ESTABLISHING A HOLOCENE TEPHROCHRONOLOGY FOR WESTERN SAMOA AND ITS IMPLICATION FOR THE RE-EVALUATION OF VOLCANIC HAZARDS by Aleni Fepuleai A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy Copyright © 2016 by Aleni Fepuleai 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. iii 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. v 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……….