-2 Unit. Charcoal is only present the top 14 cm part of the unit and is mainly tree branches and Eleocharis dulcis (utu). Lano-2 Unit contains an average of about 30% organic content determined from the CCEPC.

Lano-3 Unit

Lano-3 Unit occurs between 302 and 368 cm depth. It is dark green to brownish yellow, poorly sorted, fine to coarse grained and overlies the hydrothermal unit. This unit comprises of few highly weathered silicate and goethite minerals at the base which are depleted toward the top. Iddingsite and yellow brownish red hematite are more common towards the top of this unit and depleted toward the base. Very few fine-grained gibbsite occurs throughout the unit. Few weathered tephra fragments are also occurred at the lower part of the Lano-3 Unit. The fine greenish yellow material within the unit is referred to cryptotephra. Charcoal is present throughout the whole unit is mainly Eleocharis Dulcis (utu). Lano-3 Unit approximately comprises of an average of 41% organic content determined from the CCEPC.

Lano-4 Unit

The Lanoto-4 Unit occurs between the depths interval of 294 and 302 cm. The unit has a dark green to dark grey in colour and it overlies the Lano-Unit 3. Hematite content increases with decreasing iddingsite concentration throughout the unit. No sign of weathered silicate minerals are present, but there are very few goethite and gibbsite grains. Halloysite only occurs near the top of the unit. Charcoal fragments only occur at

122 the base of this 8 cm unit are mainly Eleocharis Dulcis (utu). The unit has elevated organic materials, estimated about an average of 48% (from the CCEPC).

Lano-5 Unit

Lano-5 Unit is situated at depths of between 268 and 294 cm. This particular unit represents the base of the eroded tephra bed-2 deposit. The unit is composed of dark greenish yellow volcanic materials, similar to those of the Lano-1 Unit. Lano-5 Unit consists of very few broken tephra sand fragments, associated with medium to fine grained and poorly sorted volcanic materials. The unit comprises of highly weathered silicate minerals with few specimens of goethite, hematite, iddingsite, gibbsite and halloysite. There are few charcoal fragments at the top of the unit are mainly tree branches and Eleocharis Dulcis (utu). The unit is approximately had an average of 41% (from CCEPC) of organic materials.

Lano-6 Unit

Lano-6 Unit is 86 cm thick and represents the top part of the tephra bed-2 deposit, occurring between depth of 269 and 180 cm. The Lano-6 Unit could be represented the second main eruption episode of the Crater Lake Lanoto. Figure 4.12 shows the image of broken tephra components commonly occur in the tephra bed-2. These broken tephra fragments are commonly associated with dark greenish yellow fine-grained volcanic sediment. The fine material of reddish yellow represents the cryptotephra component. There is very little secondary and epiclastic tephra present in this unit, indicate from chemical and physical weathering of these components. Tephra sands are well sorted, and range from fine to medium-grained (1-7 mm). The Lano-6 Unit distinguished from Lano- 5 Unit because of its high organic materials content. Highly weathered silicate minerals with few goethite, hematite, iddingsite gibbsite and halloysite are present throughout the unit. Yellow brownish red hematite is common in cavities and vesicles of tephra sand (Figure 4.12). Charcoal fragments occur between 182 and 268 cm are mainly tree branches and Eleocharis dulcis (utu). Lano-6 Unit contains an average of 46% (from CCEPC) of organic materials.

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Tephra layers (Lano-1 Unit, Lano-9 Unit and Lano-11 Unit) are comprised of 20%, 9% and 8% organic content respectively, which is interesting when compare with the 46% of the Lano-6 Unit (tephra bed-2). This is the reason why the Lano-6 Unit (tephra bed-2) could be a part of the major erosion process and may be even cone collapse event at this early stage (Figure 4.10). The discussion of this significant event is found in Section 4.7.2.2 (i) and (ii).

Lano-7 Unit

The Lano-7 Unit has a dark green to dark grey almost black colour, is 20 cm thick and overlies the Lano-6 Unit. Organic content of Lano-7 Unit is on average of 52% (from CCEPC). Silicate mineral is absent but only few iddingsite and hematite (lustre and yellowish) occurs. Very fine lustre hematite dominates the top part of Lano-7 Unit. There is no sign of charcoal fragment within the whole unit.

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Lano-8 Unit

Lano-8 Unit has a thickness of 12 cm and occurs at a depth range between 150 and 162 cm. It has lustrous appearance and consists of very fine grained, poorly sorted materials, with dark green to dark grey almost black colour. Very fine lustre hematite dominates this 12 cm unit. Few goethite and gibbsite also occur but there is lack of iddingsite. Organic material is present in average concentration of around 41% (from CCEPC). Charcoal fragment are present throughout the whole unit and are mainly Eleocharis Dulcis (utu).

Lano-9 Unit

The Lano-9 Unit occurs between depths of 74 and 150 cm. Figure 4.13 shows the image of primary tephra bed-3 deposit, which is 76 cm thick and is yellowish green to dark green or grey in colour. Several primary components could be referred to as “Pele’s tears” (named after the Hawaiian female fire goddess of volcanoes) as they have a wide head with narrow tail feature (Figure 4.13).

At the lower portion of Lano-9 Unit, the tephra is rare and weathered compare with the middle part of this unit, which has a high tephra content component with less weathered in appearance. Generally the tephra sands of the Lano-9 Unit are well sorted, highly vesicular, scoriaceous with their size ranging from very fine to very coarse (5 - 9 mm). They are mostly smooth, soft, rounded and tubulous in form. Primary tephra sands commonly have a narrow head with wider tail (Figure 4.13). Highly weathered fine to medium silicate minerals increased toward the top part of the unit. Several tephra sands comprise of interlocking silicate minerals within vesicles. Iddingsite and hematite increase their content throughout the unit. Goethite, halloysite and gibbsite also occur with various concentrations within the unit. Charcoal fragment are comparatively lacking in the Lano-9 Unit. The organic content is an average of 9% (from CCEPC).

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Lano-10 Unit

Lano-10 Unit is only 7 cm thick overlies the tephra bed-3 deposit. The unit is a dark greenish yellow in colour and has lower organic content than many of the other units (an average of 18 %). Lano-10 Unit comprises of a few specimens of iddingsite, hematite, halloysite and goethite with highly weathered silicate mineral at the top part of the unit. Iddingsite, halloysite and hematite increase in content at the top part of the Lano-10 Unit. Very fine to medium-grained charcoal fragments dominate the Lano-7 Unit, which are mainly Eleocharis dulcis (utu).

Lano-11 Unit

Lano-11 Unit is a primary tephra deposit that occurs between depths 47 and 67 cm, with a thickness of 20 cm. The tephra bed-4 deposit intermingles with poorly sorted, very fine and dark greenish to brownish yellow materials (Figure 4.14). The tephra sands are very well sorted, vesicular, scoriaceous, and brownish yellow, pinkish to grey in colour (Figure 4.14). Tephra bed-4 deposit is similar to tephra bed-3 in physical characteristics and form. Tephra is tubulous in form, and rounded to irregular in shape, with a size range from 0.5 mm to 15 mm. Charcoal fragments are rare or absent throughout the unit. Iddingsite and hematite are very common in the Lano-11 Unit. Olive yellowish green to 126 brownish yellow colour tephra sands are comprised of iddingsite. Brownish red hematite has started to fill cavities and vesicles of tephra sand. Halloysite, goethite and gibbsite all occur in various concentrations in the unit. Charcoal consists of the Eleocharis Dulcis fragments and less tree branch materials. Organic content is 8% (from CCEPC).

Lano-12 Unit

The Lano-12 Unit is the top unit of the master core D3 with a thickness of approximately 47 cm. Lano-12 unit probably blankets the broad lake floor of the Crater Lake Lanoto. The unit has 55% organic (from CCEPC) and is a fine-grained unit, consisting of poorly sorted material, dark grey to almost black in colour. The unit is dominated by brownish red and fine-grained lustre hematite mineral. Goethite is also present but not as common as hematite. Charcoal fragments almost occurred throughout the whole unit are mainly tree branches and Eleocharis dulcis (utu).

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4.4.2 MORPHOLOGY OF PYROCLASTS OF THE TEPHRA DEPOSIT

This section describes the morphology of lapilli tuff deposit (Figure 4.15) from the volcanic rim and lake tephra deposits (Figure 4.16), enabling the identification of significant features associated with magmatic activities associate with these airfall deposits. These include: size, shape, the abundance and geometry of vesicles. The presence of vesicles in the airfall deposit would provide some clues of how bubbles behaved during magmatic activities of the Crater Lanoto volcano.

The majority of lapilli tuffs are brittle whilst those from the lake deposit are smooth and soft. Brittle and soft smooth lapilli tuff about 6-20 mm thick, commonly occurred in thin batches at several sections of the inner rim wall. Like tephra lake deposits (tephra bed-1, 2, 3 and 4), lapilli tuff are uniformly scoriaceous, irregular to rounded or tubulous in form, with greenish yellow, brownish to grey and dark green to dark grey or blue colour.

FIGURE 4.15 Dark green to grey or brownish red lapilli tuff deposits with their size range from 0.5 to 1 mm. Vesicles geometry ranges from spherical to elliptical in shape. Tubulous, scoriaceous smooth pyroclasts are commonly range from 0.1 to 0.8 cm in length. Pyroclast fragments shows a mixed of “thin- wall” and “thick-wall” feature. Scale bar (red) is 5 mm.

Shorten tubulous tephra, non-tubulous and irregular shaped components could be products of eruption activity associated with less pressure. Lengthened tubulous tephras (> 10 mm) might have been propelled out of the volcano from high-pressure explosive eruption activities.

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Vesicles in lapilli tuff and lake tephra deposits are ranging from well to poorly spherical. These poorly spherical vesicles produce wide range of shape that can be characterised as: embay, elongate, half-moon curve, oval, half-oval, triangular, rain drop, pentagon, octagon, hexagon, decagon, tube and crescent. Some coarse vesicles ranging from 3 to 10 mm or more could be formed from the interconnection of multiple bubbles as discussed in Mangan (1993) and Suckale et al. (2010).

Both lapilli tuffs and tephra lake deposits have a “thinned-wall” feature, which could be formed as vesicles open and become interconnected. Thinned-wall tephra consist of coarse vesicles, range from 0.5 to 10 mm or more in diameter. This results as bubbles ascent and outrun the low viscosity rising magma, it causes the coalescence to increase dramatically (Parfitt, 2004; Carey, 2005; Parfitt, 2009; Suckale et al., 2010). This coalescence stage triggers explosion activities. Manga and Stone (1994) stated that bubbles with > 5 mm radius are evidence of coalescence, which correspond with very coarse vesicles (up to 10 mm) in lapilli tuff and lake tephra deposits (not shown in Figure

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4.15 and 4.16). The coalescence of bubbles within the tephra fragment, results in variation of their geometries, produced before and after deposition (Gottsmanm, 1999). The smallest bubble population in lapilli tuff and lake deposit, have the lowest probability of being associated with the coalescence (Mangan et al., 1993). Suckale et al (2010) showed that once a spherical bubble deforms, it would not only enhance coalescence but also generate break up system. This could explain the abundance of tiny vesicles, and also well to poorly-spherical shape in vesicles of lake tephra and lapilli tuff deposit.

It suggested that the lack of an interconnection mechanism amongst vesicles in lapilli tuff and lake tephra could be the product of a “thick-walled” features. Thicked-wall tephra commonly have fine vesicles with less than 1 mm in diameter. The thick-walled feature could have resulted, from pyroclast fragments being propelled out of the volcano, during an initially stage of bubble grow within the magma. This coincides with the fact that the low viscosity magma accends rapidly and outruns the rising bubbles reducing the likelihood of a coalescence process (Mangan et al., 1993; Parfitt, 2004; Carey, 2005; Parfitt, 2009; Suckale et al., 2010). However, slow rising magma would generate coalescence (Parfitt, 2009; Suckale et al., 2010).

Therefore, thin-walls with coarse vesicles are evidence of fast rising magma, whilst thick- wall with fine vesicles are corresponded with slow rising magma. More detail discussion of vesicle/bubble process is found in Section 4.7.1.2 (iii).

4.4.3 OPTICAL MICROSCOPY MINERALS – CRATER LANOTO

Lavas of the Crater Lanoto are mostly alkalic in nature and fine grained with a light grey to dark green or almost black colour. The rocks generally exhibit a porphyritic texture and contain phenocrysts of olivine and pyroxene. The two common mineral phases range in size from 0.1 to at least 1 cm.

Alteration of olivine to iddingsite is uncommon compared with those of Salani and Fagaloa Formations from Upolu and Savai’i. Olivine and pyroxene phenocrysts occur in numerous boulders at the inner part of the crater had much are much fresher compared with those occurring lava flows at the outer part of the crater wall. 130

4.4.2.1 Olivine

Olivine phenocrysts are the most abundant mineral phase of Crater Lanoto lavas (20- 45%). They are commonly, subhedral, round and embay in form (Figure 4.17a). The subhedral section always shows straight extinction and a yellowish brown colour under cross-polarised light (Figure 4.17b), whilst those of anhedral shape exhibit oblique extinction and very bright colours (Figure 4.17a). Several phenocrysts are resorbed extinction (Figure 4.17).

The majority olivine phenocrysts exhibit straight extinction and are commonly interlocking with pyroxene phenocryst. Inter action between olivine and pyroxene in several thin sections shows the olivine phenocryst concentrated in the centre surrounded by interlocking pyroxenes. Several olivine mega-phenocrysts show inclusions of very fine and hairy size opaque minerals. Several olivine phenocrysts consist of brownish to red iron oxide alteration to iddingsite. The iddingsite seems commonly developed around the rim and cracks of the olivine phenocryst.

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4.4.2.2 Pyroxene

Augite is a major pyroxene that commonly occurs in lavas of the Crater Lanoto with abundance ranges between 10% and 45% of the rock volume. Phenocrysts are commonly euhedral, subhedral or even rounded in form with 0.1 to 0.9 cm in size. Figure 4.18a shows that augite phenocrysts mostly show simple twinning and zoning in phenocrysts comprise of parallel and intersection cleavages. Figure 4.18b displays phenocrysts containing irregular cracks which commonly consist of brownish red colour of iron oxide mineral. The iddingsite alteration also occurs along the edge and dominates cracks. A reaction relationship between olivine and pyroxene is common where both phenocrysts interlocking with one another. The inclusion of opaque minerals is rare in most mega augite phenocrysts.

4.4.2.3 Plagioclase

Plagioclase is not a common mineral phase in lavas of the Crater Lanoto, indicated by the absence of a mega phenocryst in all thin sections. However, medium to fine laths dominated the groundmass. Commonly they are tabular prismatic and acicular in form.

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They show simple, multiple twinning and commonly interlocking with one another (Figure 4.18b).

4.4.2.4 Groundmass

The groundmass of lava flows of the Crater Lanoto region are mainly composed of opaque minerals (ulvospinel, ilmenite and titanaugite), needle plagioclase and microphenocrysts of pyroxene and olivine. Commonly groundmass of rock H comprises rare medium opaque minerals whereas that in rock G and D is dominated by very fine titanaugite minerals. The opaque minerals also occur as inclusions in several cracks of mega olivine and augite phenocrysts. Figure 4.19a shows medium to fine needle-like opaque minerals associate with lath needle feldspars under plane polarised light. Figure 4.19b indicates fine opaque minerals surrounding the olivine phenocryst under plane polarised light.

4.4.2.5 Summary of critical points from the stratigraphic column

(i) Master core D3 was subdivided into 12 units, based on their colour, mineral content, organic content and the abundance of tephra sand. 133

(ii) Four main eruption intervals are recognised in the Crater Lanoto stratigraphic column with the possibility of minor volcanic episode occurs between major activities.

(iii)Charcoal fragments imply bush fire during main eruption activities. Bush fires may have been triggered by other activities such as minor eruption episodes.

(iv) The high content of iddingsite in (tephra bed-1, 2 and 4) and low in (tephra bed-3) may correspond to variation in magma chemistry, namely its olivine content. This assumption is also reflected in the optical microscopic of the inner lava where some flows contain more olivine whilst other were dominated by pyroxene phenocrysts.

(v) The high organic content in the tephra bed-2 in comparison with the other 3 tephra deposits (tephra bed-1, 3 and 4) could signify erosion or may be a product of the cone collapse event.

(vi) High vesicularities and different geometry of vesicles in lapilli tuff and lake tephra deposit implies in variation of magma activities.

4.5 GEOCHEMISTRY

The geochemistry of lava and tephra components presented in this section provides reliable data that is hoped will improve our understanding of volcanic processes and mechanisms associated with the Crater Lanoto volcano. These data are presented in three main parts as follows:

1. XRF results (inner rim lavas) 2. EPMA and XRF results (tephra) 3. ICPMS results (lava and tephra)

4.5.1 X-RAY FLUORESCENCE (XRF) OF THE INNER RIM LAVA

The concentration major and trace elements of the inner lavas of the Crater Lanoto was determined through the XRF procedure. Seven inner rim lava samples had been analysed

134 using the fuse discs procedure. Lavas were stratigraphically sampled from the northwestern part of the crater.

4.5.1.1 Results: Major and trace element of the Crater Lanoto lava

The XRF procedure yielded 10 major elements, expressed as oxides; silica dioxide

(SiO2), titanium oxide (TiO2), aluminium oxide (Al2O3), iron II oxide (Fe2O3), manganese II oxide (MnO), magnesium oxide (MgO), calcium oxide (CaO), sodium oxide (Na2O), potassium oxide (K2O), and phosphorus pentoxide (P2O5) and 21 trace elements; aluminium (Al), barium (Ba), calcium (Ca), cobalt (Co), chromium (Cr), iron II (Fe2), iron III (Fe3), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), niobium (Nb), nickel (Ni), phosphorus (P), rubidium (Rb), silicon (Si), strontium (Sr), titanium (Ti), vanadium (V), yttrium (Y), zirconium (Zr).

Samples LLRD1, LLRD2, LLRG1, LLRG2, LLRG3, LLRH1 and LLRH2 from the inner part of the crater rim were chosen for the XRF analysis. Lavas were stratigraphically sampled from three particular locations (Figure 4.1). Table 4.1 shows grid references for the seven samples together with raw data of 10 majors and 22 trace elements.

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TABLE 4.1 XRF raw major and trace elements of the Crater Lanoto inner rim lava flow with their grid references.

The seven inner rim lava samples of the Crater Lanoto plotted into several major and trace element variation diagrams, used to simplify Crater Lanoto lava suite composition. The Crater Lanoto lavas fall between the basanite, basalt and picrite composition in the 136 Le Bas et al (1986) classification. Figure 4.20 shows the Total Alkali Silica (TAS) classification of lavas from Crater Lanoto volcano where are tightly composition at the central part of the Samoan Volcanic Field (SVF). Crater Lanoto is a low alkali volcano and ranges between 45.6 and 44.8-weightpercentage SiO2. Lava is mostly basanitic to basaltic nature, however, it also slightly overlaps the picrite composition region. The boundary of the SVF was determined from the subaerial lavas of Upolu and Savai’i included those from the shield volcanism (deep submarine flanks lava suites) of Savai’i (Fepuleai, 1997; Cibik, 1999; Workman et al 2004; Jackson et al, 2007; Konter & Jackson, 2012).

FIGURE 4.20 Total Alkali Silica plot shows that lava of the Crater Lanoto scatter heavily in the central part of the Samoan Volcanic Field (SVF). The SVF (yellow) boundary was determined from previous work of; Fepuleai (1997), Cibik (1998), Workman et al (2004), Jackson et al (2007) and Konter and Jackson (2012) (Modified from Le Bas et al., 1986 and Konter and Jackson, 2012).

Optical microscopy reveals that the basanite to basalt composition of the Crater Lanoto lava suite has resulted in a dominance of olivine, pyroxene (augite) and plagioclase. Plagioclase is not present as a mega phenocryst but commonly dominates the groundmass. Basanite is characterised by a high abundance of nickel (404-425 ppm),

137 chromium (757-789 ppm) and magnesium oxides (12.86-14.43 %) (Table 4.1). Samples LLRG1 and LLRG2 fell in the picrite composition field (Figure 4.20). This is based on low nickel and chromium content (Table 4.1) in comparison with those of LLRD1, LLRD2, LLRG3, LLRH1 and LLRH2.

The long limb of the TAS classification area, dominated by the Savai’i shield volcano, contains high to low alkalic lavas (trachyte, benmoreite, mugearite and hawaiite) (Figure 4.20). A further increase in the silica content causes the WSVF to break into small clusters in the trachyte and phonolite suite.

Figure 4.21a shows that the two major oxides SiO2and MgO are negative correlated, with a steep slope. Lavas can be separated into three distinct but close-in-range groups with silica concentrations of 44.78-44.82 %, 44.99-45.02 % and 45.49-45.60 % along the negative trench. Samples LLRH1 & LLRH2 are enriched in MgO and depleted in SiO2.

Figure 4.21b indicates a wide steep positive correlation between SiO2 versus Al2O3.

However, the LLRH1 and LLRH2 enriched in Al2O3 and depleted in SiO2. Three distinct groups also formed at the same close silica range like those of Figure 4.21a.

Figure 4.22a shows that the trace elements plot of Y versus Zr formed a steep narrow close positive correlation. The lava samples are separated into three distinct groups with close range of yttrium concentrations of 22.7-23.9, 24.5-25.1 & 26.8-29.9 (ppm). Sample LLRG2 is enriched in Y and depleted in Zr. Figure 4.22b shows that the trace elements,

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Zr and Ni indicate a narrow shallow negative correlation. The samples also scattered into three distinct groups in range of 151.9-152.7, 158.6-158.8 and 163.8-164.2 ppm of Zr content. Sample LLRG3 is enriched in Zr and reduce in Ni content.

Figure 4.23a shows the steep broad negative correlation between SiO2 and Cr. Three lava flows seems divided into three distinct groups with ranges in silica content of 44.78- 44.82 %, 44.99-45.02 % and 45.49-45.60 %. Samples LLRH1 and LLRH2 are enriched in Cr and depleted in SiO2. Figure 4.23b also shows a very steep narrow correlation between MgO versus Ba. Three distinct groups fall in the range of 12.8-12.9, 14.1-14.2 and 14.3-14.4 MgO content. Lava flows LLRG1, LLRG2 and LLRG3 are enriched in Ba and depleted in MgO.

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Figure 4.24a shows that MgO forms a narrow steep close positive correlation with Cr. However, sample LLRGI, LLRG2 and LLRG3 are enriched in Cr and depleted in MgO. Like those of MgO versus Ba the three lava flows also fall in the similar ranges of 12.8- 12.9, 14.1-14.2 & 14.3-14.4 of the MgO versus Cr. Figure 4.24b also shows a major against trace element relationship between MgO versus Ni. It forms along a narrow steep positive correlation at the similar range with those of MgO versus Cr. Rock LLRD1 and LLRD2 are enriched in Ni and depleted in MgO.

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4.5.1.2 Summary of critical points from major and trace elements

(i) Crater Lanoto volcano has a narrow compositional range plotting in the basanitic- basalt region.

(ii) The geochemical similarity of lava implies they could be originated from the same magma batch, despite being ejected from different volcanoes.

(iii) The positive correlation in major and trace element implies an olivine controlled melt.

(iv) The negative correlation in major and trace elements suggests an olivine depleted melt but one which is enriched in pyroxene.

4.5.2 EPMA AND XRF ANALYSIS – TEPHRA COMPONENT

The rim tephra deposit and four main tephra beds (tephra bed-1, 2, 3 & 4) of the Crater Lanoto were analysed through EPMA (electron probe microanalysis) and XRF (x-ray fluroscence) technique. More details of both procedures were previously discussed in Chapter 3.

4.5.2.1 EPMA: Results for tephra component

Three polished glass shard samples were systematically selected for imaging. Grains with clean volcanic shard glass sections and without inclusions, cracks or microlitic textures were targeted. The four tephra deposits of the Crater Lanoto were expected to contain fresh volcanic glass shards. This prediction was based on the fact that, the tephra deposits are deeply buried in the sediment and should be preserved fresh volcanic glass shards. However, low major element concentrations in the volcanic tephra shards implies a highly weathered process associated with these volcanic components. Even though there were very few fresh shard components, in the polished glass of the tephra bed-1 and tephra bed-4 deposits, the chemistry indicates that intense weathering processes destroyed the majority of volcanic tephra shards.

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The microlitic texture of clay mineral varies from fine to coarse in size, from simple to complex in shape with light to dark colour. The influence of weathering activities, associated with the volcanic shards reveal that, there is a limitation in identifying difference in volcanic composition and texture.

The four tephra layers (tephra bed-1, 2, 3 & 4), are homogenously microlitic. These samples are highly weathered from with those of desiccation cracks. Figure 4.25a & b show images of the tephra bed-1 glass under (x 370) and (x 800) respectively. Under the (x 370) view the entire glass is covered with light colour of halo components range from very fine to coarse in size. Networks of desiccation cracks obviously dominated the whole glass fragment under (x 800) magnification. The microlitic texture and desiccation crack be resulted in wet and dry of theses tephra component. Detail discussion of this scenario is found in Section 4.7.1.4 as follow.

FIGURE 4.25 (a) Microlitic texture of the volcanic glass shard of the tephra bed-1, under (x 370) dominates by desiccation cracks and weathering halo’s features. (b) A closer view of the tephra sand grain, under (x 800) magnification shows the microlitic volcanic glass shard, with desiccation cracks and weathering halo’s features, of the tephra bed-1 deposit.

Samples that are intensely weathered and volcanic glass dominated by desiccation cracks and haloes presented major difficulties with EPMA analysis. Geochemical data obtained from samples influenced by these feature shows weathered nature of the major elements.

We compared the microscopic volcanic glass of Crater Lanoto with deposit from the other part of the world to give an idea of how weathered are those samples from the

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Crater Lanoto. Volcanic tephra shard images from other parts of the Samoa Volcanic Field were not available for this study. However, basaltic glass shards of the similar aged (mid-Holocene) tephra from Mount Gambier, southeast South Australia were used for comparison (Figure 4.26a and 4.26b) (Lowe, 2011). A group of basaltic shards from Mount Gambier range from yellowish (golden brown) to dark brown and show numerous prismatic microlites of titanaugite together with micro-inclusion. Clean and fresh volcanic glass shards enable identification of features destroyed in tephra deposits of the Crater Lanoto volcano such as the geometry of the vesicle, and the presence of thick and thin wall of the volcanic glass shard.

Several volcanic glass shards from tephra bed-1 and tephra bed-4, were scanned through beam 10, beam 20 and beam 40 micron, for a representational analysis. Obviously, there is no significant variation amongst the three beam values, but the microlitic nature and highly weathered characteristic of these airfall deposits can be observed.

The three beams were used to scan through glass shards from tephra bed-1 (T1) and tephra bed-4 (Com T4) glass shard. In comparison these raw data with lava suites (Table

4.1) major elements of the EPMA (SiO2, Al2O3, TiO2, Fe2O3, MnO, MgO, CaO, Na2O and K2O) are all altered. This indicates intense weathering (Figure 4.25), thus justifying no further analysis, no data will be shown in this section.

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4.5.2.2 XRF: Results for tephra sand

The XRF technique yielded 10 major elements (SiO2, Al2O3, TiO3, Fe2O3, MnO, MgO,

CaO, Na2O, K2O and P2O5) from six representative samples. Like the EPMA procedure, the XRF analysis also identified significant alteration of major element content of the tephra deposits in comparison with those inner lava suites (Table 4.1). These changes

included the reduction in SiO2, CaO, Na2O, MgO and K2O content but elevated

concentrations of Al2O3, TiO2, Fe2O3, MnO and P2O5. Due to these changes in major element chemistry, no further XRF analyses for the rest of tephra samples was undertaken.

4.5.2.3 Summary of critical points from EPMA and XRF

Representative data of the EPMA and XRF technique shows alteration in all selective major elements Thus it was concluded that these methodologies are not appropriate for weathered tephra deposit analysis in the future research.

4.5.3 INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY (ICPMS) FOR TRACE ELEMENT ANALYSIS

The ICPMS technique was later chosen in this study to produce quality geochemical information of the Crater Lanoto despite highly weathered tephra deposit. The ICPMS technique involves the analysed of the four tephra deposits and lava samples through part-1 and part-2 procedure which previously discussed in Section 3.2.11.

4.5.3.1 Results

Detailed discussion of the ICPMS is included in Chapter 3. Part 1 procedure was carried out at the University of the South Pacific, Suva, and part 2 at the University of Sydney. The part 2 procedure enable us to yield concentrations of 21 trace elements; aluminium (Al), arsenic (As), barium (Ba), calcium (Ca), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium

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(Na), nickel (Ni), phosphorus (P), lead (Pb), sulphur (S),silicon (Si), strontium (Sr), vanadium (V) and zinc (Zn).

The ICPMS results are presented in three different formats: tables, variation diagrams and acid insoluble residue (AIR) plots. Variation diagrams present relationships between trace elements content of tephra sand and lava which enable us to determine the nature of the deposition. AIR comprises the content of silicate minerals dominating tephra sand which would enable to determine the widely distribution of these components downcore.

(i) Table

Table 4.2 show raw ICPMS representative data of the 21 available trace elements for tephra, soil and lava of the Crater Lanoto. The analysed samples included the tephra beds (LLT1, LLT2, LLT3, LLT4, LLCT1, LLCT3 & LLCT4), rim tephra deposit (LLRIM-A, LLRIM-F & LLRIM-I), soil deposit (LLA, LLB, LLC, LLE, LLF & LLI) and inner rim lava suites (LLRD1, LLRD2, LLRD3, LLRH1, LLRH2, LLRH3, LLRG1, LLRG2 & LLRG3).

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TABLE 4.2 Raw data of the ICPMS trace elements.

Sample Al As Ba Ca Cd Co Cr Cu Fe K LL T1t 419.85 0.04 0.02 1.68 0 0.12 2.59 0.17 354.85 1.26 LL T2t 261.75 0.02 0.01 1.42 0 0.09 1.83 0.08 145.96 0.63 LL T3t 591.19 0.03 0.02 1.49 0 0.14 3.44 0.24 563.91 0.49 LL T4t 687.38 0.04 0.02 1.55 0 0.17 4.23 0.21 569.7 0.81 LL T1b 491.73 0.03 0.03 1.81 0 0.16 3.24 0.23 512.96 1.4 LL T2b 758.41 0.05 0.04 1.57 0 0.21 5.18 0.24 592.65 1.96 LL T3b 959.78 0.05 0.04 1.6 0 0.1 0 0.24 363.68 0.93 LL T4b 733.57 0.02 0.03 1.6 0 0.17 4.7 0.32 764.38 0.89 LL T1m 636.3 0.03 0.04 1.57 0 0.19 4.15 0.29 541.01 1.99 LL T2m 681.66 0.03 0.03 1.43 0 0.18 4.73 0.21 436.59 1.57 LL T3m 983.85 0.05 0.03 1.66 0 0.16 0 0.28 593.49 0.79 LL T4m 481.35 0.03 0.02 1.49 0 0.13 2.94 0.2 516.23 0.6 LLRIMA 400.96 0.04 0.05 55.77 0 0.53 1.2 0.3 327.28 5.03 LLRIM F 311.94 0.03 0.02 48.52 0 0.33 0.85 0.12 292.22 6.63 LL RIM I 426.41 0.04 0.04 94.64 0.01 0.58 1.22 0.31 547.98 8.15 LL A 416.68 0.04 0.05 9.34 0 0.39 1.4 0.14 313.78 1.62 LL B 427.08 0.04 0.05 6.23 0 0.35 1.69 0.1 317.04 1.88 LL C 408.77 0 0.04 4.39 0 0.43 3.45 0.22 666.94 2.04 LL E 107.41 0.04 0.03 3.68 0 0.18 1 0.14 157.37 1.5 LL F 560.5 0.03 0.09 5.36 0 0.42 1.74 0.12 587.74 2.35 LL I 396.55 0.05 0.03 4.37 0 0.26 1.06 0.09 309.84 1.16 LL CT1 774.27 0.08 0.02 1.5 0.01 0.5 3.95 0.61 1227.6 1.26 LL CT3 822.87 0.07 0.02 3.53 0.01 0.2 4.8 0.62 1384.4 0.56 LL CT4 590.63 0.05 0.02 2.6 0 0.15 3.2 0.42 1062.3 0.45 LL RD 1 117.5 0.04 0.02 49.32 0 0.47 0.4 0.53 497.03 10.78 LL RD 2 131.38 0.03 0.03 54.88 0 0.52 0.44 0.59 547.02 12.07 LL RD3 450.21 0.03 0.03 4.74 0 0.51 4.73 0.26 589.27 1.31 LL RH1 130.44 0.03 0.02 64.71 0 0.44 0.38 0.53 511.23 13.84 LL RH2 87.6 0 0.01 45.19 0 0.31 0.27 0.36 355.64 9.12 LL RH3 115.18 0.02 0.02 59.47 0 0.38 0.34 0.45 444.36 11.71 LL RG1 57.94 0.02 0.02 26.89 0 0.19 0.21 0.25 214.93 5.02 LL RG2 100.13 0.02 0.03 42.94 0 0.32 0.31 0.42 395.47 9.02 LL RG3 91.6 0.02 0.03 39 0 0.3 0.3 0.39 368.68 8.2

TABLE 4.2...... continued next page………

146 S ample Mg Mn Na Ni P Pb S S i S r V LL T1t 3.21 0.23 0.76 0.47 3.94 0.05 2.09 6.49 0.1 1.19 LL T2t 1.75 0.11 0.75 0.32 2.9 0.04 1.5 6.77 0.07 0.72 LL T3t 1.33 0.2 0.63 0.72 7.87 0.06 1.12 6.35 0.11 1.77 LL T4t 2.46 0.29 0.81 0.98 7.42 0.05 2.74 6.76 0.14 1.64 LL T1b 3.67 0.34 0.65 0.53 6.27 0.05 1.53 6.62 0.11 1.43 LL T2b 4.4 0.39 0.81 0.93 5.87 0.12 2.31 6.5 0.18 1.83 LL T3b 2.83 0.19 0.82 1.32 6.94 0.11 2.31 6.39 0.31 1.1 LL T4b 2.59 0.35 0.79 1.09 8.3 0.08 1.55 6.37 0.16 2.25 LL T1m 5.02 0.44 0.66 0.77 6.46 0.08 2.06 6.05 0.16 1.54 LL T2m 4.11 0.26 0.68 0.84 5.75 0.06 2.61 6.06 0.17 1.54 LL T3m 1.9 0.26 0.78 1.46 10.2 0.08 1.33 5.98 0.21 1.42 LL T4m 1.8 0.24 0.78 0.68 6.75 0.02 1.3 6.08 0.1 1.53 LLRIMA 160 8.12 4.84 6.99 9.32 0.03 1.25 5.55 0.35 0.52 LLRIM F 156.6 4 3.68 3.74 6.72 0.05 1.35 5.06 0.16 0.37 LL RIM I 155.2 11.4 6.92 6.53 16 0.04 1.62 5.59 0.44 0.52 LL A 68.41 6.71 1.32 1.11 2.73 0.03 2.8 5.38 0.23 0.81 LL B 5.41 6.13 1.52 0.77 2.24 0.04 4.73 5.24 0.19 0.86 LL C 5.3 10.8 1.42 0.77 2.59 0.05 4.46 5.14 0.05 1.26 LL E 8.15 2.46 1.26 0.57 1.56 0 2.79 5.3 0.03 0.31 LL F 14.61 5.42 1.27 1.34 3.61 0.04 5.1 5.04 0.27 1.13 LL I 15.5 7.87 0.96 0.52 3.27 0.03 4.27 5.06 0.2 0.69 LL CT1 2.83 0.39 0.89 0.75 23.7 0.1 4.97 4.56 0.09 4.38 LL CT3 1.49 0.42 0.79 0.67 32 0.16 1.36 5.08 0.11 9.38 LL CT4 1.12 0.29 0.71 0.47 24.1 0.07 0.96 5.21 0.08 6.65 LL RD 1 153.4 6.08 30.2 2.74 5.33 0.03 0.31 5.05 0.54 0.34 LL RD 2 155 6.77 33.7 3.13 6.14 0.03 0.28 5.03 0.61 0.35 LL RD3 4.36 0 1.21 0.83 2.68 0.03 3.75 5.1 0.04 1.31 LL RH1 154.5 6.22 0 2.96 5.44 0.02 0.27 4.74 0.73 0.32 LL RH2 149.1 4.2 31 1.89 4.23 0.02 0.17 4.85 0.5 0.24 LL RH3 152 5.28 39.1 2.44 5.25 0.03 0.2 4.86 0.67 0.3 LL RG1 121.2 2.5 15.6 1.07 2.42 0.02 0.08 5.08 0.28 0.23 LL RG2 145.1 4.29 27.2 2.06 3.98 0.03 0.14 5.05 0.46 0.37 LL RG3 141.3 4 24.7 1.91 3.44 0.02 0.11 5.09 0.42 0.35

147 (ii) Variation Diagrams of the ICPMS data

Tephra deposit, rim soil and inner rim lava are plotted together in all variation diagrams. Trace elements should show significant aspects of eruption activities and the nature of deposition process within Crater Lanoto such as;

(i) Identification of contaminant tephra components and their sources within the sediment;

(ii) Determination of the four main eruption activities whether they are geochemically related;

(iii)Determine the tephra component distribution downcore using acid insoluble residue (AIR) plot.

Figure 4.27a displays a trace element plot between Ca versus Mg concentration. The relationship between the two trace elements, form a broad steep positive linear correlation. Very few tephra components (tephra bed-3, 4 and pyroclastic deposit), rim soil and inner rim lava are enriched in Ca and depleted in Mg content. The rest of the rim soil and tephra components are enriched in Mg and depleted in Ca. Tephra, rim soil and inner rim lava seems to scatter into three major groups. Tephra bed-1 2, 3 and 4 group show between 1 and 4 ppm Ca content whereas the rim soil group shows a range of 4-9 ppm and inner rim lava and rim tephras groups lie between 27 and 95 ppm. The inner rim lava is almost overlaps the entire rim tephra deposit in term of Ca concemtration. An isolated group referring to a minor component in tephra bed-3 and tephra bed-4, lies between 4 and 3 ppm in Ca content implying contaminant tephra. Similarly, an isolate rim soil value of 10 ppm in Ca content is also considered to be a contaminant component.

Figure 4.27b indicates a plot between Sr versus Ni concentrations with the two trace elements forming a positive narrow and shallow angle linear correlation. Pyroclastic deposit, rim soil, few inner rim lava, tephra bed-1, 2, 3 and 4 components are all enriched in Ni and depleted in Sr. The majority of lava components are enriched in Sr and depleted in Ni. Soil and tephra bed-1, 2, 3 and 4 with very few lava components overlap each other in to form a big group. The big group settle in the range between 0.02 and 0.38 ppm in tern of Sr composition. The pyroclastic deposits are scattered in an isolated between 0.16

148 and 0.44 ppm in Sr content. The isolated rim tephra shows that it is also a part of the contaminant component. Inner lavas also sit in an isolated group at a range between 0.41 and 0.79 ppm [Sr].

FIGURE 4.27 ICPMS trace element plots (a) Ca versus Mg shows a positive correlation. (b) Sr versus Ni also shows a positive correlation.

Figure 4.28a shows a broad positive linear relationship between P versus Cu concentrations. Inner rim lava, few rim soil, tephra bed-1 and tephra bed-3 are enriched in Cu and depleted in P. The majority of tephra and rim soil components are enriched in P and depleted in Cu. Samples start to split into two trends as both trace elements contents increase. The rim soil, very few lavas and few tephra scatter at a range between 2 and 6 ppm of P content. Tephra bed-1, 2, 3 and 4 settle in a group at a range between 7 and 10 ppm [P]. Inner rim lava components form into isolate group at range between 1 to 6 ppm [P]. Very few components of pyroclastic deposit and tephra bed-1, 3 and 4 indicates contaminant airfall, plot between 23.6 and 32 ppm of P content.

Figure 4.28b indicates a trace element plot between Cr versus V showing that the relationship between the two trace elements is characterised by a wide positive linear correlation. The rim soil, inner rim lava, tephra bed-1, 2, 3 and 4 components are enriched in V and depleted in Cr. Few components of rim soil, tephra bed-1, 2 and 4 are enriched in Cr and depleted in V. The three tephra components (tephra bed-1, 3 and 4) form an isolated group at a range between 3.6 and 4.1ppm of Cr content. This isolated group is referred to as contaminant tephra component. Lavas are tightly scattered into an

149 isolated group at a range between 0.2 and 0.4 [Cr]. The rest of tephra and soil spread along the positive lineation.

FIGURE 4.28 ICPS trace element plots (a) P versus Copper Cu shows a broad positive correlation. (b) Cr versus V shows wide positive correlations.

Figure 4.29a displays the broad positive correlation between trace elements K and Co. Soil, pyroclastic deposit, tephra bed-1, 2, 3 and 4 components are enriched in Co and depleted in K. The inner rim lava and very few pyroclastic deposit components are enriched in K and depleted in Co. The majority of tephra scatter in a tight group at a range between 0.5 and 1.5 ppm K content. Lava spread widely along the positive correlation at a range between 5 and 14 ppm K content. The pyroclastic deposit components and very few tephra bed-1 are isolated contaminant tephra components.

Figure 4.29b shows broad positive linear correlations between Ca versus Mn. The soil components are enriched in Mn and depleted in Ca. The pyroclastic deposit, inner rim lava and tephra bed-2, 3 and 4 are enriched in Ca and depleted in Mn. The soil, inner lava and tephra components are settled into 3 distinct groups. Tephra bed-1, 2, 3 and 4 group scatters at a range between 2 and 5 ppm calcium content; the rim soil group plots between 5 and 11 ppm calcium content. Lava and pyroclastic deposit group scatter at a range between 27 and 95 ppm calcim content. The inner lava is overlapping several pyroclastic deposit components.

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FIGURE 4.29 ICPMS trace element plot (a) K versus Co shows a broad positive correlation. (b) Ca versus Mn shows a wide positive correlation.

Abroad positive correlation between Ni and Al shows in Figure 4.30a. Pyroclastic deposit, inner lava, and very few soil components are enriched in Ni and depleted in Al. Tephra bed-1, 2, 3 and 4 and the majority of rim soil components are enriched in Al and depleted in Ni. Inner rim lava and pyroclastic deposit isolated further away from the soil and other tephra sands. The inner lava settles in the group at range between 1 and 3 ppm in Ni concentration. The pyroclastic deposit scatters in group at between 4 and 10 ppm Ni content. Soil and the majority of tephra components merge in a group ranging between 0.4 and 1.0 ppm. Isolate components of very few tephra bed-2, tephra bed-3, rim soil and pyroclastic deposit are considered as contaminant, and show a range between 0.3 and 6.9ppm of Ni content.

Figure 4.30b shows a broad positive correlation between Al versus Fe. Several soils, tephra bed-1, 2, 3 and 4 components are enriched in Al and depleted in Fe. The inner rim lava, very few rim soils and the rest of tephra components are enriched in Fe and depleted in Al. Tephra bed-1, 3 and 4 are isolated from the rest of the tephra components and settle at a range between 600 and 900 ppm of Al content. These tephras are part of contaminant components. Lava plots tightly within a range of 90-195 ppm of Al content. Rim soil and the rest of the tephra components are merged in a big group, scattered within a wide range between 100 and 1000 ppm in Al concentration.

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FIGURE 4.30 ICPS trace element plot (a) Ni versus Al shows a broad positive correlation. (b) Al versus Fe shows a wide positive correlation.

(iii) Acid-insoluble residue (AIR) from trace element digestion

During Part 1 of the ICPMS digestion procedure, all acidified samples were transferred into flasks via weighed filter papers. The filter papers with acid-insoluble residue (AIR) were also placed in the oven for 24 hours before being reweighed. AIR components are mainly comprised of silicate minerals. Silicate minerals (olivine, pyroxene and plagioclase) dominate the tephra deposit of the Crater Lanoto. These silicate mineral components are represented by “black dots” in Figure 4.31. Several AIR components show high and low reading enabling them to be classified in isolate group. This isolated group is known as “distinct tephra group” (this study).

Figure 4.31 shows a plot of AIR versus depth for core D3. The acid-insoluble residue (AIR) components seem dominated downcore of the master core D3. The four main tephra deposits (tephra bed-1, 2, 3 and 4) obviously dominated by tephra components. The mixed layer represents by trough in the MS plots, which contains high concentration of organic material. However, Figure 4.31 shows that the mixed layers are also dominate by tephra components. At the top mixed layer, it comprises of two distinct groups of the pyroclastic deposits: low and high percentage content. Other mixed layers underlying tephra bed-4, 3 and 2, seem to all contain tephra components. Distinct tephra groups dominated both tephra beds and mixed layers. If tephra component dominate the core D3

152 then the organic material must be occurs in lens deposit. The AIR plot shows a similar approach with those of Figure 4.7 and Figure 4.8 (frequency dependent MS versus depth).

FIGURE 4.31 Acid-insoluble residue of silicate primary and second mineral shows dominated downcore. Oval represents distinct tephra group.

4.5.3.2 Summary of critical points from ICPMS technique

(i) The positive linear correlation in various trace element plots implies genetic link.

(ii) The overlap in trace element plots implies that material is geochemically related.

(iii)The isolate components of tephra bed-1, 3 and 4 signifies contaminated components from nearby volcanoes.

(iv) Pyroclastic deposits are contaminated components, possibly derived from Maimoaga vents (down the east slope of Crater Lanoto) or even nearby volcanoes. Overlaps of

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the pyroclastic deposit and inner rim lava (Figure 4.27a and 4.29b) imply that they were derived from the same source.

(v) AIR components show contaminant tephra are widely spread downcore.

(vi) Two types of contaminant tephra characterised by the high and low AIR percentage content.

(vii) AIR component signifies two pyroclastic deposits derive from two different episodes.

(viii) Crater Lanoto volcano may have erupted at the same time with other volcanoes activities in the area. This assumption is based on the isolation of few tephra components from the big group of the same tephra bed (Figure 4.28, 4.29 and 4.30).

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4.6 DATING OF LAKE SEDIMENT

The dating section is presented in three main parts as follows:

1. Argon-Argon dating 2. Radiocarbon dating 3. Lead-210 dating

Reliable chronology for the Crater Lake Lanoto deposits were obtained from various parts of the craterusing three radiometric dating. This was to ensure that, every significant component of the eruption episodes downcore including those of the inner rim lava had been dated for this study.

Argon-Argon dating of the volcano rim lava was used as a base age with comparison those of the lake sediments. Radiocarbon dating was employed to determine the age of the four tephra layers (tephra bed-1, 2, 3 and 4). The upper part of the core (Lano-12 Unit) had been investigated using the 210Pb technique.

4.6.1 ARGON-ARGON DATING

The Argon-Argon dating is presented the results of the two methods:

(a) Plagioclase groundmass

(b) Plagioclase phenocryst

4.6.1.1 Results

Plateau ages were calculated from every individual step as weighted means. All errors were calculated as “1”sigma (1σ) or “2”sigma (2σ) based on their variable diffusion properties. Errors were treated, as a statistical reliability of 95% confidence level (2σ) (Koppers et al., 2011). Plateau and isochron plots of groundmass and phenocryst, illustrate all elements and result of the 39Ar/40Ar incremental step heating technique.

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(i) Plagioclase Groundmass

Figure 4.32 shows the relationship between the cumulative percentages of 39Ar released versus the calculated step ages radiogenic of the groundmass. The plot displays a U- shaped feature of the groundmass high-resolution incremental heating. A U-shape feature is a significant signature of a low potassium silicate mineral phase, plagioclase and clinopyroxene in the sample (Kelly, 2002).

The weighted plateau age of 143.9 ± 2.8 Ka, has a full external error of ± 4.3, and analytical error of ± 2.7. The incremental heating plateau age of 143.9 Ka, calculated between 2 and 98 cumulative 39Ar released percentage.

FIGURE 4.32 Cumulative of Argon released versus calculated age of the groundmass high-resolution incremental heating procedure yields the weighted plateau age spectra of 143.9 Ka.

A “mean sum weighted deviates” (MSWD) of 0.72 (86 %), plotted below the accepted standard value of less than 2.5 indicating that the weighted plateau age shows a “goodness of fit” (Baksi, 2003 and 2006). The groundmass age plateau is characterised by several significant components (Koppers 2000; 2011): (1) high apparent age for lower and high temperature increments and (2) a total amount of argon gas release of 98%. Kelly (2002) explained that the high initial age at the low temperature zone is the result of the breaking down of fluid inclusions. This is the stage where the liquid pressure

156 releases during heating and generates a crack within the crystal. Baksi (2003 and 2006) stated that this high age spectra scenario is also disturbed by the presence of excess 40Ar 39 39 and recoiled Ar in the sample. Koppers (2011) proposed that the loss of ArK and 37 39 40 ArCa components in a sample causes low and high apparent ages for Ar/ Ar spectra. This is due to the recoil of nucleogenic isotopes through the irradiation procedure. Heating steps are expected to yield less radiogenic argon at lower temperatures, whilst high incremental contain more radiogenic argon.

Koppers et al., (2000 and 2011), explained that the uncertainties of crystallization age in 39Ar/40Ar component, could have arisen in two different ways: through alteration processes and analytical problems. Alteration may produce artificially lower ages at high temperatures, but higher ages at low temperature increments. It has been suggested that a change from a primary into a secondary mineral phase may overprint the expected crystallization age of these basaltic lavas.

Figure 4.33 displays the cumulative 39Ar release against the K/Ca ratio of the groundmass. The plot shows a steep staircase ridge profile, with 2% and 98% increments at a rate of 0.416 ka ± 0.002. This yields a total fusion age of 144.6 ka ± 3.3 with full external error of ± 4.7 and analytical error of ± 3.3.

Initially it shows a constant mode at lower increment temperature zone until about 65- 75%, where there is a sudden decrease corresponding to the higher temperature zone. However, at this stage, the K/Ca ratio fell below the initial ratio and remains low throughout the highest temperature increment zone.

A sharp increase and rapid decrease of the K/Ca plateau is most likely influenced by the degassing of the latter mineral phases (Koppers et al., 2011). The saddle shape shows that the groundmass has a lack of potassium (Kelly, 2002). Like the weighted plateau age, the remaining alteration and recoil incident perhaps contributed to a high K/Ca ratio as shown by a gentle slope (Koppers, 2011).

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FIGURE 4.33 Cumulative of Argon released versus K-Ca ratio of high-resolution incremental heating steps procedure of groundmass.

Figure 4.34 displays the normal isochron plot between 39Ar/36Ar versus 40Ar/36Ar of the groundmass. The relationship defined by a two straight lines, calculation isochron (pink) and atmospheric (dark grey). A positive correlation between the atmospheric and radiogenic argon components, yield an age of 143.1 ± 4.4 (2 sigma), with full external error of ± 5.5 and analytical of ± 4.4. An atmospheric reference line (dark grey) and with that of calculation isochron (pink) almost form a single stripe, shows a very close relationship, between the groundmass component and with those of atmosphere. The atmospheric interception defined by 299.8 ± 4.1. The mean sum weighted deviates (MSWD) of 0.75 (82 %), is sitting below the accepted standard value, of less than 2.5. This indicates that the normal isochron is the “goodness of fit” parameter (Baksi, 2003 & 2006).

There are few points (green squares) that not define lines, refer with to contaminant phases, where no age can be calculated (Kelly, 2002). The normal calculated isochron of plateau age groundmass shows, a very close fit to the reference line, where values spreading about 80%. Koppers (2000) described that the close fit to the reference line is signature of binary mixing, between an atmospheric component and with those of the

158 radiogenic constituent. This binary relationship represents a crystallisation age, of the inner crater rim lava of the Crater Lake Lanoto.

Figure 4.35 shows the inverse isochron plot between 39Ar/40Ar versus 36Ar/40Ar of the groundmass. The relationship is defined by two negative slope lines: calculated isochron and atmospheric reference line. Like the normal isochron, the relationship between the atmospheric and radiogenic argon of the inverse isochron also closely fits. The values have almost covered the half of the slope. The atmospheric reference on the negative slope has an atmospheric intercept of 300 ka ± 4.1 of plateau ages on the 39Ar/40Ar (x- axis) and the 36Ar/40Ar (y-axis). The reference line constructs very tightly with the calculated isochron line where the two meet at the total fusion point. The reverse isochron MSWD, plotted at 0.74 (84%), where “best fit” parameter of below the 2.5 value. Like the normal isochron the inverse also yield the 143.3 ± 4.4 Ka with only ± 5.5 for full external error and ± 4.4 for the analytical error.

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(ii) Plagioclase Phenocryst

Plagioclase phenocrysts have contained the bulk of Argon released. Figure 4.36a shows cumulative 39Ar released versus the calculate step ages of the plagioclase phenocryst. The plot indicates a staircase profile, initially low as may be due to a diffuse loss of 40Ar. During step heating, the high temperature increment zone falls between 32 and 100% of cumulative 39Ar released. At between the ranges of 95 % and 100 %, it yields a much older age of 42.0 ± 0.17 Ma, compared with the groundmass. This shows that, the plagioclase phenocrysts produce discordant data, and the actual age plateau could not be calculated. The phenocryst has a full external error of ± 0.96 Ma and analytical error of 0.07 Ma.

Figure 4.36b shows the cumulative Argon released plots against the K/Ca ratio of the plagioclase phenocrysts. The plot displays a mixed staircase ridge profile. Initially, it has

160 a low increment temperature at low K/Ca ratio value. It then increases at rate of 0.0341 ± 0.0001 Ma, the heating steps giving constant until the 60% mark. This is where suddenly fell back at low temperature before reach the highest temperature at 65%. This high variation between low and higher increment temperature, at very low K/Ca ratio continue to 100%. It produces unreliable values for the phenocryst plateau age to be calculated. The total fusion age of the plagioclase phenocryst, was calculated at 42 ± 0.17 Ma with a full external error of ± 0.96, and the analytical error of ± 0.07. It seems that this particular age is much older, in contrast with those of the groundmass.

FIGURE 4.36 (a) Argon released versus calculated age of the plagioclase phenocryst. (b) Argon released versus K/Ca ratio of the plagioclase phenocryst.

Figure 4.37a displays the normal isochron plot between 39Ar/36Ar versus 40Ar/36Ar of the plagioclase phenocryst. The plot shows plagioclase phenocrysts (blue) are scattered further away from the total fusion (red) of 42.06 ± 0.17 Ma. These scattered values may be related to contamination. These phenocrysts are comprised of low in potassium, calcium and even separate mineral phases.

Figure 4.37b shows the inverse isochron plot between 39Ar/40Ar versus 36Ar/40Ar of the plagioclase phenocryst, showing a low angle positive slope. Several phenocrysts scatted closed with total fusion while the rest spread away along the slope.

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4.6.1.2 Summary of the critical points from the Argon-Argon dating

(i) Groundmass step heating procedure yields 143.9 ± 2.8 Ma of the inner rim lava.

(ii) The normal and reverse isochron of the groundmass heating method have both MSWP standard value plot below limit of 2.5 means “best fit”. This shows groundmass is the most recommended technique for future work.

(iii)Dating of the plagioclase phenocryst was not perform sucessful

(iv) Normal and reverse isochron of the phenocryst scatter around further away from the total fusion, means poor result. Unfortunately, the plagioclase phenocryst is not a reliable procedure for lava suite of Samoa.

4.6.2 RADIOCARBON DATING

Radiocarbon dating has been successfully used in several volcanology studies in Samoa to determine eruption activities and sea level change during the Holocene (Grant-Taylor & Rafter, 1962; Goodwin & Grossman, 2003; Nemeth & Cronin, 2009).

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4.6.2.1 Result

Table 4.3 shows the four dated samples with ANSTO code. Radiocarbon (14C) values relates solely to the graphite derived from the fraction that was used for the radiocarbon measurement. It was sometimes the case that the 13C of this fraction was not the same as that of the bulk material. Measurements were determined using Elemental Analysis Isotope-ratio Mass Spectrometry (EA-IRMS). Some 13C isotope values may not have an associated uncertainty due to the limited number of determination. Radiocarbon concentration for each sample listed in the percent Modern Carbon column with “1” sigma uncertainty. The recorded ages of the four samples were based on the radiocarbon count rate method, of Stuiver and Polach (1977).

TABLE 4.3 The four dated samples; LLD3/34, LLD3/49, LLD3/73 and LLD3/219. Sample LLD3/210 was based on only 10ug carbon hence the large error.

Percent modern Conventional ANSTO Sample δ13C per mil Carbon (pMC 1σ code number Radiocarbon age (yrs BP 1σ error) error) OZR028 LLD3/34 -25 65.90 ± 0.52 3,350 ± 70 OZR026 LLD3/49 -25 68.53 ± 0.61 3,040 ± 80 OZR027 LLD3/73 -26.6 ± 0.1 6.23 ± 0.08 22,300 ± 100 OZR029 LLD3/219 -25 15.36 ± 0.65 15,050 ± 350

Figure 4.38 displays the plot between the radiocarbon ages versus the depth of master core D3. The radiocarbon age of the sample LLD3/34 (3.4 Ka) from 68 cm depth seems older than sample LLD3/49 (3.0 Ka) extracted from 98 cm depth. Similarly, sample LLD3/73 (22.3 Ka) from 146 cm depth shows a much older age than sample LLD3/219 (15.0 Ka) from 436 cm. Based on the stratigraphic position of the two samples the LLD3/219 should be much older than the LLD3/73.

The four radiocarbon ages could be all related to the age of the Crater Lanoto activities. However, the dates from only two samples (LLD3/34 and LLD3/73) were selected as reliable ages. This selection was based on (1) the stratigraphic position of the samples downcore (Figure 4.38) and (2) compare the new radiocarbon age with the inner lava Argon-Argon age of 144 Ka. Despite the samples LLD3/34 and LLDD3/49 show reverse

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age scenario however, it is to be expected the two samples could have a close age range based, on their stratigraphic position (Figure 4.10). Variation in ages of the four samples could be influenced by several factors such as; laboratory error, sedimentary reworking processes and an introduction of the modern radiocarbon component into sediment (through root or stem). A detail discussion of this particular topic is found in Section 4.7.1.7 (i).

FIGURE 4.38 Plot of new radiocarbon age versus depth of core D3. Sample LLD3/49 and LLD3/219 from greater depth seem younger than of those of LLD3/34 and LLD3/73 respectively.

4.6.2.2 Summary of critical points from Radiocarbon dating

(i) The four new radiocarbon ages may all represent Crater Lanoto volcanic activities, however only two were selected as reliable ages based on their stratigraphic position. The young ages show that the Crater Lanoto volcano erupted on several occasions during the Holocene (Lefaga Formation) and classified as Mulifanua Formation in Kear and Wood’s (1959) geological map.

(ii) Variation in ages could be associated with laboratory error and the presence of the modern carbon component in the sediment.

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(iii)The most reliable age would were selected based on their stratigraphic position and with comparison with the argon-argon age of the inner lava suite.

4.6.3 LEAD-210 DATING

The 210Pb isotope dating has never been deployed in Samoa for any volcanology study. The main purpose to employ this particular technique was to determine deposition activities at the top of the core. This would provide some clues of how sediment had been laid down in the lake basin recently in comparison with the older deposition down core.

4.6.3.1 Results

Table 4.4 shows 12 sample downcore with their total 210Pb activity, support 210Pb activity and unsupported 210Pb activity. Unsupported 210Pb activity in the sediment is calculated by subtracting the supported activity 210Pb from the total activity of 210Pb. There are at least four major batches of variations identified downcore, occurring within the total, supported and unsupported 210Pb activity data of the Lano-12 Unit (Table 4.6).

TABLE 4.4 The total, supported and unsupported 210Pb activities downcore, at the top part of the master core D3.

ANSTO Sample Depth Total 210Pb Supported 210Pb Unsupported 210Pb Calculated CIC Ages ID numbers (cm) (Bq/kg) (Bg/kg) (Bg/kg) (years) P161 D3/1 0.0 – 2.0 116 ± 6 4.4 ± 0.4 112 ± 6 6 ± 6 P162 D3/2 2.0 – 4.0 255 ± 12 3.1 ± 0.3 253 ± 12 18 ± 6 P163 D3/3 4.0 – 6.0 311 ± 14 3.3 ± 0.3 309 ± 14 30 ± 7 P164 D3/4 6.0 – 8.0 293 ± 13 1.6 ± 0.2 292 ± 13 42 ± 8 P165 D3/5 8.0 – 10 264 ± 12 3.9 ± 0.4 260 ± 12 53 ± 10 P459 D3/6 10 – 12 202 ± 13 5.7 ± 0.5 200 ± 13.9 65 ± 11 P460 D3/7 12 – 14 116 ± 10 3.8 ± 0.4 114 ± 10 77 ± 13 P461 D3/8 14 – 16 72 ± 20 3.6 ± 0.4 70 ± 20 89 ± 14 P462 D3/9 16 – 18 75 ± 20 3.3 ± 0.4 73 ± 14 * P463 D3/10 18 – 20 106 ± 17 3.0 ± 0.3 105 ± 17 * P464 D3/11 20 – 22 66 ± 6 3.7 ± 0.5 63 ± 6 * P465 D3/12 22 – 24 222 ± 26 4.0 ± 0.6 222 ± 27 * * (Decline of 210Pb activity at these depths)

Figure 4.39 shows the total 210 Pb activity versus the depth of core D3. The 12 samples seem aligned up downcore like letter “Z” shaped. Total activity of 210Pb increases at

165 depth interval between 0 and 6 cm. A long decreases profile of the total activity between 6 and 16 cm depth. The activity increases twice at the depth between 16 and 26 cm. There are two major gaps formed as activity increase at depth intervals of 2.0-6.0 and 20- 24 cm.

FIGURE 4.39 The total activity of 210Pb versus depth of the core D3.

Figure 4.40 demonstrates relationships between supported activity, unsupported activity and CIC ages versus depth. Supported 210Pb activity form a thin yellow band range between 1.6 ± 0.2 and 5.7 ± 0.5 Bg/kg. The supported activity is almost consistent in size throughout the Lano-12 Unit, except at depth between 10 and 12 cm where there is a major increase. Unsupported 210Pb activity versus depth shows that the 12 samples also scatter downcore in the Z-shape. At a depth of 2.0 to 6.0 cm downcore the unsupported 210Pb activity rapidly increases from sample D3/1 to D3/3. This rapid increase generates gap “A” in the data. Between 6.0 and 16 cm depth, the 210Pb activity had a long decreasing profile downcore from sample D3/4 to D3/8. The depth interval 16-20 cm shows the 210Pb activity increasing downcore from sample D3/9 to D3/10. At lower part of the unit from 20 to 24 cm, the unsupported activity also increases downcore from sample D3/11 to D3/12. This rapidly increase in unsupported activities creates gap “B”.

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The plot of CIC ages versus depth define by a positive perfect slope (Figure 4.40). However, the 210Pb activity declines with depth (Table 4.6). The positive slope line constructed from the CIC ages between 6 and 89 years ago. CIC of the 210Pb activity determined from the slope of the decreasing profile between 6.0 and 16 cm downcore. The sedimentation rate from the least-square fit of the unsupported 210Pb versus depth estimated to be 0.017 cm per year. The unsupported 210Pb activity varies in depth, corresponding with those of higher dating ages, range due to the low sedimentation rate.

FIGURE 4.40 Supported activity, unsupported activity and CIC ages versus depth of the core D3.

4.6.3.2 Summary of critical points from Lead-210 dating

(i) Unsupported 210Pb activity dominated the top part of the core. (ii) Dilution in sedimentation of more than 89 years ago is mostly likely related to modern human activities. (iii)A low sedimentation rate of 0.017 cm per year coincides with the delay in unsupported activity.

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4.7 DISCUSSION

This section attempts to link the new information for Crater Lanoto volcano to the structures of the region and larger scale shield and post-erosional activities. There is a focus on current records which are used as a guideline to correlate with those of a similar volcanic nature, along the Samoan Volcanic Field (SVF). More importantly, the records will improve understanding, about the relationship between the volcanism of Samoa and regional tectonic processes. This allows the construction of a reliable tephrachronology for Crater Lanoto and the creation of a volcano prediction tool.

The discussion section is divided into four parts as follows:

(i) Part 1 - Interpretation of the results in more details.

(ii) Part 2 - Discussion the new age of the Crater Lanoto events. This part is also included a “cone collapsed event” occurred before Holocene time.

(iii) Part 3 - Investigates and identifies of a series of volcanic hazards associated with Crater Lanoto and implications for future eruptions.

(iv) Part 4 - Discussion about the monogenetic process of the Crater Lanoto and identification of the similarities with other eruptions on the main islands. Also included the geological history of the Crater Lanoto.

4.7.1 PART 1: INTERPRETATION OF RESULTS

The discussion Part 1 section is presented into several parts as follow:

1. Interpretation of magnetic susceptibility curves 2. Stratigraphic column interpretation 3. Geochemical interpretation of lavas 4. EMPA and XRF of tephra sand interpretation 5. ICPMS of tephra and lava interpretation 6. Argon-argon dating interpretation

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7. Radiocarbon dating interpretation 8. Lead-210 dating interpretation

4.7.1.1 Interpretation of magnetic susceptibility

The interpretation of the MS section is focused on several main issues:

1. Deposition components 2. Clarifies what are the troughs and peak in the MS of the Crater Lanoto 3. Investigates why the soil and lake sediment scatter in the high MS values (ferrimagnetic zone).

(i) Deposition components

The closed basin structure of the Lake Lanoto traps and preserves sediment. Widespread organic matter and airfall components within the lake are the two major sources of the deposition. In addition, in-wash of deeply weathered crater rim basaltic lava is a third sediment source. The first and second version of magnetic susceptibility (MS) classified the sediment into diamagnetic, paramagnetic and ferromagnetic. This classification was based on the concentration of magnetite minerals within the sediment. Values which plotted in isolation from the majority of the lake deposits in plots Figure 4.7, 4.8 and 4.9, implies the present of other volcano activities materials within the depositional basin. This conclusion is based on the fact that, if these sediments are part of Crater Lanoto activities, so they should be scattered together with the majority of lake deposit but this was not the case.

Troughs and peaks in the MS plots (Figure 4.2 & 4.5) are the organic and tephra component indicators respectively. However, FDMS plots (Figure 4.7 & 4.8) and AIR plot (Figure 4.35) indicated that tephra component is dominant in core D3. The AIR plot suggests that organic material occurs in the form of lens deposits throughout the core.

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(ii) Troughs and peaks

Logged, based on microscopic investigations, of the stratigraphic column prove that the troughs also represent depth intervals of high primary tephra content. Peaks in several occasions plot in areas of high organic content. In this case, troughs and peaks seem to indicate low and high content of organic and tephra component. The other seven cores used for the master core selection (Figure 4.2) also comprise peaks and troughs like those of D3. All cores seem continue the similar oscillating pattern. Therefore, it remains the question “What mechanism control troughs and peaks of the MS curve?”

Figure 4.5 and 4.6 show defined troughs, characterise of high content of organic materials, with low magnetite concentration. This implies that the increase in organic materials represents a hot and humid climate, associated with high evaporation rate, which correspond with extreme rainfall event (Saifaleupolu, 1998 & Trenberth, 2011). The peak contains low organic materials, but high magnetite mineral concentrations. This can be interpreted in terms of a cold climate, with low evaporation rate and associated with less rainfall (Saifaleupolu, 1998 & Trenberth, 2011).

As shown in Figure 4.7 and 4.8 troughs are not well defined like those in Figure 4.5 and 4.6. This indicates that, the core D3 is dominated by volcanic components included, those trough zones label as organic control in Figure 4.5 and 4.6. Organic materials associated with the Crater Lanoto sediment, could be described as small batches of lens deposits. This suggests that even troughs contain tephra components. Thus, the controlling mechanism of peaks and troughs is complicated and they may be linked to several factors; sea level changes, environmental factors, climate variation, human activities or regional tectonic variation. A detail discussion of an appropriate approach, for this particular issue is found in the following Section 4.7.2.1.

(iii) Why are the rim soil and lake sediment deposit contain high magnetic susceptibility (MS) values?

Sediments of the Crater Lake Lanoto plot in the low, medium and high MS zone. Overlaps between plots from fresh inner rim lava and sediments in Figure 4.9 show that, 170 low MS materials became enriched in strength through time. The catchment soil is believed to have been derived from three sources; (1) outer rim lava (parental source), (2) diamagnetic material and (3) paramagnetic material (through intense weathering). Sudden change in MS strength in lake sediment is one of the highlight of this section. Let us look at the catchment soil composition both physical and chemical in more detail.

Ferromagnetic minerals present in lava of Upolu and Savai’i, are mainly hematite, titanomagnetite, ilmenite but only contain very rare magnetite (Fepuleai, 1997 and Cibik, 1999). The ferromagnetic mineral phase, are those of opaque minerals, which dominated the groundmass, and occur as inclusion in mega-phenocryst of silicate minerals, (olivine and pyroxene). Morrison and Asghar (1992) reported that, soil of Mulifanua Formation occurs at Lalonea to the south of Apia, comprise of gibbsite (20-40%), goethite (10- 25%), maghemite (5-20%), hematite (5-15%), magnetite (<5%) and ilmenite (5-30%). A similar mixed of primary and secondary minerals of the Crater Lake Lanoto, were microscopically identified their common physically properties downcore.

Figure 4.41 shows some common secondary mineral in pyroclastic deposit and tephra bed-4. Rim soil associated with pyroclastic deposit is dominated by hematite, maghemite, and halloysite. In rim soil, hematite occurs in two forms yellowish red (Figure 4.41a) and reddish brown. The yellowish red form is commonly occurred with magnetite. Figure 4.41a indicates tephra sand comprises of hematite that has started alter to magnetite. Halloysite is a soft clay mineral occurred in bluish yellow and light yellow form (Figure 4.41b). Maghemite occurs in two form greyish red and yellow brownish red. Greyish red is the most common form in the rim catchment soil deposit (Figure 4.41c). Olivine phenocryst is commonly altered to iddingsite (Figure 4.41d). Iddingsite dominates the four tephra bed deposits. The iddingsite classified as the secondary mineral, formed through oxidation and hydration processes. Iddingsite involves the reduction of SiO2, the replacement of MgO with H2O and Fe2O3, concurrently with an increase in Al2O3 content (Fepuleai, 1997). This particular mineral is the product of either hydrothermal alteration, or precipitation of the groundwater.

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Several volcanic sediment sites in Upolu and Savai’i have their pH range from 3.4 to 5.7 (Naidu et al., 1997). Sediment associated with young volcanism in Samoa is commonly has a low pH (Naidu et al., 1997; Morrison & Asghar, 1992). Low pH is one of the major factors causes the elevated of MS strength in sediment. The low pH normally occurs as a result of substitution among cations through weathering process.

Figure 4.42 shows a flow diagram of primary minerals characterised as weak MS, converted into strong MS, through the intense of weathering process. A direction of yellow arrow shows a progression in weathering process coincides, with the MS strength of lake sediment. In other words, mineral components associated with long period of intense weathering are resulted in high MS strength.

The most commonly primary minerals in lava and volcanic sediments of the Crater

Lanoto are: titanium iron oxide (ilmenite: FeTiO3, ulvospinel: Fe2TiO4, titaniferrous

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2+ 3+ magnetite: Fe (Fe , Ti)2O4 and titanaugite (Ca, Na) (Mg, Ti, Fe, Al) ( Si, Al)2O6) and +2 +2 silicate minerals (olivine: Mg , Fe 2SiO4, pyroxene: XY (Si, Al)2O6 and plagioclase:

NaAlSi3O8-CaAl2Si2O8). A conversions from weak MS mineral into strong MS component, is based on an assumption by Dam et al (2005; 2008).

Variations in temperature and chemical composition allows disintegration and decomposition of the Crater Lanoto lavas. Chemical weathering of primary minerals are involved several major processes such as; dissolution, hydrolysis, oxidation, and alteration (Figure 4.42). The processes involve the formation of mineral solution as solute dissolve in solvent, lowering of pH, decomposing of ferrousmagnesium minerals (olivine and pyroxene) and breaking down internal structure of minerals. These processes lead into the formation of an “early secondary mineral” (this study).

“Early secondary minerals” of the Crater Lanoto volcano are mainly iron oxide (hematite:

Fe2O3), aluminosilicate (halloysite: Al2SiO2O5 (OH)4), aluminium hydroxide (gibbsite: y-

Al(OH)3), iron hydroxide (goethite: y-FeO(OH) and iddingsite (MgO *Fe2O3 *4H2O,

173 where MgO can be substituted by CaO). Very fine grain and rare titaniferrous magnetite can be either weathered to the “early secondary mineral” (hematite), or straight via the transformation process to become ferrimagnetic magnetite (Dam et al., 2005; 2008).

Further weathering of the “early secondary minerals” involves a solubilization process. Solubilization process implicates a breaking down of intermolecular and inter-ionic bonds. It involves Fe-solution where associated with leaching process (Dam et al., 2005; 2008). Normal oxidation-reduction activities of the early secondary minerals through “transformation” and “neotransformation” process leads to the formation of two “late secondary mineral” (this study) magnetite (Fe3O4) and maghemite (Fe2O3, y-Fe2O3). Dam et al., (2005; 2008) also identified the other two means of enhancement of magnetic properties included a low temperature and high temperature transformation. Low temperature may yield the transformation of titaniferrous magnetite mineral into maghemite. High temperature transformation is usually through burning of the non- magnetic (such as hematite), of the “early secondary minerals” into magnetite and maghemite.

It can be concluded that magnetite and the excess of maghemite in soil component causes an elevated the MS strength. In other words the primary minerals deposits of weak MS transformed into “late secondary minerals” giving the high MS values through the continuation of intense weathering process. These thin pocket deposits (eg. soil) are well exposed to weathering, which triggers the elevation of the MS strength in lake sediment deposits.

4.7.1.2 Interpretation of the stratigraphic column

The interpretation section of the stratigraphic column is presented into three parts as follow:

1. Discussion as to the significance of the abundance of the tephra sand, charcoal and iddingsite. 2. An outline the distinctive features of the tephra bed-2 and the reason to select the cone collapse event (CCE) over the major erosion 174

3. An outline the explosive volcanic features in lapilli tuff and tephra deposits.

(i) Abundance of tephra sand, charcoal and iddingsite

Throughout the core D3, high abundance of the tephra component occurs at four particular depths: tephra bed-1, 2, 3 and 4. These deposits could be part of the Crater Lanoto volcano or nearby eruptions. It is possible that there were also minor eruptions (short-term) occurring between the four main activities. Minor eruption episodes coincide with several features such as; a broad distribution of volcanic sediments downcore shown in Figure 4.7 and 4.8; the presence of tephra components in Lano-3 Unit and widely distribution of charcoal fragment in high organic layers (Lano-3 Unit & Lano-8 Unit).

The charcoal fragments in the tephra layers could occur in the deposition basin of the Lanoto volcano through several processes: (a) bush fires that could have occurred during an eruption (b) a the prolong dry season could destroy thick forest and (c) human activities (although these could only affected tephra bed-4 based on the first arrival of human at 3.5 Ka, refer Section 2.3.4.8).

Tephra bed-1 and tephra bed-2, contain high concentrations of charcoal fragments in comparison with those of tephra bed-3 and tephra bed-4 (based on CCEPC). A lack of charcoal fragments in the tephra bed-3 and low concentrations in tephra bed-4 implies an absence of thick forest during the last eruption activities or that charcoal fragments may have eroded. The forest could have only partly recovered from series of bush fire before that occurred before the deposition of tephra bed-3 episode.

Olivine phenocrysts dominate the tephra bed-1, 3 and 4, corresponding with the presence of iddingsite, but are slightly depleted in tephra bed-2. This implies that Crater Lanoto volcano could be associated with some magmatic variation process between an olivine- pyroxene source (more iddingsite) and depleted olivine-pyroxene (less iddingsite) source. In other words, may be the volcano activities of the Crater Lanoto associate with two magmatic sources. The abundance of iddingsite is also coincided with the optical microscopy observations that, olivine and pyroxene (augite) are the most common phenocrysts in lavas of the Crater Lanoto volcano.

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(ii) Distinctive tephra bed-2 (Lano-6 Unit) and reasons why to select the cone collapse event (CCE) over the major erosion process

Tephra bed-2 is quite distinctive compared with tephra bed-1, 3 and 4. In reference to the magnetic susceptibility second version the four tephra bed-1, 2, 3 and 4 components are all scattered together, indicating that the tephra bed-2 still contained a similar volcanic signature when compared with the other three deposits (Figure 4.7, 4.9 and 4.31). However, as previously mentioned (Section 4.4) there are features which make tephra bed-2 more unique than other tephra beds such as: (1) elevated organic contents mixed with tephra components and (2) dominated with broken tephra fragments.

The details of why this happened are still unclear at this stage i.e. whether it is associated with a cone collapse event or heavy erosion in the area. The interesting scenario in this case is the presence of the high concentration of organic material associates with the abundance of tephra fragments. A question still remained: “Why do the broken tephra fragments are dominated the tephra bed-2 layer? If the broken tephra components are part of the major erosion event, hence we do not expect the abundance of these materials in tephra bed-2 layer. In other words may be the majority of the broken fragments were eroded or could have nothing left. Hence the high organic content in tephra bed-2 could refer to the CCE. Additionally, Lano-7 Unit also comprises of high organic content that could be influenced from the same event.

Kear and Wood (1959) inferred the major unconformity between older and younger volcanism in Western Samoa, represented evidence of major erosion in the region. However, this is not the only possible explanation of the geological and geomorphological features expose on the main islands; they could also have been formed due to a cone collapse event (CCE). Indeed, Samoa volcanism is very young and it is perhaps unlikely that such fast and heavy erosion of volcanic features in the region could have occurred. Hence, in this case there could have been another event such as CCE, which was a precursor to the episode of major erosion which may be identified by looking at the structural geology nature of many parts of the main islands.

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In addition, the tight negative linear slope of the 219 samples in Figure 4.4 (saturation moisture versus dry bulk density) shows that there is no sign of reworking activities in sediments of Crater Lake Lanoto, in other words the sediments were not mobilised. This corresponds with the fact that the mixed tephra bed-2 could be a part of the CCE. Hence, if the major erosion event associated with the Crater Lake Lanoto deposits then we should expect a scatter-plot of lake sediments rather than tight linear relationship amongst each other in Figure 4.4. A discussion of this particular topic in detail is found in the following Section 4.7.2.2 (ii).

There is still not enough evidence at this stage to indicate whether this particular event, occurred after or during the tephra bed-2 activities. However, at the top of tephra bed-2 (Lano-7 Unit) there is a lack of tephra fragment and no charcoal materials present (Figure 4.10). This indicates that activities associated with tephra bed-2 activities may be ceased before the event.

(iii) Explosive and effusive volcanic signature in lapilli tuff and lake tephra deposit

A bubble network in the magmatic processes of the Crater Lanoto volcano is identified from vesicle geometry of pyroclastic deposits (lapilli tuff and lake tephra). This would enable to undersatnd and shine some lights on the history of magmatic prcesses activities associated with Lanoto volcano.

Difference vesicle shapes in lapilli tuff and lake tephra deposit are products of growth and deformation in bubbles system. Bubble growth is associated with three processes: diffusion, decompression and coalescence (Parfitt, 2009). Multiple bubbles form as a resulted of deformability mechanism, that would not only enhance coalescence but also break up (Parfitt, 2009; Suckale et al., 2010).

In the Suckale et al. (2010) stimulation model, it was demonstrated that bubbles stabilize to spherical shape depend on non-dimensional numbers (Reynolds Number: Re < 1 and Bond Number: Bo < 1) in the first regime. (Note: “Re” is defined as a ratio between magma density and sufficiently high viscosity and “Bo” is defined as a ratio between a change in magma density with respect to gravity and surface tension). A wide range of 177 distort interfaces would result in bubbles forming during second regime as Re < 1 and Bo > 1. In the third regime under (Bo > 1 and Re > 1) condition, the breakup of the isolated bubbles in the absence of distortion can be in two forms: (a) gradually breakup - small droplets starts to develop at the rear of the bubble resulted in unstable thin layer of gas and (b) catastrophic breakup – bubble rapidly collapsing and forming a large great amount of intermediate and small sizes bubbles. Hence, fine vesicles in lapilli tuff and lake tephra deposits suggest that not only was magma rising slowly, but that the vesicles formed in the catastrophic break up regime (Suckale et al., 2010).

Interconnections of multiple vesicles in lapilli tuff and lake tephra indicate that, bubbles outrun the rising magma through buoyancy mechanism and drag force of friction (Parfitt, 2004; 2009). This results in coalescence interface increase dramatically where there are large bubbles that burst intermittently as they reach the surface, in turn implying explosive activities (Parfitt, 2004; 2009; Carey, 2005; Suckale, 2010).

Those vesicles without interconnection are products of slow rising magma, which would generate effusively activity of outpouring lava. Parfitt, (2009) referred effusive eruption produces from magma without dissolved volatiles (H2O, CO2, SiO2 and H2S). This is to suggest that, Lanoto volcano erupted from explosive activity of the Strombolian and effusive style of the Hawaiian eruption. The term Hawaiian denotes to lava-fountaining activity whilst Strombolian is referred to mild explosions generates from accumulation of gas beneath the cooled upper surface of a magma column (Parfitt, 2004). Detail discussion of the two eruption styles is found in Section 4.7.3.3.

4.7.1.3 Geochemical Interpretation

Geochemical data from previous studies on both submarine and subaerial lava are recalled for this study namely Fepuleai (1997), Cibik (1999), Workman et al (2004) and Jackson et al (2007). The Crater Lanoto volcano would be compared with two settings; (a) western of the Samoa Volcanic Field (SVF) included the western seamounts and (b) eastern of the SVF (eastern subaerial volcanoes, hotspot Vailulu’u and eastern seamounts).

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There are three significant purposes of this investigation. Firstly, is to have a detailed view of the Crater Lanoto lava within the SVF. Secondly, is to verify any genetic link between Crater Lanoto volcano and those along the island chain. Thirdly, is to determine if there was any changes in the geochemistry along the SVF over the last 24 million years till the present. These relationships amongst lava suites along the Samoa Volcanic Field would also indicate the post-erosional and shield volcanism magmatic sources.

The interpretation of the geochemistry section is presented in two parts:

1. Outline of the geochemical processes associated with Crater Lanoto lava. 2. Comparison of the Crater Lanoto lava suites with other volcano activities along the island chain.

(i) Crater Lanoto lava suite

The fact that the composition of the Crater Lanoto lavas plots tightly at the central part of SVF (Figure 4.20) implies that the inner rim lavas derive from the same magma source, even if they were erupted at different times. Unfortunately, the outer rim lava was not available for the XRF analysis nonetheless physical evidence shows that the inner and outer rim lava are could be derived from difference magmatic source. This is based on the fact that, outer rim lava has enriched in olivine and pyroxene whilst the inner lava suite are depleted in these minerals.

There is a negative correlation displayed by major and trace element variation diagrams (Figure 4.21a, 4.22b, 4.23a & b). This negative correlation corresponds with the increase in pyroxene composition within the magma, reflected from the high Ba and Al2O3 content (Table 4.1). This implies that the inner rim lava derived from differentiate of partial melting rather than a fractionation trench. This differentiation trend generate from picritic source with high Mg/Fe ratio, toward low Mg ratio in the basanitic-basaltic field is reflected from TAS plot (Figure 4.20). In other words, a small portion of the inner rim lava derives from the deep picrite magma before the great volume was generated from the shallow basanitic/basaltic source. This internal variation corresponds with olivine fractionation (Cibik, 1999). Based on Falloon et al (1998) plane olivine-plagioclase-silica 179 diopside cotectic model, lavas from Upolu plot between 30 kb and -35 kb corresponding with the fractionation depth of approximately 90-100 km (Cibik, 1999). Those from Savai’i derive from lower fractionation depths of about 75-95 km.

Deeper sources expected to contain high proportions of magnesium-rich olivine and pyroxene than those derive from shallow magma. This would enables to fingerprinting a signature of peridotite source which dominate the upper part of the earth mantle. The tephra deposits (tephra bed-1, 3 and 4) contain high magnesium in ICPMS plot (Figure 4.27) in comparison to the inner rim lava, which denotes two magma sources.

The differentiate lava fingerprinted from sample LLRD1, LLRD2, LLRH1 and LLRH2. A basanite signature is associated with lava samples that are enriched in Cr and Ni. Table 4.1 shows that basanite of the Crater Lanoto is matched with the Salani lava and Fagaloa strip lava (Manase area) to the north of Savai’i (Cibik, 1999).

Figure 4.21b, 4.22a, 4.24a and 4.22b are characterised by positive correlation of major and trace elements. This implies that these lavas followed trend controlled by olivine fractionation. Further discussion of the similar approach found in the ICPMS data interpretation Section 4.7.1.5.

(ii) Lava of the Crater Lanoto versus lava from the Samoa Volcanic Field (SVF)

The basanite lavas from both Upolu and Savai’i have calcium-rich plagioclase with olivine and pyroxene. The largest group of lavas in Western Samoa, including those of the Crater Lanoto, is the alkali olivine basalt. These lava suites are fine grained, dark in colour with an olivine-Ti-pyroxene and minor plagioclase clasts. Olivine tholeiite lavas from Upolu and Savai’i exhibit, silica content ranging between 45-51%, at 2 to 4 wt % of the Na2O + K2O (Figure 4.20). Hawaiite is the smallest group on Upolu and Savai’i, with between 45 and 52% SiO2 and in 7% weight Na2O + K2O (Fepuleai, 1997; Cibik, 1999).

Fepuleai (1997) and (Cibik 1999) further subdivided the lavas from Upolu and Savai’i into olivine tholeiite, alkali basalt, hawaiite and picro-basalt. These subdivisions mostly have 41 to 51% silica content with 1 to 2% of Na2O + K2O (Figure 4.20). This particular

180 zone of the TAS plot, is the dominated zone of Crater Lanoto, the deep flank lava suites of Savai’i (Jackson et al., 2007; Konter & Jackson, 2012) and subaerial lavas from Savai’i and Upolu (Workman et al., 2004).

The data from subaerial lava of Upolu and Savai’i, deep submarine flank lava of Savai’i and lava from the Crater Lanoto were all plotted in four variation diagrams as follow to determine the relationship of the Crater Lanoto suites with those of SVF.

Figure 4.43a shows the major element plot between SiO2 versus MgO. The plot is characterised by a broad negative correlation. The lava seems split into two trend, “trend A” and “trend B”. Trend A refers to a bigger lava group. Trend B is made up of hawaiite from Upolu and Savai’i. The trend A is mainly of deep submarine lava of Savai’i, olivine tholeiite, alkali basalt, basanite and picro-basalt from both main islands. The trend B lavas are enriched in MgO and depleted in SiO2. Lava of the Crater Lanoto volcano forms into two close groups plotting on trend A. They both overlap alkali and olivine tholeiite of Savai’i.

Figure 4.43b displays a relationship between SiO2 versus Al2O3. The relationship is characterised by a broad positive correlation. Lavas split into trend A and B. Trend B seems overlap a lot into the field of trend A. The two close groups of the Crater Lanoto lava scattered in the trend A lava, overlap olivine tholeiite and alkali basalt lava. Hawaiite and few olivine tholeiite of trend B are enriched in Al2O3 and depleted in SiO2. Dashed lines indicate shield lavas are started to separate from trend “A”. Those of post-erosional suite dominate the trend “A” and “B” (Figure 4.45a & b).

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FIGURE 4.43 Major plots of the Crater Lanoto with lava from the SVF (a) SiO2 versus MgO shows negative correlation. (b) SiO2 versus Al2O3 shows positive correlation.

Figure 4.44a shows a relationship between magnesium numbers versus SiO2. Magnesium number provides information of evolution of volcanic rock and defined as 100 MgO/(MgO + FeO) in mole percent. The plot is characterised by a broad negative linear trend correlation. Lavas can be described as either plotting along trend A and trend B. Trend B seems almost completely isolated from trend A. Hawaiite and several olivine tholeiite lavas of Trend B are enriched in SiO2 and depleted in magnesium numbers. The two groups of the Crater Lanoto lava scattered in the big trend “A” lava suites. Both groups overlap basanite, olivine tholeiite and alkali basalt. Post-erosional lavas are heavily lying along trend “A and “B” whilst those of the shield volcanism have begun to separate from trend “A” shown by dashed lines (Figure 4.44a & b).

Figure 4.44b displays a trace element relationship between Y versus Zr. Trace element plot is characterised by a broad positive correlation. Trend B seems overlap a lot into trend A field. Lava of the Crater Lanoto spread widely between 30 and 38 Yttrium content, at the base of trend A. The lava overlaps deep submarine suite of Savai’i and olivine tholeiite. Shield lava starts to scatter away from the trend “A”.

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(iii) Lava of the Crater Lanoto versus lava from the eastern subaerial volcanoes, hotspot Vailulu’u, western and eastern seamounts

Several subaerial lavas from the eastern part of the chain (Tau Island), hotspot of Vailulu’u, eastern seamounts (Muli and Malumalu) and seamounts to the west of Savai’i (Pasco, Lalla Rookh, Combe and Alexa) were all plotted together with lava of the Crater Lanoto volcano. More importantly, the Crater Lanoto lava suite was plotted with older seamounts from the western part which have an age range between 6 and 24 Ma. This long range in age enables us to determine if there are any geochemical changes.

Figure 4.45a shows the major element relationship between the magnesium numbers versus Na2O. The plot is characterised by a wide negative linear correlation and lava split into trend A and B. Trend B seems isolated from trend A. Lava from the eastern seamount, eastern subaerial, Vailulu’u hotspot, western seamounts and SVF scatter along both trends. The Crater Lanoto lavas overlap with the Vailulu’u hotspot suite and eastern seamounts in the big trend A group. Shield volcanism lava, represented by the dashed line along the broad Samoa Volcanic Field, starts to become isolated from the trend “A” (Figure 4.45a) and trend “B” (Figure 4.45b). The post-erosional lavas are strongly scattered along the two trends.

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Figure 4.45b indicates a plot between Magnesium numbers versus Y. The plot is characterised by a broad negative linear correlation. The trend B also seems isolated from trend A. Lavas from Crater Lanoto scatter with other lavas from western and eastern part, in the trend A.

(iv) Summary of the relationship between the Crater Lanoto volcano with other oceanic volcanoes

A negative correlation and inflection feature represented by “trend B” are common in both major and trace element plots. This is possibly due to the entry of new phase either during crystal fractionation, or due to loss of a phase during partial melting process (Fepuleai, 1997). Trends A and B represent a different melting points associate with different fractionation depths of the Samoan volcanic sources. Cibik (1999) suggested that the “trend A” lavas formed in a fractionation process, during Bowen Reaction Series, at high temperature of more than 1200oC. Those lavas of the “trench B” melted at lower temperature.

Fepuleai (1997) suggested that “trend A” lavas are the most primitive source group, while those of trend B referred to fractionate suite origin. Trend “A” thought to be strongly controlled by olivine, pyroxene with less plagioclase. Those lavas scatter along “trend B”

184 are dominated by plagioclase with less olivine and pyroxene. In addition, subaerial Fagaloa and post-Fagaloa suites, of Upolu and Savai’i dominate the two trenches. Cibik (1999) proposed that the “trench A” align with lavas generated from parental melts, while those of “trench B” formed from partial melts.

Shied volcanism suites are the most primitive source. However, Figure 4.45b shows that shield samples from eastern seamount and subaerial lavas plotted at the fractionate trench “B” may be derived from contaminated source or could be influence by tectonism.

In Figure 4.44b and Figure 4.45a it seems lavas of the Crater Lanoto are fell in the base of trend B, which corresponds with the negative correlation in Figure 4.21a, 4.22b, 4.23a and 4.23 b. This also denotes that the inner rim lava suite derived from partial melt was previously mentioned in Section 4.7.1.3 (i).

Lavas from Crater Lanoto, western and eastern part of the island chain, commonly display lineation and overlapping in major and trace element plots. This explains that they have geochemically similarity. In other words, they could have shared the same magma source. This coincides with the fact that they are representing a continuum of the same magmatic processes (Fepuleai, 1997) and that they are petrogenetically related. Fepuleai (1997) revealed that there is no conspicuous geochemical difference, along the western and eastern part of the Samoa Volcanic Field, even though their ages varied.

This is to conclude that in the Samoa Volcanic Field, we are looking at similar source processes, similar rise processes, and eventually a fairly dispersed style.

4.7.1.4 Interpretation of tephra component from EPMA and XRF procedure

Both the weathered nature and the cracked features of the glass shards tend to collectively indicate episodes of repeated wetting and drying (subaerial exposure & weathering then immersion by lake waters). Desiccation cracks and microlitic texture imply that these deposits had been exposed several times. This coincides with elevated content of organic materials at several depths downcore. It signifies that, the lake level had fluctuated on several occasions. This could be an appropriate explanation and would account for the

185 intense weathering of volcanic deposits that are relatively young. Fluctuation in the lake level and weathering features of volcanic glass shards could describe a long duration of dry and wet seasons in the region. This assumption is also reflected from the long delayed in 210Pb activity for 89 years in the Crater Lake Lanoto basin, corresponds with the drought in the area. Trenberth (1997) and Gergis & Fowler (2005) referred to a similar length of drought at that time based on reconstruction of El Nino-Southern Oscillation (ENSO) in the Pacific Ocean. A detailed description of this finding is found in Section 4.7.1.8.

Most of phenocryst of silicate minerals and glass shard had been dissolved through hydrolysis, oxidation, dissolution and alteration during weathering process (Figure 4.42). This results in produce of weathering halo features and the presence of the secondary minerals, such as clay (halloysite and gibbsite) in the tephra deposit.

The highly weathered nature of tephra components resulted in the depletion of several major elements such as, SiO2, MgO, K2O, and Na2O content and enrichment in TiO2,

Al2O3 and FeO. The significant alteration in major elements composition of weathered tephra components are the downside of these techniques.

XRF and EPMA samples did not produce reasonable values for major elements due to the intense of weathering in tephra component. However, these data on the other hand could be very valuable to the soil investigation at this part of the island in the near future. In addition, the information would also improve our understanding in the nature of weathering process associated with primary to early secondary and late secondary minerals (Figure 4.42).

4.7.1.5 Interpretation of ICPMS data and AIR

The interpretation section of the ICPMS procedure is presented in two parts as follows:

1. Variation ICPMS plots 2. AIR plot

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(i) ICPMS plots

The positive linear correlations in trace element variation plots imply that rim soil components, inner rim lava suites and tephra sands are all geochemically related. It suggests that the inner rim lava is only separate from these lake deposits in two main reasons (1) the degree of weathering of the volcanic components and (2) difference in original sources. Overlaps between the inner rim lava and pyroclastic deposit, rim soil and the four tephra beds (1, 2, 3, and 4) components, show derivative from a same magmatic source.

Some components of tephra bed-1, 2, 3 and 4 give isolated plot values, as shown in Figure 4.27a, 4.28a, 4.28b, 4.29a, 4.29b, 4.30a and 4.30b. This suggests that these tephra components are from contaminant airfall. The fact that these contaminant components all seemed to occur in all four layers suggests that nearby volcanoes could have erupted simultaneously with those of Crater Lanoto activities. The second version of the magnetic susceptibility (MS) also shows similar isolated contaminant tephra components (Figure 4.7, 4.8 and 4.9). In Figure 4.9 for example the contaminant components scatter away from the heavy overlap of lake deposits, at diamagnetic, paramagnetic and ferrimagnetic zones. This indicates that low and high MS volcanic materials are associated with contaminant airfall.

The widespread presence of contaminant downcore from the MS curves and AIR plot (Figure 4.31) imply that there was heavy intense volcanic activity in the area at these particular times. Rim soil is also the part of airfall from nearby volcanoes as it overlaps with those of contaminant tephra component (Figure 4.27b, 4.28a, 4.28b, 4.30a and 4.30b).

Pyroclastic components commonly plotted close or overlap with inner lava suites (Figure 4.27a, 4.27b, 4.29a, 4.29b and 4.30a). This implies that pyroclastic deposits and inner lava are geochemically related and derived from a similar source. However the pyroclastic deposits plotted in two distinct tephra groups denoting that they are contaminant components (Figure 4.31). If this is the case, geochemical similarity

187 suggests that pyroclastic deposits could be airfall from the parasitic vents (Maimoaga) along the east slope of the Crater Lanoto (Figure 2.17).

The pyroclastic components are pocket deposits, which are abundant on the east and rare to the west. Hence if these contaminant pyroclasts derive from the Maimoaga vents on the east then indeed, the prevailing southeast wind was the main transport mechanism. The pyroclastic deposit is commonly isolated from tephra bed-1, 2, 3 and 4 components (Figure 4.27b, 4.28b and 4.29a) could be weathering factors reflects from increase in magnetic susceptibility (Figure 4.9) associates with the increase in oxidation-reduction reaction (Figure 4.42).

The two magma source generated from the Crater Lanoto eruption activities also appeared in ICPMS plots (Figure 4.27b). The pyroclastic deposit, inner rim lava, tephra bed-1, 2, 3 and 4 are scattered into two groups, on the same positive lineation (Sr versus Ni) implyings that they are all related (Figure 4.29b). However, the pyroclastic deposit and inner rim lava are enriched in Ni content in comparison with the tephra group and rim soil denoting the presence of two magma sources. The two magma sources could also correspond with the two positive trends in Figure 4.28a, 4.29a, 4.29b, 4.30a and 4.30b. This approach of two magmatic sources is also reflected in the magnetic susceptibility characteristic (Figure 4.9).

Unfortunately, the ICPMS data for the outer rim lava was not available for this study. However, the soil could also have derived from the outer rim lava as parental source hence in this case the soil, represents the outer rim lava suite in the ICPMS plots. All ICPMS plots (Figure 4.27 to 4.30) show that the rim soil and inner rim lava suite are plotted away from each other (i.e., do not overlap). This is also implies that the Crater Lanoto eruption activities generate from the two magma sources.

In Figure 4.20 (TAS plot) the inner rim lava represents the basanite and basalt field whilst the picrite refers to the outer rim lava. This indicates that the earlier eruption of the Crater Lanoto originated from a deeper picritic magma source. As previously discussed in Section 4.7.1.3 (i) the negative correlation of major and trace elements in the XRF implies that the inner rim lava derived from differentiate of the partial melting. In other

188 words the tephra bed-2 activities erupted from a shallower mantle source. The differentiation from high Mg/Fe to low Mg also indicates the presence of very few components of the inner rim lava in the tephra bed-1, 2, 3 and 4 mixtures (Figure 4.27b). Additionally, the tephra bed-2 components never overlap with the inner rim lava in the ICPMS plot, which indicates that the tephra bed-2 component could be a part of picritic magmatic source. If this is the case, then the tephra bed-2 activities could partly derive from shallow and deep source. The detail discussion of how this happened is found in Section 4.7.4.3 and Section 4.7.5 (ii) as follow.

The overlaps of the four tephra layers in the ICPMS plots denote that, these tephra components are deeper picritic magma in origin. In other words, tephra bed-3 and 4 represent the re-eruption of the Crater Lanoto from the deeper picritic magma source since the tephra bed-1 activities.

Similarly, the presence of contaminant in the same tephra mixes (tephra bed-1, 2, 3 and 4) of the ICPMS plot indicates that the volcanoes nearby could also have erupted from the same deeper picritic magma. This assumption coincides with the Natland (2003) hypothesis that a laterally widespread layer of heterogeneously enriched mantle could be lying along the entire island chain of Samoa. The lithospheric cracking process creates multiple centres, allowing the mantle-melts to seep through and erupt simultaneously during post-Fagaloa (post-erosional) activities. In addition, the overlaps between the Crater Lanoto lava with other suites along the island chain in XRF plots (Figure 4.43a, 4.43b, 4.44a and 4.45b) also support the idea of the widespread heterogeneous mantle signature.

The differentiation from deeper picritic to shallower basanitic/magma could be a product of some tectonic activities in the region, during the middle part of Salani Formation volcanism. A continuation in tectonic activities could be the result of the re-eruption of the picritic magma during tephra bed-3 and tephra bed-4 episodes.

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(ii) AIR plot

Sediment layers between the four tephra beds, are characterised by high concentrations of organic materials in the first version of the magnetic susceptibility procedure. However, the AIR indicates that these particular depths also contained tephra sand components. This considers that organic materials in the lake basin are not continuous sedimentary layer but occur as lens deposits. In addition, this indicates that Crater Lanoto volcano could also be associated with minor volcanic episodes that occurred before tephra bed-2 and 3 and after tephra bed-4 activities. These particular zones may be comprised of weathered primary tephra sand, epiclastic and secondary tephra deposit.

It was difficult to determine the abundance of the fine cryptotephra component under the microscope in several units, especially those units (Lano-4, Lano-7 and Lano-8) with yellow greenish or dark greenish brown/grey in colour and elevate organic material. However, the AIR plot displays that these particular units are also contain tephra or pyroclasts components. Hence, the AIR plot also confirms that trough and peak in the MS curve are both represent high and low concentration of magnetite downcore. This topic is discussed in more detail at Section 4.7.2.1.

Large numbers of distinct group tephra implies a widespread contaminant tephra component from nearby volcano (Figure 4.31). There are two types of contaminated tephras; shows in the AIR plot represent by low and high percentage values. The two types of tephra components seem occurred simultaneously based on their stratigraphic position. This implies that contaminant components at the rim deposit derive from two different volcanic episodes (Figure 4.31). The widespread presence downcore of the contaminated tephra in the AIR plot, also corresponds with a widely simultaneous style activities between the Crater Lanoto and other volcanoes nearby.

4.7.1.6 Interpretation of the Argon-Argon dating

This section presents into two parts; firstly, is to identify the most reliable Argon dating procedure and secondly, compare the new argon-argon age with other volcanoes along the island chain. 190

(i) Crater Lanoto Argon-Argon dating

The step heating procedures seem worked well on the plagioclase groundmass in contrast with the phenocryst. The normal and inverse isochron (Figure 4.34 & 4.35) of the groundmass have the best-fit value (MSWD) plotted below the 2.5 standard limits. The plateau age of 143.9 ± 2.8 Ka could be used as a base age for the Crater Lanoto volcano. This new age of the inner rim lava could be used to predict the age at the base of the tephra bed-2 activities, whilst the outer rim lava is the product of the tephra bed-1 and that much older. There are more discussion of this particular issue is found in Section 4.7.2.1 and 4.7.2.2.

The plagioclase phenocryst step heating method did not perform well throughout the whole process. This is also indicated from the normal and inverse isochron plots (Figure 4.9), which shows that phenocryst component scattered further away from the total fusion. The 42 Ma year age is not plausible for the inner rim lava of the Crater Lanoto ,and this was likely due to the excess of 40Ar component. This new age could not fit this part of the western volcanic province of Samoa Volcanic Field, as the oldest subaerial lava is only 2.8 Ma from the northeast Upolu (Natland and Turner, 1985).

This suggests that, the total fusion values fall on both normal and reverse isochron of the groundmass indicating that, the system has remained closed. This interpretation is based on the fact that, the Crater Lanoto basaltic lava contain no additional or even loss of any Argon components during the eruption activities of the tephra bed-2 episode.

(ii) Compare the Crater Lanoto groundmass dating with other volcanoes along the Samoan island chain

Groundmass dating of Crater Lanoto was compared with several subaerial and submarine volcanoes along the Samoa island chain and determine if the new age is compatible with existing data. The previous argon-argon dating project was a part of the hotspot reconstruction of Samoa archipelago by Koppers et al (2011). The groundmass steps heating was the most reliable procedure employed during this work in contrast with the plagioclase phenocryst. 191

Figure 4.46 displays a plot between mean sums weighted deviated (MSWD) of the inverse isochron of the groundmass versus age (Ma). The plot shows almost all samples scatter inside the “best-fit zone”. The plagioclase phenocryst is associated with the majority of the groundmass group. The groundmass age of the Crater Lanoto settle close to the middle of MSWD zone 0.75. This is to signify that like other volcanoes the groundmass argon-argon age of the Crater is the most reliable age use in this study. The previous works are also indicated that the plagioclase phenocryst step heating procedure was not popular during the dating project. Hence, the groundmass step heating procedure is highly recommend is the best method for dating lava of the Samoa Volcanic Field in the near future.

FIGURE 4.46 MSWD of inverse isochron of the groundmass versus groundmass age. The Crater Lanoto plots together with subaerial and submarine other volcanoes along the Samoan island chain.

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4.7.1.7 Interpretation of the Radiocarbon age

The interpretation of the Crater Lanoto radiocarbon age presents into two parts. (i) Identify of a reliable age for the chronology (ii) Comparison between the Crater Lanoto radiocarbon age with other Holocene eruptions in both Upolu and Savai’i.

(i) Crater Lake Lanoto Radiocarbon Dating

Radiocarbon ages were determined based on the fact that Crater Lake Lanoto has no sign of reworking process. This is reflected in the plot from 219 samples in saturation moisture and dry bulk density (Figure 4.4). In other words, the sediment had very low mobilisation activities.

Laboratory error could have affected the variation of ages because only very small samples (LLD3/49 and LLD3/219) were used for dating. The introduction of the modern carbon components, for instance plant roots, could have also penetrated into sediment deposition. A good example is the Eleocharis Dulcis, the most common swamp plant in the Crater Lake Lanoto depositional basin, which has it main root at least 2 m in length.

Based on the stratigraphic position (Figure 4.10) samples LLD3/34 (at the base of tephra bed-4) was expected to be younger than LLD3/49 (top of tephra bed-3). The sample LLD3/73 at the base of tephra bed-3 has the radiocarbon age of 22.3 ka. This suggests that the age of the sample LLD3/49 should be much older than the 3.4 Ka of sample LLD3/34. This corresponds with the fact that, the abundance of primary tephra sand throughout the tephra bed-3 layer implies a continuation of activities during this particular time. In other words, there is no evidence of any break in the volcanic activities in the sediment. Hence, the age of the LLD3/34 should be older than 3.4 ka and younger than 22.3 ka.

The sample LLD3/219 is the primary tephra deposit of the tephra bed-1, which suggests that is represents the earliest eruption episode of the Crater Lanoto. This first episode suggests it produces the outer rim lava. The inner rim lava has argon-argon age of 144 ka, despite the fact it was expected to have been younger than the outer rim lava of the

193 sample LLD3/219. The physical characteristic of the inner and outer lava flow support this conclusion. Hence, in this case the LLD3/219 tephra deposit should be much older than the radiocarbon age of 15.4 ka. Additionally, it is believed that the LLD3/219 age could lies is well beyond the limited of 14C dating at between 40 and <60 Ka, depending on the technique employed (Goodwin, 1946; Stuiver and Polach). Hence if these old deposits (tephra bed-1) are penetrated by the long roots of sedges growing in the lake, then this means that even old deposits can contain relatively young carbon components, and thus give 14C ages of far too young.

Finally, the samples LLD3/34 and LLD3/73 were selected to be the most reliable and useful for the construction of a Holocene chronology. The stratigraphic position of samples LLD3/49 and LLD4/219 would estimate their age using a marine sediment oxygen isotope curve, which discussed in more detail in Section 4.7.2.1.

This is to conclude that, tephra bed-4 activities were active during the last 3.4 Ka. In addition the new age of the tephra bed-4 falls in the Lefaga Volcanic Formation. However, it was classified as part of Mulifanua Formation by Kear and Wood (1959). Radiocarbon age from sample LLD3/73 indicated that the tephra bed-3 episode initially erupted during the last 22.3 Ka and could be represented the lower part of the Mulifanua Formation activities.

(ii) Crater Lake Lanoto versus other Holocene eruption in Upolu and Savai’i

The new radiocarbon ages of Crater Lanoto volcano are compared with those from previous works on Upolu and Savai’i and determine, if they can fit perfectly. Nemeth and Cronin (2009) carried out numerous of radiocarbon dating of volcanic ash and lava flow in Savai’i (Figure 4.47). The location of samples for radiocarbon dating is described in Section 2.4.5 (Chapter 2). Some of these new radiocarbon ages, would be used to reconsider the extension of several geological boundaries in the geological map by Kear and Wood (1959).

Figure 4.47 shows the Holocene formation of Western Samoa versus radiocarbon age. The plot indicates that Holocene activities were erupted in close age range on both Upolu 194 and Savai’i. Sample LLD3/34 has sat perfectly with the Lefaga lava (Goodwin & Grossman, 2003) and has a very close-range with those from Puapua Volcanic Formation and Mulifanua Volcanic Formation of Savai’i. The sample LLD3/73 has a closed age variation with those from the south western part of Savai’i. The new radiocarbon age of the tephra bed-4 (LLD3/34) shows that the latest episode of the Crater Lanoto volcano seems to have erupted simultaneously with Lefaga Formation (in the central part of Upolu) and Mulifanua Formation (on the north west of Savai’i).

FIGURE 4.47 Radiocarbon age of the Crater Lanoto plots with radiocarbon ages of other Holocene formation from Upolu and Savai’i. Horizontal scale is not to scale.

4.7.1.8 Interpretation of Lead-210 activity

The similarity of the total 210Pb activity (Figure 4.39), supported and unsupported 210Pb activity (Figure 4.40) implies that, the 12 samples from the top of the Lano-12 Unit are strongly controlled by unsupported 210Pb activities. 195

The two significant gaps “A” and “B” (Figure 4.40) occurred as the unsupported activity increase. These gaps are regarded as eveidence of 210Pb activity dilution result in accelerated sediment accumulation. Gap “A” represents a dilution of organic material and gab “B” is referred to as a dilution in mineral matter due to weathering and erosion. Dilution at gab “A” suggests it associated with a lot of modern human activities in the region especially agriculture. The CIC age model declined after 89 years before reach the gab “B” (Figure 4.40). The dilution of mineral matter at gap “B” associated with erosion and weathering suggessts is also part of the modern human activities in the region.

The low sedimentation rate of 0.017 cm per year in the basin influence the age of the deposition at the top part of the core. This conincide with the delay between supported and unsupported components to enter the deposition basin. The delayed in activities indicates by the long decresing profile of the unsupported 210Pb activity (6-16 cm depth) (Figure 4.40). This delayed approximately occurred between the last 30 and 89 years ago. Low sedimentation rate corresponds with the long decreasing profile, which is also parallel with a long dropped of the lake level during 59 years interval. This long interval drought occurred sometime from the early to mid 19th century as previously mentioned (Trenberth 1997; Gergis & Fowler, 2005).

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4.7.2 PART 2: THE AGE OF THE CRATER LANOTO VOLCANIC EVENTS

This section is divided into three main parts as follows:

1. Comparison between the magnetic susceptibility curve and the marine sediment oxygen isotope curve to determine appropriate new ages of the tephra bed-1 and 3. 2. Use the new radiometric age to construct an appropriate chronology of the Crater Lanoto. This part will also discuss the reconstruction of the cone collapse event. 3. Discussion of the age-relationship and different aspect of the isotope signature in shield and post-erosional volcanism.

4.7.2.1 MS curve – Lake Lanoto versus the marine sediment oxygen isotope (MSOI)

Firstly, we have the inner rim lava of 144 ka argon-argon age suggested to be formed during the tephra bed-2 activities. However, it is still believed that the original age of the Lanoto volacano is preferred to the outer rim lava, a part of the tephra bed-1 episode. Secondly, if the top of the tephra bed-3 should be much older than tephra bed-4, based on their stratigraphic position as discussed in Section 4.7.1.7 (i), then how do we prove this? Hence, we need to determine the new age of the tephra bed-1 and 3, using the MSOI curve. A similarity of the two curves (MS and MSOI) will enable us to determine few appropriate unknown ages of the Crater Lanoto volcano shown in Table 4.5. This would tie the sediment record of the Crater Lake Lanoto into the ocean record with some confidence.

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Dated materials Radiometric ages (Ka) Tephra bed-4 3.4 Tephra bed-3 top (unknown) base (22.3) Tephra bed-2 144 (inner lava flow)

Tephra bed-1 unknown

Let us recall the magnetic susceptibility (MS) curve of Crater Lanoto (Figure 4.5) and compare it with those of Bintanja et al (2005) data: of the marine sediment oxygen isotope (MSOI) records. The paleoceanography study by Bintanja et al (2005) used the ratio between stable oxygen isotopes (16O and 18O), as guide to paleotemperature and global ice volume (which corresponds to major changes in sea level). During evaporation of seawater, the heavier isotope 18O becomes enriched in the remaining water but depleted in atmospheric water vapour as the lighter isotope 16O, is evaporated more easily. This work involved 57 globally distributed sediment cores at several locations in the Northern Hemisphere, used to determine long records of sea level and deep-ocean temperature in the past.

Figure 4.48a shows the MS curve (depth of the core versus volume specific MS). The yellow arrows indicate radiometrically-dated samples. Figure 4.48b indicates a relationship between times and sea level of the MSOI curve. The marine curve is subdivided into seven stages. The three spike peaks of the tephra bed-2 coincide with the three peaks at stage 5 of the MSOI curve. The area between tephra bed-2 and tephra bed- 1 is matched with stage 6 and 7 of the MSOI. A long positive slope between tephra bed-2 and tephra bed-3 corresponds to an area between the stage 1 and 2 of the MSOI curve. Three reliable ages, tephra bed-4 (3.4 ka), tephra bed-3 (22.3 ka) and inner lava (144 ka) of the Crater Lanoto (green arrow) are plotted on the MSIO curve.

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FIGURE 4.48 (a) Magnetic susceptibility oscillation records, of the Crater Lake Lanoto master core D3. Yellow arrows (MS curve) indicate radiocarbon dated samples position with respect to depth. (b) Sea level fluctuate based on the marine sediment oxygen isotope data (Bintanja et al, 2005). Green arrows (MSOI curve) represent reliable radiometric age of the Crater Lanoto. Dashed red arrow represents the new age position of the tephra bed-3 (top) and tephra bed-1. Numbers on the MSOI represent stage.

The scenarios between the two curves are matched. This implies that troughs and peaks of the MS are also similar to those of the MSOI and therefore that the MSOI curve is controlling the MS troughs and peaks. This is to say that the six volcanic formations of Samoa were erupted during trough and peak of the sea level curve (Kear and, 1959). In other words, the volcanic activities of the Crater Lanoto appear o have been associated with the fluctuation in sea level. This is still a preliminary hypothesis and needs more rigorously tested using radiometric and argon-argon dating.

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Tephra bed-4 (Lefaga Formation) and tephra bed-3 (Mulifanua Formation) activities seem to have occurred at the peak of sea level rise with respect to the MSOI curve. Kear and Wood (1959) also suggested that the the two formations were erupted through the transgression of Flandrian sea level in post glacial time (Figure 2.7). Stage 2 of the MSOI curve (base of tephra bed-3) seems to represent the initial part of the Mulifanua activity. This marks the lowest sea level during the last glaciation period (Kear & Wood, 1959). The inner rim lava represents the middle-upper part of Salani Formation. This eruptive episode is thought to have occurred very close to the peak of the Quaternary sea level transgression, during the last interglacial period of the Salani Formation (Kear &Wood, 1959).

Radiocarbon ages of 3.4 ka (tephra bed-4) and 22.3 ka (tephra bed-3) from Crater Lanoto plot within stages 1 and 2 respectively of the MSOI. The age at the top part of the tephra bed-3 should have in been close-range with tephra bed-4 (Figure 4.48a). This is based on their position on the MS curve with respect to the MSOI. On the other hand, a similarity in physical characteristics (colour) of the Lefaga and Mulifanua lavas on the southern Upolu indicates a very close age. However, Kear and Wood (1959) distinguished the two formations based the fact that Mulifanua has a wide fringing reef in contrast with the Lefaga. Hence the propose age for the top part of tephra bed-3 with respect to the MSOI curve is approximately 11 ka represents by dashed red arrow in Figure 4.48b.

The inner lava of 143.9 ka, plots at stage 6 on the MSOI curve (Figure 4.48b). This indicates that, the lava flow is either a part of early tephra bed-2 or late tephra bed-1 volcanic episode. Thus, the tephra bed-1 should be much older than anticipated: approximately 200 ka or even more, based on the MSOI records indicates by dashed red arrow in Figure 4.48b.

The highly weathered thin-sheeted pahoehoe outcrop (outer rim lava), exposed to the southeast of the Crater Lanoto rim consists of onion skin basalt. This distinctive feature is a part of the mechanical weathering process and commonly occurs in the Salani Formation and the Upper Fagaloa Formation (Kear and Wood, 1959). The thin-sheeted pahoehoe at the outer part of the crater rim could be formed during the earliest volcanic

200 episode of the Crater Lanoto. Hence, the outer rim lava has an estimated age of at least 200 ka and falls between stage 6 and 7 of the MSOI. Hence, the MSOI age, suggests that Crater Lanoto was emplaced, during the early Salani Formation volcanism. At the same time, the Upper Fagaloa Formation activities started to wane.

4.7.2.2 Chronology construction of the Crater Lake Lanoto

The chronology construction section is divided into two parts;

(i) Known age of the Lanoto volcano; (ii) Reconstruction of the “cone collapse event” (CCE) and estimate the most appropriate radiometric age of the event. The known radiometric age determined from the deposition samples of the Crater Lanoto. The most appropriate age of the CCE could be occurred sometimes toward the end of the tephra bed-2 activities.

(i) Known radiometric age event of the Crater Lanoto

The new radiocarbon and argon-argon ages enable the construction the chronology for the Crater Lake Lanoto. The volcano had been quiet for tens to thousands of years before re-erupting. Figure 4.49 shows the chronology plot of the Crater Lake Lanoto. The Crater Lanoto volcano erupted from the Late Pleistocene and continued toward Holocene times. Crater Lanoto is a part of Vini Tuff Formation. Kear and Wood (1969) described the Vini Tuff Formation, as a pre-Salani or intra-Salani Formation in age. However, the Vini Tuff expose at Cape Tapaga (north of Crater Lanoto) has a radiocarbon age of 1915 years (Grant-Taylor & Rafter, 1962; Nemeth & Cronin, 2009). Hence, in this study the Vini Tuff Formation corresponds to tephra bed-1, 2 and 4 but ceased during the episode associated with tephra bed-3. Crater Lanoto is classified as the post-Fagaloa Formation ranging from middle Salani Formation to Lefaga Formation (Figure 4.49).

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FIGURE 4.49 Chronology of the Crater Lanoto volcano. This chronology construct based on the new radiometric age and geological formations from Kear and Wood (1959).

Tephra bed-1 could have been erupted during the time equivalent to lower part of Salani Formation, sometime around 200 Ka based on the MSOI age (Figure 4.49). This corresponds to a time when Quaternary sea level rise about 9 m during the middle Pleistocene time (Kear and Wood, 1959). The ICPMS data shows that the early eruption generated from the deep picritic magma and produced the outer rim lava flow, exposed in the southeast part of the crater.

Argon-argon ages reveal that the inner rim lava emplaced about 143.9 ka during time corresponding to the middle-upper part of Salani Formation. Based on the ICPMS and XRF plots, the inner rim lava could have derived from the shallow basanitic magma

202 source. Tephra bed-2 lava flow dominated the inner part of the volcano rim. Other lavas discharged via the southeast part of the crater, toward the Sinoi valley.

The tephra bed-3 eruption episode could have produced vast volcanic ash and only small volume of lava flow extending about 100-200 m from the eruptive centre. This assumption about a small volume of lava is based on the fact that if the tephra bed-3 had generated a larger volume, it would have covered parts of the 143.9 ka inner rim lavas. The tephra bed-3 activities continue to about 11 ka based on the MSOI proposed age. This upper part of the Mulifanua Formation episode corresponds with the sea level rise at stage 1 of the MSOI curve. Minor activities that occurred after the major tephra bed-3 episode signified a waning stage.

The 7 cm thick Lano-10 Unit could represents an unconformity between tephra bed-3 and tephra bed-4 implies the quiescence in volcanism at this stage (Figure 4.10). A thin unconformity layer may be associated with heavy erosion and low sedimentation rate which coincides with a long drought in the area. This is reflected in the 210Pb activities at the top part of the core which might also have occurred downcore. Rare charcoal fragments in the tephra bed-3 unit imply that the lower vegetation cover could have triggered heavy erosion.

Radiocarbon ages reveals that the tephra bed-4 activities could have erupted sometime around 3.4 ka as the sea level slightly falls here in the MSOI curve. The tephra bed-4 episode is the part of Lefaga Formation erupted during the Post Glacial stage when the sea level was 4.6 m high (Kear and Wood, 1959). The fourth episode represents the continuing re-eruption of the Crater Lanoto volcano from the deeper picritic magma source. Like tephra bed-3 the tephra bed-4 eruption also produced a small volume of lava. The morphology of the tephra sands shows that the tephra bed-4 was an explosive episode. A lack of volcanic sediment present at a depth of 46 cm (Lano-12 Unit) implies that minor activities could have continued for a short period before they completed ceased.

Few minor activities occurred after the main tephra bed-1 eruption episode ceased (Appendix 3). If minor activities were associated with lake-infill processes then there

203 would be expected phreatomagmatic activities from every four episodes. It seems that, the minor activities during the four tephra episodes could be associated with hydrothermal processes, after every major eruption and may have been present during a stage of volcanic quiescence. This assumption is based on yellowish and fine material associate with the abundance of secondary minerals iddingsite, goethite, halloysite and hematite.

The hydrothermal alteration processes could signify the infilling stages of the Crater Lake Lanoto. A very thin (millimetre scale) lens of organic materials associated with the components from the minor activities could be evidence of the lake infilling process. Based on the abundance of the secondary minerals, the lake infilling process could have lasted longer than the interval spanning between the activities associated with tephra bed- 1 and 2, but only a small amount of time in the interval associated with tephra beds-3 to 4. This variation in lake infilling processes could also have coincided with the long wet and dry periods, resulting in desiccation cracks in the tephra components that are also inferred from the supported and unsupported 210Pb activities at the top of the core.

(ii) Reconstruction of the cone collapse event (CCE ) and estimate the most appropriate radiometric age of the event

This section discusses the cone collapse event (CCE) in the region. The reconstruction is based on landforms, sediments deposits, potential consequences of a collapse on the volcano landforms, the surrounding landscape and few locations in the Pacific region. An appropriate age of the CCE will be determined from the relationship between geological structures on the main islands.

Several questions are still unanswered at this stage such as “If the CCE really occurred in the region, then how would this be generated?” and “If the magnetic susceptibility (MS) curve is matched with those of the marine sediment oxygen isotopes (MSOI), then is the CCE a part of the sea level fluctuation process?” More importantly at this stage, if the CCE occurred locally then it could be also fingerprinted on the MSOI curve, implies that the event could be widely spread in the region.

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Table 4.6 summarises the events and features that are suggested to be associated with the CCE. These features and events selected based on field observation, similarity in geological age and expose geological structures and landforms as described in Kear and Wood (1959).

TABLE 4.6 Summary of features and events in the Crater Lanoto and Samoan region that could be associated with the cone collapse event.

EVENTS / FEATURES DESCRIPTION Sediment core B2, B3, B4, C2, C3, C4 and D2 Sediment at the top of the other seven cores are all part of the low mobility like those of the master core D3 Low lying part of the western part of the rim Boulders dominate the rim (pit-crater) Collapse of nearby scoria/spatter cones Crater Olomaga, Crater Olomauga, Crater Tialata, Crater Lanotai and Crater Lanomoa Cut-off of Salani Formation activities on Upolu Cut-off associates with the two major slip and Savai’i, include Lanoto volcano faults Subsidence of the north western part of Savai’i Cause the upthrown of the Salani Formation to the south of the Matavanu crater Collapse of phreatomagmatic cones (Namua May be associated with the Fanuatapu Fault, island, Nuutele Island, Nuulua and Fanuatapu) Lepa Fault and Sinoi Fault around the study on the northeast of the study area area (refer Section 2.6) Upthrown of the Salani Formation on the Broad Salani lava suites dominates the study easternmost part of Upolu area upthrown about 60 m (refer Section 2.6) Collapse of the Fagaloa caldera (northwest of Kear and Wood (1959) labelled the area as an Lanoto volcano) exposed evidence of the unconformity between the older and young rocks Flank collapsed of Tau Island (American Flank collapse could be a part of the CCE Samoa) based on the new age Submarine avalanche at the foot of Savai’i and May be coincided with the subsidence, collapse Upolu and uplift parts of the main islands

Let us recall Figure 4.2 and identity whether the magnetic susceptibility (MS) curves of the other seven cores show features of the cone collapse event (CCE). A straight line implies a long consistent low volume-specific magnetic susceptibility shows at the top of core B2, B3, B4, C2, C3, C4 and D2. These sediment cores refer to the secondary deposit even though they are comprised of high concentrations of magnetite. This coincides with the fact that troughs of the MS coincide with high concentration of both organic and magnetite. The CCE sediment deposits seem dominate the top part of the seven cores (B2, B3, B4, C2, C3, C4 and D2) which suggests that they are all parts of the low mobilised components signifying the CCE. In other words, the CCE thick sediments

205 blanketed the broad swamp area and several pat of the lake. The low mobility of the core D3 sediment deposits, as inferred from two parameters (saturation moisture content against dry bulk density), as previously discussed in Section 4.3.1.1 and 4.7.1.2) suggests the occurrence of the CCE.

The low lying western part of the Lanoto crater, a result of the collapse rim, is dominated by boulders ranging from centimetre-scale to many metres in size. Despite the high elevation on the southeast part of the rim, however, piles of boulders along the slope also signify the collapse event. The CCE could also correspond with the collapse of other cones nearby: western part of Crater Olomauga, eastern and western portion of the Crater Olomaga, western part of Crater Tialata, southern part of Crater Lanotai and the western part of Crater Lanomoa (Figure 2.14 for location). It is still unclear at this stage whether the collapse of the nearby volcanoes occurred at the same time as the Crater Lanoto. However, Kear and Wood (1959) mapped these volcanoes as Mulifanua Formation meaning a similar age and therefore could correspond with the same CCE.

The CCE could be triggered from a volcanic activity cut-off event (this study). The cut- off event (COE) offsets the alignment of the Salani Formation cones on Upolu (Hawkins, 1987) and Savai’i. The COE suggests that is associated with the high tectonic stress activities at the sharp bending (NT) point to the south of Samoa (Hawkins, 1987). It suggests that the presence of the two magmatic sources (picritic and basanitic magma) of the Crater Lanoto could be products of the COE. This indicates that the eruption activities between Salani Formation and Mulifanua Formation could be described as “structural tectonically control volcanism”.

Interpretation based on aerial photographs and geological maps (Kear and Wood, 1969) indicate that the COE may be represented by the two major strike slip faults, the Fagaloa- Falealili Fault (Upolu) (Figure 2.8) and Manase-Gataivai Fault (Savai’i) (Figure 2.7). Gudge and Hawkins (1991) calculated that the Fagaloa-Falealili Fault has an average movement of 50 mm per year. The two strike slip faults parallel with the propagation of fracture perpendicular to the least principle stress of the Pacific Plate (Natland, 1980; 2003).

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In addition, the Sataua-Ologogo Arc Fault (Figure 2.7) to the northwest of Savai’i could be also evidence of the COE. Kear and Wood (1959) described the fault represents the vast volcanoes subside as “en masse” on the northeast of Savai’i. This results in groundwater drought condition at this part of the island (Kear and Wood, 1959; Butcher et al., 2000). The fault exposed on the northern part of the island suggests it triggered the exposure of the narrow strip of the Fagaloa Formation in the Manase area. The Sataua- Ologogo Arc Fault has up-thrown the Salani Formation to the south of Matavanu Crater. At the north-western part, the fault is unconformable and overlain by younger units (Mulifanua, Puapua and Aopo).

Based on ages and previous descriptions of the region (Kear and Wood, 1959; Hawkins, 1987; Keating, 1992) the CCE may be associated with the Fagaloa caldera (northeast Upolu), northern part and south-west flank of Savai’i, southeast flank of Upolu, collapsed of the phreatomagmatic cones on the northeast of the study area (Namua Island, Nuutele Island, Nuulua Island and Fanuatapu Island) and many other eroded old cones along the central and coastal part of the main islands. More evidence that could suggest the occurrence of a CCE is listed in Table 4.7. The collapsed of the phreatomagmatic cones could be associated with movement along the Fanuatapu Fault, Lepa Fault and Sinoi Fault, as described in detail in Section 2.6. This CCE may trigger the upthrowing of the Salani Formation (an inlier) which dominates the study area, about 60 m along the Lepa Fault.

The Fagaloa caldera is mentioned in several literatures (Natland, 1980; Hawkins, 1987; Keating 1992) and is described in reference to exposed dyke networks (Fagaloa Intrusion and Lemafa Intrusion), as previously described in Section 2.3.4.1. Kear and Wood labelled this caldera collapse as exposed evidence of the main unconformity that separates the older rocks (Fagaloa Formation) from the younger one (post-Fagaloa). Lava suites in the area are highly jointed, fractured, weathered and eroded, which could explain why a “ring fault” is not well exposed in northeast Upolu, this being the most obvious characteristic of calderas in many other parts of the world. This particular area could be between 2 and 4 km in diameter which falls in the caldera category as given in Gudmundsson and Nilsen (2006) and Gudmundsson (2008).

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The Sataua-Ologogo Arc Fault extends at least 50 km and is down-thrown toward the north. The fault is suggested to have triggered the submarine avalanches at the foot of Savai’i, on the north-west and south-west (Hill and Tiffin, 1989 and Keating 1992). The COE could be the other significant reason for rare Fagaloa Formation cone occurrences in Upolu or Savai’i. This coincides with the fact that most of these older cones were collapsed and eroded (Keating, 1992).

The MSOI curve predicts that the CCE must be older than 22,300 but younger than 60,000 years old. Let us consider that a significant geological or tectonic event occurred in the Pacific region between stages 2 and 4 of the MSOI curve. The majority of information relating to this particular period relates to volcanic eruptions, and details about structural tectonism is rare. The Taupo Volcano erupted between 65,000 and 27,000 years ago in the central north island of New Zealand (Froggatt, 1997). The eruption recorded is one of the world most violent eruptions in its geological history. The late rifting stage generated the Ba basaltic volcanic group, which dominated the northern part of Viti Levu, Fiji, and other island groups to the southeast (Rodda 1967; 1994). This volcanism continued until the Late Pleistocene; however, it still unclear whether the cessation of Ba volcanism is related to the COE of Salani Formation. At the same period, during the Late Pliocene to Quaternary, the uplift of subaerial units occurred along the coast of Eua Island, the Kingdom of Tonga (Tappinand Balance, 1994). On the southern part of the island of Niue, to the southeast of Samoa, a submarine landslide occurred. However, the age of this submarine landslide is still unclear (Pearce, 2007).

The southern flank of Ta’u Island, located to the eastern end of the Samoan island chain, collapsed at 22.4 ka (Williams et al., 2014). This could be part of mass wasting activities occurred during Pleistocene time in many other parts of American Samoa (Tutuila Island, Ofu Island, Olosega Island and Ta’u Island) outlined in Thornberry-Ehrlich (2008). The new radiometric age of the flank-collapse involved use of the cosmogenic nuclide, 36Cl. Based on the radiometric age of the Crater Lanoto activity the flank collapse could have occurred before the tephra bed-3 episode of the Mulifanua Formation (Figure 4.49). In other words, if the collapsed flank is really a part of the CCE then, this new age could support the exact timing predicted in Figure 4.49. This requires further investigation.

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The flank-collapse of Ta’u suggests a possible influence from the climatic-eustatic sea level during the last glacial maximum (Williams et al., 2014). If this is the case, then flank failures of islands to the eastern end of Upolu (Namua, Nuutele, Nuulua and Fanuatapu) could have collapsed via a similar mechanism. However, the collapse of these islands could also have been associated with the downthrow of the Fanuatapu Fault to the northeast and Lepa Fault to the south (Figure 2.8 and 2.13), all believed to be part of the CCE. In addition, this flank-collapse of Ta’u could have generated a massive tsunami in the territory of American Samoa. A tsunami of this size would have reached Upolu Island about 200 km to the west with a wave amplitude of > 5 m (Williams, 2009).

If evidence of the CCE is exposed on the main islands, then the seafloor of the Samoan region should also have been impacted. Figure 4.50 shows the Gloria Seamarc II seafloor images of offshore Western Samoa. The islands are surrounded by large-scale mass movements and a series of faults (Hill and Tiffin, 1993). At the sharp bend (NT), in the northeast corner of the Kermadec-Tonga Trench (southwest Samoan), there are series of east-west strike normal dip-slip faults covering an area of about 50 km (Figure 4.50). Hill and Tiffin (1993) believed that these faults run parallel to a main thrust fault at the hinge of a down drag slab portion of the Pacific Plate. The faults have vertical displacement up to 800 m elongate from 25 to 80 km.

The area is also covered by a series of debris avalanches, flanking down slope toward abyssal plains, to the west and north of the islands. For example, a slump block of about 20 km long and 8 km wide flanks down-slope between Savai’i and Upolu. It is suggested that this slump block is a part of a volcano or an island located to the northeast of Apolima Island. A small portion left behind from this down-slope slip volcano/island still exposed like a razorback ridge above sea level to the northwest of Apolima Island between Upolu and Savai’i. Nunn and Pastorizo (2007) described this as a product of a series of underwater gravity slides known as “volcanic shoal.”

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Debris avalanches and the slump block suggested were all associated with the CCE. The increase in tensions activities of the sharp bend at the Tonga Terminus are evidenced from elongates faults in the region (Figure 4.50).

The age of the CCE lies sometime between the equivalent age of late tephra bed-2 and early tephra bed-3(Figure 4.49). In other words, the CCE marked the waning of the vents linked to the deposition of the Salani Formation while waxing of those relating to the Mulifanua Formation on both main islands. The age is also reflected from the relationship between the Sataua-Ologogo Arc Fault with the post-Fagaloa units on Savai’i. The widespread Mulifanua Formation unconformably overlies the Sataua-Ologogo Arc Fault on the northwestern part of Savai’i, implying the CCE is much older.

Onion skin-like structure (Figure 2.19) is commonly occurred in lavas of Salani Formation. The onion structure forms as unloading pressure release for the underlying stresses lava suites. The CCE could be responsible for the development of these physical weathering features in the Salani lava suites. This piece of information is also supported

210 by the fact that the CCE occurred during the time corresponding to the late Salani Formation period.

Kear and Wood (1959) suggested that the northern portion of Savai’i collapsed during the lowest sea level at the Last Glaciation stage. This implies that the CCE is part of the Mulifanua Formation and occurred between 18 and 12 ka, which is too young. However, the up-thrown of the Fagaloa Formation and Salani Formation at the northern part of the island, signifies the CCE is older than Mulifanua Formation. This suggests that the upper part of the tephra bed-2 is marked by the CCE which occurred at least at 22.3 ka; the event occurred between the Last Interglacial and Last Glaciation stage. In other words, it occurred sometimes just before the Mulifanua Formation activities began. This may correspond to the collapsed flank of Ta’u Island at 22.4 ka, which could imply that the event is also the part of CCE.

Additionally, it is also explained that may be at the same period of time, the CCE triggered a magmatic source level swifted, from shallow (tephra bed-2) to deep (tephra bed-3 and 4) source. This assumption is also discussed in more detail in Section 4.7.4.3 and Section 4.7.5 (ii) as follows.

Based on satellite images, interpretations of aerial photographs, field observations, physical characteristics and the age-relationship between old and young formations, we could identify the impact of the CCE, which left some scars on the main islands. Table 4.7 shows a summary of the CCE impacts, which are exposed as geomorphological landmark on Upolu and Savai’i.

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TABLE 4.7 List shows some of the impact the CCE scarred the geomorphology of the main islands.

UPOLU ISLAND SAVAI’I ISLAND

1. Fagaloa caldera collapse and formed; Mauga o 1. Vaipouli valley (north) Fao (northeast), Lemafa zone (northeast), Afulilo zone, Fagaloa Bay (northeast) 2. Avao Bay (north)

2. Fuipisia fall at Sopoaga (south eastern) 3. Manase-Safotu headland (tolotolo) (north)

3. Cone collapse of Mauga o Vaea volcanic zone 4. Maliolio valley (north) (south of Apia) 5. Uplift formed the Le-agi’agi Safune (north) 4. Alaoa-Ma’agiagi valleys 6. Uplifted formed the Le-mako at Samata 5. Vaiusu Bay (south west)

6. Narrow leap between Vavau and Lepa (tulilima) 7. Vanu valley at Gataivai-Palauli (south) (south east) 8. Steep hill to the west of Sataua (north 7. Lava tunnel collapsed form Tiavi waterfall western end)

8. Collapse of the islands to the eastern end of Upolu 9. Down-slope slip of a volcano/island (Fanuatapu, Namua, Nu’utele and Nu’ulua) located to the north east of Apolima

4.7.2.3 Crater Lanoto radiometric age relative to the hotspot and isotopic signature

This section is presented into two parts:

1. A discussion about whether the new radiometric ages of the Crater Lanoto are consistent with hotspot or post-erosional volcanism.

2. An outline of the isotopic process relating to shield and post-erosional volcanism along the island chain.

(i) Age-distance relationship

The Crater Lanoto volcano was active since the deposition of the Salani Formation during the Early Pleistocene. Let us determine whether the new ages of the Crater Lanoto fits in the shield or post-erosional volcanism.

Figure 4.51 shows a relationship between the distances of volcanoes from the Vailulu’u hotspot and their ages. The plot also included the current Pacific Plate speed of 7.1 cm per year (red line) and its speed at 13 million years ago of 9.3 cm per year (purple line).

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The new volcanic ages of Crater Lanoto together with other post-Fagaloa and Manase shield are plotted further from the current hotspot velocity line. This implies that these volcanoes are part of the post-erosional process. The Lower Fagaloa lavas with their ages ranging between 2.05 and 2.65 Ma (including the Vanu cobble) plot not far away from current hotspot line, which implies a shield origin. There is a suggestion that changes in the speed of the Pacific Plate, from 9.3 to 7.1 cm per year, could have changed the volcanic activities of other Fagaloa suites. In other words, these Fagaloa deposits could have, rather than having been erupted via a plume mechanism, been generated from post- erosional activities (eg. Manase Shield). The deep submarine flanked lavas of Savai’i with ages of 5 Ma fit perfectly in the Samoan plume. Lavas from the Eastern Samoa province included those of Tau, Ofu, the subaerial volcano of Tutuila and eastern seamount all perfectly fitted along the current hotspot slope.

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Western seamounts (young-Lalla Rookh, Field Bank and Basco Bank) and Wallis Island are all parts of the post-erosional volcanism. A few lavas from young-Combe and old- Lalla Rookh correspond go the hostpot volcanism. The Bayonaise and Faavevesi seamounts were part of the 13 million year old hotspot, as the velocity of the Pacific Plate increased at 9.3 cm per year. Within the same period, an old-Combe seamount was a part of the post-erosional volcanism process.

There is not simple age progression along the Samoan island chain, which may show similar ages in a wide range of volcanic locations. This indicates that the post-erosional process dominated the volcanism of Samoa through time, and explains why there is no westward age progression as with the Hawaii Island chain.

Koppers et al (2011) suggested that the Pacific Plate motion in the Samoa region is much slower, than the Hawaiian and other hotspot volcanism. This could be something to do with the closer of the island chain to the sharp bend at the Northern Terminus (NT). However, the suddenly change in the speed of the Pacific Plate at this part of the region is still uncleared what triggers this (Koppers et al., 2011).

Samoan hot spot volcanism occurred between 22.9 and 23.9 Ma. This is based on reconstructions of the motions of the Fiji Plateau, Vitiaz Lineament and Tonga Arc in relation to the seamounts on the western part of the Samoan island chain (Hart et al., 2004). The Alexa seamount northwest of Rotuma Island (northwest of Fiji) is thought to represent the initial hotspot location of Samoa, which was located further north-west of the NT.

The deep submarine lava of Savai’i referred as a “true intraplate” setting (Koppers et al., 2008). Based on the seamount reconstruction of the Samoan region, Savai’i was part of the hotspot during 5.0 Ma and was located northwest of NT, 1400 km west of Vailulu’u. The NT was located close to Savai’i around 4.5 Ma due to a rapid eastern motion of the rolled-back Pacific Plate (Hart et al., 2004). This rapid eastern motion could be responsible for generating voluminous post-erosional volcanism of Savai’i and Upolu (Hart et al., 2004; Konter and Jackson, 2012).

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Based on the radiometric ages of the submarine and subaerial volcanoes from previous studies, the Samoan island chain can be subdivided into three main divisions. The three divisions are referred to as (1) eastern sequential, (2) western sequential and (3) mixture of synchronous and sequential process. Figure 4.52 shows the three significant subdivision of the island chain of Samoa. Sequential divisions are dominated by plume volcanism (erupt in good sequence) whilst the mixed division is associated with plume and post-erosional volcanism (may erupt simultaneously). The new ages of the Crater Lanoto volcano settle in the mixed division, which extends from Upolu to Combe seamount to the west.

Both ends of the island chain show evidence of the westward age progression relating to the hotspot volcanism in comparison with the middle part. The mid-part of the chain seems to have been initially formed via the plume volcanism and then later changed into post-erosional process (eg. Savai’i was part of the plume at 5 Ma). This indicates that the mid-part of the island chain is associated with high tectonic stresses in contrast to both ends. Sequential volcanism has less of a tectonic influence in comparison with those

215 generated by synchronous processes (Hart et al., 2004; Konter and Jackson, 2012; Price et al., 2013). Hence, the widespread post-erosional activities on the main islands Upolu and Savai’i) are the product of high tectonic stresses associated with the sharp bend (NT) of the Pacific Plate. Hence, the Samoa volcanism would correspond with the definition of the “tectonically controlled volcanism”. Striation features exposed on the seafloor (Figure 4.50) which run parallel or perpendicular with the west-east orientation of the main islands are evidence of the tectonic stress in the region (Hill and Tiffin, 1989). These stresses result from a sideways bend of the Pacific Plate (Natland, 1980; 2003).

(ii) Isotope signature in the shield and post-erosional volcanism

The Samoa Volcanic Field (SVF) is strongly characterised by EM2 signatures. Variations in the ratios of radiogenic isotopes (87Sr/86Sr, 206Pb/204Pb, 143Nd/144Nd, 187Os/188Os and 3He/4He) are the perfect components to distinguish shield and post-erosional volcanism along the SVF, as previously mentioned.

The isotopic signature of lava suites from Crater Lanoto volcanic region, it also supports the fact that Lanoto volcano is linked to post-erosional volcanism origin. The same can be said for the major and trace elements composition of the Crater Lanoto volcano compoared with other lavas along the (Figure 4.43, 4.44 & 4.45). Radiogenic isotope components show that lava suites from the northwest of the Crater Lanoto volcano comprises of have low 87Sr/86Sr, 206Pb/204Pb and 3He/4He but high in 143Nd/144Nd (Figure 2.3, 2.4 and 2.5). Workman (2004) outlined that, low 87Sr/86Sr and 206Pb/204Pb ratios in shield and post-erosional corresponded with HIMU signature, of buoyancy layer underneath the Samoan lithosphere. Buoyancy layer is known as “depleted refractory viscous residue keel” (Jackson et al., 2010) which also characterised as a perisphere layer (Anderson, 1995; Natland 2003). This is an evidence of an interloping of three Cook- Austral hotspots (Rarotonga, Rurutu and Macdonald) to the east along the Samoan volcanic region known as a “hotspot hight way” during 10 Ma (Jackson et al, 2010). The depleted refractory viscous residue keel calculated that, it also moves west at 71 mm/year corresponding with the Pacific Plate motion (Jackson et al., 2010). Trails of the interloping process, fingerprint along the SVF in lava of Waterwitch seamount (western

216 part), Papatua seamount (eastern part), Malu’lu seamount (eastern end) and Rose Ialsnd (Figure 1.1).

Additionally, as previously mentioned in Section 2.2, the Samoan mantle is leaking from the western part of the SVF toward Fiji region, based on high 3He/4He ratio in several seamounts. This leakage suggests being re-entrace into the Samoan volcanism, may also influencing the isotopic variation in the post-erosional and shielding volcanism. No study has been carried out todate in relation with this assumption however; it believes that this could be the case. The mantle leakage is thought to flow from a thicker Pacific lithosphere to a thinner Lau lithosphere through adiabatic upwelling mechanism (Price et al, 2014). Such a mechanism suggests that is possible that a portion of this mantle leakage seep back into the cracked lithosphere of Samoa. This could be triggered through a mantle flow drag force mechanism associated with the downward drag caused by subduction of the Australian Plate at the Vitiaz Lineament (Figure 2.1). The flow- back mantle could also contribute to the broad post-erosional activities in the SVF. Although such information provides important background for this research, a detailed investigation into such mechanism is beyond the scope of this study.

Isotopic composition variation associate with a great volume of post-erosional volcanism in Samoa suggests could trigger, from SVF location near the Northern Terminus (NT) (Konter and Jackson, 2012). In other words, flexural bending at NT and lithospheric metasomatism process of HIMU signatures indicate that, the Samoan lithosphere may plays an important role in the post-erosional volcanism. This assumption is based on a “temperature drops” as the original magmatic source, has shifted from plume environment (deep) to shallow source, dominated by melting just below and within the lithosphere (Konter and Jackson, 2012).

The radiogenic isotope composition of the submarine lavas from Savai’i and other shield volcanoes on the eastern volcanic province indicate a similar composition. Despite the presence of post-erosional activities, however, isotopic fingerprints suggest that plume volcanism continued to be active through 5 Ma (Hart et al., 2004; Koppers et al., 2008).

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This indicates that the shield and post-erosional volcanism could have occurred simultaneously during the Pliocene to present.

The variation among the radiogenic isotopes could be product of the three scenarios; (1) More tectonic activities associated with the post-erosional volcanism (Hart et al., 2004; Konter and Jackson, 2012; Price et al., 2013), this being the reason why Samoa Volcanic Field has low magma supply monogenetic volcanism relating to tectonically controlled activities (Kereszturi and Nemeth, 2013); (2) Formation of deep and shallow mantle environments (Workman et al. (2004) and (3) The mantle underneath (eg. Ofu Island) has a large primitive reservoir, but only hosts a small portion of recycled materials (Jackson, 2007; 2009).

4.7.2.4 Summary of critical points from the age of Crater Lanoto events

(I) MS troughs and peaks match the MSOI curve enable us to determine the Crater Lanoto age.

(II) The outer rim lava has a proposed MSOI age of 200 Ka, represents the initial age of the Crater Lanoto volcano.

(III) The presence of early secondary mineral may signifies the infilled process of the lake.

(IV) Unusual high concentrations of organic material and abundance of broken tephra components in tephra bed-2 suggest a cone collapse event.

(V) The cone collapse event may have been generated from the cut-off of the Salani Formation related activities in Upolu and Savai’i by the two major strike slip faults.

(VI) Activities associated with tephra bed-3 & 4 activities are suggested to be dominanted by volcanic ash deposit with only thin tongue of lava flow.

(VII) The explosiveness of the four major episodes associated with bursting of large bubble when reach the surface (dry explosive).

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(VIII) Two main volcanoes group along the Samoan Volcanic Field are: sequential (erupts in good sequence) and synchronous (erupts in simultaneous style).

(IX) Synchronous volcanism is associated with tectonic stresses whilst sequential has less influence on tectonism.

(X) Crater Lanoto volcano falls in the region of the mixed, sequential and synchronous group.

(XI) Variation in isotope ratio (strontium, lead, helium, neodymium and osmium) distinguish post-erosional and shield volcanism.

(XII) The Pacific Plate changed it speeds from 9.3 cm per year at 13 Ma to 7.1 cm per year at 5 Ma influence the volcanic age progessive along the Samoa Volcanic Field.

(XIII) Crater Lanoto is not the part of shield process but originated from widespread post-erosional volcanism.

4.7.3 PART 3: VOLCANIC HAZARDS OF CRATER LANOTO

This section is highlights the volcanic hazards associated with the Crater Lanoto volcano:

1. Evidence of human occupation in the sediment deposit of the Crater Lake Lanoto. Here I discuss the oral indigenous knowledge of how early occupants identify various volcanic hazards included those of the Crater Lanoto volcano.

2. An outline of the eruption episode intervals of the Crater Lanoto volcano in comparison with other volcanoes.

3. Discussion of eruption styles associated with the Crater Lanoto volcano.

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4.7.3.1 Evidence of human occupation and indigineous knowledge

(i) Occupation in the Crater Lanoto region

The latest eruption episode of Crater Lanoto at 3.4 ka coincides with the first human settlement of Samoa (Green, 1974; Petchey, 1995 and 2001; Dickson and Green, 1998; Martinsson Wallin, 2007). Crater Lake Lanoto is one of many sites in Samoa that could have been targeted by the many first arrivals. Their site selection criteria were based on water resources, high elevation, enabling them to locate enemies, thick forest for shelter and hunting, and a location close to the coast line. A few human occupation features, are found on the southeastern part of the crater rim wall. These are circular rock fence features which could represent a meeting area, animal fencing, fire place or hut foundation. The features could be part of the modern human occupation or could originate from earlier in the Holocene.

Evidence of occupation in the lake sediment is still unclear. The increase in sedimentation associated with erosion during the Holocene could be considered evidence of human occupation. For example, the 7-cm-thick Lano-10 Unit represents the unconformity between tephra bed-3 and tephra bed-4 (Figure 4.10). This thin layer could indicate heavy erosion processes occurring before tephra bed-4 activities. However, there are two scenarios that could contribute to the rapid erosion at this certain depth. The first is human occupation and the second is an eruption which could have destroyed vegetation which in turn caused an increase in erosion. At this stage, more work is needed to investigate the idea of human occupation within the area during Holocene time.

(ii) Indigenous knowledge relating to the Crater Lanoto volcano

Indigenous knowledge can be seen as a Holocene geological library of Samoa. It includes several components, such as traditional dances, traditional songs, legends, places names and Samoan proverbs. Many of those give clues about the style of eruptions associated with Holocene activities on the main islands.

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Samoa is one of many Pacific islands for which there has been little research on past Holocene volcanism, in the context of dealing with disaster management (Nemeth and Cronin, 2009). Despite the lack of an eruptive history of Crater Lanoto and many other volcanic centres, the Samoan culture contains several traces of volcano components. The value of using a combination of modern science and indigenous knowledge has been recognised very recently in the Pacific as a very valuable approach to contructing any natural disaster history (Nemeth and Cronin, 2009). Indigenous knowledge, stories and myths passed down over generation, are significant indicators of earlier Holocene activities.

The name Lanoto can be broken down into two words “Lano” and “to”. “Lano” refers to a permanent place and “to” is a valley with great depth. This indicates that the first occupants could have observed a deep valley in the central part of the volcano, after Holocene activities (may be tephra bed-3 or tephra bed-4 episode). The great deep valley must refer to the eruption centre (deep part of the lake). There are other nearby volcanoes that have the same prefix “Lano”, such as Lano-o-lepa, Lanotai and Lano’omoa. Lano-o- lepa refers to a permanent lake for the Lepa village the land/territory owner, and could therefore represent the first arrivals in the area. Lanotai refers to a permanent lake to the south toward the ocean and Lano’omoa refers to a permanent central lake which could represent a meeting place for everyone. It is still unclear as to why the occupants added the suffix “moa” (meaning the centre) to the word “Lano”. However, perhaps the occupants firstly observed eruption activities from this particular crater, before any other craters on the easternmost part of Upolu. In other words they may have referred to this as the original or the main source of other later volcanic eruptions.

An appropriate explanation for the similar prefixes (Lano) perhaps represents a similar event. Either the similar event can be described as having the same eruption style activity or volcanoes erupted simultaneously.

Using the same prefix to explain the same volcanic event can be extended to other part of the main islands; for example, Tafua-upolu, a scoria cone located to the central westernmost part of Upolu and Tafua-savaii, a tuff scoria cone to the northeastern end of

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Savai’i. The word “tafua” means fire mountain/volcano, which also relates to the Tonga version of “tofua” and describes a volcanic island (Nemeth and Cronin, 2009). Both Tafua-upolu and Tafua-savaii had similar activities, known as “dry style” eruptions. This typical volcano is associated with large amounts of dissolve gases in the magma (Cronin et al., 2006). In addition, the name of Crater Mauga-o-savai’i to the southwest of the Crater Lanoto could derive from some similarities in eruption features with those of Savai’i activities.

Early occupants employed similar skills on the western part of Savai’i Island. The name “Mauga Mu”, “Mauga Afi”, “Mata ole Afi” and “Matavanu” refer to recent eruptions of the Aopo Formation. These volcanoes are located towards the central western part of Savai’i (Figure 2.7). All names derived from various common features produced by these particular volcano activities. This shows that the earlier occupants distinguished volcanic activities in Savai’i a long time ago. The volcano names were first mentioned in the literature by several German authors (Wegner, 1902; Weber, 1902; Angenheister, 1909; Friedlander, 1910) before the English version (Anderson, 1910).

Volcanic activity that emits thick “smoke” is referred to “Mauga Mu”, which produces more volcanic ash with less lava. Those volcanoes associated with less “smoke” but that are dominated by fire fountains are referred to “Mauga Afi”, i.e. these particular volcanoes produce less volcanic ash but emit great volume of lava. The words “Mata ole Afi” refers to a stage of the eruption that has a massive fire column associated with thick smoke. The word “Matavanu” refers to a valley with an eye-shaped structure. Both terms, Mata-ole-Afi and Matavanu, do not contain the word “Mauga”, in front. The word Mauga means crater. This suggests that the two particular volcanoes did not erupt from a crater but from a fissure style eruption.

If a “tulafale failauga” (orator speechmaker), has a “lauga” (speech) during a big gathering, without disturbance from other local paramounts, it is called an “asu faaniu’tu” speech. This refers to a thick long perpendicular smoke column standing straight like a long coconut tree. The early settlers seem to use smoke as a significant signal to describe the magnitude of an eruption.

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Cronin et al. (2006) described that the early occupants in the Holocene must have experienced the eruptions of Crater Lanoto, Tafua-upolu, Tafua-savai’i, Apolima Island and Cape Tapaga to the north of Crater Lanoto. Unfortunately, there is no evidence of how the earlier occupants responded to the volcanic hazards, nor is there oral historical evidence or indigenous knowledge amongst indigenous communities to provide any clue. However, Lapita components found to the northeast Upolu, Mulifanua district reveal that the earlier occupants seem settled along the coastal area for their safety. In addition, William (2014) suggested that these costal occupants could also coincide with the charcoal deposit which was laid down from 3.4-3.2 ka at Fagali’i beach (north central Upolu).

Most Holocene and present eruptions occurred in the high central ridge of the two main islands. This suggests that the first occupants monitored the eruptions from the coastal area. They may have used the magnitude of the volcano smoke and column of fire to assess the magnitude of the eruption. In the daytime, thick smoke must have been used to to identify an active volcano. At night time, the column of lava was most likely a tool for identifying an active eruption.

There were no casualties reported during the Matavanu eruption in 1902 to 1911 (Anderson 1910). This implies that skills and experience of the first occupants were successfully passed down to the later generations.

4.7.3.2 Intervals of Lanoto volcano in contrast with other Samoan eruptions

The aim of this section is to determine if there is consistent pattern of eruption interval between the Crater Lanoto and other subaerial volcanoes. A long and consistent pattern would be a valuable tool for predicting future eruption in Samoa. This section is presented into three parts as follows:

(1) Investigation of the eruption interval of the Crater Lanoto

(2) Merging of the eruption interval of Crater Lanoto with the rest of Western Samoa

(3) Identification the most appropriate intervals for future volcanic prediction

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(i) Crater Lanoto eruption intervals

If we had the radiometric and the marine sediment isotope (MSOI) ages of tephra bed-1, 2, 3 and 4, then we would be able to determine the eruption intervals between the four eruptive episodes of the Crater Lanoto volcano (Table 4.8). The lack of radiometric dating resulted in the eruption intervals being less accurate than they could have been (underestimated). In saying this, let us compare these intervals with those of the Aopo Volcanic Formation (Matavanu, Mauga Afi, Mauga Mu and Mata-ole-afi). These latest activities occurred between 1760 and 1911 with their eruption intervals only ranging from 11 to 150 years. In addition, the island of Taveuni (northeast of the Fiji group) has an eruption interval of at least 25 years based on abundant radiometric ages (Cronin, 2001). However, the Samoa Volcanic Field activities are very difficult to predict as apparent intervals between eruptions are wide ranging.

Tephra beds Radiometric age (Ka) Estimated interval (Ka) Tephra bed-4 3.4 (tephra) 7.6

Tephra bed-3 (top) 11.0 (MSOI) 11.3 Tephra bed-3 (base) 22.3 (tephra) 121.7 Tephra bed-2 144 (inner rim lava) 56.1 Tephra bed-1 200 (MSOI)

The long interval between tephra bed-1 and tephra bed-2 could be part of the early Salani Formation activities. An interval between the activities associated with tephra bed-2 and tephra bed-3 is the longest and could be influenced by the cut-off of the Salani Formation activities. The base and top of tephra bed-3 could produce a better estimate of the episode duration. A close interval between tephra bed-3 and 4 episodes still shows that Crater Lanoto is a long sleeping volcano. This long interval scenario could be an appropriate characteristic to define behaviour of the post-erosional volcanism along the Samoa Volcanic Field.

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(ii) Other subaerial eruption intervals

Previously published radiometric dates of volcanic suites of Western Samoa were mainly from the Fagaloa Formation and Salani Formation. There is a lack of Holocene dating in both main islands (Figure 2.12).

Figure 4.53 shows the relationship between the eruptions intervals of Western Samoa versus time passed. Time passed is represented by the radiometric age of each formation. The relationship between the two variables (eruption interval and time waited) is defined by the best-fit steep solid blue line of y = 23x - 86. This best fit steep line represents an approximately average position of radiometric dating age, which can provide a long continue perfect intervals for future volcano prediction. Samples plot further away from the line believes that, those volcanic lava/tephra were not stratigraphy sampling. The plot indicates that the eruption interval has increased toward the older units but decreased toward young formations.

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Jackson et al (2009), Hart et al (2004), Gudge & Hawkins (2004), Koppers et al (2008), Nemeth & Cronin (2009), McDougall (2010) and Koppers et al (2011).

The plot displays three volcanic interval divisions: long-range interval (LRI), medium range interval (MRI) and short-range interval (SRI). Tephra bed-1 and 2 fall in the LRI, tephra bed-3 plots in the MRI and tephra bed-4 scatters in the MRI.

The tephra bed-1, 2 and 3 intervals merge with Salani Formation consist of 56 and 34 kyr intervals respectively. Tephra bed-3 and 4 intervals plot with the Mulifanua Formation comprise of 18.7 kyr and 480 years intervals, respectively.

The plot displays that older volcanism commonly comprises of LRI compared with those of younger eruptions. There are only few Mulifanua samples plotting in the MRI zone. Holocene to Present volcanism has an interval ranging between 3 and 870 years. These radiocarbon dated samples are mainly volcanic ash and lava suite. The Salani Formation has intervals ranging between 4 and 84 kyrs. Fagaloa Formation comprises of the longest intervals range between 10 kyrs and 1.3 myrs. The LRI samples are mainly of potassium- argon and argon-argon dated lava suites.

(iii) The most appropriate volcanic eruption interval for prediction

As previously discussed, the synchronous process dominates the volcanism of Western Samoa volcanic province. This creates more difficulties in constructing any consistent long ranging pattern of the eruption interval. The lack of radiometric dating in both main islands is another major factor contributing to a poor understanding of volcanic intervals in Samoa. In addition, LRI can be a result of non-stratigraphic sampling procedure of lava suites and tephra components. This complexity in volcanism age is reflected in the large variations in volcanic eruption intervals of the older formations.

If the tephra bed-4 of the Lefaga Formation merges with volcanism of the SRI zones then it produces intervals ranging between 3 and 870 years. It is calculated that a recurrence interval of eruptions from Holocene to Historical seems to lie between 118 and 480 years. Taylor and Talia (1999) predicted that there is a possibility of the next Aopo Formation

226 eruption occurring within the next 100 years with a recurrence interval of approximately 150-200 years.

The Holocene to present activities on Savai’i has duration of 6 to 650 years, while those of Upolu approximately at least 2990 years. Long intervals between main episodes of the Crater Lanoto shows the life span of volcano in Samoa can be much longer than expected. This becomes more challenging in construction an appropriate time line for the next eruption.

The Aopo Formation has short-range activities. The Matavanu volcano erupted in 1905 then re-ignited in 1911; Mauga Afi, Mauga Mu and Mata-ole-Afi erupted in 1760 to 1902. Puapua Formation activities on the main islands show short-range eruption intervals of 71, 45 and 35 years before the next eruption occurred 270 years later. Since 1911, it is predicted that the next eruption in Western Samoa could occur in the next 270 years. This will represent a continuation of the Aopo Formation short-range interval activity. It coincides with the fact that the Samoan active volcanism is at the peak of high sea level fluctuation process (Figure 2.7). There is a chance that the recurrence prediction could be too short, too long or inaccurate. In other words, the next eruption could occur at any time based on the geological setting of the Samoan island chain near the Northern Terminus. The next activity of the Aopo Formation could fall in the category of the SRI (Figure 4.53). In terms of the Crater Lanoto, there would be a possibility of simultaneous activities occur along the same fissure line with a new eruption crater.

The volcanic prediction timeline is dependent on variations within the dynamics of the tectonic activities along the Samoan island chain. The accuracy of the prediction is dependent on the availability of more sufficient data and further comprehensive studies.

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This would improve knowledge and understanding of volcanic activities pattern along the Samoa Volcanic Field.

4.7.3.3 Eruption style of the Crater Lanoto volcano

Typical eruptions on Upolu and Savai’i are characterised by a composition poor in silica and rich in magnesium, iron and calcium (Fepuleai, 1997 and Cibik, 1999). This reflects that, the chemistry is not the major factor controlling the explosiveness scenario of the Samoan volcano, in comparison with andesitic and rhyolitic eruptions in other part of the world. The explosiveness of basaltic magma of the Crater Lanoto depends on two major mechanisms: (1) a great volume of volatiles degassing and (2) the expansion during interaction of the hot magma with groundwater aquifer to form phreatomagmatic phase of “maar-forming eruption”.

The volcanic hazard evaluation by Cronin et al (2006), classified that, the Crater Lanoto volcano is an “explosive short term scoria cone” eruption. It is also suggested that activities of the Crater Lanoto, may be similar to the Tafua-upolu volcano to the western end of Upolu which is characterised as an explosive “dry style” eruption (Cronin et al., 2006).

As previously mentioned in Section 4.7.1.2, Hawaiian lava fountain and Strombolian type eruption are the dominant styles of the Lanoto volcano. Lava fountain activity results from the lowest energy magma fragmentation associated with the dissolved gas content of the melt (Kereszuri and Nemeth, 2013). This poor degree of fragmentation in the Hawaiian eruption may be signified by coarse ejectas along the slope and around the inner part of the volcanic rim (Carey, 2005). Fine pyroclasts may cool sufficiently and fall back in the deposition basin whilst other are controlled by the direction of the trade winds in the area.

Table 4.9 summaries the three eruption styles (Hawaiian, Strombolian and Phreatomagmatic phase) and hazards associated with the Crater Lanoto volcano. Areas that are identified as having potential human impact are based on measurements by Cronin et al. (2006) and Taylor & Talia (1999) of the Savai’i activities. 228

The Crater Lanoto is a compound monogenetic volcano that erupted from double craters during Salani Formation to Lefaga Formation activities. It is suggested that the narrow graben-like activity and pit-crater eruption seem to be have transitioned from a Hawaiian lava-fountain type then to a Strombolian style. Kereszuri and Nemeth (2013) described that the lava fountain could have been up to 500 m high and have ejected highly deformable lava rags with an exit velocity of 200-300 m/sec (Table 4.9). Ballistic ejecta (large rock fragments) are common in Hawaiian and Strombolian eruptions from narrow graben-like and pit-crater activity and may reach about <100 m from the vent.

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TABLE 4.9 Eruption style of the Crater Lanoto volcano and associated hazards.

Crater Lanoto Hazard Area affected Potential human Volcano eruption impacts style HAWAIIAN Lava flow (thin sheet pahoehoe Moderate to large area High potential for ERUPTION STYLE: signify very fluid lava flow) (1-8 km2). Fluid flow can be loss of life, (lava fountain) in advanced rapidly down the slope property and “narrow graben-like approximately about >10 m/sec) farmland would be crater” and “pit-crater” permanently damage Fire fountain (up to 500 m) Lava rag has exit speed of 200- High potential to 300 m/sec cover area up to 2 km area close to the vent Volcanic ash (Pele’s tears) Spread up to 3 km radius Low potential for loss of life but property would destroy Volcanic bomb Ejected about 1.5 km radius Moderate for loss of life Ballistic ejecta (5-20 cm in Large fragments (100 m from the Low potential to diameter) vent) loss of life at >100 m zone Crater floor subsidence/collapse May be affected area at 100-200 Loss potential of (increase in activity) m from the vent loss of life Pyroclastic flow May be covered area about High potential to <1km loss of life Forest fire Cover great area (>2km radius) High potential STROMBOLIAN Lava flow (expect thin sheet May be covered area up to 1-4 Moderate potential ERUPTION STYLE in pahoehoe) km2 and fluid pahoehoe could for loss of life but “narrow graben-like advance rapid downhill at >10 property and crater” and “pit-crater” m/sec. farmland would be destroyed Volcanic ash (produce great Wide spread tephra may be >5 volume-Pele’s tears) km radius Volcanic bomb Thrown out about 0.5-3 km) from the vent Ballistic ejecta (5-20 cm in Scatter around the crater and diameter) down the slope (>100 m from the vent) Pyroclastic flow Cover area down the slope about < 1km from the vent Forest fire Cover area (<1km radius) PHREATOMAGMATIC Lava flow (expected thin sheet May be produce narrow tongue Moderate-low PHASE of “maar- pahoehoe) of flow (<1km), fluid pahoehoe potential for loss of forming eruption” advance dowhill in the great life but damage in speed >10 m/sec. property and farmland. Volcanic ash (lapilli) Cover area about 3 km radius Volcanic bomb (cauliflower bomb May be spread about 500 m and ballistic fragments) radius but cauliflower bomb dominate area around the vent Pyroclastic base surge Occurs within 2 km of the vent, it can travel >32 km/hr downslope Forest fire Cover area (<1km radius)

Narrow graben-like eruption outpoured great volumes of lava to the southeast of the crater during tephra bed-1 eruption episode. At this stage of the eruption, it is associated 230 with low explosiveness as the gases escape before the basaltic magma reaches the surface (Kear and Wood, 1959; Cronin et al., 2006). In other words, the low silica content of the Samoan basalt gives the magma a low viscosity allowing gas bubbles to expand easily and escape resulting in effusive activities. Fluid lava travelling down a steep volcano like Crater Lanoto could be a hazard in the future. Postulated lava flows could extend further south along the Sinoi valley, toward Saleapaga village by a few kilometres but the area is entirely blanketed by eroded soil and slump materials. The geological map by Kear and Wood (1959) does not show any extension of the Mulifanua lava to the south of Crater Lake Lanoto toward Saleapaga and Lepa village. However, boulders dominating the surface suggested are part of the Mulifanua Formation, meaning that Lanoto lava may have reached this point or may be further toward the coast.

The pit-crater activity had a lava-fountain style, producing a great volume of lava during the tephra bed-2 episode, but perhaps not during tephra bed-3 and 4. These eruption episodes are associated with several explosive activities as the northwestern part of the narrow graben widened and extended and possibly resulted in tension/stress from local faults and the major fissure system. The Hawaiian eruption style could generate a massive forest fire of up to >2 km in radius during narrow-graben and pit-crater activities.

Despite the degree of fragmentation being fairly poor, the Crater Lanoto became explosive (Strombolian stage) through volatile degassing (Parfitt and Wilson 1995; Suckale, et al., 2010). Greater acceleration of the ascending magma triggers, as the expansion of dissolves volatile turn into bubbles, a reduction in the magma density (Kereszturi and Nemeth, 2013). This is a stage where the bubbles start to overtake the rising magma and form coalescences, resulting in explosive Strombolian style activities (Parfitt, 2004).

If the bubble growth is controlled by coalescence in the basaltic magma, then bubbles could grow to more than 1 metre in diameter (Carey, 2005; Parfitt, 2009; Suckale et al., 2010). Hence, the Strombolian activity of Crater Lanoto could be associated with a burst of several large bubbles near the surface, also labelled by Cronin et al. (2001; 2010) as

231 dry explosive. Suckale et al. (2010) also suggested that Strombolian eruptions are triggered by rapid ascent of the gas slug with speeds of up to 10-70 m/sec. Parfitt (2004) stated that cooling at the top of the rising magma column would develop a “skin”. A short interval between the arrival of bubbles would trigger an updoming of the “skin” which would then burst, whilst a longer interval between the development of giant bubbles would allow the “skin” to cool and thicken. At this point a number of arrival bubbles may cause them to trap together and generate sufficient pressure to break through the “skin”. A continuation of the cooling mechanism and gas accumulation at the top of the rising magma of the Lanoto volcano could produce a series of transient explosions.

Strombolian eruptions usually last from few seconds to several hours (Vergniolle and Brandeis, 1996; Parfitt, 2004). Volcanic bombs range from 2-5 cm long by 3 cm in diameter, as observed in the welded pyroclastic deposit matrix to the southwest. In addition, several bombs 2-3 cm long and 1-2 cm wide occur at the eastern and southern part of the outer rim wall. The presence of volcanic bombs in several sections of pit- crater and narrow graben-like crater, together with Pele’s tears are evidence of explosions. This supports the idea that the melt was relatively degassed and large bubbles outburst, propelling degassed melt fragments out from the vent during Strombolian style fragmentation (Parfitt and Wilson 1995; Mastin et al., 2004; Carey, 2005).

Eruption materials show that the Crater Lanoto volcano erupted from Strombolian to Hawaiian style or vice versa, known as “transitional eruption” (Parfitt, 2004). This “transitional eruption” is associated with a change in the speed of the rising magma from 0.01 to 0.1 ms-1 (Parfitt and Wilson, 1995). Based on the Etna eruption (1989), Parfitt and Wilson (1995) described that the transitional stage represents the change from a widely spaced to more frequent Strombolian explosion. The Strombolian activities rapidly increase in violence and eject clasts much higher during transitional stage before the subsequent lava fountain style starts to emerge.

The maar-forming eruption of the phreatomagmatic phase of the Crater Lanoto volcano could have occurred during tephra bed-2, 3 and 4 activities. Maar-forming eruptions are associated with juvenile lapilli tuff, several cauliflower bombs and ballistics fragments

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(discussed in Section 2.7) propelled out from an explosive phreatomagmatic stage. A mixture of deep rock fragments and shallow fragments could indicate the explosion phase may have occurred at some depths during pit-crater activities (Lorenz, 2003). Additionally, this explosive stage could be also contributed to the extension of the pit- crtater. Cronin et al. (2006) stated that the phreatomagmatic and high explosive activity (like Strombolian) perhaps disperses the volcanic ash within 3 to 5 km radius. Strombolian generally ejects clasts in a speed ranging between 50 and 100 ms-1 (Parfitt, 2004), and the phreatomagtic phase could have had a similar impact.

Limited exposure and thick soil makes it impossible to trace evidence of the pyroclastic base surge during the phreatomagmatic phase, but surely these features are expected to be associated with Lanoto volcano activities. It is a combination of radial blast of rock debris, hot steam and gaseous, travelling at great speeds of up to 300 km/hr, which could reach 2 km away from the vent (Carey, 2005). This may be associated with pyroclastic deposits on the western slope of the volcano. The phreatomagmatic phase and Strombolian activity may both have produced forest fires within a radius of up to < 1 km rduring narrow graben and pit-crater eruptions.

Figure 4.54 shows the volcanic ash dispersal during activities of the Crater Lanoto. The yellow circle represents the low explosivity episode whilst the red circle denotes violent activities. The wide yellow arrow represents the lava flow direction. Presumably, this widespread volcanic ash mostly covered the nearby villages of Saleapaga and Lepa to the south. However, a great pressure underneath the Crater Lanoto volcano would have extended volcanic ash over a wider area, possibly 5 km in radius during the pit-crater activities, as indicated by the big red circle. The volcanic ash would blanket the entire villages to the easternmost end of the Fagaloa Bay communities, to the north and the western side toward the village of Vavau. The worst case scenario would be if simultaneous activities occurred at this part of the island; in this case, volcanic ash could have dispersed much further toward the west than predicted, covering a broad area along the south and north coast of Upolu. This could explain the presence of contaminant tephra components in the Crater Lanoto basin.

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Pyroclastic deposits show evidence of hot emplacement, as indicated by welded volcanic material resting at the foot of the volcano. These deposits dominated the western and eastern part of the crater. The pyroclastic flow from a steep-sided volcano like Crater Lanoto would represent a high risk in the near future as residential areas are continuing to extend toward the foot of the volcano. Pyroclastic flows could cover an area less than 1 km from the vent, during Hawaiian and Strombolian eruptions from both the narrow graben-like crater and the pit-crater (Table 4.9).

Based on the ejecta and the volume of lava examined in the Crater Lanoto and a comparison between them and those on Savai’i (Cronin et al., 2006), it is estimated that the eruption could have lasted for weeks, month or even years.

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4.7.3.4 Holocene bush fire hazards on the easternmost part of Upolu

Aside from other causes that could have destroyed vegetation (discussed in Section 4.7.1.2), the presence of charcoal fragments in all four layers that represent major episodes (tephra bed-1, 2, 3 and 4) implies the occurrence of bush fires associated with each interval of volcanic activity. Bush fires are the most dangerous and common volcanic hazard associated with the Samoan volcanic activity in the near future. Eyewitness during the Matavanu 1905-1911, Mauga Mu and Mata-ole-afi, 1902 eruption (central western part of Savai’i) described that the accompanying massive forest fires (> 8 km2) destroyed more areas than the erupted material.

The effects of simultaneous eruptions could have extended further west or east along the Upolu Major Fissure System (UMFS), possibly generating massive bush fires during Holocene time. This is supported by the presence of contaminant tephra in the tephra layers of the four major eruptive episodes of Lanoto volcano, including the tephra bed-4; however, it is still unknown at this stage how widespread was the simultaneous style activity.

Holocene bush fires could have extended to the central part of Upolu that corresponds with a Fagali’i charcoal deposit dated at 3.4-3.2 ka, along the north coast, east of Apia (Williams, 2014). This suggests that bush fire could have been triggered from the eruption of the Mauga Fito at the central part of Upolu (Figure 2.8 and 2.10a). Kear and Wood (1959) classified Mauga Fito as a part of Puapua Formation activity. However, a narrow strip of Puapua lava from the Mauga Fito eruption which travelled via a long lava tunnel is exposed along the Alaoa stream (south of Apia) and Lauli’i (east of Apia) and looks older. Based on its physical appearance, this particular lava suite could be Lefaga Formation in age, equivalent to the 3.4 kyr-old tephra bed-4 eruption episode. If this is the case, the simultaneous style activity could have extended further west about > 20 km from the Crater Lanoto volcano during Holocene time. This typical eruption behaviour of the monogenetic volcanism field still needs more work to obtain a better understanding of possible future eruptions.

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4.7.3.5 Summary of critical points from volcanic hazards of the Crater Lanoto

(i) Evidence of human occupation in the Crater Lake Lanoto sediment is still unclear;

(ii) Indigenous knowledge informs us about how the first human settler classified volcano eruption activities;

(iii)The eruption intervals of the Crater Lanoto volcano fall in the long-range category, but this may be an underestimation due to lack of radiometric dating;

(iv) Holocene to Present eruption fall in medium range interval and short-range interval, but still needs more dates;

(v) Crater Lanoto volcano erupted from three eruption styles: Hawaiian lava-fountain, Strombolian and Phreatomagmatic phase;

(vi) Wide dispersal of tephra from explosive stages of the Crate Lanoto can be up to 5 km in radius;

(vii) Explosiveness of the Crater Lanoto volcano depends on the amount of dissolved volatiles and the interaction of the hot magma with cold maar lake.

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4.7.4 PART 4: MONOGENETIC PROCESS OF THE LANOTO VOLCANO

This section presents varies aspect of the monogenetic processes occurring in the Crater Lanoto. These include:

1. A discussion of whether the Crater Lanoto is monogenetic or polygenetic;

2. An outline of the distribution of monogenetic processes occurring in Samoa;

3. Discussion of the tectonics involved in the monogenetic process;

4. The feeder dyke concept models as a means of calculating the effusive emplacement of Crater Lanoto. This would determine the risk associated with lava flow of this typical monogenetic volcano;

5. Comparison of the Crater Lanoto volcanic features to determine the widespread monogenetic activities on the main islands enables, to construct a potential vent for future prediction.

4.7.4.1 What is the monogenetic and polygenetic volcano?

Monogenetic and polygenetic activities are difficult to classify because of a lack of radiometric dates of individual cones. Like many other monogenetic cones scattered along the main islands, the Crater Lanoto is a fairly small volcano with an effusive volume of 0.00324 km3. Even generous assessments of potential ash and effusive products would still make it difficult to envisage the volume being greater than 1 km3. This volume plus the general volcanic landform aspects help to categorise the Crater Lanoto volcano as a typical monogenetic volcano, a scoria cone with, perhaps, some affinity to spatter cones. It might have erupted through a fissure, perhaps in a few repeated phases, but through a simple plumbing/conduit system. It may be part of a large fissure network that erupted simultaneously along the dorsal ridge, but more data would be required in order to support or refute this idea.

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Kereszturi and Nemeth (2013) and Blake et al. (2006) distinguished the two types (monogenetic and polygenetic) in term of magma volumetrics. Monogenetic eruptions are fed from a small volume of ascent magma of about ≤ 1 km3. Those from polygenetic activities derived from multiple ascending magma of ≥ 1 km3. The multiple conduit system (dyke network) uses the same network over thousands or million years.

Crater Lanoto is made up of the products of four main eruption episodes (tephra bed-1, 2, 3 and 4). Based on the ejectas and the volume of lava emits from every episode they are characterised by short term eruptions. Crater Lanoto activities suggest generated from the single injection of new or the same feeder dyke, which could have repeated over thousands of years. This may be described as a “polymagmatic simple monogentic volcano” in the theorectical monogenetic-polygenetic model of Nemeth and Kereszturi (2015).

Figure 4.55 outlines the monogenetic and polygenetic activities in the Samoa Volcanic Field. The monogenetic and polygenetic activities are comprised of single and multiple injections, respectively. Sheth and Canon-Tapia (2014) refer to “single” and “multiple injections” as feeder dyke networks, which generate monogenetic and polygenetic volcanoes. Feeder dykes refer to those reach the surface. Both “single” and “multiple injections” are subdivided into two parts: new and old feeder dykes. New and old feeder dyke of the single injection could produce either a new monogentic or compound monogenetic phase of small and large volume volcanoes. Similarly, in the case of multiple injections, a new and repeated-polygenetic phase would be formed (Figure 4.55). A combination of new and repeated-monogenetic or polygenetic activity which overlap each other or emerge from the same volcanic rim would be product of “compound monogentic” or “compound polygenetic”.

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FIGURE 4.55 Flow diagram simplifies the monogenetic and polygenetic eruption activities in Upolu and Savai’i.

Polygenetic activity in Western Samoa is referred as the shield volcanism of the Fagaloa Formation, which is well exposed on the northeast Upolu. The area is comprised of the broad dyke networks (Fepuleai, 1992) and it previously mentioned as the Fagaloa caldera (Natland, 1980; Hawkins, 1987; Keating, 1992). It is suggested that maybe the Fagaloa caldera fits perfectly into the term “compound polygenetic volcano” outlined in the Nemeth and Kereszturi (2015).

The Fagaloa Intrusions are non-porphyritic, fine-grained and medium- to coarse-grained porphyritic dykes (Fepuleai, 1997). These igneous intrusions are strongly oriented in a northwest to southeast direction and parallel to the Upolu Major Fissure System (Fepuleai, 1997). A massive porphyritic dyke known as the Lemafa Intrusion, radiates out and dominates the northeast Upolu. This massive intrusion is a part of the Upper Fagaloa Formation.

The presence of the multiple feeder dykes in the Fagaloa Formation classifies shows it was generated from polygenetic processes. However, the scarcity of dykes in the post- Fagaloa Formation (Aopo, Puapua, Lefaga, Mulifanua and Salani) put those into the monogenetic category. The Fagaloa lava suite on the northeast Upolu has an eruptive volume of approximately > 6 km3. This is much greater than several large-volume

239 monogenetic eruptions in the South and North Island of New Zealand (Kaulfuss et al., 2012; Kereszturi and Nemeth, 2013; Nemeth and Kereszturi, 2015). Hence, the Fagaloa lava of the northeast Upolu may be classified as polygenetic origin.

Additionally, the geochemistry of dykes indicates variations in major and trace elements (Fepuleai, 1997; Cibik, 1999). This corresponds with the fact that the Fagaloa Formation caldera consists of multiple injections from the feeder dyke networks.

4.7.4.2 Distribution of the monogenetic volcanoes in Samoa

Interpretation of aerial photographs and fieldwork observation allow us estimate that there are at least 153 monogenetic cones observed in Savai’i and more than 57 in Upolu. Long term and short term monogenetic types were classified based on the volume of emitted lava. Polygenetic volcanoes only crop-out to the northeast of Upolu as previously mentioned. Like the Crater Lanoto the short and long term monogenetic volcanic activity on Upolu and Savai’i could be all classified in term of a compound monogenetic origin. However, more work is needed to support this conclusion.

Figure 4.56 shows the monogenetic and polygenetic eruption centres on Upolu Island. The short term monogenetic volcano of the Crater Lanoto is flanked by long and short term monogenetic volcanoes of the Salani and Mulifanua Formations. The alignment of monogenetic cones is shadowed by the polygenetic Fagaloa caldera to the northwest. The long term monogenetic centres of the Salani Formation dominated the central part of Upolu. The Mulifanua Formation has long term monogenetic activities, which commonly occurred at the eastern part of the island. Tafua-upolu and Mount Fito are short term monogenetic types associated with the Puapua Formation, and it is suggested that these eruptions were witnessed by many human occupants during the Holocene. The Vini Tuff activities occurred in the islands at the eastern part of Upolu together with Apolima and Manono are all parts of the short term monogenetic eruption.

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Figure 4.57 shows the monogenetic eruption centre of Savai’i Island. Short- and long term monogenetic eruptions associated with the Mulifanua and Puapua Formations dominated the western half of the island. Several monogenetic activities of the Mulifanua Formation erupted from octuple or nonuple craters. These multiple craters are parts of a single volcano edifice, commonly occurring in the central part of Savai’i, to the east and west of Mauga Afi craters. The Aopo Formation erupted from series of long and short term monogenetic activities. Those on the eastern half of the island are mainly short- and long-term monogenetic activities associated with the Salani Formation and Puapua Formation.

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4.7.4.3 Tectonic movement along the Crater Lanoto volcanic line

It is suggested that the transition from one eruption activity to another (eg. tephra bed-1 to tephra bed-2) could correspond with the most significant break in eruptions as the subsequent magma erupted at new site to the west. This western vent migration could be related to the eruption of several magmas from different dyke systems (Sohn et al., 2012). Additionally, the migration may be also triggered by a solidified residual magma at shallow depth within the magma tube which blocked a path for the next magma batch.

Satellite images from Google Earth imply the western motion of a volcanic trace at the central easternmost part of Upolu. Figure 4.58 shows physical evidence of the western movement along the central main fissures. The green arrow indicates the motion direction. The trail of motion occurs mainly on western part of the Crater Lake Lanoto, 242

Crater Lano-o-lepa, Crater Lake Olomaga, Crater Olomauga, Crater Lanotai and Crater Lano’omoa. Crater Fili, Crater Mauga-o-savaii and Crater Tialata further west are the single cones which could be all parts of the western motion. It seems the younger vent is always on the western part of the older one at the easternmost part of Upolu (Figure 4.58). The age among the vents of an individual crater was determined from aerial photographs and their physical characteristics. The westward movement trail is known as a “western-slide motion mechanism” (WSMM) in this study. Natland (2003) referred to a tapping mechanism. This occurs as the Samoan lithosphere allows heterogeneous enriched lavas to seep in multiple centres and erupt through many fractures. The WSMM process suggests it may have been the main driver of the cone collapse event. This could be the main reason for assuming that the CCE occurred globally rather than locally.

FIGURE 4.58 Google Earth image shows the western-slide motion mechanism (yellow arrow) trail, expose along the Crater Lake Lanoto, Crater Olomauga, Crater Lanotai, Crater Lano’omoa, Crater Lano-o- lepa and Crater Lake Olomaga. Crater Fili, Crater Tialata and Crater Mauga-o-savaii are single cones, which all part of the monogenetic-polygenetic process.

The age of the WSMM is difficult to determine in the Crater Lanoto volcanic. However, the inner rim lava of argon age of 144 Ka generates from the western portion of the crater implying that, the WSMM process was active during this time. This shows that the WSMM could have be much older than expected.

The earliest monogenetic activity of the Crater Lanoto thought was initiated at the Crater Fili (Figure 2.17 and 4.58) to the southeast before the locus of volcanism (eruption

243 centre) shifted to west through the WSMM process. If the eruption centre shifted to the west and erupted as the tephra bed-1 around 200 ka then this means that the WSMM moved about 0.1 cm per year. The deeper part of the lake is considered to be the tephra bed-2 eruption centre with respect to the WSMM process. This implies that the monogenetic activities shifted to the west about 100 m at 144 ka yielding a speed of the WSMM of approximately 0.07 cm per year. George Island (Figure 4.1) may represent the “intra-crater spatter/scoria cone” outlined in the maar-diatreme volcano model of the Nemeth and Keresturi (2015). The island could be part of the WSMM process during tephra bed-3 and tephra bed-4 episodes after the cone collapse event. If the locus of the two episodes of volcanism shifted to the west about 60 m at 22.3 ka and 3.4 ka then the WSMM has a speed of 0.27 and 1.8 cm per year, respectively.

Lavas from Crater Fili were also not available for XRF analysis; however, their physical characteristics indicate a highly weathered volcanic cone, which is olivine and pyroxene dominated, like the outer rim lava. This suggests that Crater Fili could also be derived from a deep picritic magma source. Hence, the shift of the eruption centre through WSMM processes from Crater Fili to the west (outer rim lava episode) could be slightly, or not at all, influenced by the deep picritic source. However, based on the XRF and ICPMS plots, the WSMM triggered the risen of the deep mantle (picritic source) to the shallow level (basanitic source), which generated the inner rim lava.

Fepuleai (1997) described something similar in terms of a deep alkaline source (Lower Fagaloa Formation) to shallow tholeiitic and hawaiite suites (Upper Fagaloa). The WSMM was also responsible in the re-eruption of the tephra bed-3 and tephra bed-4 from the deep picritic source during the emplacement of the Mulifanua to Lefaga Formation. This reveals that the WSMM process could be associated with the eruption activities of the six volcanic formations of Western Samoa.

In addition, the change in magmatic source level deep underneath Samoa through the WSMM could be also accountable for the isotopic variations along the island chain. This assumption paralleled with the lithospheric cracking model of Natland (2003), where post-erosional volcanism erupted simultaneously from multiple centres.

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The WSMM is parallel with the western Pacific Plate motion, implying a lithospheric- control. This relationship is based on the close location of the Samoan island chain to the sharp bend (NT) of the Pacific Plate. The WSMM seems to moves opposite to the eastward motion of the mantle, as determined from the asymmetries of plate tectonic features during global polarized motion of the lithosphere (Doglioni et al., 2015). The velocity of the WSMM (0.07 cm/yr) does not match the 7.1 cm per year speed of the western motion of the Pacific Plate. This indicates that the least principle stress (Pacific Plate motion) could not be the only dynamism of the WSMM. However, Natland (1980; 2003) describes that extending of the post-Fagaloa activities along the central rift is associated with the sideways bend of the Pacific Plate. Tension stresses across the bend generates an orthogonal rift system. The orthogonal rift system of Savai’i is controlled by the length and width of the island. Lithospheric stress is the main drive associated with the widening and lengthening of the central rift zone.

In addition, Doglioni and Panza (2015) and Doglioni et al. (2015) stated that the polarized western plate motions across the six major plate boundaries from Indian ridge across the Pacific to the Mid-Atlantic ridge indicate that the lithospheric plates move along a mainstream known as “tectonic equator” from millions of years ago, and continue to present. Doglioni (1990) interpreted that heterogeneities in both the lithosphere and in mantle could be a part of a differential angular velocity induced by deceleration of the earth’s rotation during the westward motion of plates. As previously mentioned, Koppers et al. (2011) also outlined that variations in the speed of the Pacific Plate from 9 cm/yr (13-5 Ma) to 7.1 cm/yr (5 Ma to present) per year could have contributed to the formation of the post-erosional volcanism. Hence, the polarized plate tectonic west-motion process together with variations in the Pacific Plate speed could be all major factors driving the WSMM activity.

Based on field observations, the monogenetic activities on the easternmost part of Upolu may be comprised of two main parts: the “early and late monogenetic phase”. Figure 4.59 shows a model of the “early monogenetic phase” at the eastern most part of Upolu.

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During an early monogenetic phase, the tension stress associated with the WSMM allows a pressurised magma source deeper in the lithosphere to ascend through feeder dyke networks. The monogenetic activity of Samoa is referred to as tectonically controlled volcanism, where tectonic shear forces extract the melts (Kereszuri and Nemeth, 2013) from the heterogeneous source along the Samoa Volcanic Field (Natland, 2003). These melts could be accommodated in storage batches at different levels approximately 90-100 km beneath Upolu whilst Savai’i has depths ranging from 75 to 95 km (Cibik, 1999). The presence of storage chambers at different levels could also help explain isotopic variations in the post-erosional lava as discussed in Section 2.3.3.

Picritic and basanitic/basaltic sources of the inner rim lava suites derive from difference magma batch levels (deep and shallow, respectively). This shows that there is a “transition process” amongst the magma batches, i.e. a shift from a lower to the upper level source or vice versa, during the same eruption episode. However, more work is needed to improve our understanding of the nature of this “transition process”. It is suggested that if the “transition process” had succeeded it would have triggered large- volume monogenetic activity but, if it had not, then short-lived or low volume monogenetic activity would have been the outcome. This corresponds to the fact that the eruptive volume of the tectonically controlled volcanism may not only be dependent on the size of the magma batch, but also associates with the success of the transition process. Additionally, those magma batches that fail in the “trasition process” could move west through WSMM and erupt from new feeder dykes via either low or large volume monogentic activity (Figure 4.60). The transition process may correspond with different fractionation depths, results in geochemical signature variation of Samoan lava, through lithospheric tapping system, described in Cibik (1999).

The ascending magma seeped through a cracking and tapping mechanism network to the weakest part of the central ridge, and yielded multiple centres of low and large monogenetic eruption. Low eruptive volume monogenetic with short-lived activities dominated (e.g., Crater Lanoto and Crater Olomauga), generating ≤ 0.004 km3 of lava, whilst those with large volumes (eg. Tafua-savaii and Matavanu) may have produced ≥ 0.6 km3 (Table 2.1). The tephra bed-1 episode is referred as the early monogenetic phase

246 of the Crater Lanoto, derived from a single injection. There is a possibility that an arrested feeder dyke network developed during the early monogenetic stage. Arrested dykes are those terminated at depth (Sheth and Canon-Tapia, 2014). This could be due to a smaller volume of injection magma or the fact that there is no continuity in the crack networks at certain depths.

Figure 4.60 displays the “late monogenetic phase” of the easternmost part of Upolu. The late monogenetic phase represents a continuation of the WSMM process. An increase in tension stress at the sharp bend (NT) of the Pacific Plate (Natland, 1980; 2003) suggests that it is the major driver of the WSMM process. There are two significant features of the WSMM continuity. Firstly, the birth of a single or “multiple monogenetic cones” to the west of older cones through feeder dykes is a result of compound monogenetic activity. These multiple cones result as the acending magma is not always generated in a single batch, but commonly produces “multiple tapping” known as multiple magma batches (Kereszuri and Nemeth, 2013). Maimoaga vents (Figure 2.17) along the northern slope

247 could be characterised as part of the “multiple monogenetic cone” (Figure 4.60). The Crater Lanoto is referred to as an old compound monogenetic volcano (Pelistocene – Holocene), whilst the Tafua-savai’i volcano is a good example of a young compound monogenetic (Holocene).

Secondly, re-eruptions of the older cones (low and large volume monogenetic) may have occurred along the central rift. Feeder and arrested dyke networks increase at this stage correspond with the increase in WSMM activities. Tephra bed-2 eruption episode represents the pit-crater eruption at the deepest part of the lake, as the eruption centre shifted to the west of the tephra bed-1 cone. It suggests that the tephra bed-2 episode occurs at the “late monogenetic phase” (Figure 4.60), associated with an increase in WSMM activities triggered the shifted of the volcanic locus to the west. This is where the feeder dyke could be repetitively activated along the same central rift plane, as also discussed in Section 4.7.5 (ii) as follow. This could have also triggered the eruption of the tephra bed-3 & 4 at the George Island location represent the final stage of the late monogenetic phase of the Crater Lanoto volcano.

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4.7.4.4 Feeder dyke model of the Crater Lanoto Volcano

The feeder dyke concept model is used in this study to determine the effusive emplacement of the Crater Lanoto. These calculations may be significant to the volcanic predictions in the near future. There are no signs of exposed feeder dykes in the study site; however, dyke dimension from Fagaloa caldera (northwest of the Crater Lanoto) were recalled for this study (Fepuleai, 1997). Major and trace elements of the Fagaloa dykes and the Crater Lanoto lava suites are similar, thus justifying the recalling of these data. The Fagaloa dykes are ranging from 0.1 to 30 metres in width.

There were few Crater Lanoto “dummy” dykes with similar widths and lengths to those of the Fagaloa intrusions. The silicate melt density of the Fagaloa and Crater Lanoto volcano can be determined from thermodynamic properties and major element

249 composition of their lava suites. This would give some indication of the effusive emplacement nature of the Crater Lanoto volcano and it details in Section (iii) as follows.

The concept model is based, on the Auckland Volcanic Field model of Blake et al (2006). This model is considered the vertical propagation of the feeder dyke but not lateral emplacement. In addition, the model will enable consideration of the timing of the ascending magma as it reaches the surface during activities of the typical compound monogenetic volcano like Lanoto volcano.

Some of the significant parameters considered in this model such as: flow rate of the dyke, width of the dyke, length of the dyke, velocity of the flow, the flow travel mode (vertical or horizontal), viscosity, pressure (hydrostatic, viscous & extension), elastic force, density (solid and silicate melt), and dimension of the crack.

This section is divided into five main parts:

1. An outline of the theory of propagation of feeder dyke from deeper source; 2. Consideration of several parameters (width, length, speed, flow rate & time) versus the distance above source; 3. Determination of a deeper source; 4. Determination of a near surface flow; 5. Model interpretation in relation to the volcano prediction.

(i) Propagation of feeder dyke from deeper sources

Consider that a melt source in at the upper part of the asthenosphere rises through the brittle cold rock of the Samoan lithosphere. This melt source might accommodate a storage chamber of magma for some time (Lister, 1990). As the storage chamber became filled from the main source, pressure within the magma chamber would be elevated. This would generate a fracture network in the chamber wall, allowing the dense melt to escape through a network of new feeder dykes network. The magma fracture is a means by which allows the deeper source to advance through the network of open cracks within the lithosphere (Lister, 1990; Lister and Kerr, 1991).

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It is proposed that the melt generates at the upper part of the mantle is less dense than the surrounding rock (Lister, 1990; Lister & Kerr, 1991). In this case, the melt would rise and collect at the base of the lithosphere. In term of hydrostatic pressure if the density of the magma (pm) is equal or has a gravitational equilibrium with the host rock (pr), then “neutral buoyancy” would be the resulted. Put simply if the magma has a lower density than the host rock (pr>pm) it would ascend whilst a magma with greater (pr

Figure 4.61 shows a plan view of the ascent dyke in a form of half-elliptical shaped model with a closed lower tip but one which is open at the upper tip (from Lister, 1990; Lister and Kerr, 1991, figure 1 & figure 11 respectively). The model considers the dyke has half length (2b) and half width (2w). This dyke propagates upward from deeper down the lithosphere, under buoyancy fluid regime of density (pm) with viscosity (n), injects through cold country rock of elastic modulus (m).

Lister and Kerr (1991) suggested that if the dyke does not close at the lower tip, then internal pressure, (∆Po) and hydrostatic pressure, (∆Ph) are perhaps comparable. However if it is closed at the lower tip, it must have an internal pressure less than three factors:(1) a gravitational variation (2) pressure among the surrounding rock and (3) the melt pressure. This would allow the dyke to ascent as the internal pressure is less than the surrounding rock. The fact that dykes do not propagate with their upper tips closed suggests that the combination of the internal pressure with the hydrostatic pressure (∆Po

+ ∆Ph), must be less than those of the fracture extensive pressure ∆Pf.

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Lister (1990) experimentally determined that the lateral spread of magma would be generated if it is denser than the overlying rock but less dense than the underlying rock. Figure 4.62 shows the lateral spread of the magma in a form of a half-elliptical shaped model with a closed front tip (from Lister, 1990, figure 1; Lister and Kerr, 1991, figure 1). This magma would accommodate at a zone known as a “level of neutral buoyancy”

(LNB) (Lister, 1991). At the LNB (z=0) the magma descend if the density (pm) is greater than the density (p) of overlying rock but ascend if less than the underlying rock. The LNB is a region, where the feeder dyke becomes widened and magma is emplaced laterally, through either dyke or sill (Lister, 1990; Lister and Kerr, 1991). The pressure of an inflated magma at the LNB, could be deflated through the network, of fractures propagate along the zone. This relief in magma pressure produces an interconnection, between dykes and sills (Lister, 1990; Lister and Kerr, 1991).

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Stability between the two factors (viscous and elastic pressure) would trigger the vertical motion of dykes (Lister and Kerr, 1991). Those that spread laterally at the LNB region are an outcome of cross-stream variation in elastic force without thin thermal boundary (Lister and Kerr, 1991).

The magma flows in two fashion regimes, laminar and turbulent. Turbulent flow would be formed if the magmatic viscosity significantly drops. Laminar flow is consistent with high intensity (Lister and Kerr, 1991).

In terms of the fluid mechanics of material with variable density like those of gases and fluids of variable viscosity, they can be calculated by using the Reynolds Number. The Reynold Number is defined as a ratio between “inertial forces” versus viscous forces”. This can be expressed by the equation Re = pVL / u, where p = density, V = velocity and u = viscosity (Lister, 1990; Lister and Kerr, 1991). If the Reynolds Number of a fluid is less than 103 (Re = pVL / u < 103) laminar flow occur where viscous forces would dominate. However, if the Reynolds Number is greater than104 (Re = pVL / u > 104), then should be turbulent flow with inertia forces dominate (Lister, 1990; Lister & Kerr,

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1991). The turbulent flow produce a flow separation mechanism. This generates drag forces behind a major magma injection, which causes a pipe of magma along the transport dyke to be separated, while still in vertical motion (Lister & Kerr, 1991).

(ii) Determine the deeper source

Fracture toughness of the lithosphere underneath the Crater Lanoto could influence the dimensions, speed, flow rate and the time of the ascend feeder dyke. A stress intensity factor coefficient (K) of the lithospheric crack is only extending slowly in association with chemical corrosion. This will be only if the fracture toughness (Kc) of surrounding rock is much greater (Irwin, 1958; Lawn & Wilshaw, 1975). However if the pressure within the magma increases, then the stress intensity factor coefficient exceeds the fracture toughness, and would trigger the crack to propagate faster than the magma (Lister and Kerr, 1991).

To determine the deeper source let us assume that the Crater Lanoto and Fagaloa have feeder dyke of low viscosity (n) with density (pm) less than the surrounding lithospheric density (Δp). The feeder dyke ascends from the deeper source (z) through cold country of elastic modulus (m) with acceleration due to gravity (g). The width of the dyke (w), average speed (b), flow rate (Q) and time to reach the surface (t) will vary throughout certain distances (z).

Let us recall the half-elliptical shaped model (Figure 4.61) and consider the half width of the dyke (w) is defined by the Equation-1, half-length (b) is expressed by Equation-2, average rise speed at height (z)is defined by Equation-3 and time to reach the height z (t)is expressed by Equation-4.

Equation-1: w = 0.904 [Q3 n3 / (m (g Δp) 2 z)]1/10(Eq-36 of Lister & Kerr, 1991), where w=width of the dyke, Q=flow rate, n=viscosity, m=modulus, g=gravity, Δp=lithospheric density and z=height (source).

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Equation-2: b = 2.62 [Q n m3 z3 / (g Δp)4] (Eq-38a of Lister & Kerr, 1991), where b=half length of the dyke, Q=flow rate, n=viscosity, m=modulus, g=gravity, Δp=lithospheric density and z=height (source).

3 3 2 1/5 Equation-3: uz ~ Q / (bw) ~ (Q (g Δp) / n m z) (Eq-3 of Blake et al, 2006), where u=average of the height z, w=width of the dyke, Q=flow rate, n=viscosity, m=modulus, g=gravity, Δp=lithospheric density and z=height (source).

Equation-4: t = 5 z / 6 uz (Eq-4 of Blake et al, 2006), where t= time, u=initial speed and z=height (source).

Input parameters for the model obtain from several sources. The escape melt with a viscosity (n), calculated from anhydrous silicate liquids at “1 atmosphere pressure”. Measurements are based on the experimental calculation of Botting and Weill (1972). The viscosity was determined from the silica content of the Fagaloa Formation dykes and lava of the Crater Lanoto versus log viscosity. These measurements were based on the 1200oC and 1400oC temperature of the magma. Laboratory results indicates that the majority of dyke sand lava flows have a low viscosity, range from 0.2 (poise) to 1.10 (poise) with temperature of 1400oC. Only a very few measurement falls between 2.90 and 2.89 (poise) at the 1200oC level.

The feeder dyke model is also used the same parameters as those of the Blake et al (2006) used by several oceanic basalt models. These include the density (Δp = 300 kg m-3), modulus (m = 20-50 GPa) and volumetric flow rate Q = 102 m3 s-1, from an experimental outcome of Lister & Kerr (1991) and Ruin (1995).

Figure 4.63 shows the distance above the source versus dyke dimensions (width, length, average rise speed, flow rate and time) of the Crater Lanoto feeder and the Fagaloa dykes. The length of the Crater Lanoto and Fagaloa Formation feeder dykes represented by straight line indicates that dyke lengths were unchanged since ascent from the source. The width of several Fagaloa feeder dykes seems suddenly narrow at the first 10 km from the source and then consistent with those of the Crater Lanoto until between 90 and 100 km, where few Fagaloa dykes suddenly became narrower. The average speed and flow

255 rate of the feeder dykes are both suddenly drop at the first 10 km before gradually fall throughout the 100 km distance. The Fagaloa feeder dykes quickly ascend until the 10 km where gradually slow like those of the Crater Lanoto as further away from the source.

FIGURE 4.63 The distance above the source versus the dyke dimension (width and length), speed, flow- rates and time (days). Fagaloa Formation dykes (red, green, dark blue, light blue and purple) plot with those of Crater Lanoto in oval (Modified from Blake et al, 2006).

(iii) Near-surface feeder dykes

To determine the near surface feeder dykes of Crater Lanoto and Fagaloa, let us assume that the density (p) of the feeder dyke lower than the surrounding rock. This would allow the basaltic feeder dyke to rise at certain depths into two fashion regimes, laminar and turbulent. The nature of the two flows would depend on the Reynold Number (Re) where the “Re” of the Crater Lanoto/Fagaloa is defined as 103 > Re < 104.

The solid density (p) of the Crater Lanoto / Fagaloa dykes determined from Murase and McBirney (1973) laboratory measurements are expressed as; p = M / V (where M=Mass and V=volume). The silicate melt density, calculated from the thermodynamic properties

256 of silicates, at high temperature and high pressures, represent by the expression as followed (Murase & McBirney, 1973);

Where i=oxide, N= total number of oxide, Xi=the mole fraction of oxides, Mi=molecular mass of the oxide, Vi= the fraction volume of oxide.

Let us consider that the basaltic feeder dyke of the Crater Lanoto/Fagaloa has the Re = D u p/n < 1.3 x 103 then the average length at the height “z” will be expressed in Equation- 5. But if the 6 x 103< Re < 6 x 105, then the average length at the height “z” will be defined by Equation-6. The Equation (5 & 6) of this model is referred to Equation (8 and 9) of the Blake et al (2006) model respectively, where experimental determined from Dean (1979).

Equation-5: u = g Δp D2 / (12 n), when Re = D u p/n < 1.3 x 103(Eq-9 of Blake et al, 2006), where D = width of the dyke, u = average length at the height “z”, p = density of the melt, n = viscosity, g=gravity and Δp=lithospheric density

Equation-6: u = 0.224 [(g Δp)4 D5 / (n p3)]1/7, when 6 x 103< Re < 6 x 105(Eq-9 of Blake et al, 2006), where D = width of the dyke, u = average length at the height “z”, p = density of the melt, n = viscosity, g=gravity and Δp=lithospheric density.

Figure 4.64 shows the plot between the total feeder dyke widths versus flow rate of the Crater Lanoto and Fagaloa sample. Dykes of 1000 m in length with their width ranges from 0.1-1.0 metre are comprised of flow rate range between180 and 884 m3 s-1. Those of 100 m long of the same widths range between 18 and 84 m3 s-1 in flow rate. This indicates than longer dykes have high flow rate than shorter dykes.

Negative and positive gradients imply a change from laminar to turbulent flow, respectively. Based on the Reynold Number, a reduction in the width of the Crater Lanoto/Fagaloa feeder dykes generates laminar flow (Figure 4.64). Widening of the

257 feeder dykes width reduces in the flow rate results in turbulent flow. This change from laminar to turbulent flow could be triggered from decrease in temperature and increase in magmatic viscosity of the silicate melt. In addition the flow rate reduction is also associated if the fracture toughness of the surrounding rock is much greater than the stress intensity factor coefficient. Overlap of the Crater Lanoto and Fagaloa dykes (Figure 4.64) imply they behave in the same sense from laminar stage (narrow dyke) toward turbulence phase (wide dyke).

FIGURE 4.64 The total dyke widths versus flow rate of the Crater Lanoto and Fagaloa Formation dykes (blue and green). (Modified from Blake et al, 2006).

In order to investigate if there are variations during emplacement of the Crater Lanoto and Fagaloa lava suites, let us plots the concept model against three different depths in the Samoan lithosphere. The three depths included those of 7 km from the Moho (boundary between the crust and the mantle) beneath the oceanic crust, 25 km of the Moho deep in the Auckland Volcanic Field region, and 100 km somewhere deep underneath the earth (Blake et al, 2006).

Figure 4.65 shows a plot between the feeder dyke widths versus the time. Crater Lanoto and Fagaloa feeder dykes travel from a source at different depths (7 km, 25 km and 100 km). It shows that the narrower dykes from the three particular depths seem arrive to the 258 surface quicker than those of wider dykes. In addition, if the temperature still higher (1400oC) then the feeder dykes from the three depths also increase their speed toward the surface correspond with their widths.

Positive gradient may corresponds with slowly ascend of feeder dykes from the three depths that could be associated with turbulence flow regime. Negative gradient refers to the fact that feeder dykes, may be suddenly increase their speeds through laminar flow regime in corresponds with increase in their width.

It predicted that from the 7 km depth Moho beneath the oceanic crust the narrow feeder dyke (< 0.4 m) of the Crater Lanoto ascends to the surface within 1.6 days, with an average speed of 0.05 m/sec. With the same velocity at the 25 and 100 km depth, the feeder dyke predicts, to reach the surface, within 6 and 23 days, respectively.

If the feeder dyke of Crater Lanoto and Fagaloa increases their width from 0.4-1 m at 7 km depth, it would be predicted to reach the surface within 14 days, with an average speed of 0.006 m/sec. At depths of 25 and 100 km with the same widths (from 0.4 m up

259 to 1 m), the feeder dyke expects to reach the surface approximately within 48 and 192 days, respectively.

(iv) Model Interpretation

The dimension of the Crater Lanoto and Fagaloa feeder dykes show little variation, almost constant to the surface. This implies that, the “stress intensity factor coefficient” exceeds the fracture toughness. In other words, the feeder dykes propagate through the open cracks in the Samoan lithosphere. This supports the hypothesis of lithospheric cracking model of the Samoan volcanism (Natland, 2003). The speeds of feeder dykes gradually decrease which correspond as the flow rates ascend further away from the source. This implies that as the feeder dykes move further away from the source and their temperature drop, then viscosity and pressure increase. At this stage some feeder dykes never reach the surface and become arrested instead (Figure 4.59 and 4.60). Hence, the reduction in temperature and increase in viscosity and pressure of the feeder dyke could generate more bubble in the basaltic magma result in explosive activity.

The thin-sheeted pahoehoe flow (outer rim lava) to the northeast of the crater is evident of high fluidity of lava suites during the tephra bed-1 episode. In reference to the flow rate regime of the feeder dyke the thin-sheeted lava suite is a part of the lamination flow. The rapid ascent of the narrow feeder dyke from the three different depths (7, 25 and 100 km) is triggered by four main factors. These included the high temperature (1400oC) and density of the silicate melt, low viscosity, lamination flow and network of open cracks. With the single injection of the narrow feeder dyke speed of 0.05 m/sec, it predicts to reach the surface within 1.6 day and this could be considered vulnerable for such kind of eruption.

The “stress intensity factor coefficient” over fracture toughness indicates that this part of the Samoan lithosphere contains network of open cracks. The cracks are products of tension stress as the Samoan island chain as it locates close to the Northern Terminus of the Tongan Trench (Hawkins and Natland, 1975; Hawkins, 1987; Natland 2003; Hart et al., 2004).

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4.7.4.5 The similarities of Lanoto Volcano with other monogenetic eruptions

The aim of this section is to extend the similarities of the Crater Lanoto with the widespread monogenetic activities on the two main islands. Based on physical characteristics and geochemical similarities these would enable to construct a new potential vent for future eruption prediction in Samoa.

The broad distribution of the contaminated tephra downcore reveals that the simultaneous activities are likely to continue to the near future. Despite the lack of radiometric dating during Holocene activities, however, evidence of the WSMM trace on central Upolu and Savai’i indicates a wide extension of the simultaneous eruption. The consistent overlap in major and trace elements plots (Figure 4.43 & 4.44) indicate the geochemical similarities of Crater Lanoto with other monogenetic activities. Fepuleai (1997) characterised this as the “shared magma batches hypothesis” which also supports the simultaneous activities scenario in Samoa.

The new potential vent is based on three measures, high, medium and low as follows:

1. High potential vent zone (HPVZ) referring to those associated with fault networks, interconnection fissures and dominated by young cones (Aopo Formation &Puapua Formation). 2. Medium potential vent zone (MPVZ) mostly associated with minor fissure and more spacing of young volcano. 3. Low potential vent zone (LPVZ) dominated by the Salani Formation and more spacing Mulifanua Formation cones.

The construction of the three potential measures is dependent on the four structurally related features. These included fault-fault, fault-fissure, fissure-fissure and WSMM trail. The structural interaction mechanism suggests there are four major sources of the wide spreading monogenetic activities.

The new potential vent construction is also based on the first volcanic hazard map of Western Samoa constructed by Cronin et al (2006). This section will be presented into two parts, Upolu and Savai’i new potential vent. 261

(i) Upolu new potential vent

The elongated form of Upolu Island is controlled by the central major fissure system. Figure 4.66 shows the map of potential vent zone of Upolu Island. Crater Lanoto is one of many Holocene cones scattered along the HPVZ of the island. The HPVZ is occurred along the central rift where link to the Inter-Island Fissure System to the west.

FIGURE 4.66 Potential vent zone of Upolu Island, constructs based on volcanic hazard map of Samoa by Cronin et al (2006).

The Fagaloa-Falealili Fault offsets the alignment of volcano cones along the Upolu Major Fissure System to the eastern part (Figure 4.66). This zone has a possibility of generation of a new HPVZ. The assumption is based on the fact that this major fault is still active. Mr Unwin (Apia Observatory Superintendent) reported seismic activities of 24 earthquakes with S-P of 12 seconds occurred along the fault between 1979 and 1981 (Hawkins, 1987). This information classifies the particular zone as the HPVZ in the near future.

The HPVZ extends further to the east of Namua Island. This is where it intersected with the Lepa Fault then dissected by the Fanuatapu Fault running parallel along with the

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Aleipata Fissure System. The intersection between the fault and central rift suggests has a high possibility of a new vent to be generated at this part of the island.

Tafua-savaii and the Tafua-upolu of the Puapua Formation almost erupted simultaneously during Late Holocene to the present. The two volcanoes are thought to be triggered from same tectonic stress activities of the Pacific Plate. This suggests that the eruption of the Puapua Formation activity from Mount Fito at the central Upolu extends the HPVZ from the west toward the east.

A medium potential vent seems to run parallel with that of high potential, as represented by four ovals in the central part of the island. These zones are mainly dominated by Salani Formation cones but very few of Mulifanua Formation.

There is a small portion of low potential vent zone determined in the central fissure. This is due to a high concentration of young and old cones occurring at the narrow central fissure. The Upolu Major Fissure System is suggested to active especially in the section that runs parallel, intersecting and dissecting with network of faults.

(ii) Savai’i new potential vent

Volcanic cones on Savai’i form in the broad complex plain, results of orthogonal rift system (Natland, 1980; 2003). Younger cones (Aopo Formation & Puapua Formation), are suggested to be parallel with an active volcanic rift along the island (Taylor & Talia, 1999; Cronin et al, 2006).

Figure 4.67 shows the map of the potential vent of Savai’i Island. The volcanic hazard assessment of Savai’i from previous studies emphasized that, the northwest part of the island is most vulnerable. This part of the island is classified as the HPVZ in the near future (Taylor & Talia, 1999; Cronin et al, 2006). The assumption is based on the fact that, the Sataua-Ologogo Arc Fault opens northwest and strike along the zone of recent Aopo Formation eruptions. This fault-central fissure relationship is the reason for the extension of the HPVZ along the western central half of the island.

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FIGURE 4.67 Potential vent zone on Savai’i Island, where links to Upolu through the Inter-island Fissure System. This map based on the volcanic hazard map of Samoa by Cronin et al (2006).

Closed cones space of the Puapua Formation allows the HPVZ to extend to the east and connects to the IIFS (Figure 4.67). The HPVZ runs along Tafua-savaii, thought to be the young active volcano on the south east end of the island.

Medium potential vent occurs on the eastern half of the island. These zones are mainly comprised of Salani Formation, Mulifanua Formation but rare cones of the Puapua Formation.

The low potential vent zone is characterised by the wide cones space of the Mulifanua Formation and several from the Salani Formation (Figure 4.67). The LPVZ occurs in a finger-like shape on the eastern part, and broadens toward Manase-Gataivai Fault and Salailua Fault on the south.

(iii) Summary of the critical points from monogenetic process of the Crater Lanoto (i) Crater Lanoto is a compound monogenetic short term volcano; (ii) Polygenetic activity is rare due to the lack of radiometric of a single crater.

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(iii) Most of the post-Fagaloa activities on the island can perhaps be classified as short- and long-term compound monogenetic volcano: however, more work is needed to prove this assumption. (iv) WSMM is associated with the formation of monogenetic activities on the easternmost part of Upolu Island. (v) Similarities of the monogenetic activities on the main island enable to construct potential vent zone for future eruption. (vi) The HPVZ is located along the main fissure of the main islands.

4.7.5 GEOLOGICAL HISTORY – LANOTO VOLCANO

The sequence of events in the geological history of the Crater Lake Lanoto is based on several criteria. These include: the ukulele-formed feature, the collapse of the northwestern part, stratigraphic column, magnetic susceptibility data, occurrence of contaminated tephra sand, radiometric ages and geochemical analysing (XRF and ICPMS) of lava flow and tephra deposits. The Crater Lake Lanoto is possibly formed from two phases; (i) the narrow graben-like eruption and (ii) the pit-crater activity. Tephra bed-1 and 2 activities are referred to as large volume monogenetic volcanoes (but still less than Tafua-savai’i and Matavanu in Table 2.1), whist those of tephra bed-3 and 4 characterise as low volume monogenetic phase.

(i) Phase 1: Narrow graben-like eruption

Crater Fili volcano to the south east of the Crater Lanoto (Figure 2.17) is thought to represent the location of the initial monogenetic activity before the volcanism locus shifted to the west. This assumption is based on the fact that Crater Fili’s highly weathered rim overlaps toward the southeastern part of the Lanoto volcano. In other words the crater is part of the Lanoto volcanic field.

The two trends of major and trace elements reflected from XRF and ICPMS plots show that, the Crater Lanoto volcano was generated from the two magma batches: picritic and basanitic/basaltic sources. The physical characteristic of the outer rim lava and its XRF

265 and ICPMS signatures indicate the tephra bed-1 activities derived from the deep picritic source.

The WSMM shifted the magma chamber to the west approximately 80 m from Crater Fili eruption zone. Figure 4.68 show the schematic of the narrow graben-like activities of the Lanoto volcano. The narrow single injection of the feeder dyke rapid ascends via laminar flow through the cold lithosphere toward the Lanoto volcanic field along the UMFS. The arrested dyke was also developed at this stage. Feeder dyke had a stress intensity factor coefficient exceeding over the fracture toughness. This implies that it propagates through the open cracks of the UMFS. The Maimoaga vent to the southwest slope of the Lanoto volcano started to emerge during the Phase 1 activities (Figure 4.68).

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The silica-poor hot basaltic magma charged through the surface with the pressure of the escaping gases. The great volume of dissolved volatiles in the initial stage generated the dry explosive activities of the tephra bed-1 at 200 Ka. The explosive stage disperses the high vesicular tephra in an area 5 km in radius. This stage included the outpouring of the great volume of fluid lava, which now crop-out to the north east as thin-sheeted pahoehoe.

Fluid lava formed spatter ramparts on both side of the elongated fissure. A greater explosive phase of the narrow graben-like episode resulted in the widening and lengthening of the fissure. This caused the south eastern end to open up and drained out great volume of lava toward the coast via Sinoi Fault plane. The presence of an elongated crater implies that the narrow graben-like eruption extends approximately about 100 m northwest-southeast, parallel with the UMFS.

During tephra bed-1 episode, it believed that, there were several volcanoes nearby erupted simultaneously with Crater Lanoto. These activities eject the widespread contaminated tephras within the Crater Lanoto depositional basin.

Hydrothermal alteration occurred at the end of the narrow graben-like activities. This indicates that the narrow graben-like eruption excavated deeper and dissects the water table, resulting in the formation of maar. Vesicularities of tephra sand imply that the hydrothermal stage was also associated with explosive activities. Desiccation cracks dominate the volcanic glass shard, implying that the maar level had fluctuated, during the long cessation in volcanism.

(ii) Phase 2: Pit-crater eruption

A continuation of the WSMM activities parallel the UMFS causes the magma batch to move from a deep to shallow level at west approximately about 100 m. Figure 4.69 shows the pit-crater activities of the tephra bed-2 episode at 143.9 ka. More tension along the central fissure system, associated with thermohydraulic explosions at the top of feeder dyke resulted in the formation of pit-crater.

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The tephra bed-2 episode generated a fair volume of lava, which elevated the volcanic wall and poured out along the Sinoi valley to the southeast along the coast. The inner rim lava of the tephra bed-2 has the signature of shallow basanitic/basaltic and deep picritic source. This corresponds with the fact that, the tephra bed-2 was partly derived from the magma batch of the tephra bed-1, before the new magma batch form at a shallow level known as the “transition process” (Section 4.7.4.3). This change from the deeper source to a shallower source could be associated with more tectonic activities in the region. The single injection magma interacted with the cold lake generating explosive activities. This episode also dispersed volcanic ash in areas within the 5 km radius. Volcanic ash possibly carpeted most areas between the north and northwest, relating to the dominant southeast trade winds. The presence of contaminate tephra within the tephra bed-2 sediment implies simultaneous activities of volcanoes nearby. Highly explosive activities disperse volcanic ash over area within 5 km in radius.

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The Maimoaga vents activities could increase during tephra bed-2 episode, based on the the overlap relationship in trace elements between the inner lava suites and the rim tephra deposit (Figure 4.69). A continuation in violent activities could be resulted in the extensive of the crater toward the western part and the pit-crater formation. This also generated the broad pyroclastic deposit toward the western and southeastern part of the volcano foot.

The rim wall was elevated many metres and dominated by enormous volume of unconsolidated materials, overlying the unstable and deeply jointed lava flow. Increasing in tension stress across the Pacific Plate at the Tonga Terminus, triggers seismic activities along the UMFS. This generated the cone collapse event of the Crater Lanoto volcano, which marks the cessation of the Salani Formation activities.

After another long volcanic interval of at least 121.7 kyrs increased WSMM activities in the region sparks the tephra bed-3 activities during 22.3 Ka. Feeder dykes ascend through the old conduit underneath the lake basin, and generated an explosive eruption. This violent behaviour is shown by the high vesicularities of tephra sands. The episode ejects the great volume of volcanic ash and the outpouring of a narrow tongue of lava, which drained out to the southeast. The activities terminated for a long period based on 7,600 years interval between tephra bed-3 and tephra bed-4 episode. This long interval allowed the volcanic locus to move to the west through WSMM for several metres and igniting the tephra bed-3 activities around 11 ka. The ICPMS data indicates that the two episodes (tephra bed-3 and 4) represent the re-eruption of the Crater Lanoto from the deeper picritic magma source. This suggests that its source could be located at the same level as the tephra bed-1 source (Figure 4.69).

Continuation in WSMM activities sparked the eruption of the tephra bed-4 at 3.4 ka. A feeder dyke at greater depth rapidly ascended through a new conduit to the west deep underneath George Island. It suggested that more tension and stress in the region could have generated further subsidence (may be another 10 m) of the pit-crater which allows the “intra-crater spatter/scoria cone” of George island to be exposed above the lake surface.

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Like the tephra bed-3, the tephra bed-4 episode was initially explosive as the magma come in contact with the lake. The episode generated a narrow tongue of lava, which also pours out to the southeast. Contaminant tephra components associated with the tephra bed-4 indicates that there were other Lefaga Formation activities occurring simultaneously.

George Island (Figure 4.1) in the central north western part of the pit-crater is characterised as a eroded cinder cone dominated by a high weathered scoria. The island represents a dying stage of the volcanic process, which developed during a waning stage episode of tephra bed-4. This is where a lower pressure depleted magma, dominated by gas bubble-rich cinders, started to solidify as it was injected quietly to the surface.

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CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

5.1 OVERVIEW

This final chapter presents the summary of new research findings that would improve our understanding and knowledge in volcanism process along the Samoa Volcanic Field. The new findings relate to deposition components, geochemistry, radiometric dating, monogenetic processes, volcanic hazards and volcanic mechanisms that can explain the age patterns of volcanism in the main islands. These findings do not only relate to Crater Lanoto volcanic processes but also inform us about its relationship with the broader volcanism pattern on the main islands.

5.2 DEPOSITION BASIN COMPONENTS

Volcanic sediments and organic materials are the main depositional components. The volcanic material is found throughout the entire core whilst the organic matter occurs in the form of lens deposits. In addition, Lanoto basin also contains tephra components from nearby eruption activities. It is believed that the contaminant component is not only from neighbour volcanoes but also from the parasitic volcanic vents (Maimoaga) of the Crater Lanoto based on geochemical signature of each.

Trough and peaks of the magnetic susceptibility (MS) curve correspond with high and low evaporation rates of wet and drought season, respectively. The ferrimagnetic properties in lake sediments on the other hand are the product of continued intense weathering of the “early secondary mineral”. This would result in the formation of the “late secondary minerals” magnetite and maghemite. The “early secondary mineral” and “late secondary mineral” transformation stage are associated with low fertility soil in Samoa.

High concentration of magnetite and elevated organic matter content in sediment also correspond to peak and trough respectively, however, the two elements seem mixed in

271 many occasion and raising questions about the major controlling factor. The similarity between the MS and the marine sediment oxygen isotope (MSOI) curve enables us determine that MSOI is the major controller. If this is the case then fluctuations in sea level control the volcanism in Samoa. This is similar to the scenario described in Kear and Wood (1959). However, more work is needed to substantiate this claim.

An abundance of tephra components in four layers (tephra bed-1, 2, 3 & 4) suggests that the Lanoto volcano erupted from four main episodes with associated minor activities. Charcoal fragments presence in every tephra layer could be not only indicates fire during eruption, but also could be associated with prolong drought and human activities.

Erosion seems to have occurred after every eruption episode corresponds with the organic rich sediment among the eruption intervals. Despite evidence for erosion processes in the depositional basin, there is no clear sedimentary information about human occupation. There is a possibility that the erosion at the top of the tephra bed-3 could relate to human causes. However, more work is needed at this stage to confirm this conclusion.

5.3 GEOCHEMISTRY – LAVA AND TEPHRA COMPONENT

The tight composition in TAS plot of the Lanoto lava suites indicates that the volcano had erupted from magma sources with close chemical relationship. The positive and negative correlations in major and trace elements support the idea of two magma sources of the Lanoto volcano: a deep picritic source and a shallow basanitic/basaltic source. This supports the suggestion that the outer rim lavas derive from an olivine-pyroxene enriched source whilst the inner rim suite formed from olivine-pyroxene depleted magma. The volcanism seems to have switched back to picritic activity to form the Mulifanua Formation to Lefaga Formation and the tephra bed-4 episode, perhaps related to tectonic activities.

Lanoto volcano characterise as the post-erosional origin signifies from the overlap of trace and major elements with other lava suites along the Samoa Volcanic Field (SVF). Isotopic composition of post-erosional lava samples from the Crater Lanoto volcanic

272 region also indicates the parallel conclusion. Despite variations in radiogenic isotopes of lava along the SVF however, the major and trace elements of older and younger volcanism are related.

Alteration in major elements from XRF and EMPA shows that these two techniques are not recommended for weathered tephra analysis in the near future. Desiccation cracks and the microlitic texture of volcanic glass shards present in the four tephra layers, signify the instability in lake level, corresponding with long wet and dry period in the area. This is also reflected in the low sedimentation rate shown in the unsupported 210Pb activities at the top of the core D3, which imply that the lake level had been dropped for 59 years interval.

Parasitic vents of Maimoaga also erupted with the four Lanoto volcano episodes, reflected in the overlaps in the ICPMS trace elements plots. Contaminant tephra seems to dominate the four major eruption episodes implying simultaneous eruption of the Crater Lanoto with other nearby volcanoes. Similarity in geochemical signatures of nearby volcanoes and Crater Lanoto prove the hypothesis of laterally widespread layer of heterogeneously mantle along the SVF.

The match in geochemistry of the tephra bed-4 of Lefaga Formation with those of the contaminant cones nearby denotes that there were more Lefaga Formation cones concurrently active during the time. However, the geological map (Kear and Wood, 1959) classifies these cones on the easternmost part of Upolu as part of Mulifanua Formation volcanism. Hence, the new geological map of Western Samoa should reconsider the extent of Mulifanua Formation at the easternmost part of Upolu.

5.4 RELIABLE AGE OF THE CRATER LANOTO VOLCANO

The Crater Lanoto volcano erupted since the Salani Formation (Pleistocene) was deposited throughout the interval during which the Mulifanua Formation formed and ceased with the emplacement of Lefaga Formation (Holocene). The low viscosity magma reached the surface and formed the narrow graben-like during 200 ka (MSOI-age) and

273 continues through 144 ka (Ar-Ar) before it ceased and re-ignited at 22 ka (14C) until it terminated around 3.4 Ka (14C). The western slide motion mechanism (WSMM) shifted the volcanism locus to the west to erupt as the pit-crater during the 144 Ka.

Based on relationship between major faults and rock formation on the main islands, a cone collapse event (CCE) is thought to have occurred at the top of tephra bed-2, sometimes at least 22.3 Ka. The CCE is associated with many geological / geomorphological landmarks on both main islands and could be also responsible in the groundwater drought on the north-western part of Savai’i. Groundwater condition changes at this part of the island, as volcanic ash and tuff beds, which are good elements for groundwater aquifer, were all subsided in a large scale. In addition, the CCE may be also responsible for the switched in volcanism from deep picritic of Salani Formation to shallow basanitic source magma of Mulifanua Formation. This is to conclude that the CCE is the product of the WSMM process.

5.5 MONOGENETIC PROCESS – LANOTO VOLCANO

Effusive product of < 1km3 characterises in volume characterise Crater Lanoto as the monogenetic volcano. A wide spread of a compound monogenetic short-term volcano (like Crater Lanoto), along the UMFS and SMFS suggested, to be triggered from the WSMM activities. Crater Lanoto activities were generated from a combination of single and multiple magma injections from the feeder dykes. Short-term and long-term eruptions in Samoa could be labelled as compound monogenetic activities; however, more work is needed to clarify this description. Polygenetic volcanoes are deemed rare in Samoa due to the lack in radiometric dating; however, they are exposed well in the Fagaloa Formation at the northeast Upolu.

Simultaneous eruption style of the Lanoto and nearby volcanoes denotes that the WSMM process had been active since the tephra bed-1 episode (200 Ka). The WSMM generates volcanism in several fashions such as re-eruption of the older crater and the birth of single and multiple eruption centres. If this is the case then volcano along the UMFS and SMFS, previously thought to be extinct, could expected to re-erupt in the near future.

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The age of the WSMM could plot between that of the early Salani Formation and the Upper Fagaloa Formation. This is based on the fact that the Upper Fagaloa lava plots further away from the current hotspot velocity line, implying a post-erosional origin. At this stage, it is suggested that the post-erosional activities along subaerial and submarine volcano of the SVF could be the product of WSMM. This reveals that the WSMM should be much older than expected, based on the radiometric ages of post-erosional volcanic seamounts at the western end of the island chain. The WSMM marked the waning of the Fagaloa Formation while waxing of Salani Formation. In other words, the WSMM occurs before the Quaternary sea level rise between Penultimate Glaciation and Last Interglacial stage.

The wide distribution of monogenetic activities on the main islands enables us to construct high, medium and low potential vent zones for future prediction. These three categories are based on fault networks, interconnection fissures and abundance of younger and older cones. The high potential vent zone (HPVZ) of Upolu extends along the UMFS from the west and then runs parallel to the major faults on the eastern part. Savai’i has an HPVZ extending along the SMFS and running parallel to the major faults. The HPVZ extends to the southeast toward the Tafua-savai’i volcano and connects with the IIFS.

5.6 ERUPTIVE SCENARIO – LANOTO VOLCANO

Indigenous knowledge is very useful tool or determining historic records of volcanic activity and therefore future hazard associated with Crater Lanoto and many other volcanoes. Features of the traditional speech (lauga), traditional dances and other culture activities contain many significant elements of volcanic eruptions. The names given many volcanoes on the main island correspond to exposed volcano features or eruption style of that particular activity. Cross-usage of names from the two main islands imply similarity in volcanic activities. This includes the use of the word “Lano” to name other volcanoes nearby that may signify simultaneous style activities. Many unpublished myths and stories link to the volcano activities in many parts of the island and show that these people were very close to the eruption zone. The main reason for this proximity could be 275 that they were trying to identify how dangerous the volcanoes were and what benefits they could gain from naturally occurring features. The fact that no casualties were reported for historical eruptions in the first geological publication of Samoa suggests that the indigenous knowledge passed to later generations was an efficient means of hazard avoidance.

There is no long term consistency in terms of the interval between the volcanic eruptions of the Crater Lanoto and other Holocene activities on the main islands. This creates more difficulties in determining any appropriate pattern for the next Aopo Formation eruption. As discussed in the Section 4.7.3.2 it predicts that the next Aopo Formation activities could occur in the next 270 years. This timing is dependent on the nature of tectonic activities associate with the sharp bend (NT) of the Pacific Plate, in relation to the geological setting of Samoa island chain.

Long intervals between eruptions could be an artefact of the lack of radiometric dating in the region. Close-range radiometric dating of tephra layers and lava flows is recommended in this study and would enable to refine the eruption interval in the near future.

Based on the simultaneous style activities during the Crater Lanoto episodes, the next eruption should be expected from any part of the fissure system. This includes the medium and low potential vent zone on the main islands. This is because the WSMM process could re-ignite most of the older cones along the medium and low potential vent zone.

The Crater Lanoto erupted in two ways: from a narrow graben-like crater and from pit- crater activities. The vesicularities of tephra components, Pele’s tears, volcanic bombs, cauliflower bombs and brownish-yellowish juvenile lapilli tuff all can be used to infer the Lanoto volcano eruption style (Hawaiian, Strombolian and Phreatomagmatic). The three eruption styles ejected great volumes of volcanic ash and could cover an area with a radius up to 5 km whilst only generating a narrow tongue of lava flow extending ≤ 1km.

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Examination of various eruption features of the Crater Lanoto enables us to construct an appropriate near future volcanic hazards scenario for this volcano. Table 5.1 shows appropriate analogous prediction of the compound-monogenetic short-term volcano. This prediction is based on an assessment of previous volcanic eruptions (Taylor & Talia 1999; Cronin et al., 2006). The prediction would look at four significant issues: time- frame, geological/volcanic activities, hazard impact and likely response. This information will be valued to calculate and anticipate the appropriate analogous of such eruptions in the near future.

TABLE 5.1 An appropriate analogous predict to be associated with short term compound monogenetic type eruption like Crater Lanoto. (Modified from Cronin et al., 2006)

Approximate Geological and Volcanic Hazard impact Likely response time frame for Activities activities

As magma and volcanic gaseous Inexperience amongst Identify the location force their way up to the surface population about and quickly go through triggers series of earthquakes volcano eruption the which, will be felt in the area, might cause panic, volcanology/geology perhaps 2-5 in the magnitude. confuse and fear. overview of the specific area. Some of these earthquakes are Crime will be created strong enough to generate as very few people Public warning via all landslide/rockfall at several take advantage of means of vulnerable high elevated areas eg. evacuate procedure communication. Mauga o Vaea, Mauga o Fao, (break in or stealing Fagaloa Bay and many more. other people Evacuate people at At least 0-10 belonging). least 3km zone. days Based on the volcanic model the rapid ascend of narrow feeder Very fluid lava travel Collect as much dyke of less viscosity and high down the steep slope seismic information temperature magma can reach the of the volcano in a from a nearby station surface from 7 km and 25 km great speed. or install one closer to depth within at least 1.6 and 6 the volcano. days respectively in the speed of 0.05 m/sec. The slow rising Record water magma of 0.006 m/sec from the 7 temperature of any km erupts at least within 14 days. nearby lake. Determine the chemistry of the surrounding air.

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Eruption initially starts with Volcanic bomb and Regular update of the massive blast of thick materials thick volcanic ash situation. within the crater zone. cover the area of at least 500 m radius. Determine the wind Volcano initially erupts through direction with respect elongate fissure east to west Massive bush fires to the ash fall. parallel with the major fissure generate from one system or spherical scoria cone active volcano or Quick assess of high form. simultaneous style elevated area in the At least 10-12 activities. With region where days Explosive eruption along the prevailing wind will vulnerable to be central rift as the magma comes terrify a very broad collapse due to the in contact with the water table. area. series tremors.

Post-erosional volcanism generate Strong prevailing Continue collecting from WSMM hence there is a south east wind can information, including possibility of simultaneous extend the dispersal those of volcanic ash eruption will be occurred. of the volcanic ash to for chemical analysis. the north west side.

Elevated scoria cone crater form. Volcanic bomb Regular update of the continue to disperse situation. Activities continue ejecting of at least 5000 m radius lava and volcanic ash. Continue monitor the Very fluid lava flow volcano and collecting Earth tremor from more tectonic flows down the slope information. stress along the major fissure may in great speed. be occurred. Series of bush fires Increase in activities generates continue At least 12-20 pyroclastic flow. days WSMM activities continue perhaps simultaneous eruption increase.

Based on the model the fast rising magma reaches the surface from 100 km depth within at least 23 days.

Activities continue perhaps, More volcanic bomb Regular update the might shift to the west due to the continues to disperse situation western slide motion mechanism at least 5000 m At least 20 days- trigger the extension of the crater radius. Continue monitor the many years (can along the fissure system. volcano and collecting be up to 200,000 More bush fire will information. years) New location initially generates be generated. more explosive activities. Should have a fully Very fluid lava flow understanding of how Explosive as the magma come in will travel at the the volcano behaves

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contact with the ground water and greater speed throughout different the lake downhill via valleys episodes. and allies nearby. WSMM activities continue along the major fissure system.

Slow ascend magma from 25 km would erupt approximate at least 48 days

5.7 VOLCANISM AGE PROGRESSION

Lanoto volcano has a post-erosional origin and is suggested to have been generated from the WSMM activities. The age progression of the Samoan hotspot is contrary to that seen in the Hawaiian chain and many other shield volcanoes around the world. Several shield lava suites from the eastern part of the island chain have the same radiometric age as those of post-erosional lavas from Upolu and Savai’i. If the post-erosional activity of the SVF is a product of the WSMM, then the two processes (WSMM and hotspot) must have been activated simultaneously.

Older post-erosional activities of seamounts on the western part of the island chain, e.g. the Combe seamount (Figure 4.52) show that, the WSMM had been active at least 14 million years ago. Put simply, it seems that the “structural controlling volcanism” is the most appropriate term to describe the volcanic Samoa island chain. In addition, the western volcanic age progression was in place before the birth of Savai’i and Upolu.

5.8 ADDITIONAL FEATURES – GEOLOGICAL MAP

The construction of fault locations and fault-naming procedures was also part of the field work reconnaissance on the two main islands. The aim was to identify how the structural and tectonic processes fit in the volcanism of Samoa. This fault-naming procedure would enable to identify these structural features for future works.

In an effort to determine the age of the cone collapse event (CCE), this study identifies and named several major and minor faults. The main faults are the Manase-Gataivai Fault, Sataua-Ologogo Arc Fault, Fagaloa-Falealili Fault and Fanuatapu Fault. The

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Sataua-Ologogo Arc Fault first described by previous studies as two separate faults (Sataua & Ologogo). The Fagaloa–Falealili Fault was unnamed by previous studies and was used to explain the displacement of the post-Fagaloa cones. Minor faults on Upolu and Savai’i were all named including the Sinoi Fault and Lepa Fault, which bounded the study area.

This study also classified and named the alignments of volcanic cones in the major and minor fissures system, to facilitate future reference to these fissures. The major fissures included those of Savai’i Major Fissure System, Upolu Major Fissure System, Inter- Island Fissure System and Aleipata Fissure System. Minor fissures dominate the eastern part of Savai’i.

5.9 SUMMARY OF THE RESEARCH FINDINGS

This section outlines all the research findings that could satisfy hypothetical questions in Section 1.3:

1. Crater Lanoto volcano presumably formed at least 200,000 years ago (Salani Formation) and re-eruted several times (forming Mulifanua Formation) before it terminated around 3,400 years ago (Lefaga Formation);

2. Surprisingly long volcanic intervals between Lanoto volcano eruptions could be due to a lack of radiometric dating, which would hampers our ability to predict the next eruption;

3. Based on ejecta volumes the Crater Lanoto is a short-lived or compound monogenetic short-term volcano;

4. Crater Lanoto changed its behaviour from Hawaiian eruption style (less explosive) to Strombolian (more explosive) and phreatomagmatic (more explosive) activities on several occasions;

5. The presence of “contaminant tephra” implies inputs from more than one volcano. Contaminant components occurred in four eruption deposits of the Lanoto volcano,

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showing that nearby volcanoes were derived from the similar source, thus implying the laterally widespread of the heterogeneous mantle along the SVF;

6. The fact that contaminant components present in every Lanoto volcano tephra deposit is most likely because the Crater Lanoto erupted simultaneously with nearby volcanoes;

7. The combination of physical characteristic, structural interpretation, radiometric age and geochemical signatures enables to undestand the WSMM process that might have been responsible for the formation of post-erosional activities in the regional;

8. The characteristics of cored sediments, the collapse of the Lanoto rim and nearby craters, fault activities on the main islands and the age relationship of rock on the main islands were all used to reconstruct the CCE. The age relationship between the post-erosional activities (Salani Formation and Mulifanua Formation) suggests that the CCE is the product of the WSMM process;

9. Charcoal fragments in the sediment may not only be indicative of bush fires but may also evidence of long drought, erosion and perhaps human occupation although more work is needed to prove this;

10. Indigenous knowledge and other traditional activities in the region provide significant clues to reconstruct the eruptive style of the Lanoto volcano and how the earlier occupants used volcanic features to determine the magnitude of the eruption;

11. Continuing intense weathering of the “early secondary mineral”, resulted in formation of the “late secondary mineral”. This transformation produces low fertility soils for Samoa and perhaps other volcanic region;

12. The long decreasing profile of the 210Pb activities suggests that the lake level has been falling for 59 years corresponds for long drought;

13. Volcanic activities of the Crater Lanoto seem associated with the sea level fluctuation, based on the similarities in MS and MSOI curve. Recent volcanism of Samoa coincides with a peak in sea level rise; 281

14. Like Crater Lanoto, volcanoes that are scattered along the UMFS and SMFS and whose activity is thought to have long ceased, may continue to erupt through WSMM process;

15. The WSMM process could account for isotopic variations within tha SVF, associated with the deep and shallow magmatic sources;

16. Based on several old post-erosional activities along the western part of the Samoa Volcanic Field, the WSMM was active before the birth of Savai’i and Upolu;

17. Radiometric ages show the shield and post-erosional activities occurred simultaneously thus showing that Samoa volcanism is tectoically controlled;

18. Geomorphological/geological landmarks in Western Samoa represent exposed evidence of the CCE activities;

19. The next Aopo Formation eruption is predicted to occur at least in the next 270 years along the major fissure system. The narrow dykelet of fluid lava from this eruption could reach the surface within 1.6 day with a speed of 0.05 m/sec, if propagated through high fracture lithosphere of Samoa.

5.10 RECOMMENDATIONS FOR FUTURE WORK

The results and interpretation from this study enable us to put volcanism in Samoa in a proper context. This will benefit scholar research and help us obtain a better understanding in various volcanic hazards in the near future. Table 5.2 shows various scientific tasks and methods recommended to accomplish and satisfy the requirement records of the past volcanic activities. Intense weathering of tephra sand in tropical environment such as Samoa means the ICPS is recommended as a technique rather than XRF and EPMA. Higher resolution stratigraphic sampling and dating of tephra layers from the core and lava flow suites will better refine the volcanic eruption intervals between the six formations. This will enable us to establish a more accurate pattern of volcanism to improve preparedness for future eruption.

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Seismic investigation is required at some of the main faults and fissures, such as those of the Sataua-Ologogo Arc Fault, Manase-Gataiva Fault, Fanuatapu Fault, Fagaloa-Falealili Fault, Fito-Alaoa Fault, Upolu Major Fissure System, Savaii Major Fissure System, Inter- island Fissure System and Aleipata Fissure System. This will provide good framework for geophysical data, which enable to understand the structural-geology nature and tectonic process associate with the Samoan island chain.

It is also recommended to undertake detailed indigenous knowledge study to gain a more comprehensive understanding of volcanic style and history. This will provide better knowledge of how the first occupant engages with the previous volcanic activities. The cross-usage of names among the main islands or even between Samoa and Tonga, provide some glues about the nature of activities in the past.

TABLE 5.2 Various tasks and methods to benefit future research and improve understanding in the volcanic field of Samoa.

Task Method

VOLCANOLOGY (i) Coring volcanic lake or crater with swamp area in more detail

(ii) A long undisturbed core (6-7 m) extract from Lake Lanoto (south of Apia) or any other crater lake will produce a perfect history of the volcanism in Samoa. Longest core will reach the Fagaloa Formation episode which enable to compare in more detail the older and younger activities

(iii) Run the core through the first MS first version, this will rapidly identify tephra layer

(iv) Sub-samples every 2 cm downcore and dry for 24 hours

(v) Microscopic logging the core and identify all the contents

(vi) Loss of ignition for the core, this will identify the content of organic material

(vii) Run every sub-sample through the MS second version. Isolate component on MS plots imply contaminate tephra

(viii) Radiocarbon dating tephra layers or other sediment layers between

(ix) Thick tephra bed need to date the top and lower part, this will reduce interval among every eruption episode

(x) Stratigraphic sampling the inner and outer rim lava

(xi) Argon-Argon dating (plagioclase groundmass procedure) lava suite

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(xii) Compare the MS curve with the marine sediment oxygen isotope (MSOI) age curve. This will give some appropriate correlation age for the volcano activities

(xiii) Collect catchment soil sample at the inner part, these deposits have high content of various tephra for comparison, especially contaminate component

(xiv) Tephra morphology is a perfect tool to determine the explosive nature of the volcano. Vesicle geometry (mature and immature) perfectly displays an overview of the magma before erupt

(xv) Tradition knowledge (traditional speech, dances & cultural activities) is the perfect tool to describe Holocene and present eruption activities

(xvi) Names of the volcanoes and other historical places hidden the style and history of activity in the area

GEOCHEMISTRY (i) ICPS for major and trace elements is recommended in this study is the most sufficient technique to study weathered tephra in the humid and wet environment like Samoa

(ii) XRF and EPMA can be only work perfectly if tephra deposit is fresher. The two techniques are perfectly display weathered tephra features for environmental study and climate change record

(iii) XRF and EPMA for inner and outer rim lava suites of individual crater rim

(iv) Isotope analysis for lava suites and tephra component

(v) Extend the method (iii) & (iv) to the nearby volcano cones

(vi) XRF and isotopic analysis of all crater lava suites to determine the simultaneous activity in the region with respect to the weathered tephra components

STRUCTURAL (i) Identify major and minor faults in the area. Those elongate north-south GEOLOGY coincide with the tension stress across the Pacific Plate at the Tonga Terminus

(ii) Identify if the eruption centre of the study volcano is shifted to the west, implies is the product of WSMM or post-erosional activities

(iii) Identify all older cones (weathered) nearby could be the initial parts of the WSMM process

(iv) Use satellite image or aerial photograph to identify the extension of the WSMM along the UMFS and SMFS with respect to the coring volcano

(v) Determine the cone collapse event along the line with respect to the study volcano. This can be also determine from the mix of the great volume of organic materials and primary tephra sand components

(vi) The age of the cone collapse event can be also determined from the MSOI

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(vii) Need to dig deeper for more information about the tectonic activities in the region. This include information about sedimentary coring in other part of the Pacific

We should monitor Samoan volcanoes with modern techniques in real-time level. This can be done through a wide seismic network, reliable geochemical and geophysical analysis, regular field observation along the high potential vent fissure system and measurements of water chemistry and temperature of lakes in those particular areas.

The older version of the geological map of Western Samoa needs to be updated. This includes a reconsideration of the six rock formation boundaries based on new radiometric ages from previous studies and this one. The new geological map should also include the series of faults and inferred fissure system location. Detailed cross sections of the structural and stratigraphic relationships between the six volcano units on the main island should also be added.

As with the new version for the geological map, a geohazard map needs to be updated using all research findings from the past few decades. The map should be constructed base on previous volcanic hazard assessment and this study. The geohazard map should include several high peaks in the region, which may at risk of collapse at any time. These high risk populated peak areas include Mount Vaea, Mount Fao, Fagaloa Bay (northeast Upolu) and several locations on Savai’i (northwest, south west & mid-south). A detailed accurate of the geohazard map would sustaintially help volcanic prediction on the island.

Features of the Magnetic Susceptibility and Marine Sediment Oxygen Isotope curve can be matched although the relationship between the two needs to be investigated further. This will improve our understanding as whether the fluctuations in sea level are controlling the volcanism activities in Samoa.

Work with government and other agencies is needed so that police is scientifically informed. This will enable us to outline various strategies and priorities vulnerable communities. For instance, it is recommended that there are more scientists involved in government advisory committees to give scientific input to the advisory process and to provide advice in emergencies.

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APPENDICES APPENDIX 1: FIRST VEERSION OF THE MS-TECHNIQUE

The first version of the magnetic susceptibility technique was deployed in the field, to determine and identify the most detail and long continue records core, which appropriate for further study. There were 8 best cores selected to pick the master core for this project, are listed as follow with their plots find in Chapter 4 section 4.2;

B3 = LL 11 B4 = LL 14 Mean corrected Plotted Corrected Mean corrected Plotted susceptibility (SI x 10- Corrected depth (m) susceptibility (SI x 10-5) susceptibility (SI x depth (m) susceptibility (SI x 5) 10-5) 10-5) -0.68 1.32 0.01 -0.350 1.650 0.044 -0.78 1.22 0.03 -0.833 1.167 0.133 -0.80 1.20 0.06 -1.200 0.800 0.222 -0.90 1.10 0.08 -1.200 0.800 0.311 -0.82 1.18 0.10 -0.867 1.133 0.400 -0.65 1.35 0.12 -0.550 1.450 0.489 -0.63 1.37 0.15 -0.167 1.833 0.578 -0.68 1.32 0.17 0.167 2.167 0.667 -0.73 1.27 0.19 0.317 2.317 0.756 -0.78 1.22 0.21 0.617 2.617 0.845 -0.72 1.28 0.24 1.000 3.000 0.934 -0.87 1.13 0.26 1.217 3.217 1.023 -0.62 1.38 0.28 1.067 3.067 1.111 0.15 2.15 0.30 0.433 2.433 1.200 0.25 2.25 0.33 0.167 2.167 1.289 0.90 2.90 0.35 -0.017 1.983 1.378 1.42 3.42 0.37 0.117 2.117 1.467 0.87 2.87 0.39 0.300 2.300 1.556 0.45 2.45 0.42 0.500 2.500 1.645 0.13 2.13 0.44 0.600 2.600 1.734 1.05 3.05 0.46 0.667 2.667 1.823 4.42 6.42 0.48 0.667 2.667 1.912 18.28 20.28 0.50 0.733 2.733 2.001 60.22 62.22 0.53 1.117 3.117 2.090

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112.85 114.85 0.55 1.250 3.250 2.179 162.12 164.12 0.57 1.683 3.683 2.267 150.33 152.33 0.59 3.150 5.150 2.356 143.95 145.95 0.62 5.050 7.050 2.445 149.70 151.70 0.64 8.217 10.217 2.534 152.83 154.83 0.66 11.867 13.867 2.623 154.02 156.02 0.68 14.800 16.800 2.712 151.72 153.72 0.71 16.333 18.333 2.801 153.70 155.70 0.73 17.683 19.683 2.890 161.82 163.82 0.75 19.033 21.033 2.979 167.23 169.23 0.77 20.133 22.133 3.068 171.28 173.28 0.80 20.450 22.450 3.157 174.50 176.50 0.82 21.433 23.433 3.246 177.90 179.90 0.84 23.000 25.000 3.334 180.92 182.92 0.86 24.800 26.800 3.423 188.93 190.93 0.89 24.000 26.000 3.512 174.35 176.35 0.91 19.633 21.633 3.601 166.02 168.02 0.93 18.133 20.133 3.690 159.03 161.03 0.95 18.317 20.317 3.779 147.70 149.70 0.98 20.133 22.133 3.868 134.92 136.92 1.00 21.600 23.600 3.957 118.47 120.47 1.02 21.850 23.850 4.046 111.68 113.68 1.04 20.117 22.117 4.135 116.48 118.48 1.07 17.833 19.833 4.224 119.98 121.98 1.09 18.600 20.600 4.313 113.82 115.82 1.11 20.050 22.050 4.402 112.62 114.62 1.13 20.367 22.367 4.490 113.02 115.02 1.16 16.150 18.150 4.579 111.32 113.32 1.18 12.933 14.933 4.668 110.22 112.22 1.20 8.067 10.067 4.757 111.87 113.87 1.22 5.100 7.100 4.846 116.63 118.63 1.25 4.467 6.467 4.935 121.17 123.17 1.27 2.300 4.300 5.024 121.98 123.98 1.29 0.267 2.267 5.113 119.20 121.20 1.31 0.483 2.483 5.202 114.77 116.77 1.34 4.450 6.450 5.291 112.57 114.57 1.36 12.867 14.867 5.380 110.92 112.92 1.38 19.283 21.283 5.469

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110.32 112.32 1.40 21.517 23.517 5.557 117.03 119.03 1.42 22.267 24.267 5.646 117.80 119.80 1.45 21.250 23.250 5.735 113.90 115.90 1.47 20.750 22.750 5.824 116.25 118.25 1.49 20.933 22.933 5.913 118.17 120.17 1.51 21.267 23.267 6.002 118.28 120.28 1.54 19.200 21.200 6.091 114.00 116.00 1.56 12.600 14.600 6.180 C2 = LL12 C3 = LL10 Mean corrected Plotted Corrected Mean corrected Plotted susceptibility (SI x 10- Corrected depth (m) susceptibility (SI x 10-5) susceptibility (SI x depth (m) susceptibility (SI x 5) 10-5) 10-5) -0.525 1.475 0.019 -0.440 1.560 0.014 -0.580 1.420 0.057 -0.720 1.280 0.042 -0.617 1.383 0.095 -1.100 0.900 0.069 -0.700 1.300 0.133 -1.200 0.800 0.097 -0.933 1.067 0.172 -1.317 0.683 0.125 -1.150 0.850 0.210 -1.050 0.950 0.153 -1.250 0.750 0.248 -1.183 0.817 0.180 -1.267 0.733 0.286 -1.233 0.767 0.208 -1.300 0.700 0.324 -1.250 0.750 0.236 -1.375 0.625 0.362 -1.288 0.713 0.264 -1.400 0.600 0.400 -1.217 0.783 0.291 -1.367 0.633 0.439 -0.783 1.217 0.319 -1.263 0.738 0.477 -1.233 0.767 0.347 -1.317 0.683 0.515 -1.300 0.700 0.375 -1.217 0.783 0.553 -1.333 0.667 0.402 -1.250 0.750 0.591 -1.367 0.633 0.430 -1.100 0.900 0.629 -1.267 0.733 0.458 -0.950 1.050 0.667 -1.283 0.717 0.486 -0.900 1.100 0.706 -1.217 0.783 0.513 -0.933 1.067 0.744 -1.267 0.733 0.541 -0.917 1.083 0.782 -1.200 0.800 0.569 -0.883 1.117 0.820 -1.250 0.750 0.597 -1.050 0.950 0.858 -1.250 0.750 0.624 -0.850 1.150 0.896 -1.120 0.880 0.652 -1.267 0.733 0.934 -1.033 0.967 0.680 -0.900 1.100 0.973 -1.150 0.850 0.708 -0.850 1.150 1.011 -1.167 0.833 0.735 308

-0.783 1.217 1.049 -1.017 0.983 0.763 -0.767 1.233 1.087 -0.967 1.033 0.791 -0.733 1.267 1.125 -1.013 0.988 0.819 -0.467 1.533 1.163 -0.983 1.017 0.846 -0.317 1.683 1.201 -1.033 0.967 0.874 -0.167 1.833 1.240 -0.917 1.083 0.902 -0.183 1.817 1.278 -0.733 1.267 0.930 -0.267 1.733 1.316 -0.800 1.200 0.957 -0.583 1.417 1.354 -0.967 1.033 0.985 -0.500 1.500 1.392 -0.875 1.125 1.013 -0.500 1.500 1.430 -1.033 0.967 1.041 -0.717 1.283 1.468 -0.863 1.138 1.068 -0.717 1.283 1.506 -0.967 1.033 1.096 -0.817 1.183 1.545 -0.888 1.113 1.124 -0.650 1.350 1.583 -0.950 1.050 1.152 -0.183 1.817 1.621 -0.700 1.300 1.179 0.800 2.800 1.659 -0.983 1.017 1.207 1.633 3.633 1.697 -1.150 0.850 1.235 2.133 4.133 1.735 -1.083 0.917 1.263 2.867 4.867 1.773 -0.983 1.017 1.290 5.200 7.200 1.812 -0.633 1.367 1.318 8.450 10.450 1.850 -0.225 1.775 1.346 12.850 14.850 1.888 -0.017 1.983 1.374 16.850 18.850 1.926 0.000 2.000 1.401 20.967 22.967 1.964 -0.138 1.863 1.429 20.767 22.767 2.002 -0.217 1.783 1.457 23.433 25.433 2.040 0.383 2.383 1.485 28.417 30.417 2.079 0.913 2.913 1.512 31.650 33.650 2.117 1.550 3.550 1.540 36.217 38.217 2.155 3.450 5.450 1.568 33.950 35.950 2.193 7.383 9.383 1.596 27.233 29.233 2.231 13.067 15.067 1.623 20.650 22.650 2.269 12.067 14.067 1.651 19.488 21.488 2.307 6.383 8.383 1.679 12.017 14.017 2.346 2.300 4.300 1.707 8.317 10.317 2.384 -0.017 1.983 1.734 7.933 9.933 2.422 -0.367 1.633 1.762 8.817 10.817 2.460 -0.417 1.583 1.790

309

11.050 13.050 2.498 -0.233 1.767 1.818 12.417 14.417 2.536 -0.233 1.767 1.845 14.117 16.117 2.574 -0.113 1.888 1.873 15.100 17.100 2.612 -0.117 1.883 1.901 15.033 17.033 2.651 -0.100 1.900 1.929 14.600 16.600 2.689 0.217 2.217 1.956 16.117 18.117 2.727 1.017 3.017 1.984 16.867 18.867 2.765 2.167 4.167 2.012 17.783 19.783 2.803 3.833 5.833 2.040 17.817 19.817 2.841 4.933 6.933 2.067 16.800 18.800 2.879 7.217 9.217 2.095 13.850 15.850 2.918 10.683 12.683 2.123 9.783 11.783 2.956 11.917 13.917 2.151 6.567 8.567 2.994 10.700 12.700 2.178 3.967 5.967 3.032 11.083 13.083 2.206 1.517 3.517 3.070 15.333 17.333 2.234 -0.183 1.817 3.108 14.183 16.183 2.262 -0.683 1.317 3.146 9.867 11.867 2.289 -0.967 1.033 3.185 6.833 8.833 2.317 -1.183 0.817 3.223 5.667 7.667 2.345 -1.000 1.000 3.261 5.950 7.950 2.373 6.583 8.583 2.400 8.600 10.600 2.428 10.300 12.300 2.456 9.650 11.650 2.484 8.600 10.600 2.511 8.525 10.525 2.539 10.483 12.483 2.567 13.183 15.183 2.595 13.775 15.775 2.622 12.267 14.267 2.650 11.138 13.138 2.678 C4 = LL 13 D2 = LL 15 Mean corrected Plotted Corrected Mean corrected Plotted susceptibility (SI x 10- Corrected depth (m) susceptibility (SI x 10-5) susceptibility (SI x depth (m) susceptibility (SI x 5) 10-5) 10-5) -0.800 1.200 0.017171 -0.338 1.663 0.010 -1.017 0.983 0.051514 -0.300 1.700 0.030 -0.983 1.017 0.085856 -0.367 1.633 0.050 310

-1.050 0.950 0.120198 -0.550 1.450 0.070 -1.017 0.983 0.154541 -0.733 1.267 0.090 -0.967 1.033 0.188883 -0.883 1.117 0.110 -0.250 1.750 0.223225 -0.850 1.150 0.130 0.417 2.417 0.257568 -0.867 1.133 0.150 -0.800 1.200 0.29191 -0.900 1.100 0.170 -0.933 1.067 0.326253 -0.833 1.167 0.190 -1.017 0.983 0.360595 -0.483 1.517 0.210 -0.967 1.033 0.394937 -0.450 1.550 0.230 -1.000 1.000 0.42928 -0.500 1.500 0.250 -1.017 0.983 0.463622 -0.767 1.233 0.270 -1.017 0.983 0.497965 -0.883 1.117 0.290 -0.983 1.017 0.532307 -0.688 1.313 0.310 -1.067 0.933 0.566649 -0.217 1.783 0.330 -1.017 0.983 0.600992 1.583 3.583 0.350 -0.983 1.017 0.635334 3.950 5.950 0.370 -1.083 0.917 0.669676 7.500 9.500 0.390 -1.067 0.933 0.704019 18.217 20.217 0.410 -1.183 0.817 0.738361 30.517 32.517 0.430 -1.250 0.750 0.772704 43.267 45.267 0.450 -1.200 0.800 0.807046 74.838 76.838 0.470 -1.100 0.900 0.841388 94.550 96.550 0.490 -1.117 0.883 0.875731 100.233 102.233 0.510 -1.100 0.900 0.910073 107.588 109.588 0.530 -1.363 0.638 0.944415 141.500 143.500 0.550 -1.033 0.967 0.978758 154.667 156.667 0.570 -0.867 1.133 1.0131 161.233 163.233 0.590 -0.567 1.433 1.047443 177.950 179.950 0.610 -0.117 1.883 1.081785 218.400 220.400 0.630 0.283 2.283 1.116127 265.800 267.800 0.650 0.717 2.717 1.15047 231.417 233.417 0.670 0.400 2.400 1.184812 207.083 209.083 0.690 0.033 2.033 1.219154 190.483 192.483 0.710 -0.333 1.667 1.253497 132.733 134.733 0.730 -0.617 1.383 1.287839 132.817 134.817 0.750 -0.767 1.233 1.322182 146.933 148.933 0.770 -0.767 1.233 1.356524 156.083 158.083 0.790 -0.633 1.367 1.390866 160.933 162.933 0.810

311

-0.533 1.467 1.425209 173.583 175.583 0.830 -0.517 1.483 1.459551 219.750 221.750 0.850 -0.567 1.433 1.493894 378.367 380.367 0.870 -0.567 1.433 1.528236 469.750 471.750 0.890 -0.450 1.550 1.562578 314.750 316.750 0.910 -0.300 1.700 1.596921 266.250 268.250 0.930 -0.133 1.867 1.631263 267.400 269.400 0.950 0.483 2.483 1.665605 294.233 296.233 0.970 1.983 3.983 1.699948 318.983 320.983 0.990 4.667 6.667 1.73429 287.083 289.083 1.010 6.667 8.667 1.768633 209.283 211.283 1.030 6.717 8.717 1.802975 180.033 182.033 1.050 6.067 8.067 1.837317 193.133 195.133 1.070 6.033 8.033 1.87166 248.638 250.638 1.090 4.850 6.850 1.906002 268.700 270.700 1.110 3.033 5.033 1.940344 257.133 259.133 1.130 1.733 3.733 1.974687 239.400 241.400 1.150 1.633 3.633 2.009029 191.900 193.900 1.170 3.217 5.217 2.043372 209.500 211.500 1.190 5.433 7.433 2.077714 233.125 235.125 1.210 5.900 7.900 2.112056 235.800 237.800 1.230 6.833 8.833 2.146399 255.683 257.683 1.250 6.533 8.533 2.180741 269.250 271.250 1.270 2.750 4.750 2.215084 316.900 318.900 1.290 0.467 2.467 2.249426 304.483 306.483 1.310 -0.467 1.533 2.283768 299.638 301.638 1.330 -0.750 1.250 2.318111 311.325 313.325 1.350 -0.833 1.167 2.352453 316.283 318.283 1.370 -0.260 1.740 2.386795 310.850 312.850 1.390 -1.133 0.867 2.421138 320.600 322.600 1.410 -1.317 0.683 2.45548 325.225 327.225 1.430 -1.333 0.667 2.489823 325.933 327.933 1.450 -1.300 0.700 2.524165 324.667 326.667 1.470 -1.333 0.667 2.558507 323.113 325.113 1.490 -1.267 0.733 2.59285 328.133 330.133 1.510 -1.367 0.633 2.627192 329.250 331.250 1.530 -1.283 0.717 2.661534 319.300 321.300 1.550 -1.150 0.850 2.695877 302.583 304.583 1.570

312

-1.300 0.700 2.730219 234.067 236.067 1.610 -1.267 0.733 2.764562 201.883 203.883 1.630 -1.200 0.800 2.798904 178.275 180.275 1.650 -1.083 0.917 2.833246 152.700 154.700 1.670 -0.883 1.117 2.867589 135.800 137.800 1.690 -0.683 1.317 2.901931 127.967 129.967 1.710 -0.367 1.633 2.936273 126.283 128.283 1.730 0.233 2.233 2.970616 125.717 127.717 1.750 1.467 3.467 3.004958 129.933 131.933 1.770 3.217 5.217 3.039301 135.217 137.217 1.790 4.867 6.867 3.073643 137.550 139.550 1.810 8.383 10.383 3.107985 138.267 140.267 1.830 11.117 13.117 3.142328 12.650 14.650 3.17667 D3 = LL3 (master core) D3 = LL3 (master core) Mean corrected Plotted Corrected Mean corrected Plotted susceptibility (SI x 10- Corrected depth (m) susceptibility (SI x 10-5) susceptibility (SI x depth (m) susceptibility (SI x 5) 10-5) 10-5) 4.817 6.817 0.010 62.833 64.833 2.450 4.783 6.783 0.030 66.600 68.600 2.470 4.700 6.700 0.050 71.775 73.775 2.490 3.813 5.813 0.070 76.867 78.867 2.510 3.617 5.617 0.090 77.017 79.017 2.530 5.383 7.383 0.110 74.317 76.317 2.550 4.308 6.308 0.130 70.300 72.300 2.570 4.083 6.083 0.150 68.463 70.463 2.590 4.163 6.163 0.170 64.650 66.650 2.610 3.800 5.800 0.190 64.533 66.533 2.630 2.050 4.050 0.210 61.817 63.817 2.650 1.575 3.575 0.230 58.983 60.983 2.670 2.100 4.100 0.250 56.850 58.850 2.690 2.713 4.713 0.270 52.467 54.467 2.710 3.517 5.517 0.290 49.113 51.113 2.730 3.817 5.817 0.310 45.830 47.830 2.750 4.638 6.638 0.330 43.513 45.513 2.770 5.067 7.067 0.350 42.450 44.450 2.790 6.275 8.275 0.370 41.413 43.413 2.810 10.200 12.200 0.390 38.713 40.713 2.830 16.350 18.350 0.410 34.263 36.263 2.850 313

23.600 25.600 0.430 29.900 31.900 2.870 33.867 35.867 0.450 24.838 26.838 2.890 44.200 46.200 0.470 23.400 25.400 2.910 52.350 54.350 0.490 21.863 23.863 2.930 58.567 60.567 0.510 15.575 17.575 2.950 61.750 63.750 0.530 10.188 12.188 2.970 63.063 65.063 0.550 7.400 9.400 2.990 65.250 67.250 0.570 7.000 9.000 3.010 67.917 69.917 0.590 7.670 9.670 3.030 70.450 72.450 0.610 7.683 9.683 3.050 72.550 74.550 0.630 5.725 7.725 3.070 75.183 77.183 0.650 3.800 5.800 3.090 79.117 81.117 0.670 3.925 5.925 3.110 81.617 83.617 0.690 4.475 6.475 3.130 83.767 85.767 0.710 7.875 9.875 3.150 87.033 89.033 0.730 9.213 11.213 3.170 88.550 90.550 0.750 13.813 15.813 3.190 86.867 88.867 0.770 16.975 18.975 3.210 85.983 87.983 0.790 20.125 22.125 3.230 87.783 89.783 0.810 22.167 24.167 3.250 90.433 92.433 0.830 22.833 24.833 3.270 94.217 96.217 0.850 22.333 24.333 3.290 99.333 101.333 0.870 22.350 24.350 3.310 103.283 105.283 0.890 22.833 24.833 3.330 105.417 107.417 0.910 23.788 25.788 3.350 108.100 110.100 0.930 25.550 27.550 3.370 110.667 112.667 0.950 27.975 29.975 3.390 111.917 113.917 0.970 26.967 28.967 3.410 111.767 113.767 0.990 26.267 28.267 3.430 110.583 112.583 1.010 25.438 27.438 3.450 108.400 110.400 1.030 26.188 28.188 3.470 105.900 107.900 1.050 28.700 30.700 3.490 104.367 106.367 1.070 31.150 33.150 3.510 102.233 104.233 1.090 28.200 30.200 3.530 100.167 102.167 1.110 27.480 29.480 3.550 98.800 100.800 1.130 27.763 29.763 3.570 97.683 99.683 1.150 26.688 28.688 3.590 95.750 97.750 1.170 30.000 32.000 3.610

314

93.483 95.483 1.190 33.000 35.000 3.630 91.800 93.800 1.210 35.500 37.500 3.650 86.683 88.683 1.230 36.000 38.000 3.670 79.000 81.000 1.250 36.000 38.000 3.690 71.550 73.550 1.270 35.000 37.000 3.710 64.967 66.967 1.290 33.500 35.500 3.730 59.983 61.983 1.310 32.000 34.000 3.750 55.067 57.067 1.330 32.000 34.000 3.770 52.233 54.233 1.350 33.000 35.000 3.790 48.800 50.800 1.370 34.000 36.000 3.810 43.250 45.250 1.390 34.000 36.000 3.830 40.450 42.450 1.410 33.000 35.000 3.850 31.527 33.527 1.430 33.000 35.000 3.870 28.200 30.200 1.450 32.500 34.500 3.890 20.675 22.675 1.470 32.500 34.500 3.910 15.450 17.450 1.490 32.500 34.500 3.930 12.183 14.183 1.510 33.000 35.000 3.950 11.364 13.364 1.530 35.000 37.000 3.970 8.629 10.629 1.550 39.000 41.000 3.990 6.917 8.917 1.570 43.000 45.000 4.010 5.675 7.675 1.590 46.000 48.000 4.030 5.492 7.492 1.610 49.000 51.000 4.050 5.175 7.175 1.630 52.500 54.500 4.070 6.040 8.040 1.650 56.500 58.500 4.090 6.475 8.475 1.670 59.000 61.000 4.110 7.820 9.820 1.690 59.000 61.000 4.130 8.988 10.988 1.710 59.500 61.500 4.150 10.313 12.313 1.730 59.000 61.000 4.170 13.838 15.838 1.750 59.500 61.500 4.190 16.063 18.063 1.770 61.000 63.000 4.210 19.833 21.833 1.790 64.000 66.000 4.230 23.313 25.313 1.810 66.000 68.000 4.250 29.500 31.500 1.830 69.000 71.000 4.270 36.038 38.038 1.850 74.000 76.000 4.290 41.675 43.675 1.870 80.000 82.000 4.310 46.763 48.763 1.890 58.050 60.050 2.190 50.625 52.625 1.910 60.583 62.583 2.210 54.550 56.550 1.930 61.513 63.513 2.230

315

57.350 59.350 1.950 62.400 64.400 2.250 59.350 61.350 1.970 66.310 68.310 2.270 60.417 62.417 1.990 67.525 69.525 2.290 62.400 64.400 2.010 67.800 69.800 2.310 64.413 66.413 2.030 66.288 68.288 2.330 64.038 66.038 2.050 62.850 64.850 2.350 64.063 66.063 2.070 58.700 60.700 2.370 65.300 67.300 2.090 56.513 58.513 2.390 66.963 68.963 2.110 59.063 61.063 2.410 65.438 67.438 2.130 58.050 60.050 2.430 60.075 62.075 2.150 58.825 60.825 2.170

316

APPENDIX 2: MASTER CORE D3 SUBSMAPLED – PETRIL DISHES

The master core D3 was carefully cut vertically open and sediment subsampled into petril dishes before dry up in the oven at 90oC for 24 hours. Bulk density and saturation moisture were calculated during the operation as listed below;

Depth (m) Midpoint (m) Code Mass of petri Mass of petri Mass of Saturation Bulk density Smoothed Smoothed bulk dish (g) dish + moist petri dish + moisture content (kg/m3) saturation density (kg/m3) sample (g) dry sample (%) moisture (g) content (%) 0.00-0.02 0.01 1 6.74 106.4 17.36 838.42 105.6 1031.4 86.2 0.02-0.04 0.03 2 6.73 95.73 13.45 1224.40 66.8 1102.9 77.8 0.04-0.06 0.05 3 6.715 89.02 12.83 1245.95 60.8 1259.6 63.1 0.06-0.08 0.07 4 6.73 94.2 12.94 1308.53 61.8 1286.9 59.6 0.08-0.10 0.09 5 6.725 85.96 12.36 1306.12 56.1 1294.0 62.7 0.10-0.12 0.11 6 8.045 104.79 15.12 1267.42 70.4 1343.0 61.2 0.12-0.14 0.13 7 8.06 97.34 13.8 1455.40 57.1 1379.0 62.1 0.14-0.16 0.15 8 8.055 97.47 13.96 1414.23 58.7 1459.4 56.9 0.16-0.18 0.17 9 8.055 96.93 13.58 1508.60 55.0 1476.3 56.6 0.18-0.20 0.19 10 8.055 98.56 13.69 1506.12 56.1 1501.8 53.2 0.20-0.22 0.21 11 8.065 85.93 12.96 1490.70 48.7 1535.4 53.4 0.22-0.24 0.23 12 6.735 102.04 12.31 1609.51 55.5 1546.3 53.3 0.24-0.26 0.25 13 8.02 99.62 13.61 1538.64 55.6 1544.9 55.6 0.26-0.28 0.27 14 6.75 95.76 12.36 1486.63 55.8 1457.6 57.4 0.28-0.30 0.29 15 8.025 96.55 14.14 1347.67 60.8 1386.4 60.3 0.30-0.32 0.31 16 6.75 98.8 13.21 1324.92 64.3 1302.1 63.7 0.32-0.34 0.33 17 6.75 95.45 13.4 1233.83 66.1 1254.1 68.2 0.34-0.36 0.35 18 8.035 105.09 15.48 1203.63 74.1 1170.6 73.9 0.36-0.38 0.37 19 8.045 104.27 16.24 1074.19 81.5 1024.8 88.2 0.38-0.40 0.39 20 6.705 104.94 17.66 796.71 109.0 778.0 124.8 0.40-0.42 0.41 21 8 112.09 26.49 462.95 183.9 550.8 166.7

317

0.42-0.44 0.43 22 8.04 110.72 28.88 392.71 207.3 383.8 222.7 0.44-0.46 0.45 23 8.065 118.15 35.89 295.63 276.8 298.6 286.9 0.46-0.48 0.47 24 6.75 123.08 44.6 207.34 376.5 227.5 365.9 0.48-0.50 0.49 25 8.055 132.94 52.74 179.48 444.5 178.5 429.3 0.50-0.52 0.51 26 6.75 123.44 53.7 148.54 467.0 156.0 478.7 0.52-0.54 0.53 27 8.04 134.64 60.79 140.00 524.7 144.7 490.1 0.54-0.56 0.55 28 8.015 126.18 56.12 145.64 478.5 141.7 518.7 0.56-0.58 0.57 29 6.71 139.84 62.29 139.53 552.9 136.9 531.1 0.58-0.60 0.59 30 6.715 134.13 63.21 125.53 562.0 128.7 564.4 0.60-0.62 0.61 31 6.735 135.21 64.89 120.92 578.5 123.0 580.7 0.62-0.64 0.63 32 6.73 141.29 67.2 122.52 601.5 121.4 579.8 0.64-0.66 0.65 33 8.02 132.16 64.27 120.69 559.5 120.5 612.6 0.66-0.68 0.67 34 6.75 155.22 74.78 118.24 676.7 120.1 590.0 0.68-0.70 0.69 35 8.05 126.79 61.72 121.24 533.9 119.5 612.2 0.70-0.72 0.71 36 8.05 145.81 70.98 118.91 626.0 119.0 594.0 0.72-0.74 0.73 37 6.735 142.35 69.27 116.86 622.0 115.5 626.6 0.74-0.76 0.75 38 8.05 141.86 71.56 110.69 631.7 113.7 639.4 0.76-0.78 0.77 39 6.735 149.36 73.52 113.56 664.3 112.8 648.4 0.78-0.80 0.79 40 8.045 147.87 73.3 114.27 649.1 111.9 647.1 0.80-0.82 0.81 41 6.755 137.94 69.89 107.78 628.0 110.4 626.2 0.82-0.84 0.83 42 7.95 134.37 68.41 109.10 601.4 108.1 634.7 0.84-0.86 0.85 43 6.67 147.42 74.49 107.53 674.6 107.2 642.9 0.86-0.88 0.87 44 6.725 141.18 72.35 104.88 652.8 105.0 688.1 0.88-0.90 0.89 45 8.03 158.01 82.1 102.48 736.8 103.3 682.6 0.90-0.92 0.91 46 6.73 140.73 72.91 102.48 658.3 101.4 711.1 0.92-0.94 0.93 47 8.03 155.82 82.23 99.18 738.1 99.0 702.1 0.94-0.96 0.95 48 6.73 146.17 78.1 95.38 709.9 98.7 719.1 0.96-0.98 0.97 49 8.06 151.8 79.37 101.57 709.3 99.4 725.6 0.98-1.00 0.99 50 8.035 161.19 84.18 101.14 757.4 101.9 717.2 1.00-1.02 1.01 51 6.715 146.5 75.56 103.04 684.8 101.2 696.9

318

1.02-1.04 1.03 52 8.02 138.02 73.21 99.42 648.5 101.0 675.9 1.04-1.06 1.05 53 6.73 146.67 76.54 100.46 694.4 99.4 672.1 1.06-1.08 1.07 54 6.74 140.94 74.43 98.26 673.3 99.7 696.4 1.08-1.10 1.09 55 8.065 153.48 80.6 100.48 721.5 100.4 691.2 1.10-1.12 1.11 56 8.06 146.21 76.29 102.48 678.7 101.7 692.4 1.12-1.14 1.13 57 6.73 144.29 74.78 102.15 676.9 102.2 700.5 1.14-1.16 1.15 58 8.05 159.57 83.05 102.03 746.0 102.5 724.2 1.16-1.18 1.17 59 6.74 159.87 82.09 103.22 749.5 103.8 708.8 1.18-1.20 1.19 60 8.045 138.74 71.46 106.09 630.8 105.1 710.6 1.20-1.22 1.21 61 6.73 162.27 82.27 105.90 751.4 106.4 688.8 1.22-1.24 1.23 62 8.03 150.65 76.82 107.33 684.3 107.4 690.8 1.24-1.26 1.25 63 6.74 140.39 70.74 108.83 636.6 110.2 643.4 1.26-1.28 1.27 64 8.06 139.38 69.3 114.44 609.2 114.2 633.2 1.28-1.30 1.29 65 6.75 151.01 72.49 119.44 653.9 121.6 618.8 1.30-1.32 1.31 66 8.03 145.69 67.67 130.82 593.3 136.7 574.4 1.32-1.34 1.33 67 6.73 130.99 54.57 159.74 475.9 143.8 509.8 1.34-1.36 1.35 68 6.74 118.18 53 140.90 460.2 144.5 512.7 1.36-1.38 1.37 69 8.025 149.03 68.54 133.01 602.0 137.0 532.1 1.38-1.40 1.39 70 6.73 134.09 60.42 137.21 534.1 141.2 514.1 1.40-1.42 1.41 71 8.05 111.49 48.89 153.28 406.2 147.1 464.3 1.42-1.44 1.43 72 6.75 120.83 52.26 150.67 452.7 151.5 475.1 1.44-1.46 1.45 73 8.025 150.71 64.97 150.57 566.4 179.9 451.0 1.46-1.48 1.47 74 6.75 120.38 40.32 238.49 333.9 239.5 380.5 1.48-1.50 1.49 75 8.04 112.12 32.28 329.37 241.1 263.8 311.2 1.50-1.52 1.51 76 6.74 123.37 42.8 223.43 358.7 288.2 290.4 1.52-1.54 1.53 77 8.025 120.4 35.32 311.71 271.5 329.3 274.2 1.54-1.56 1.55 78 6.76 113.59 26.09 452.66 192.3 434.3 207.3 1.56-1.58 1.57 79 8.065 109.54 23.96 538.41 158.1 532.6 165.3 1.58-1.60 1.59 80 6.74 110.12 21.37 606.63 145.5 595.5 145.1 1.60-1.62 1.61 81 8.045 106.27 21.29 641.60 131.8 632.0 138.6

319

1.62-1.64 1.63 82 6.74 110.85 20.66 647.92 138.5 641.9 135.1 1.64-1.66 1.65 83 8.04 108 21.62 636.08 135.1 626.5 139.1 1.66-1.68 1.67 84 6.74 107.24 21.19 595.50 143.7 602.1 140.0 1.68-1.70 1.69 85 8.005 103.83 22.21 574.59 141.3 572.9 148.6 1.70-1.72 1.71 86 6.735 111.58 22.9 548.59 160.8 531.2 155.7 1.72-1.74 1.73 87 8.04 102.72 24.64 470.36 165.1 482.9 174.7 1.74-1.76 1.75 88 6.74 112.2 26.65 429.68 198.0 430.3 188.4 1.76-1.78 1.77 89 8.04 107.78 28.36 390.85 202.1 385.0 210.7 1.78-1.80 1.79 90 6.725 107.98 30.03 334.48 231.8 347.7 227.7 1.80-1.82 1.81 91 8.025 112.69 33.07 317.91 249.1 303.3 256.0 1.82-1.84 1.83 92 6.72 109.82 35.57 257.37 287.0 265.3 290.2 1.84-1.86 1.85 93 8.05 115.92 41.68 220.76 334.5 227.7 340.5 1.86-1.88 1.87 94 6.75 129.43 46.96 205.10 400.0 204.8 397.9 1.88-1.90 1.89 95 8.04 141.33 54.21 188.69 459.3 190.9 426.1 1.90-1.92 1.91 96 6.73 124.18 48.85 178.85 419.0 178.4 456.4 1.92-1.94 1.93 97 8.06 140.18 57.41 167.72 490.9 171.1 447.2 1.94-1.96 1.95 98 6.77 122.61 50.18 166.85 431.8 166.3 457.1 1.96-1.98 1.97 99 8.06 127.28 53.15 164.40 448.5 164.4 439.9 1.98-2.00 1.99 100 6.76 122.46 50.92 162.00 439.3 161.6 459.8 2.00-2.02 2.01 101 8.035 135.74 57.47 158.33 491.7 158.3 471.7 2.02-2.04 2.03 102 6.74 130.59 55.4 154.52 484.0 156.3 482.5 2.04-2.06 2.05 103 3.495 124.84 50.91 155.92 471.6 155.5 489.4 2.06-2.08 2.07 104 3.54 135.45 55.05 156.09 512.4 155.5 502.0 2.08-2.10 2.09 105 3.445 137.02 55.92 154.55 522.0 154.1 498.1 2.10-2.12 2.11 106 3.49 119.9 49.74 151.70 460.1 153.7 506.2 2.12-2.14 2.13 107 3.52 140.98 57.45 154.89 536.5 150.4 504.8 2.14-2.16 2.15 108 3.49 130.83 55.56 144.56 517.9 145.7 528.3 2.16-2.18 2.17 109 3.49 130.3 56.83 137.74 530.6 140.0 531.7 2.18-2.20 2.19 110 3.52 134.13 58.46 137.73 546.5 137.3 552.0 2.20-2.22 2.21 111 3.515 141.18 61.71 136.56 578.9 127.5 568.9

320

2.22-2.24 2.23 112 3.51 125.15 61.94 108.18 581.2 128.9 573.8 2.24-2.26 2.25 113 3.515 140.09 59.95 142.00 561.4 150.2 519.9 2.26-2.28 2.27 114 3.465 129.44 45.4 200.41 417.1 157.3 517.1 2.28-2.30 2.29 115 3.565 135.62 61.14 129.36 572.7 142.6 552.3 2.30-2.32 2.31 116 3.58 136.46 70.64 98.15 667.1 119.1 596.9 2.32-2.34 2.33 117 3.445 130.63 58.82 129.68 550.8 119.6 581.6 2.34-2.36 2.35 118 3.53 125.96 56.51 131.09 527.0 132.0 535.5 2.36-2.38 2.37 119 3.52 128.62 56.67 135.37 528.7 130.9 546.5 2.38-2.40 2.39 120 7.7 140.5 66.39 126.27 583.8 130.4 557.4 2.40-2.42 2.41 121 6.745 135.89 63 129.57 559.6 130.5 561.3 2.42-2.44 2.43 122 6.81 134.85 61.14 135.67 540.4 134.2 559.9 2.44-2.46 2.45 123 6.7 145.06 64.99 137.36 579.8 136.2 557.4 2.46-2.48 2.47 124 6.745 137.44 62.22 135.59 551.8 136.7 559.4 2.48-2.50 2.49 125 7.53 137.76 62.48 137.00 546.6 134.4 562.5 2.50-2.52 2.51 126 6.74 143.34 65.97 130.63 589.2 133.4 576.2 2.52-2.54 2.53 127 7.24 145.91 66.83 132.71 592.8 133.5 563.6 2.54-2.56 2.55 128 6.87 128.29 58.04 137.29 509.0 137.7 562.1 2.56-2.58 2.57 129 6.855 149.79 65.62 143.23 584.5 139.9 537.8 2.58-2.60 2.59 130 6.98 131.92 59.23 139.12 519.7 142.9 545.7 2.60-2.62 2.61 131 7.305 139.19 60.86 146.26 532.7 144.3 539.6 2.62-2.64 2.63 132 6.71 147.52 63.63 147.38 566.2 147.4 536.9 2.64-2.66 2.65 133 6.835 134.68 58.3 148.41 511.9 150.1 523.9 2.66-2.68 2.67 134 6.755 132.98 56.37 154.41 493.5 153.5 505.4 2.68-2.70 2.69 135 6.755 139.02 58.09 157.65 510.6 157.8 493.1 2.70-2.72 2.71 136 6.75 131.5 54.51 161.20 475.1 161.1 477.2 2.72-2.74 2.73 137 7.34 125.98 52.18 164.59 446.0 164.8 463.7 2.74-2.76 2.75 138 6.86 133.85 54.12 168.71 470.1 166.6 461.1 2.76-2.78 2.77 139 6.92 132.11 53.89 166.53 467.2 167.0 468.9 2.78-2.80 2.79 140 6.86 132.22 54.05 165.65 469.4 167.3 456.0 2.80-2.82 2.81 141 6.88 123.91 50.26 169.78 431.5 170.2 441.6

321

2.82-2.84 2.83 142 7.62 124.83 50.23 175.08 423.8 176.2 431.3 2.84-2.86 2.85 143 6.885 131.97 50.98 183.67 438.6 187.0 413.6 2.86-2.88 2.87 144 6.825 121.73 44.85 202.18 378.2 199.0 397.6 2.88-2.90 2.89 145 6.845 124.45 44.64 211.17 376.0 202.2 382.1 2.90-2.92 2.91 146 7.66 123.31 47.09 193.30 392.2 207.9 373.9 2.92-2.94 2.93 147 6.86 120.3 42.4 219.19 353.5 243.7 337.2 2.94-2.96 2.95 148 7.22 119.14 33.95 318.71 265.9 285.7 289.6 2.96-2.98 2.97 149 6.81 111.95 31.89 319.22 249.5 323.3 253.8 2.98-3.00 2.99 150 6.67 113.47 31.39 332.04 245.9 305.9 261.7 3.00-3.02 3.01 151 6.735 113.46 35.85 266.56 289.6 269.7 300.6 3.02-3.04 3.03 152 6.83 121.2 43.65 210.62 366.3 267.1 294.8 3.04-3.06 3.05 153 6.75 104.2 29.72 324.25 228.5 343.1 252.6 3.06-3.08 3.07 154 6.81 104.18 23.19 494.44 162.9 431.6 191.1 3.08-3.10 3.09 155 7.6 112.93 25.88 476.20 181.8 482.6 173.8 3.10-3.12 3.11 156 6.77 109.25 24.53 477.03 176.7 471.6 171.7 3.12-3.14 3.13 157 6.53 94.94 22.27 461.69 156.6 444.1 182.5 3.14-3.16 3.15 158 6.72 112.96 28.25 393.45 214.2 402.9 202.7 3.16-3.18 3.17 159 6.755 115.02 30.63 353.47 237.5 355.5 229.5 3.18-3.20 3.19 160 6.91 106.83 30.73 319.48 236.9 323.3 253.2 3.20-3.22 3.21 161 6.715 120.45 35.37 296.91 285.0 289.8 274.3 3.22-3.24 3.23 162 6.84 113.64 37.1 252.94 301.0 259.2 305.3 3.24-3.26 3.25 163 7.76 116.49 40.92 227.90 329.8 237.0 328.2 3.26-3.28 3.27 164 7.365 124.75 42.92 230.15 353.7 225.8 338.2 3.28-3.30 3.29 165 6.76 113.03 40.05 219.22 331.1 220.1 356.5 3.30-3.32 3.31 166 6.76 127.03 45.44 210.94 384.8 214.0 353.9 3.32-3.34 3.33 167 7.34 115.81 42.11 211.96 345.9 213.8 366.2 3.34-3.36 3.35 168 7.525 125.43 44.53 218.62 368.1 211.3 364.1 3.36-3.38 3.37 169 6.76 122.12 44.8 203.26 378.4 207.3 372.7 3.38-3.40 3.39 170 6.59 118.68 43.95 200.03 371.6 200.8 374.2 3.40-3.42 3.41 171 6.525 118.58 43.98 199.17 372.6 203.5 367.5

322

3.42-3.44 3.43 172 7.66 119.8 43.67 211.41 358.2 205.6 374.2 3.44-3.46 3.45 173 7.65 128.26 47.04 206.19 391.8 206.9 378.3 3.46-3.48 3.47 174 6.76 124.02 45.46 203.00 385.0 204.0 372.3 3.48-3.50 3.49 175 7.31 110.79 41.49 202.75 340.0 200.1 371.5 3.50-3.52 3.51 176 6.84 122.16 46 194.48 389.5 198.4 363.9 3.52-3.54 3.53 177 6.545 115.05 42.96 197.97 362.2 199.9 375.7 3.54-3.56 3.55 178 6.78 122.64 44.5 207.16 375.2 204.5 351.9 3.56-3.58 3.57 179 6.715 105.45 38.72 208.50 318.4 211.3 344.0 3.58-3.60 3.59 180 6.73 114.95 40.75 218.11 338.4 205.6 351.0 3.60-3.62 3.61 181 7.36 122.98 47.2 190.21 396.3 193.2 402.4 3.62-3.64 3.63 182 7.62 136.45 55.13 171.16 472.6 176.4 430.0 3.64-3.66 3.65 183 6.805 120.21 49.14 167.88 421.1 168.8 444.5 3.66-3.68 3.67 184 6.775 125.02 50.99 167.43 439.8 169.6 422.5 3.68-3.70 3.69 185 6.795 118.65 47.68 173.58 406.7 171.9 425.8 3.70-3.72 3.71 186 6.73 125.8 50.06 174.80 431.0 176.4 417.0 3.72-3.74 3.73 187 7.205 123.93 48.76 180.89 413.4 181.7 415.9 3.74-3.76 3.75 188 6.795 124.15 47.33 189.52 403.2 180.8 408.1 3.76-3.78 3.77 189 6.65 118.14 47.64 171.99 407.7 179.7 401.6 3.78-3.80 3.79 190 6.855 116.79 46.45 177.65 393.9 178.3 404.9 3.80-3.82 3.81 191 6.68 125.14 48.21 185.24 413.1 182.6 407.7 3.82-3.84 3.83 192 6.75 125.92 48.58 184.89 416.1 183.7 411.3 3.84-3.86 3.85 193 7.325 121.65 48 181.07 404.6 181.3 407.1 3.86-3.88 3.87 194 6.525 118.39 46.79 177.82 400.5 178.4 408.3 3.88-3.90 3.89 195 6.76 123.38 48.97 176.29 419.9 176.6 403.6 3.90-3.92 3.91 196 7.38 115.59 46.63 175.69 390.4 175.2 403.9 3.92-3.94 3.93 197 7.53 117.91 47.87 173.62 401.3 175.3 398.8 3.94-3.96 3.95 198 7.54 120.08 48.22 176.65 404.7 174.8 414.3 3.96-3.98 3.97 199 7.56 128.06 51.5 174.24 437.1 174.2 419.8 3.98-4.00 3.99 200 6.59 120.65 48.58 171.64 417.7 169.5 433.2 4.00-4.02 4.01 201 7.51 124.92 52.23 162.54 444.8 165.0 439.4

323

4.02-4.04 4.03 202 7.33 126.81 53.13 160.87 455.6 159.3 443.1 4.04-4.06 4.05 203 6.81 116.55 49.92 154.56 428.8 154.2 451.1 4.06-4.08 4.07 204 6.725 123.24 53.87 147.14 469.0 147.3 464.7 4.08-4.10 4.09 205 6.56 126.41 56.46 140.18 496.4 142.4 484.4 4.10-4.12 4.11 206 6.805 124.48 55.84 139.98 487.8 141.2 488.1 4.12-4.14 4.13 207 7.34 124.82 55.6 143.43 480.1 141.9 481.6 4.14-4.16 4.15 208 6.815 123.02 54.76 142.37 476.9 142.2 500.0 4.16-4.18 4.17 209 6.535 137.93 61.12 140.72 543.0 143.3 508.8 4.18-4.20 4.19 210 7.405 133.09 58.34 146.76 506.7 144.3 513.8 4.20-4.22 4.21 211 6.75 128.05 56.19 145.35 491.8 144.2 500.5 4.22-4.24 4.23 212 6.72 128.36 57.29 140.54 503.0 142.2 488.1 4.24-4.26 4.25 213 6.53 120.12 53.74 140.61 469.6 137.8 494.7 4.26-4.28 4.27 214 6.57 126.04 58 132.30 511.6 133.7 505.4 4.28-4.30 4.29 215 6.695 129.44 60.48 128.21 535.0 128.3 509.8 4.30-4.32 4.31 216 6.84 115.81 55.39 124.45 482.9 125.4 519.2 4.32-4.34 4.33 217 6.77 128.08 61.01 123.65 539.5 123.4 511.2 4.34-4.36 4.35 218 7.51 79.18 39.79 122.03 117.1 4.36-4.38 4.37 219 7.57 40.2 23.45 105.48 113.8

324

APPENDIX 3: SECOND VERSION – MS TECHNIQUE

The second version of the magnetic susceptibility was utilized to determine the relationship between the mass-specific magnetic susceptibility, against the frequency-dependent magnetic susceptibility, of dry lake sediments, catchment soils and catchment basaltic lava. Code Depth (m) Middle Low- Standard High- Standard Frequency- Standard Middle depth frequency deviation frequency deviation (10-5 dependent deviation depth (m) (m) mass-specific (10-8 volume- SI units) magnetic (%) magnetic m3kg-1) specific susceptibilit susceptibility magnetic y (%) (10-8 m3kg-1) susceptibility (10-5 SI units) A Soil 458.851 0.019 282.71 1.22 3.56 0.65 B Soil 338.410 0.045 190.92 1.30 5.80 1.26 C Soil 156.233 0.012 96.52 0.45 5.99 0.91 D Soil 473.124 0.010 297.13 1.10 4.11 0.44 E Soil 920.597 0.024 442.67 1.75 9.64 0.45 F Soil 347.610 0.006 257.64 1.10 3.83 0.46 I Soil 597.846 0.013 435.07 1.57 2.85 0.45 D Rock 73.556 0.003 79.82 0.17 4.58 0.63 G Rock 131.959 0.002 158.24 0.65 2.87 0.50 H Rock 97.046 0.023 165.44 2.20 2.22 1.99 J1 Rock 464.80 26.192 520.76 24.159 J2 Rock 479.65 18.523 463.19 14.584 K1 Rock 927.04 28.43 928.55 27.509 K2 Rock 832.42 40.261 805.91 25.911 D3/35 0.68-0.70 0.69 59.597 69.597 0.016 32.83 0.53 3.01 2.23 0.69 D3/36 0.70-0.72 0.71 59.302 69.302 0.012 37.61 0.31 3.24 1.56 0.71 D3/37 0.72-0.74 0.73 55.954 65.954 0.004 38.09 0.57 1.55 1.64 0.73 D3/38 0.74-0.76 0.75 59.613 69.613 0.026 39.11 0.49 2.84 2.39 0.75 D3/39 0.76-0.78 0.77 56.825 66.825 0.021 35.63 0.38 3.73 2.13 0.77 D3/40 0.78-0.80 0.79 48.871 58.871 0.005 32.43 0.44 8.29 1.55 0.79 D3/41 0.80-0.82 0.81 58.195 68.195 0.009 37.89 0.52 3.00 1.78 0.81 D3/42 0.82-0.84 0.83 58.105 68.105 0.030 30.04 0.31 2.62 2.46 0.83 D3/43 0.84-0.86 0.85 60.071 70.071 0.009 36.70 0.44 2.91 1.63 0.85 D3/44 0.86-0.88 0.87 59.239 69.239 0.007 38.99 0.44 3.06 1.47 0.87 D3/45 0.88-0.90 0.89 60.929 70.929 0.016 41.11 0.42 3.64 1.87 0.89 D3/46 0.90-0.92 0.91 63.054 73.054 0.014 40.17 0.43 2.85 1.77 0.91 D3/47 0.92-0.94 0.93 63.127 73.127 0.013 39.06 0.58 2.74 1.97 0.93 D3/48 0.94-0.96 0.95 60.475 70.475 0.015 35.48 0.53 3.91 2.10 0.95

325

D3/49 0.96-0.98 0.97 63.539 73.539 0.004 38.34 0.38 2.95 1.17 0.97 D3/50 0.98-1.00 0.99 66.471 76.471 0.016 43.31 0.69 2.79 2.15 0.99 D3/51 1.00-1.02 1.01 67.503 77.503 0.016 43.51 0.76 2.33 2.25 1.01 D3/52 1.02-1.04 1.03 63.563 73.563 0.012 43.58 0.67 1.93 1.99 1.03 D3/53 1.04-1.06 1.05 68.543 78.543 0.003 44.36 0.48 1.65 1.21 1.05 D3/54 1.06-1.08 1.07 57.412 67.412 0.006 34.51 0.64 2.02 2.05 1.07 D3/55 1.08-1.10 1.09 60.153 70.153 0.023 40.48 0.43 3.41 2.16 1.09 D3/56 1.10-1.12 1.11 57.847 67.847 0.016 40.10 0.54 3.48 2.07 1.11 D3/57 1.12-1.14 1.13 58.826 68.826 0.012 34.69 0.39 3.82 1.74 1.13 D3/58 1.14-1.16 1.15 55.514 65.514 0.007 36.49 0.51 2.62 1.74 1.15 D3/59 1.16-1.18 1.17 61.199 71.199 0.016 42.01 0.42 3.07 1.84 1.17 D3/60 1.18-1.20 1.19 57.264 67.264 0.013 33.27 0.45 2.92 1.96 1.19 D3/61 1.20-1.22 1.21 57.882 67.882 0.012 33.94 0.71 2.39 2.48 1.21 D3/62 1.22-1.24 1.23 51.560 61.560 0.018 28.90 0.35 3.82 2.19 1.23 D3/63 1.24-1.26 1.25 49.986 59.986 0.011 31.62 0.62 3.41 2.40 1.25 D3/64 1.26-1.28 1.27 42.496 52.496 0.023 24.31 0.19 4.50 2.42 1.27 D3/65 1.28-1.30 1.29 43.650 53.650 0.004 31.80 0.22 4.32 1.13 1.29 D3/66 1.30-1.32 1.31 42.185 52.185 0.012 23.35 0.38 3.22 2.27 1.31 D3/67 1.32-1.34 1.33 41.290 51.290 0.041 23.10 0.35 4.76 3.43 1.33 D3/68 1.34-1.36 1.35 51.623 61.623 0.013 27.95 0.18 3.84 1.66 1.35 D3/69 1.36-1.38 1.37 38.854 48.854 0.008 20.16 0.29 4.10 1.97 1.37 D3/70 1.38-1.40 1.39 36.870 46.870 0.009 22.49 0.20 4.06 1.75 1.39 D3/71 1.40-1.42 1.41 30.240 40.240 0.004 17.82 0.22 3.35 1.57 1.41 D3/72 1.42-1.44 1.43 28.817 38.817 0.017 16.45 0.15 4.95 2.56 1.43 D3/73 1.44-1.46 1.45 19.457 29.457 0.008 11.01 0.21 3.25 2.74 1.45 D3/74 1.46-1.48 1.47 14.826 24.826 0.012 8.69 0.22 1.61 3.73 1.47 D3/75 1.48-1.50 1.49 12.122 22.122 0.005 6.38 0.11 2.75 2.68 1.49 D3/76 1.50-1.52 1.51 15.076 25.076 0.012 6.88 0.11 3.84 3.15 1.51 D3/77 1.52-1.54 1.53 12.176 22.176 0.005 6.30 0.10 3.45 2.55 1.53 D3/78 1.54-1.56 1.55 10.390 20.390 0.007 4.94 0.07 4.08 2.98 1.55 D3/79 1.56-1.58 1.57 10.685 20.685 0.002 4.88 0.11 4.20 2.56 1.57 D3/80 1.58-1.60 1.59 11.518 21.518 0.018 3.76 0.07 2.72 4.25 1.59 D3/81 1.60-1.62 1.61 11.429 21.429 0.014 3.69 0.09 2.70 4.17 1.61 D3/82 1.62-1.64 1.63 12.089 22.089 0.026 3.97 0.07 2.88 4.89 1.63 D3/83 1.64-1.66 1.65 14.842 24.842 0.012 4.44 0.09 3.48 3.45 1.65 D3/84 1.66-1.68 1.67 18.213 28.213 0.016 5.58 0.07 2.11 3.14 1.67 D3/85 1.68-1.70 1.69 21.311 31.311 0.009 7.19 0.09 2.90 2.27 1.69 D3/86 1.70-1.72 1.71 25.352 35.352 0.030 9.40 0.09 4.42 3.52 1.71 D3/87 1.72-1.74 1.73 26.767 36.767 0.003 9.27 0.09 5.39 1.30 1.73 D3/88 1.74-1.76 1.75 33.546 43.546 0.008 11.62 0.20 5.71 2.19 1.75 D3/89 1.76-1.78 1.77 34.931 44.931 0.005 13.60 0.15 4.57 1.48 1.77 D3/90 1.78-1.80 1.79 38.335 48.335 0.024 15.96 0.13 3.65 2.57 1.79 D3/91 1.80-1.82 1.81 41.623 51.623 0.026 18.46 0.16 3.57 2.62 1.81 326

D3/92 1.82-1.84 1.83 43.255 53.255 0.007 20.28 0.15 3.13 1.41 1.83 D3/93 1.84-1.86 1.85 49.562 59.562 0.005 26.78 0.24 3.40 1.29 1.85 D3/94 1.86-1.88 1.87 46.674 56.674 0.008 25.89 0.17 3.81 1.37 1.87 D3/95 1.88-1.90 1.89 50.434 60.434 0.005 25.73 0.15 4.11 1.09 1.89 D3/96 1.90-1.92 1.91 50.326 60.326 0.012 28.73 0.17 4.21 1.61 1.91 D3/97 1.92-1.94 1.93 49.949 59.949 0.005 29.53 0.24 3.65 1.17 1.93 D3/98 1.94-1.96 1.95 50.887 60.887 0.003 39.84 0.43 2.85 1.24 1.95 D3/99 1.96-1.98 1.97 52.305 62.305 0.002 34.18 0.50 3.66 1.49 1.97 D3/100 1.98-2.00 1.99 54.462 64.462 0.002 38.46 0.70 2.61 1.81 1.99 D3/101 2.00-2.02 2.01 52.081 62.081 0.002 32.70 0.30 4.92 1.03 2.01 D3/102 2.02-2.04 2.03 54.128 64.128 0.008 41.10 0.54 3.98 1.73 2.03 D3/103 2.04-2.06 2.05 55.287 65.287 0.003 33.48 0.31 5.80 1.03 2.05 D3/104 2.06-2.08 2.07 54.743 64.743 0.002 33.16 0.32 4.29 1.05 2.07 D3/105 2.08-2.10 2.09 56.136 66.136 0.002 32.96 0.25 4.57 0.89 2.09 D3/106 2.10-2.12 2.11 56.503 66.503 0.007 33.73 0.20 3.57 1.19 2.11 D3/107 2.12-2.14 2.13 52.909 62.909 0.003 26.69 0.26 3.57 1.07 2.13 D3/108 2.14-2.16 2.15 41.528 51.528 0.008 26.51 0.19 3.24 1.48 2.15 D3/109 2.16-2.18 2.17 39.433 49.433 0.009 25.09 0.18 3.90 1.59 2.17 D3/110 2.18-2.20 2.19 38.873 48.873 0.009 22.89 0.29 3.19 1.88 2.19 D3/111 2.20-2.22 2.21 42.088 52.088 0.004 24.45 0.32 3.20 1.59 2.21 D3/112 2.22-2.24 2.23 41.845 51.845 0.002 34.28 0.48 3.31 1.45 2.23 D3/113 2.24-2.26 2.25 45.191 55.191 0.004 26.99 0.32 3.86 1.45 2.25 D3/114 2.26-2.28 2.27 50.167 60.167 0.008 32.07 0.21 1.10 1.34 2.27 D3/115 2.28-2.30 2.29 46.994 56.994 0.006 32.19 0.17 2.57 1.20 2.29 D3/116 2.30-2.32 2.31 47.602 57.602 0.004 29.97 0.21 1.92 1.10 2.31 D3/117 2.32-2.34 2.33 45.644 55.644 0.014 30.09 0.22 2.98 1.85 2.33 D3/118 2.34-2.36 2.35 45.241 55.241 0.006 28.52 0.18 2.82 1.21 2.35 D3/119 2.36-2.38 2.37 38.100 48.100 0.004 25.73 0.21 2.17 1.19 2.37 D3/120 2.38-2.40 2.39 41.348 51.348 0.004 24.39 0.17 1.84 1.14 2.39 D3/121 2.40-2.42 2.41 44.226 54.226 0.002 30.87 0.11 2.06 0.69 2.41 D3/122 2.42-2.44 2.43 42.027 52.027 0.004 27.70 0.15 1.61 1.00 2.43 D3/123 2.44-2.46 2.45 44.921 54.921 0.003 28.12 0.24 1.26 1.14 2.45 D3/124 2.46-2.48 2.47 47.085 57.085 0.009 31.82 0.25 1.79 1.54 2.47 D3/125 2.48-2.50 2.49 57.589 67.589 0.006 34.31 0.21 2.10 1.11 2.49 D3/126 2.50-2.52 2.51 53.750 63.750 0.006 34.17 0.15 1.79 1.04 2.51 D3/127 2.52-2.54 2.53 54.231 64.231 0.012 32.68 0.24 2.33 1.60 2.53 D3/128 2.54-2.56 2.55 51.090 61.090 0.003 31.72 0.19 1.41 0.85 2.55 D3/129 2.56-2.58 2.57 47.610 57.610 0.006 32.09 0.16 2.45 1.13 2.57 D3/130 2.58-2.60 2.59 50.270 60.270 0.012 30.38 0.33 1.86 1.86 2.59 D3/131 2.60-2.62 2.61 54.036 64.036 0.013 37.64 0.22 2.58 1.58 2.61 D3/132 2.62-2.64 2.63 44.182 54.182 0.004 32.97 0.18 2.10 1.00 2.63 D3/133 2.64-2.66 2.65 48.887 58.887 0.006 30.12 0.24 1.38 1.33 2.65 D3/134 2.66-2.68 2.67 43.778 53.778 0.005 29.78 0.28 2.08 1.36 2.67 327

D3/135 2.68-2.70 2.69 44.613 54.613 0.015 29.09 0.31 1.86 2.09 2.69 D3/136 2.70-2.72 2.71 41.505 51.505 0.013 29.08 0.19 2.94 1.81 2.71 D3/137 2.72-2.74 2.73 38.352 48.352 0.004 24.71 0.23 2.02 1.27 2.73 D3/138 2.74-2.76 2.75 36.799 46.799 0.007 25.59 0.11 2.38 1.38 2.75 D3/139 2.76-2.78 2.77 37.226 47.226 0.002 27.44 0.19 2.75 0.98 2.77 D3/140 2.78-2.80 2.79 34.281 44.281 0.003 22.26 0.23 2.60 1.29 2.79 D3/141 2.80-2.82 2.81 35.601 45.601 0.006 23.72 0.15 3.02 1.42 2.81 D3/142 2.82-2.84 2.83 32.842 42.842 0.005 22.03 0.21 2.32 1.52 2.83 D3/143 2.84-2.86 2.85 29.938 39.938 0.004 19.01 0.16 2.74 1.33 2.85 D3/144 2.86-2.88 2.87 24.721 34.721 0.004 15.12 0.11 3.54 1.36 2.87 D3/145 2.88-2.90 2.89 22.177 32.177 0.003 13.31 0.17 2.60 1.65 2.89 D3/146 2.90-2.92 2.91 25.831 35.831 0.005 16.46 0.17 2.62 1.70 2.91 D3/147 2.92-2.94 2.93 18.954 28.954 0.004 11.01 0.20 1.96 2.28 2.93 D3/148 2.94-2.96 2.95 10.485 20.485 0.008 5.84 0.12 2.06 3.39 2.95 D3/149 2.96-2.98 2.97 9.984 19.984 0.012 5.05 0.10 1.85 3.96 2.97 D3/150 2.98-3.00 2.99 9.232 19.232 0.002 4.96 0.07 1.71 1.96 2.99 D3/151 3.00-3.02 3.01 10.371 20.371 0.002 5.36 0.10 0.37 2.32 3.01 D3/152 3.02-3.04 3.03 11.814 21.814 0.001 5.85 0.10 0.95 1.96 3.03 D3/153 3.04-3.06 3.05 6.660 16.660 0.002 2.98 0.07 -0.07 -2.92 3.05 D3/154 3.06-3.08 3.07 4.407 14.407 0.006 1.92 0.05 4.77 4.43 3.07 D3/155 3.08-3.10 3.09 6.965 16.965 0.002 3.23 0.07 2.94 2.71 3.09 D3/156 3.10-3.12 3.11 9.597 19.597 0.004 4.13 0.08 2.69 2.73 3.11 D3/157 3.12-3.14 3.13 11.565 21.565 0.003 4.62 0.07 2.33 2.07 3.13 D3/158 3.14-3.16 3.15 20.020 30.020 0.005 10.78 0.12 2.60 1.82 3.15 D3/159 3.16-3.18 3.17 25.138 35.138 0.003 14.16 0.23 1.84 1.93 3.17 D3/160 3.18-3.20 3.19 28.651 38.651 0.004 17.52 0.17 2.86 1.44 3.19 D3/161 3.20-3.22 3.21 31.086 41.086 0.002 19.69 0.10 2.68 0.89 3.21 D3/162 3.22-3.24 3.23 32.575 42.575 0.007 18.28 0.26 2.99 1.94 3.23 D3/163 3.24-3.26 3.25 32.259 42.259 0.012 17.85 0.22 3.47 2.23 3.25 D3/164 3.26-3.28 3.27 29.052 39.052 0.001 19.57 0.20 1.36 1.11 3.27 D3/165 3.28-3.30 3.29 24.526 34.526 0.007 14.35 0.15 2.28 1.89 3.29 D3/166 3.30-3.32 3.31 24.626 34.626 0.003 15.75 0.16 1.61 1.44 3.31 D3/167 3.32-3.34 3.33 24.144 34.144 0.003 14.34 0.21 1.85 1.76 3.33 D3/168 3.34-3.36 3.35 24.483 34.483 0.004 14.68 0.11 1.64 1.41 3.35 D3/169 3.36-3.38 3.37 29.913 39.913 0.002 19.72 0.19 1.50 1.21 3.37 D3/170 3.38-3.40 3.39 29.043 39.043 0.002 17.60 0.22 1.63 1.45 3.39 D3/171 3.40-3.42 3.41 26.840 36.840 0.003 16.57 0.19 1.09 1.51 3.41 D3/172 3.42-3.44 3.43 27.646 37.646 0.008 15.91 0.13 1.12 1.86 3.43 D3/173 3.44-3.46 3.45 27.710 37.710 0.002 16.75 0.09 1.06 0.92 3.45 D3/174 3.46-3.48 3.47 28.704 38.704 0.004 18.65 0.18 0.59 1.47 3.47 D3/175 3.48-3.50 3.49 30.495 40.495 0.001 20.28 0.13 0.41 0.85 3.49 D3/176 3.50-3.52 3.51 30.903 40.903 0.006 19.38 0.17 0.70 1.59 3.51 D3/177 3.52-3.54 3.53 31.648 41.648 0.008 21.72 0.17 1.35 1.74 3.53 328

D3/178 3.54-3.56 3.55 29.331 39.331 0.011 16.98 0.15 1.69 2.12 3.55 D3/179 3.56-3.58 3.57 29.050 39.050 0.006 18.08 0.14 0.43 1.59 3.57 D3/180 3.58-3.60 3.59 29.067 39.067 0.003 17.84 0.09 2.10 1.03 3.59 D3/181 3.60-3.62 3.61 24.419 34.419 0.008 17.04 0.15 2.78 1.98 3.61 D3/182 3.62-3.64 3.63 31.111 41.111 0.004 20.25 0.15 1.40 1.31 3.63 D3/183 3.64-3.66 3.65 32.370 42.370 0.011 22.81 0.28 2.16 2.21 3.65 D3/184 3.66-3.68 3.67 31.558 41.558 0.009 21.48 0.16 2.05 1.81 3.67 D3/185 3.68-3.70 3.69 31.212 41.212 0.012 21.30 0.26 1.56 2.29 3.69 D3/186 3.70-3.72 3.71 31.030 41.030 0.006 17.43 0.19 1.18 1.76 3.71 D3/187 3.72-3.74 3.73 30.223 40.223 0.011 20.02 0.15 1.50 2.03 3.73 D3/188 3.74-3.76 3.75 28.428 38.428 0.003 18.23 0.13 1.50 1.15 3.75 D3/189 3.76-3.78 3.77 27.255 37.255 0.002 18.24 0.11 1.63 0.98 3.77 D3/190 3.78-3.80 3.79 31.638 41.638 0.015 21.10 0.24 2.39 2.40 3.79 D3/191 3.80-3.82 3.81 32.267 42.267 0.009 22.96 0.28 2.31 2.02 3.81 D3/192 3.82-3.84 3.83 29.754 39.754 0.005 19.42 0.14 1.86 1.45 3.83 D3/193 3.84-3.86 3.85 29.441 39.441 0.009 20.43 0.29 2.12 2.19 3.85 D3/194 3.86-3.88 3.87 29.088 39.088 0.002 20.58 0.16 2.30 1.04 3.87 D3/195 3.88-3.90 3.89 30.159 40.159 0.005 19.36 0.21 2.53 1.65 3.89 D3/196 3.90-3.92 3.91 28.380 38.380 0.003 19.00 0.17 2.46 1.26 3.91 D3/197 3.92-3.94 3.93 29.120 39.120 0.001 17.10 0.25 3.91 1.47 3.93 D3/198 3.94-3.96 3.95 31.302 41.302 0.001 19.86 0.32 4.75 1.61 3.95 D3/199 3.96-3.98 3.97 35.341 45.341 0.003 21.13 0.33 4.39 1.68 3.97 D3/200 3.98-4.00 3.99 38.242 48.242 0.003 20.75 0.33 7.12 1.67 3.99 D3/201 4.00-4.02 4.01 41.205 51.205 0.004 27.48 0.31 3.77 1.41 4.01 D3/202 4.02-4.04 4.03 38.190 48.190 0.002 24.41 0.12 4.97 0.83 4.03 D3/203 4.04-4.06 4.05 41.470 51.470 0.002 27.56 0.35 3.89 1.33 4.05 D3/204 4.06-4.08 4.07 43.958 53.958 0.002 30.75 0.11 3.50 0.60 4.07 D3/205 4.08-4.10 4.09 47.391 57.391 0.002 32.79 0.15 3.49 0.75 4.09 D3/206 4.10-4.12 4.11 47.784 57.784 0.002 30.92 0.20 3.21 0.75 4.11 D3/207 4.12-4.14 4.13 47.498 57.498 0.001 34.19 0.15 3.70 0.56 4.13 D3/208 4.14-4.16 4.15 49.414 59.414 0.004 34.08 0.13 4.08 0.88 4.15 D3/209 4.16-4.18 4.17 47.274 57.274 0.001 32.06 0.16 2.46 0.55 4.17 D3/210 4.18-4.20 4.19 51.238 61.238 0.002 38.09 0.19 2.33 0.74 4.19 D3/211 4.20-4.22 4.21 50.442 60.442 0.001 35.47 0.19 3.01 0.60 4.21 D3/212 4.22-4.24 4.23 54.619 64.619 0.001 40.21 0.22 3.01 0.65 4.23 D3/213 4.24-4.26 4.25 49.892 59.892 0.004 31.54 0.18 4.15 0.98 4.25 D3/214 4.26-4.28 4.27 53.784 63.784 0.002 40.72 0.12 2.90 0.64 4.27 D3/215 4.28-4.30 4.29 61.265 71.265 0.010 41.76 0.18 3.63 1.28 4.29 D3/216 4.30-4.32 4.31 61.535 71.535 0.006 42.31 0.18 3.53 1.03 4.31 D3/217 4.32-4.34 4.33 59.691 69.691 0.023 45.14 0.28 3.45 2.03 4.33 D3/218 4.34-4.36 4.35 56.948 66.948 0.012 42.43 0.16 3.76 1.48 4.35 D3/219 4.36-4.38 4.37 56.615 66.615 0.006 36.40 0.12 3.88 1.01 4.37

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APPENDIX 4: CORE DESCRIPTION

The master core D3 was logged microscopically allow to yield 12 units describe in detail as follow. These 12 units classification were based on colour, texture, organic content, mineral content and abundance of tephra. Organic content was estimate from the composition chart for estimating percentage composition (CCEPC). Secondary mineral, iddingsite, hematite, goethite, gibbsite and halloysite occur throughout the core in various contents.

Unit Depth Sample Overall unit Organic (O) Tephra Sand Mineral content Charcoal Other features number colour and and volcanic fragment grain size (V) content (CCEPC) Lano-12 Unit 2 cm D3/1 Dark grey almost O = 42 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 58 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish red) and eleocharis goethite (lustre to dull) dulcis) Lano-12 Unit 4 cm D3/2 Dark grey almost O = 40 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 60 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish red) and eleocharis goethite (lustre to dull) dulcis) Lano-12 Unit 6 cm D3/3 Dark grey almost O = 40 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 60 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish red) and eleocharis goethite (lustre to dull) dulcis) Lano-12 Unit 8 cm D3/4 Dark grey almost O = 40 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 60 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish red) and eleocharis goethite (lustre to dull) dulcis) Lano-12 Unit 10 cm D3/5 Dark grey almost O = 37 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 63 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish red) and eleocharis goethite (lustre to dull) dulcis) Lano-12 Unit 12 cm D3/6 Dark grey almost O = 37 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 63 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish red) and eleocharis goethite (lustre to dull) dulcis) Lano-12 Unit 14 cm D3/7 Dark grey almost O = 37 % No tephra Very fine hematite No charcoal Poorly sorted and black and fine to V = 63 % fragment (occur in two form; lustre plenty of pollen coarse grained and yellowish red) and goethite (lustre to dull)

330

Lano-12 Unit 16 cm D3/8 Dark grey almost O = 37 % No tephra Very fine hematite No charcoal Poorly sorted and black and fine to V = 63 % fragment (occur in two form; lustre plenty of pollen coarse grained and yellowish red) and goethite (lustre to dull) Lano-12 Unit 18 cm D3/9 Dark grey almost O = 37 % No tephra Very fine hematite No charcoal Poorly sorted and black and fine to V = 63 % fragment (occur in two form; lustre plenty of pollen coarse grained and yellowish red) and goethite (lustre to dull) Lano-12 Unit 20 cm D3/10 Dark grey almost O = 38 % No tephra Very fine hematite No charcoal Poorly sorted and black and fine to V = 62 % fragment (occur in two form; lustre plenty of pollen coarse grained and yellowish red) and almost black goethite (lustre to dull) Lano-12 Unit 22 cm D3/11 Dark grey almost O = 50 % No tephra Very fine hematite No charcoal Poorly sorted and black and fine to O = 50 % fragment (occur in two form; lustre plenty of pollen coarse grained and yellowish red) and goethite (lustre to dull) Lano-12 Unit 24 cm D3/12 Dark grey almost O = 50 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to O = 50 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 26 cm D3/13 Dark grey almost O = 50 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to O = 50 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 28 cm D3/14 Dark grey almost O = 50 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to O = 50 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 30 cm D3/15 Dark grey almost O = 50 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to O = 50 % fragment (occur in two form; lustre branches & plenty of pollen coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 32 cm D3/16 Dark grey almost O = 60 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 40 % fragment (occur in two form; lustre branches & few pollen coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 34 cm D3/17 Dark grey almost O = 60 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 40 % fragment (occur in two form; lustre branches & few pollen coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 36 cm D3/18 Dark grey almost O = 60 % No tephra Very fine hematite Charcoal (tree Poorly sorted and black and fine to V = 40 % fragment (occur in two form; lustre branches & few pollen coarse grained and yellowish) eleocharis dulcis)

331

Lano-12 Unit 38 cm D3/19 Dark grey almost O = 60 % No tephra Very fine hematite Charcoal (tree Poorly sorted black and fine to V = 40 % fragment (occur in two form; lustre branches & coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 40 cm D3/20 Dark grey almost O = 60 % No tephra Very fine hematite Charcoal (tree Poorly sorted black and fine to V = 40 % fragment (occur in two form; lustre branches & coarse grained and yellowish) eleocharis dulcis) Lano-12 Unit 42 cm D3/21 Dark grey almost O = 60 % No tephra Very few hematite and Charcoal (tree Poorly sorted black and fine to V = 40 % fragment goethite branches & coarse grained eleocharis dulcis) Lano-12 Unit 44 cm D3/22 Dark green to O = 40 % No tephra Very few hematite and Charcoal Poorly sorted grey and fine to V = 60 % fragment goethite (eleocharis coarse grained dulcis) Lano-12 Unit 46 cm D3/23 Dark green to O = 10 % No tephra Very few hematite Charcoal Poorly sorted grey and fine to V = 90 % fragment (yellowish red) (eleocharis coarse grained dulcis) Lano-11 Unit 48 cm D3/24 Dark green to O = 10 % tephra fragment Highly weathered silicate No charcoal Poorly sorted (tephra bed-4) Eruption grey and fine to V = 90 % present (> than minerals, goethite stop coarse grained D3/25) phenocrysts present, increase in hematite (yellowish red), very few halloysite and iddingsite present Lano-11 Unit 50 cm D3/25 Dark greenish O = 10 % tephra fragment Highly weathered silicate No charcoal Poorly sorted (tephra bed-4) Eruption yellow to grey V = 90 % present (> than minerals, goethite dying and fine to very D26) phenocrysts present, stage coarse grained increase in hematite (yellowish red), very few halloysite and iddingsite present Lano-11 Unit 52 cm D3/26 Dark greenish O = 10 % tephra fragment Highly weathered silicate No charcoal Poorly sorted (tephra bed-4) Eruption yellow to grey V = 90 % present (> than minerals, goethite dying and fine to very D3/27) phenocrysts present, stage coarse grained increase in hematite (yellowish red), very few halloysite and iddingsite present Lano-11 Unit 54 cm D3/27 Dark greenish O = 10 % tephra fragment Highly weathered silicate No charcoal Poorly sorted (tephra bed-4) Eruption yellow to grey V = 90 % present (> than minerals, goethite dying and fine to very D3/28) phenocrysts present, stage coarse grained increase in hematite (yellowish red), very few

332

halloysite and iddingsite present Lano-11 Unit 56 cm D3/28 Dark greenish O = 10 % tephra fragment Highly weathered silicate Charcoal Poorly sorted (tephra bed-4) Eruption yellow and fine to V = 90 % present (> than minerals, goethite (eleocharis dying very coarse D3/29) phenocrysts present, dulcis) stage grained increase in hematite (yellowish red), very few halloysite and iddingsite present Lano-11 Unit 58 cm D3/29 Dark greenish O = 7 % tephra fragment Highly weathered silicate Charcoal Poorly sorted (tephra bed-4) Eruption yellow and fine to V = 93 % present (> than minerals, goethite (eleocharis alive very coarse D3/30) phenocrysts present, dulcis) grained increase in hematite (yellowish red), very few halloysite and iddingsite present Lano-11 Unit 60 cm D3/30 Dark greenish O = 7 % Plenty of tephra Highly weathered silicate Charcoal Poorly sorted (tephra bed-4) Eruption yellow and fine to V = 93 % fragments, 2 mm minerals, goethite (eleocharis alive very coarse to 5 mm, phenocrysts present, dulcis) grained scoriaceous, increase in hematite tubulous, highly (yellowish red), very few weathered and halloysite and iddingsite highly vesicular present

Lano-11 Unit 62 cm D3/31 Dark greenish O = 7 % Plenty of tephra Highly weathered silicate Charcoal Poorly sorted (tephra bed-4) Eruption yellow and fine to V = 93 % fragments, 2 mm minerals, goethite (eleocharis alive very coarse to 5 mm, phenocrysts present, dulcis) grained scoriaceous, increase in hematite tubulous, highly (yellowish red), very few weathered and halloysite and iddingsite highly vesicular present

Lano-11 Unit 64 cm D3/32 Dark greenish O = 7 % Plenty of tephra Highly weathered silicate Charcoal Poorly sorted (tephra bed-4) Eruption yellow and fine to V = 93 % fragments, 2 mm minerals, goethite (eleocharis alive very coarse to 5 mm, phenocrysts present, dulcis) grained scoriaceous, increase in hematite tubulous, highly (yellowish red), very few weathered and halloysite and iddingsite highly vesicular present

333

Lano-10 Unit 66 cm D3/33 Dark greenish O = 7 % No tephra Highly weathered silicate Charcoal Poorly sorted Eruption yellow and fine to V = 93 % minerals, goethite & (eleocharis ceased very coarse halloysite phenocrysts dulcis)t grained present, increase in hematite (yellowish red) and iddingsite Lano-10 Unit 68 cm D3/34 Dark green to O = 20 % No tephra increase in hematite Charcoal Poorly sorted Eruption grey and fine to V = 80 % (yellowish red) and few (eleocharis ceased RADIO very coarse iddingsite dulcis) CARBON grained DATING

Lano-10 Unit 70 cm D3/35 Dark greenish O = 20 % No tephra few hematite (yellowish Charcoal Poorly sorted Eruption yellow to grey V = 80 % red) and iddingsite (eleocharis ceased and fine to very dulcis) coarse grained

Lano-9 Unit 72 cm D3/36 Dark greenish O = 20 % Less tephra no silicate mineral, few Charcoal Poorly sorted (tephra bed-3) Eruption yellow to grey V = 80 % hematite (yellowish red) (eleocharis dying and fine to very and iddingsite dulcis) stage coarse grained

Lano-9 Unit 74 cm D3/37 Dark greenish O = 10 % Less tephra no silicate mineral, few Charcoal Poorly sorted (tephra bed-3) Eruption yellow to grey V = 90 % hematite (yellowish red), (eleocharis dying and fine to very gibbsite, halloysite and dulcis) stage coarse grained iddingsite

Lano-9 Unit 76 cm D3/38 Dark greenish O = 15 % Reduction in Few highly weathered Charcoal Poorly sorted (tephra bed-3) Eruption yellow to grey V = 85 % tephra content silicate mineral, increase (eleocharis alive and fine to very in hematite (yellowish dulcis) coarse grained red) and iddingsite, few goethite and halloysite

Lano-9 Unit 78 cm D3/39 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

334

Lano-9 Unit 80 cm D3/40 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

Lano-9 Unit 82 cm D3/41 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

Lano-9 Unit 84 cm D3/42 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

Lano-9 Unit 86 cm D3/43 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

Lano-9 Unit 88 cm D3/44 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and 335

highly vesicular

Lano-9 Unit 90 cm D3/45 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

Lano-9 Unit 92 cm D3/46 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite tubulous, highly and halloysite weathered and highly vesicular

Lano-9 Unit 94 cm D3/47 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite weathered and highly vesicular

Lano-9 Unit 96 cm D3/48 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3)t Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive to very coarse mm in size (yellowish red) and grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite weathered and highly vesicular

336

Lano-9 Unit 98 cm D3/49 Dark greenish O = 5 % Plenty of tephra More silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 95 % fragments, 5 - 9 increase in hematite alive RADIO to very coarse mm in size (yellowish red) and CARBON grained scoriaceous, iddingsite, few goethite, DATING tubulous, highly gibbsite and halloysite weathered and highly vesicular

Lano-9 Unit 100 cm D3/50 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite weathered and highly vesicular

Lano-9 Unit 102 cm D3/51 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

Lano-9 Unit 104 cm D3/52 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

Lano-9 Unit 106 cm D3/53 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

337

Lano-9 Unit 108 cm D3/54 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

Lano-9 Unit 110 cm D3/55 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

Lano-9 Unit 112 cm D3/56 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

Lano-9 Unit 114 cm D3/57 Dark greenish O = 10 % Plenty of tephra Very few silicate No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 minerals, few hematite alive to very coarse mm in size (yellowish red) grained scoriaceous, iddingsite, few goethite, tubulous, highly gibbsite and halloysite 1 weathered and highly vesicular

Lano-9 Unit 116 cm D3/58 Dark greenish O = 10 % Plenty of tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 hematite (yellowish red) alive to very coarse mm in size iddingsite, few goethite, grained scoriaceous, gibbsite and halloysite 1 tubulous, highly weathered and highly vesicular

338

Lano-9 Unit 118 cm D3/59 Dark greenish O = 10 % Plenty of tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 hematite (yellowish red) alive to very coarse mm in size iddingsite, few goethite, grained scoriaceous, gibbsite and halloysite 1 tubulous, highly weathered and highly vesicular

Lano-9 Unit 120 cm D3/60 Dark greenish O = 14 % Plenty of tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 86 % fragments, 5 - 9 hematite (yellowish red) alive to very coarse mm in size iddingsite, few goethite, grained scoriaceous, gibbsite and halloysite 1 tubulous, highly weathered and highly vesicular

Lano-9 Unit 120 cm D3/60 Dark greenish O = 14 % less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 86 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1

Lano-9 Unit 122 cm D3/61 Dark greenish O = 14 % Less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 86 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1 Lano-9 Unit 124 cm D3/62 Dark greenish O = 12 % Less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 88 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1

Lano-9 Unit 126 cm D3/63 Dark greenish O = 10 % Less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1

339

Lano-9 Unit 128 cm D3/64 Dark greenish O = 10 % Less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1

Lano-9 Unit 130 cm D3/65 Dark greenish O = 10 % Less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1

Lano-9 Unit 132 cm D3/66 Dark greenish O = 10 % Less tephra no silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % hematite (yellowish red) alive to very coarse iddingsite, few goethite, grained gibbsite and halloysite 1

Lano-9 Unit 134 cm D3/67 Dark greenish O = 10 % Plenty of tephra Few silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 few hematite (yellowish alive to very coarse mm in size red) iddingsite, few grained scoriaceous, goethite, gibbsite and tubulous, highly halloysite 1 weathered and highly vesicular

Lano-9 Unit 136 cm D3/68 Dark greenish O = 10 % Plenty of tephra Few silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 few hematite (yellowish alive to very coarse mm in size red) iddingsite, few grained scoriaceous, goethite, gibbsite and tubulous, highly halloysite 1 weathered and highly vesicular

Lano-9 Unit 138 cm D3/69 Dark greenish O = 10 % Plenty of tephra Few silicate minerals, No charcoal Poorly sorted (tephra bed-3) Eruption yellow and fine V = 90 % fragments, 5 - 9 few hematite (yellowish alive to very coarse mm in size red) iddingsite, few grained scoriaceous, goethite, gibbsite and tubulous, highly halloysite 1 weathered and highly vesicular

340

Lano-9 Unit 140 cm D3/70 Dark greenish O = 10 % Very rare tephra No silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Early yellow and fine V = 90 % hematite (yellowish red) stage of to very coarse and no iddingsite the grained eruption

Lano-9 Unit 142 cm D3/71 Dark greenish O = 10 % Very rare tephra No silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Early yellow and fine V = 90 % hematite (yellowish red) stage of to very coarse and no iddingsite the grained eruption

Lano-9 Unit 144 cm D3/72 Dark greenish O = 10 % Very rare tephra No silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Early yellow and fine V = 90 % hematite (yellowish red) stage of to very coarse and few iddingsite the grained eruption

Lano-9 Unit 146 cm D3/73 Dark green and O = 10 % Very rare tephra No silicate minerals, few No charcoal Poorly sorted (tephra bed-3) Early fine to very V = 90 % hematite (yellowish red) stage of RADIO coarse grained and few iddingsite the CARBON eruption DATING

Lano-9 Unit 148 cm D3/74 Dark green to O = 20 % Very rare tephra Very fine hematite Charcoal (tree Poorly sorted (tephra bed-3) Early dark grey almost V = 80 % (lustre and yellowish branches & stage of black and fine to red). Lustre hematite eleocharis the very coarse content elevated, few dulcis) grained goethite & gibbsite and eruption no iddingsite Lano-8 Unit 150 cm D3/75 Dark green to O = 30 % No tephra Very fine hematite Charcoal (tree Poorly sorted dark grey almost V = 70 % (lustre and yellowish branches & black and fine to red). Lustre hematite eleocharis very coarse content elevated, few dulcis) grained goethite & gibbsite and no iddingsite

341

Lano-8 Unit 152 cm D3/76 Dark green to O = 30 % No tephra Very fine hematite Charcoal (tree Poorly sorted dark grey almost V = 70 % (lustre and yellowish branches & black and fine to red). Lustre hematite eleocharis very coarse content elevated, few dulcis) grained goethite & gibbsite and no iddingsite Lano-8 Unit 154 cm D3/77 Dark green to O = 30 % No tephra Very fine hematite Charcoal (tree Poorly sorted dark grey almost V = 70 % (lustre and yellowish branches & black and fine to red). Lustre hematite eleocharis very coarse content elevated, few dulcis) grained goethite & gibbsite and no iddingsite Lano-8 Unit 156 cm D3/78 Dark green to O = 46 % No tephra Very fine hematite Charcoal Poorly sorted dark grey almost V = 54 % (lustre and yellowish present black and fine to red). Lustre hematite very coarse content elevated, few grained goethite & gibbsite and no iddingsite Lano-8 Unit 158 cm D3/79 Dark brown, dark O = 46 % No tephra Very fine hematite Charcoal (tree Poorly sorted green to dark V = 54 % (lustre and yellowish branches & grey almost black red). Lustre hematite eleocharis and fine to very content elevated, few dulcis) coarse grained goethite & gibbsite and no iddingsite Lano-7 Unit 160 cm D3/80 Dark brown, dark O = 52 % No tephra Very fine hematite No charcoal Poorly sorted green to dark V = 48 % (lustre and yellowish grey almost black red). Lustre hematite and fine to very content elevated, few coarse grained goethite & gibbsite and no iddingsite Lano-7 Unit 162 cm D3/81 Dark brown, dark O = 52 % No tephra Very fine hematite No charcoal Poorly sorted green to dark V = 48 %% (lustre and yellowish grey almost black red). Lustre hematite and fine to very content elevated, few coarse grained goethite & gibbsite and no iddingsite

342

Lano-7 Unit 164 cm D3/82 Dark brown, dark O = 52 % No tephra Few hematite (lustre and No charcoal Poorly sorted green to dark V = 48 % yellowish) and no grey almost black iddingsite and fine to very coarse grained

Lano-7 Unit 166 cm D3/83 Dark brown, dark O = 52 % No tephra No silicate mineral, few No charcoal Poorly sorted green to dark V = 48 % hematite (lustre and grey almost black yellowish) and and fine to very iddingsite coarse grained

Lano-7 Unit 168 cm D3/84 Dark brown, dark O = 52 % No tephra No silicate mineral, few No charcoal Poorly sorted green to dark V = 48 % hematite (lustre and grey almost black yellowish) and and fine to very iddingsite coarse grained

Lano-7 Unit 170 cm D3/85 Dark brown, dark O = 52 % No tephra No silicate mineral, few No charcoal Poorly sorted green to dark V = 48 % hematite (lustre and grey almost black yellowish) and and fine to very iddingsite coarse grained

Lano-7 Unit 172 cm D3/86 Dark brown, dark O = 52 % No tephra No silicate mineral, few No charcoal Poorly sorted green to dark V = 48 % hematite (lustre and grey almost black yellowish) and and fine to very iddingsite coarse grained

Lano-7 Unit 174 cm D3/87 Dark brown, dark O = 52 % No tephra No silicate mineral, few No charcoal Poorly sorted green to dark V = 48 % hematite (lustre and grey almost black yellowish) and and fine to very iddingsite coarse grained

343

Lano-7 Unit 176 cm D3/88 Dark brown, dark O = 52 % No tephra No silicate mineral, very No charcoal Poorly sorted green to dark V = 48 % few hematite (lustre and grey almost black yellowish) and and fine to very iddingsite coarse grained

Lano-7 Unit 178 cm D3/89 Dark brown, dark O = 52 % No tephra very few hematite (lustre No charcoal Poorly sorted green to dark V = 48 % and yellowish) and grey almost black iddingsite and fine to very coarse grained

Lano-6 Unit 180 cm D3/90 Dark green to O = 65 % No tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded dark grey and V = 35 % minerals very few tephra fine to coarse hematite, goethite and grained iddingsite

Lano-6 Unit 182 cm D3/91 Dark green to O = 65 % No tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded dark grey and V = 35 % minerals very few tephra fine to coarse hematite, goethite and grained iddingsite

Lano-6 Unit 184 cm D3/92 Dark green to O = 65 % No tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded dark grey and V = 35 % minerals very few tephra fine to coarse hematite, goethite and grained iddingsite

Lano-6 Unit 186 cm D3/93 Dark greenish O = 65 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 35 % fragments minerals very few tephra brownish yellow hematite, goethite and and fine to coarse iddingsite grained

344

Lano-6 Unit 188 cm D3/94 Dark greenish O = 65 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 35 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 190 cm D3/95 Dark greenish O = 65 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 35 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 192 cm D3/96 Dark greenish O = 46 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 54 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 194 cm D3/97 Dark greenish O = 46 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 54 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 196 cm D3/98 Dark greenish O = 46 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded yellow to V = 54 % fragments minerals very few branches & tephra brownish yellow hematite & goethite but eleocharis and fine to coarse no iddingsite dulcis) grained

Lano-6 Unit 198 cm D3/99 Dark greenish O = 46 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 54 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

345

Lano-6 Unit 200 cm D3/100 Dark greenish O = 65 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 35 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 202 cm D3/101 Dark greenish O = 46 % Broken tephra Highly weathered silicate Less charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 54 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 204 cm D3/102 Dark greenish O = 65 % Broken tephra Highly weathered silicate Less charcoal Poorly sorted (tephra bed-2) Eroded yellow to V = 35 % fragments minerals very few tephra brownish yellow hematite & goethite but and fine to coarse no iddingsite grained

Lano-6 Unit 206 cm D3/103 Dark green and O = 65 % Broken tephra Highly weathered silicate Less charcoal Poorly sorted (tephra bed-2) Eroded fine to coarse V = 35 % fragments minerals very few tephra grained hematite & goethite but no iddingsite

Lano-6 Unit 208 cm D3/104 Dark green O = 41 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 59 % fragments minerals very few branches & tephra and fine to coarse hematite, goethite and eleocharis grained iddingsite dulcis)

Lano-6 Unit 210 cm D3/105 Dark green O = 41 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 59 % fragments minerals, few goethite, branches & tephra and fine to coarse very few hematite and eleocharis grained iddingsite dulcis)

346

Lano-6 Unit 212 cm D3/106 Dark green O = 65 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 35 % fragments minerals, few goethite, tephra and fine to coarse very few hematite and grained iddingsite

Lano-6 Unit 214 cm D3/107 Dark green O = 40 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 60 % fragments minerals, few goethite, branches & tephra and fine to coarse very few hematite and eleocharis grained iddingsite dulcis)

Lano-6 Unit 216 cm D3/108 Dark green O = 40 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 60 % fragments minerals, few goethite, branches & tephra and fine to coarse very few hematite and eleocharis grained iddingsite dulcis)

Lano-6 Unit 218 cm D3/109 Dark green O = 36 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments minerals, few goethite, branches & tephra and fine to coarse very few hematite and eleocharis grained iddingsite dulcis)

Lano-6 Unit 220 cm D3/110 Dark green O = 36 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments minerals, few goethite, branches & tephra and fine to coarse very few hematite and eleocharis grained iddingsite dulcis)

Lano-6 Unit 222 cm D3/111 Dark green O = 36 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments minerals, few goethite, branches & tephra and fine to coarse very few hematite and eleocharis grained iddingsite dulcis)

347

Lano-6 Unit 224 cm D3/112 Dark green O = 36 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly very few hematite and eleocharis grained weathered tephra iddingsite dulcis) sands

Lano-6 Unit 226 cm D3/113 Dark green O = 36 % Broken tephra Highly weathered silicate Less charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments with minerals, few goethite, present tephra and fine to coarse few highly very few hematite and grained weathered tephra iddingsite sands

Lano-6 Unit 228 cm D3/114 Dark green O = 36 % Broken tephra Highly weathered silicate Less charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite and grained weathered tephra iddingsite sands

Lano-6 Unit 230 cm D3/115 Dark green O = 36 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite and eleocharis grained weathered tephra iddingsite dulcis) sands

Lano-6 Unit 232 cm D3/116 Dark green O = 36 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 64 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

Lano-6 Unit 234 cm D3/117 Dark green O = 35 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 65 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

348

Lano-6 Unit 236 cm D3/118 Dark green O = 35 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 65 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

Lano-6 Unit 238 cm D3/119 Dark green O = 30 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

Lano-6 Unit 240 cm D3/120 Dark green O = 65 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 35 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

Lano-6 Unit 242 cm D3/121 Dark green O = 35 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 65 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

Lano-6 Unit 244 cm D3/122 Dark green O = 35 % Broken tephra Highly weathered silicate Less charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 65 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 246 cm D3/123 Dark green O = 35 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (tephra bed-2) Eroded brownish yellow V = 65 % fragments with minerals, few goethite, branches & tephra and fine to coarse few highly few hematite & eleocharis grained weathered tephra iddingsite and very few dulcis) sands gibbsite & halloysite

349

Lano-6 Unit 248 cm D3/124 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 250 cm D3/125 Dark green O = 65 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 35 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 252 cm D3/126 Dark green O = 29 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 71 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 254 cm D3/127 Dark green O = 28 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 72 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 256 cm D3/128 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 258 cm D3/129 Dark green O = 32 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 68 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

350

Lano-6 Unit 260 cm D3/130 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 262 cm D3/131 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments with minerals, few goethite, tephra and fine to coarse few highly few hematite & grained weathered tephra iddingsite and very few sands gibbsite & halloysite

Lano-6 Unit 264 cm D3/132 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments with minerals, few goethite, tephra and fine to coarse few highly very few hematite, grained weathered tephra iddingsite, gibbsite & sands halloysite

Lano-6 Unit 266 cm D3/133 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 70 % fragments minerals, few goethite, tephra and fine to coarse very few hematite, grained iddingsite, gibbsite & halloysite

Lano-5 Unit 268 cm D3/134 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 70 % fragments minerals, few goethite, bed-2) tephra and fine to coarse very few hematite, grained iddingsite, gibbsite & halloysite

Lano-5 Unit 270 cm D3/135 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 70 % fragments with minerals, few goethite, bed-2) tephra and fine to coarse few highly very few hematite, grained weathered tephra iddingsite, gibbsite & sands halloysite

Lano-5 Unit 272 cm D3/136 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 70 % fragments minerals, few goethite, bed-2) tephra and fine to coarse very few hematite, grained iddingsite, gibbsite & halloysite

351

Lano-5 Unit 274 cm D3/137 Dark green O = 32 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 68 % fragments minerals, few goethite, bed-2)) tephra and fine to coarse very few hematite, grained iddingsite, gibbsite & halloysite Lano-5 Unit 276 cm D3/138 Dark green O = 25 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 75 % fragments minerals, few goethite, bed-2) tephra and fine to coarse very few hematite, grained iddingsite, gibbsite & halloysite Lano-5 Unit 278 cm D3/139 Dark green O = 30 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 70 % fragments minerals, few goethite, bed-2) tephra and fine to coarse very few hematite, grained iddingsite, gibbsite & halloysite Lano-6 Unit 280 cm D3/140 Dark green O = 70 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (tephra bed-2) Eroded brownish yellow V = 30 % fragments minerals, few goethite & tephra and fine to coarse hematite, very few grained iddingsite, gibbsite & halloysite Lano-5 Unit 282 cm D3/141 Dark green O = 39 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (base of the tephra Eroded brownish yellow V = 61 % fragments minerals, few goethite, branches & bed-2) tephra and fine to coarse very few iddingsite, eleocharis grained gibbsite & halloysite dulcis)

Lano-5 Unit 284 cm D3/142 Dark green O = 55 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 45 % fragments minerals, few goethite, bed-2) tephra and fine to coarse very few iddingsite, grained gibbsite & halloysite

Lano-5 Unit 286 cm D3/143 Dark green O = 40 % Broken tephra Highly weathered silicate Charcoal (tree Poorly sorted (base of the tephra Eroded brownish yellow V = 60 % fragments minerals, few goethite, branches & bed-2) tephra and fine to coarse very few iddingsite, eleocharis grained gibbsite & halloysite dulcis)

Lano-5 Unit 288 cm D3/144 Dark green O = 60 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 40 % fragments minerals, few goethite & bed-2) tephra and fine to coarse hematite, very few grained iddingsite, gibbsite & halloysite

352

Lano-5 Unit 290 cm D3/145 Dark green O = 42 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded brownish yellow V = 58 % fragments minerals, few goethite & bed-2) tephra and fine to coarse hematite, very few grained iddingsite, gibbsite & halloysite Lano-5 Unit 292 cm D3/146 Dark green to O = 48 % Broken tephra Highly weathered silicate No charcoal Poorly sorted (base of the tephra Eroded grey and fine to V = 52 % fragments minerals, iddingsite bed-2) tephra coarse grained content elevated, few goethite & hematite, very few gibbsite & halloysite Lano-4 Unit 294 cm D3/147 Dark green to O = 48 % No tephra No silicate minerals, few No charcoal Poorly sorted grey and fine to V = 52 % goethite & hematite, very coarse grained few iddingsite and gibbsite & halloysite Lano-4 Unit 296 cm D3/148 Dark green to O = 48 % No tephra No silicate minerals, very No charcoal Poorly sorted grey and fine to V = 52 % few goethite, hematite & coarse grained iddingsite content elevated and very few gibbsite & halloysite Lano-4 Unit 298 cm D3/149 Dark green to O = 48 % No tephra No silicate minerals, very No charcoal Poorly sorted grey and fine to V = 52 % few goethite, hematite coarse grained increase but iddingsite and very few gibbsite & halloysite Lano-4 Unit 300 cm D3/150 Dark green to O = 48 % No tephra No silicate minerals, very No charcoal Poorly sorted grey and fine to V = 52 % few goethite, hematite coarse grained increase but less iddingsite and very few gibbsite Lano-4 Unit 302 cm D3/151 Dark green to O = 48 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 52 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 304 cm D3/152 Dark green to O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 306 cm D3/153 Dark green to O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite

353

Lano-3 Unit 308 cm D3/154 Dark green to O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 310 cm D3/155 Dark greenish O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 312 cm D3/156 Dark greenish O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 314 cm D3/157 Dark greenish O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 316 cm D3/158 Dark greenish O = 45 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 55 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 318 cm D3/159 Dark greenish O = 40 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 60 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 320 cm D3/160 Dark greenish O = 40 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 60 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 322 cm D3/161 Dark greenish O = 40 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 60 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 324 cm D3/162 Dark greenish O = 40 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 60 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few

354

gibbsite

Lano-3 Unit 326 cm D3/163 Dark greenish O = 36 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 64 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 328 cm D3/164 Dark greenish O = 35 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 65 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 330 cm D3/165 Dark greenish O = 35 % No tephra No silicate minerals, very Charcoal Poorly sorted grey and fine to V = 65 % few goethite, hematite (eleocharis coarse grained increase but less dulcis) iddingsite and very few gibbsite Lano-3 Unit 328 cm D3/164 Dark greenish O = 35 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 65 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 330 cm D3/165 Dark greenish O = 40 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 60 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 332 cm D3/166 Dark greenish O = 40 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 60 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 334 cm D3/167 Dark greenish O = 40 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 60 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 336 cm D3/168 Dark greenish O = 30 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 70 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 338 cm D3/169 Dark greenish O = 28 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 72 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite

355

Lano-3 Unit 340 cm D3/170 Dark greenish O = 30 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 70 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 342 cm D3/171 Dark greenish O = 30 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 70 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 344 cm D3/172 Dark greenish O = 30 % No tephra No silicate minerals, Charcoal Poorly sorted grey and fine to V = 70 % hematite increase but less (eleocharis coarse grained iddingsite and very few dulcis) gibbsite Lano-3 Unit 346 cm D3/173 Dark greenish O = 48 % No tephra Few fine highly Charcoal Poorly sorted grey and fine to V = 52 % weathered silicate (eleocharis coarse grained minerals, very few dulcis) goethite, hematite increase but less iddingsite and very few gibbsite Lano-3 Unit 348 cm D3/174 Dark greenish O = 48 % No tephra Few fine highly Charcoal Poorly sorted grey and fine to V = 52 % weathered silicate (eleocharis coarse grained minerals, very few dulcis) goethite, hematite increase but less iddingsite and very few gibbsite Lano-3 Unit 350 cm D3/175 Dark greenish O = 48 % No tephra Few fine highly Charcoal Poorly sorted grey and fine to V = 52 % weathered silicate (eleocharis coarse grained minerals, very few dulcis) goethite, hematite increase but less iddingsite and very few gibbsite Lano-3 Unit 352 cm D3/176 Dark greenish O = 48 % No tephra Few fine highly Charcoal Poorly sorted grey and fine to V = 52 % weathered silicate (eleocharis coarse grained minerals, very few dulcis) goethite, hematite increase but less iddingsite and very few gibbsite Lano-3 Unit 354 cm D3/177 Dark greenish O = 48 % No tephra Few fine highly Charcoal Poorly sorted grey and fine to V = 52 % weathered silicate (eleocharis coarse grained minerals, very few dulcis) goethite, hematite

356

increase but less iddingsite and very few gibbsite Lano-3 Unit 356 cm D3/178 Dark greenish O = 48 % No tephra Few fine highly Less Charcoal Poorly sorted grey and fine to V = 52 % weathered silicate (eleocharis coarse grained minerals, very few dulcis) goethite, hematite increase but less iddingsite and very few gibbsite Lano-3 Unit 358 cm D3/179 Dark greenish O = 42 % Very few Few fine highly Less Charcoal Poorly sorted grey and fine to V = 58 % weathered tephra weathered silicate (eleocharis coarse grained fragments minerals, very few dulcis) goethite, hematite increase but less iddingsite and very few gibbsite Lano-3 Unit 360 cm D3/180 Dark greenish O = 38 % Very few Few fine highly Less Charcoal Poorly sorted grey and fine to V = 62 % weathered tephra weathered silicate (eleocharis coarse grained fragments minerals, very few dulcis) goethite, hematite, iddingsite & gibbsite Lano-3 Unit 362 cm D3/181 Dark greenish O = 30 % Very few Few fine highly No charcoal Poorly sorted grey and fine to V = 70 % weathered tephra weathered silicate coarse grained fragments minerals, very few goethite, hematite, iddingsite & gibbsite Lano-3 Unit 364 cm D3/182 Dark greenish O = 40 % Very few Few fine highly No charcoal Poorly sorted grey and fine to V = 60 % weathered tephra weathered silicate coarse grained fragments minerals, very few goethite, hematite, iddingsite & gibbsite Lano-3 Unit 366 cm D3/183 Dark greenish O = 40 % Very few Few fine highly Less Charcoal Poorly sorted grey and fine to V = 60 % weathered tephra weathered silicate (tree branches coarse grained fragments minerals, very few & eleocharis goethite, hematite, dulcis)l iddingsite & gibbsite Lano-3 Unit 368 cm D3/184 Dark greenish O = 40 % Very few Few fine highly Charcoal (tree Poorly sorted grey and fine to V = 60 % weathered tephra weathered silicate branches & coarse grained fragments minerals, very few eleocharis goethite, hematite, dulcis) iddingsite & gibbsite

357

Lano-3 Unit 370 cm D3/185 Dark greenish to O = 40 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 60 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-3 Unit 372 cm D3/186 Dark greenish to O = 28 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 72 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 374 cm D3/187 Dark greenish to O = 28 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 72 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 376 cm D3/188 Dark greenish to O = 28 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 72 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 378 cm D3/189 Dark greenish to O = 28 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 72 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 380 cm D3/190 Dark greenish to O = 28 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 72 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 382 cm D3/191 Dark greenish to O = 22 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 78 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 384 cm D3/192 Dark greenish to O = 22 % Highly weathered Iddingsite content Charcoal (tree Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 78 % tephra elevated, few fine highly branches & eruption dying thermal and fine to coarse weathered silicate eleocharis stage stage alteration grained minerals, few goethite, dulcis) halloysite & hematite Lano-2 Unit 386 cm D3/193 Dark greenish to O = 20 % Highly weathered Iddingsite content No charcoal Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 80 % tephra elevated, few fine highly eruption dying thermal and fine to coarse weathered silicate stage alteration grained minerals, few goethite, 358

halloysite & hematite

Lano-2 Unit 388 cm D3/194 Dark greenish to O = 20 % Highly weathered Iddingsite content No charcoal Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 80 % tephra elevated, few fine highly eruption dying thermal and fine to coarse weathered silicate stage alteration grained minerals, few goethite, halloysite & hematite Lano-2 Unit 390 cm D3/195 Dark greenish to O = 30 % Highly weathered Iddingsite content No charcoal Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 70 % tephra elevated, few fine highly eruption dying thermal and fine to coarse weathered silicate stage alteration grained minerals, few goethite, halloysite & hematite Lano-2 Unit 392 cm D3/196 Dark greenish to O = 30 % Highly weathered Iddingsite content No charcoal Poorly sorted Tephra bed-1 Hydro- brownish yellow V = 70 % tephra elevated, few fine highly eruption dying thermal and fine to coarse weathered silicate stage alteration grained minerals, few goethite, halloysite & hematite Lano-1 Unit 394 cm D3/197 Dark greenish to O = 10 % Highly vesicular, Iddingsite content No charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % dark green to grey elevated, few fine highly alive and fine to very brownish yellow, weathered silicate coarse grained 0.5 to 10mm in minerals, few goethite, size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 396 cm D3/198 Dark greenish to O = 10 % Highly vesicular, Iddingsite content Less Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % dark green to grey elevated, few fine highly alive and fine to very brownish yellow, weathered silicate coarse grained 0.5 to 10mm in minerals, few goethite, size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 398 cm D3/199 Dark greenish to O = 10 % Highly vesicular, Iddingsite content Less Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % dark green to grey elevated, few fine highly Charcoal) alive and fine to very brownish yellow, weathered silicate coarse grained 0.5 to 10mm in minerals, few goethite, size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 400 cm D3/200 Dark greenish to O = 10 % Highly vesicular, Iddingsite content Less Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % dark green to grey elevated, few fine highly alive and fine to very brownish yellow, weathered silicate coarse grained 0.5 to 10mm in minerals, few goethite, size scoriaceous, halloysite & hematite

359

tubulous and highly weathered

Lano-1 Unit 402 cm D3/201 Dark greenish to O = 15 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 85 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 404 cm D3/202 Dark greenish to O = 15 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 85 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite 2 tubulous and highly weathered Lano-1 Unit 406 cm D3/203 Dark greenish to O = 15 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 85 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 408 cm D3/204 Dark greenish to O = 17 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 83 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 410 cm D3/205 Dark greenish to O = 25 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 75 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 412 cm D3/206 Dark greenish to O = 25 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 75 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and

360

highly weathered

Lano-1 Unit 414 cm D3/207 Dark greenish to O = 18 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 82 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, gibbsite, halloysite & tubulous and hematite highly weathered Lano-1 Unit 416 cm D3/208 Dark greenish to O = 18 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 82 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 418 cm D3/209 Dark greenish to O = 18 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 82 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 420 cm D3/210 Dark greenish to O = 18 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 82 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, gibbsite, halloysite & tubulous and hematite highly weathered Lano-1 Unit 422 cm D3/211 Dark greenish to O = 18 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 82 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 424 cm D3/212 Dark greenish to O = 18 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 82 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and

361

highly weathered

Lano-1 Unit 426 cm D3/213 Dark greenish to O = 10 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 428 cm D3/214 Dark greenish to O = 10 % Highly vesicular, Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % dark green to grey elevated, few fine highly present (tree alive and fine to very brownish yellow, weathered silicate branches coarse grained 0.5 to 10mm in minerals, few goethite, materials) size scoriaceous, halloysite & hematite tubulous and highly weathered Lano-1 Unit 430 cm D3/215 Dark greenish to O = 10 % Abundance of Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 90 % tephra sands, elevated, few fine highly present (tree alive and fine to very highly vesicular, weathered silicate branches coarse grained dark green to grey minerals, few goethite, materials) brownish yellow, halloysite & hematite 0.5 to 10mm in size scoriaceous, tubulous and highly weathered Lano-1 Unit 432 cm D3/216 Dark greenish to O = 14 % Abundance of Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 86 % tephra sands, elevated, few fine highly present (tree alive and fine to very highly vesicular, weathered silicate branches coarse grained dark green to grey minerals, few goethite, materials) brownish yellow, halloysite & hematite 0.5 to 10mm in size scoriaceous, tubulous and highly weathered Lano-1 Unit 434 cm D3/218 Dark greenish to O = 14 % Abundance of Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 86 % tephra sands, elevated, few fine highly present (tree alive and fine to very highly vesicular, weathered silicate branches coarse grained dark green to grey minerals, few goethite, materials) brownish yellow, halloysite & hematite 0.5 to 10mm in size scoriaceous, tubulous and highly weathered

362

Lano-1 Unit 436 cm D3/219 Dark greenish to O = 15 % Abundance of Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 85 % tephra sands, elevated, few fine highly present (tree alive RADIO and fine to very highly vesicular, weathered silicate branches CARBON coarse grained dark green to grey minerals, few goethite, materials) DATING brownish yellow, halloysite & hematite 0.5 to 10mm in size scoriaceous, tubulous and highly weathered Lano-1 Unit 438 cm D3/220 Dark greenish to O = 20 % Abundance of Iddingsite content Charcoal Poorly sorted (tephra bed-1) Eruption brownish yellow V = 80 % tephra sands, elevated, few fine highly present (tree alive and fine to very highly vesicular, weathered silicate branches coarse grained dark green to grey minerals, few goethite, materials) brownish yellow, halloysite & hematite 0.5 to 10mm in size scoriaceous, tubulous and highly weathered

363

APPENDIX 5: ARGON-ARGON DATING

The Argon-Argon dating was analysed in two ways: groundmass and plagioclase phenocryst. Groundmass was recommended as the most reliable procedure for Argon-Argon dating in lava of the Crater Lanoto whilst the plagioclase phenocryst method did not perform well. The groundmass procedure has yielded the reliable plateau age of 143.9 ± 2.8 Ka in comparison with the 42 ± 0.17 Ma of the plagioclase. Tables below are records of (a) groundmass producer (incremental heating, normal isochron and reverse isochron) and (b) some examples of the plagioclase phenocryst (relative abundance and inverse isochron).

(a) Groundmass

Incremental 36Ar(a) 37Ar(ca) 38Ar(cl) 39Ar(k) 40Ar(r) Age 40Ar(r) 39Ar(k) K/Ca Heating [fA] [fA] [fA] [fA] [fA] (Ka) (%) (%)

13D06010 1.8 % 0.1408261 14.1193 0.0244594 12.2420 0.62609 149.1 ± 167.7 1.48 0.44 0.373 ± 0.059 13D06012 2.0 % 0.0579924 11.1236 0.0438019 11.0745 0.60654 159.6 ± 142.0 3.42 0.39 0.428 ± 0.083 13D06013 2.2 % 0.0454474 13.1824 0.0172682 14.2850 1.18519 241.8 ± 104.8 8.10 0.51 0.466 ± 0.075 13D06014 2.4 % 0.0476086 15.9863 0.0163060 19.8172 0.79985 117.7 ± 76.9 5.37 0.71 0.533 ± 0.074 13D06016 2.7 % 0.0455982 29.7108 0.0445023 33.3783 1.91109 166.9 ± 45.3 12.39 1.19 0.483 ± 0.038 13D06017 3.0 % 0.0411096 36.1811 0.0293206 41.1940 1.93820 137.1 ± 36.2 13.72 1.47 0.490 ± 0.029 13D06018 3.3 % 0.0336363 40.8798 0.0417516 47.0613 2.54918 157.9 ± 31.5 20.33 1.68 0.495 ± 0.028 13D06020 3.6 % 0.0415230 63.1777 0.0000000 73.5116 3.08599 122.4 ± 21.0 20.00 2.62 0.500 ± 0.018 13D06021 3.9 % 0.0347573 72.0238 0.0288351 83.1097 4.00237 140.4 ± 18.0 27.88 2.96 0.496 ± 0.016 13D06022 4.2 % 0.0368281 91.6611 0.0674643 107.4893 5.35750 145.3 ± 14.7 32.77 3.83 0.504 ± 0.014 13D06024 4.5 % 0.0312954 101.1782 0.0111011 120.7313 6.31400 152.4 ± 13.1 40.26 4.30 0.513 ± 0.012 13D06025 4.8 % 0.0288653 104.7997 0.0509628 129.6316 6.54346 147.1 ± 11.8 43.04 4.62 0.532 ± 0.013 13D06026 5.1 % 0.0271745 104.3762 0.0373025 137.8748 6.83765 144.6 ± 11.1 45.56 4.91 0.568 ± 0.013 13D06028 5.4 % 0.0269816 105.0153 0.0000000 149.8704 7.26630 141.3 ± 9.9 47.21 5.34 0.614 ± 0.015 13D06029 5.7 % 0.0255714 96.7888 0.0502006 145.2877 6.84965 137.4 ± 9.9 47.07 5.17 0.645 ± 0.016 13D06030 6.1 % 0.0252192 98.7369 0.0523133 158.6795 7.72182 141.8 ± 9.2 50.36 5.65 0.691 ± 0.017 13D06032 6.5 % 0.0227893 89.3784 0.0000000 149.4532 7.63649 148.9 ± 10.4 52.59 5.32 0.719 ± 0.019 13D06033 6.9 % 0.0242395 85.3848 0.1134095 152.0770 7.73115 148.2 ± 9.5 51.38 5.42 0.766 ± 0.021

364

13D06034 7.3 % 0.0274966 74.9708 0.0419516 140.1618 6.76388 140.7 ± 10.8 45.00 4.99 0.804 ± 0.024 13D06036 7.8 % 0.0277810 72.6839 0.0454306 137.3138 6.99981 148.6 ± 10.5 45.61 4.89 0.812 ± 0.026 13D06037 8.3 % 0.0273170 64.6745 0.0513678 119.1093 5.88294 144.0 ± 12.2 41.80 4.24 0.792 ± 0.028 13D06038 8.8 % 0.0281423 56.6934 0.0594978 102.5039 5.03282 143.1 ± 14.1 37.41 3.65 0.777 ± 0.031 13D06040 9.3 % 0.0286830 54.7574 0.0415057 92.5918 4.56486 143.7 ± 15.2 34.76 3.30 0.727 ± 0.030 13D06041 9.9 % 0.0287862 48.1489 0.0524504 78.7857 3.53465 130.8 ± 17.8 29.16 2.81 0.704 ± 0.034 13D06042 10.5 % 0.0315096 47.3573 0.0533098 71.0033 3.38591 139.0 ± 19.8 26.52 2.53 0.645 ± 0.030 13D06044 11.2 % 0.0371920 55.0240 0.0539344 69.3291 3.35526 141.1 ± 20.9 23.28 2.47 0.542 ± 0.023 13D06045 11.9 % 0.0361580 56.8000 0.0407448 59.8305 3.11821 151.9 ± 24.3 22.49 2.13 0.453 ± 0.019 13D06046 12.8 % 0.0508424 81.9178 0.0576721 62.9460 2.84917 131.9 ± 24.8 15.88 2.24 0.330 ± 0.009 13D06048 13.9 % 0.0603716 115.1646 0.1106917 65.6904 3.46669 153.8 ± 27.2 16.22 2.34 0.245 ± 0.005 13D06049 15.2 % 0.0715709 156.8364 0.0970356 69.5982 3.64044 152.5 ± 26.5 14.64 2.48 0.191 ± 0.003 13D06050 16.7 % 0.0704744 211.6548 0.0499946 58.6457 2.99020 148.6 ± 32.0 12.52 2.09 0.119 ± 0.002 13D06052 18.2 % 0.0597886 245.7713 0.0542695 44.0688 2.54211 168.1 ± 43.3 12.55 1.57 0.077 ± 0.001 13D06053 19.7 % 0.0465103 204.7326 0.0000000 29.8923 0.99672 97.2 ± 60.8 6.75 1.06 0.063 ± 0.001 13D06055 21.2 % 0.0335878 179.9086 0.0000000 19.4995 1.20921 180.8 ± 90.2 10.84 0.69 0.047 ± 0.001

Ʃ 1.4036749 2900.8000 1.4388557 2807.7383 139.29540

Results 40(r)/39(k) ± 2s Age ± 2s 39Ar(k) K/Ca ± 2s

(Ka) MSWD (%,n)

Age Plateau 0.04938 ± 0.00093 143.9 ± 2.8 0.72 96.90 0.124 ± 0.043 ± 1.89% ± 1.93% 86% 29 Full External Error ± 4.3 1.53 2σ Confidence Limit Analytical Error ± 2.7 1.0000 Error Magnification

Total Fusion Age 0.04961 ± 0.00112 144.6 ± 3.3 34 0.416 ± 0.002 ± 2.26% ± 2.29% Full External Error ± 4.7 Analytical Error ± 3.3

Normal 39(k)/36(a) 40(a+r)/36(a) r.i.

365

Isochron

13D06010 1.8 % 86.93 ± 1.55 299.95 ± 5.07 0.9003 13D06012 2.0 % 190.96 ± 5.90 305.96 ± 9.60 0.9291 13D06013 2.2 % 314.32 ± 11.55 321.58 ± 12.21 0.9475 13D06014 2.4 % 416.25 ± 14.83 312.30 ± 11.55 0.9498 13D06016 2.7 % 732.01 ± 26.85 337.41 ± 12.85 0.9581 13D06017 3.0 % 1002.05 ± 40.05 342.65 ± 14.23 0.9592 13D06018 3.3 % 1399.12 ± 67.84 371.29 ± 18.62 0.9650 13D06020 3.6 % 1770.38 ± 72.82 369.82 ± 15.70 0.9676 13D06021 3.9 % 2391.14 ± 113.63 410.65 ± 20.05 0.9722 13D06022 4.2 % 2918.68 ± 138.21 440.97 ± 21.34 0.9777 13D06024 4.5 % 3857.80 ± 216.71 497.26 ± 28.41 0.9827 13D06025 4.8 % 4490.91 ± 262.42 522.19 ± 31.02 0.9832 13D06026 5.1 % 5073.67 ± 314.14 547.12 ± 34.39 0.9844 13D06028 5.4 % 5554.54 ± 335.43 564.81 ± 34.62 0.9848 13D06029 5.7 % 5681.65 ± 351.45 563.36 ± 35.41 0.9837 13D06030 6.1 % 6292.01 ± 400.69 601.69 ± 38.84 0.9860 13D06032 6.5 % 6558.04 ± 494.86 630.59 ± 48.11 0.9887 13D06033 6.9 % 6273.92 ± 412.51 614.45 ± 40.94 0.9863 13D06034 7.3 % 5097.43 ± 308.21 541.49 ± 33.25 0.9841 13D06036 7.8 % 4942.73 ± 282.29 547.46 ± 31.80 0.9827 13D06037 8.3 % 4360.26 ± 255.57 510.86 ± 30.52 0.9806 13D06038 8.8 % 3642.35 ± 205.74 474.34 ± 27.39 0.9774 13D06040 9.3 % 3228.11 ± 172.89 454.65 ± 24.99 0.9735 13D06041 9.9 % 2736.93 ± 146.03 418.29 ± 23.01 0.9691 13D06042 10.5 % 2253.39 ± 110.28 402.96 ± 20.37 0.9670 13D06044 11.2 % 1864.09 ± 79.59 385.71 ± 17.04 0.9648 13D06045 11.9 % 1654.70 ± 73.18 381.74 ± 17.44 0.9665 13D06046 12.8 % 1238.06 ± 42.21 351.54 ± 12.38 0.9656 13D06048 13.9 % 1088.10 ± 36.08 352.92 ± 11.99 0.9732 13D06049 15.2 % 972.44 ± 28.15 346.36 ± 10.26 0.9734 13D06050 16.7 % 832.16 ± 24.96 337.93 ± 10.37 0.9733 13D06052 18.2 % 737.08 ± 26.55 338.02 ± 12.44 0.9745 13D06053 19.7 % 642.70 ± 28.21 316.93 ± 14.31 0.9677

366

13D06055 21.2 % 580.55 ± 34.08 331.50 ± 20.01 0.9675 Results 40(a)/36(a) ± 2s 40(r)/39(k) ± 2s Age ± 2s

(Ka) MSWD MSWD

Normal Isochron 296.13 ± 4.19 0.04908 ± 0.00151 143.1 ± 4.4 0.75 ± 1.41% ± 3.09% ± 3.11% 82% Full External Error ± 5.5 Analytical Error ± 4.4

Statistics 2σ Confidence 1.54 Convergence 0.000000458928 Limit Error 1.0000 Number of 11 Magnification Iterations Number of Data 29 Calculated Line Weighted York-2 Points

Inverse 39(k)/40(a+r) ± 2s 36(a)/40(a+r) ± 2s r.i. Isochron

13D06010 1.8 % 0.2898195 ± 0.0022585 0.00333394 ± 0.00005637 0.1156 13D06012 2.0 % 0.6241503 ± 0.0073239 0.00326841 ± 0.00010256 0.2266 13D06013 2.2 % 0.9774289 ± 0.0118892 0.00310966 ± 0.00011806 0.2585 13D06014 2.4 % 1.3328575 ± 0.0154292 0.00320204 ± 0.00011838 0.2707 13D06016 2.7 % 2.1694877 ± 0.0236748 0.00296374 ± 0.00011287 0.2690 13D06017 3.0 % 2.9244469 ± 0.0343480 0.00291845 ± 0.00012122 0.2722 13D06018 3.3 % 3.7683102 ± 0.0495940 0.00269334 ± 0.00013508 0.2556 13D06020 3.6 % 4.7871480 ± 0.0513056 0.00270402 ± 0.00011476 0.2462 13D06021 3.9 % 5.8227983 ± 0.0665781 0.00243515 ± 0.00011890 0.2296 13D06022 4.2 % 6.6187178 ± 0.0672270 0.00226771 ± 0.00010972 0.2054 13D06024 4.5 % 7.7581970 ± 0.0819812 0.00201104 ± 0.00011488 0.1817 13D06025 4.8 % 8.6001568 ± 0.0931399 0.00191501 ± 0.00011374 0.1793 13D06026 5.1 % 9.2734261 ± 0.1024403 0.00182775 ± 0.00011490 0.1729

367

13D06028 5.4 % 9.8344214 ± 0.1047994 0.00177052 ± 0.00010852 0.1710 13D06029 5.7 % 10.0852255 ± 0.1141280 0.00177505 ± 0.00011157 0.1773 13D06030 6.1 % 10.4572660 ± 0.1124004 0.00166199 ± 0.00010729 0.1639 13D06032 6.5 % 10.3998283 ± 0.1190177 0.00158581 ± 0.00012099 0.1478 13D06033 6.9 % 10.2106630 ± 0.1122346 0.00162748 ± 0.00010845 0.1624 13D06034 7.3 % 9.4137060 ± 0.1027534 0.00184676 ± 0.00011341 0.1749 13D06036 7.8 % 9.0284049 ± 0.0972129 0.00182660 ± 0.00010610 0.1823 13D06037 8.3 % 8.5351664 ± 0.0999530 0.00195749 ± 0.00011693 0.1931 13D06038 8.8 % 7.6788461 ± 0.0936936 0.00210821 ± 0.00012174 0.2080 13D06040 9.3 % 7.1002241 ± 0.0893419 0.00219950 ± 0.00012091 0.2254 13D06041 9.9 % 6.5431358 ± 0.0888435 0.00239069 ± 0.00013151 0.2435 13D06042 10.5 % 5.5921370 ± 0.0720122 0.00248166 ± 0.00012543 0.2502 13D06044 11.2 % 4.8328162 ± 0.0561797 0.00259259 ± 0.00011455 0.2574 13D06045 11.9 % 4.3346346 ± 0.0507892 0.00261959 ± 0.00011966 0.2502 13D06046 12.8 % 3.5218288 ± 0.0322397 0.00284463 ± 0.00010017 0.2500 13D06048 13.9 % 3.0831143 ± 0.0240731 0.00283348 ± 0.00009625 0.2181 13D06049 15.2 % 2.8075497 ± 0.0190602 0.00288713 ± 0.00008555 0.2142 13D06050 16.7 % 2.4625104 ± 0.0173385 0.00295920 ± 0.00009084 0.2133 13D06052 18.2 % 2.1805815 ± 0.0180111 0.00295842 ± 0.00010890 0.2073 13D06053 19.7 % 2.0279001 ± 0.0230775 0.00315527 ± 0.00014245 0.2351 13D06055 21.2 % 1.7512877 ± 0.0267385 0.00301658 ± 0.00018208 0.2330

Results 40(a)/36(a) 40(r)/39(k) Age

(Ka) MSWD

Inverse Isochron 296.29 ± 4.18 0.04916 ± 0.00150 143.3 ± 4.4 0.74 ± 1.41% ± 3.06% ± 3.08% 84% Full External Error ± 5.5 Analytical Error ± 4.4

Statistics 2σ Confidence 1.54 Convergence 0.0245237150 Limit Error 1.0000 Number of 3 Magnification Iterations 368

Number of Data 29 Calculated Line Weighted York-2 Points Spreading Factor 44.9%

(b) Plagioclase phenocryst Relative 36Ar 37Ar 38Ar 39Ar 40Ar Abundances [fA] [fA] [fA] [fA] [fA]

13D05981 1.6 % 0.0678457 1.212 210.1177 0.655 0.2346662 15.887 16.16182 0.228 42.1186 0.099 13D05982 2.0 % 0.1252307 0.731 413.1276 0.520 0.4012725 8.739 33.07663 0.110 94.4234 0.048 13D05984 2.4 % 0.1183074 0.752 392.7580 0.536 0.3698763 11.099 33.16361 0.119 103.6676 0.043 13D05985 2.8 % 0.1090474 0.811 351.8328 0.551 0.3275184 11.903 30.97939 0.127 147.1313 0.031 13D05987 3.4 % 0.1079729 0.897 351.4030 0.569 0.4179577 8.427 32.12033 0.118 264.5012 0.019 13D05988 4.0 % 0.0696862 0.983 211.1415 0.690 0.2489021 15.616 20.16114 0.189 281.4467 0.018 13D05990 4.2 % 0.0299692 2.084 88.6117 1.259 0.0919525 42.603 8.15363 0.451 158.0186 0.030 13D05991 4.8 % 0.0366596 1.621 99.1036 1.148 0.0760152 50.845 8.61159 0.407 226.9388 0.022 13D05993 5.6 % 0.0487970 1.378 116.8212 1.029 0.1233365 30.635 9.26909 0.381 356.9850 0.016 13D05994 6.6 % 0.0312999 2.100 95.8420 1.267 0.1069005 37.146 7.20032 0.485 234.9420 0.022 13D05996 7.6 % 0.0308429 1.961 90.0427 1.345 0.0882699 46.218 6.40913 0.597 169.7203 0.029 13D05997 8.8 % 0.0243724 2.405 70.0659 1.616 0.0438420 92.552 5.23564 0.686 417.9365 0.015 13D05999 10.0 % 0.0209604 2.701 51.8328 2.076 0.0316758 119.688 3.18536 1.014 71.3455 0.060 13D06000 11.5 % 0.0354775 1.695 98.4295 1.181 0.0870593 47.904 6.83872 0.511 709.3764 0.011 13D06002 13.0 % 0.0761706 1.018 201.2686 0.737 0.1119641 36.285 12.32003 0.287 205.7349 0.023 13D06003 15.0 % 0.0581629 1.227 166.6979 0.830 0.1268026 31.976 10.33942 0.331 177.0409 0.030 13D06005 17.0 % 0.0276852 2.092 70.3650 1.594 0.0197217 194.015 4.48859 0.815 44.5124 0.099 13D06006 19.0 % 0.0146307 3.412 43.8826 2.462 0.0310144 129.365 2.54449 1.384 5.5365 0.720 13D06008 21.0 % 0.0165605 3.043 48.0045 2.450 0.0314299 120.928 2.96490 1.204 5.2143 0.744

Ʃ 1.0496793 0.293 3171.3485 0.198 2.9307342 5.802 253.22385 0.062 3716.5909 0.006

369

40(r)/39(k) Age 40Ar(r) 39Ar(k) K/Ca

(Ma) (%) (%)

2.39990 ± 0.03535 7.01 ± 0.10 91.28 6.38 0.0328 ± 0.0005 2.73224 ± 0.02052 7.97 ± 0.06 94.91 13.06 0.0341 ± 0.0004 3.01874 ± 0.02037 8.81 ± 0.06 95.80 13.10 0.0360 ± 0.0004 4.62953 ± 0.02315 13.49 ± 0.07 96.73 12.24 0.0376 ± 0.0004 8.15388 ± 0.02840 23.69 ± 0.08 98.29 12.70 0.0390 ± 0.0005 13.85210 ± 0.05785 40.07 ± 0.17 98.53 7.97 0.0408 ± 0.0006 19.28186 ± 0.18262 55.53 ± 0.52 98.77 3.22 0.0393 ± 0.0011 26.19441 ± 0.22006 75.03 ± 0.62 98.63 3.40 0.0371 ± 0.0009 38.26459 ± 0.29850 108.59 ± 0.82 98.51 3.66 0.0338 ± 0.0007 32.67506 ± 0.32607 93.13 ± 0.91 99.24 2.84 0.0320 ± 0.0009 26.40364 ± 0.32508 75.62 ± 0.91 98.77 2.53 0.0303 ± 0.0009 80.21517 ± 1.11280 220.59 ± 2.88 99.58 2.07 0.0318 ± 0.0011 21.96241 ± 0.46669 63.12 ± 1.32 96.98 1.25 0.0261 ± 0.0012 104.32880 ± 1.07965 281.97 ± 2.70 99.60 2.70 0.0296 ± 0.0008 16.32520 ± 0.10390 47.13 ± 0.30 96.69 4.85 0.0260 ± 0.0004 16.90076 ± 0.12274 48.77 ± 0.35 97.63 4.07 0.0264 ± 0.0005 9.41544 ± 0.17877 27.33 ± 0.52 93.94 1.77 0.0271 ± 0.0010 1.84256 ± 0.14806 5.38 ± 0.43 83.70 1.00 0.0246 ± 0.0014 1.38532 ± 0.12676 4.05 ± 0.37 77.91 1.17 0.0263 ± 0.0014

Inverse 39(k)/40(a+r) 36(a)/40(a+r) r.i. Isochron

13D05981 1.6 % 0.3805108 ± 0.0019046 0.00029379 ± 0.00004272 0.0054 13D05982 2.0 % 0.3474784 ± 0.0008402 0.00017126 ± 0.00002283 0.0028 13D05984 2.4 % 0.3174552 ± 0.0008108 0.00014107 ± 0.00002024 0.0020 13D05985 2.8 % 0.2089908 ± 0.0005515 0.00010988 ± 0.00001389 0.0012 13D05987 3.4 % 0.1205579 ± 0.0002914 0.00005748 ± 0.00000834 0.0004 13D05988 4.0 % 0.0711342 ± 0.0002721 0.00004955 ± 0.00000558 0.0003 13D05990 4.2 % 0.0512244 ± 0.0004663 0.00004162 ± 0.00000874 0.0002

370

13D05991 4.8 % 0.0376543 ± 0.0003093 0.00004625 ± 0.00000587 0.0002 13D05993 5.6 % 0.0257454 ± 0.0001982 0.00005030 ± 0.00000416 0.0002 13D05994 6.6 % 0.0303736 ± 0.0002978 0.00002552 ± 0.00000623 0.0001 13D05996 7.6 % 0.0374073 ± 0.0004516 0.00004166 ± 0.00000806 0.0001 13D05997 8.8 % 0.0124147 ± 0.0001718 0.00001406 ± 0.00000315 0.0000 13D05999 10.0 % 0.0441600 ± 0.0009074 0.00010200 ± 0.00001776 0.0004 13D06000 11.5 % 0.0095472 ± 0.0000987 0.00001338 ± 0.00000190 0.0000 13D06002 13.0 % 0.0592282 ± 0.0003445 0.00011197 ± 0.00000844 0.0005 13D06003 15.0 % 0.0577710 ± 0.0003884 0.00007996 ± 0.00000906 0.0005 13D06005 17.0 % 0.0997854 ± 0.0016561 0.00020466 ± 0.00002924 0.0017 13D06006 19.0 % 0.4544580 ± 0.0143141 0.00055037 ± 0.00020794 0.0174 13D06008 21.0 % 0.5627377 ± 0.0160651 0.00074595 ± 0.00022744 0.0255 Results 40(a)/36(a) 40(r)/39(k) Age

(Ma) MSWD

Inverse Isochron Cannot Calculate

371