Measurement and Implication of “Effective” Viscosity for Rhyolite Flow Emplacement
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Controls on Rhyolite Lava Dome Eruptions in the Taupo Volcanic Zone
Controls on rhyolite lava dome eruptions in the Taupo Volcanic Zone Paul Allan Ashwell A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geological Sciences at the University of Canterbury October 2013 P a g e | II Dedicated to Eva Ashwell P a g e | III View from Ruawahia, across the 1886AD fissure and Wahanga dome towards the Bay of Plenty and White Island (extreme distance, centre left) P a g e | IV Abstract he evolution of rhyolitic lava from effusion to cessation of activity is poorly understood. T Recent lava dome eruptions at Unzen, Colima, Chaiten and Soufrière Hills have vastly increased our knowledge on the changes in behaviour of active domes. However, in ancient domes, little knowledge of the evolution of individual extrusion events exists. Instead, internal structures and facies variations can be used to assess the mechanisms of eruption. Rhyolitic magma rising in a conduit vesiculates and undergoes shear, such that lava erupting at the surface will be a mix of glass and sheared vesicles that form a permeable network, and with or without phenocryst or microlites. This foam will undergo compression from overburden in the shallow conduit and lava dome, forcing the vesicles to close and affecting the permeable network. High temperature, uniaxial compression experiments on crystal-rich and crystal-poor lavas have quantified the evolution of porosity and permeability in such environments. The deformation mechanisms involved in uniaxial deformation are viscous deformation and cracking. Crack production is controlled by strain rate and crystallinity, as strain is localised in crystals in crystal rich lavas. -
ERUPTIONAL and POST-ERUPTIONAL PROCESSES in RHYOLITE DOMES Volume 2: Drafts of Papers
ERUPTIONAL AND POST-ERUPTIONAL PROCESSES IN RHYOLITE DOMES Volume 2: Drafts of papers A THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF Doctor of Philosophy in Geological Sciences IN THE UNIVERSITY OF CANTERBURY by J ens Richnow University of Canterbury March 2000 1/ I' "1 I I \' I j(' / j ; ! Chapter 14 Discussion 14.1 Introduction In the review of the thesis by the examiners it was suggested that the summary given on pages 351-355 does not reflect the important results of the thesis in a generic manner. Therefore an additional synthesis chapter was required which interprets the results of the main findings in terms of testing a hypothesis (or hypotheses). This chapter is written in the form of drafts of potential papers, which stress important findings in the study. I would like to thank the examiners for suggesting this approach for two reasons: (i) it allows me to present results in a way more accessible to readers and (ii) it prepares and eases the publishing of these findings as papers. ! 1 - 7 APR 2000 14.2. DRAFT OF PAPER 1 14.2 Draft of paper 1: "Relationship between Cooling, Development and Distribu tion of Textures and Lithologies in Rhyolite Domes" Abstract Detailed studies of the distribution and significance of textural/lithological units in rhyolite domes and flows provide valuable insight into cooling, degassing and crystallisation processes during and after their emplacement. In this paper I investigate the relationship between the main lithologies present in rhyolite domes, morphological dome parameters such as dome height and radius, and the cooling history. -
The Origin and Evolution of Breakouts in a Cooling-Limited Rhyolite Lava Flow
Breakouts in a cooling-limited rhyolite lava flow The origin and evolution of breakouts in a cooling-limited rhyolite lava flow Nathan Magnall1,†, Mike R. James1, Hugh Tuffen1, Charlotte Vye-Brown2, C. Ian Schipper3, Jonathan M. Castro4, and Ashley Gerard Davies5 1Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK 2The Lyell Centre, British Geological Survey, Edinburgh EH14 4AP, UK 3School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand 4Institute of Geosciences, University of Mainz, Becherweg 21, Mainz D-55099, Germany 5Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA ABSTRACT and inflation. The extended nature of some sessment, as well as for interpreting prehistoric breakouts highlights the role of lava supply deposits, improving our understanding of silicic Understanding lava flow processes is im- under a stationary crust, a process ubiqui- lava emplacement processes may be more press- portant for interpreting existing lavas and tous in inflating basalt lava flows that reflects ing than previously considered. for hazard assessments. Although substantial the presence of thermally preferential path- Lava flows initially advance in the direction of progress has been made for basaltic lavas ways. Textural analyses of the Cordón Caulle steepest gradient and their preliminary paths are our understanding of silicic lava flows has breakouts also emphasize the importance of thus relatively easy to forecast. However, after seen limited recent advance. In particular, late-stage volatile exsolution and vesicula- the lava flow front advance ceases, secondary the formation of lava flow breakouts, which tion within the lava flow. -
FT1 Jim Cole Field Symposium: Taupo Volcanic Zone
Geosciences 2013 Annual Conference of the Geoscience Society of New Zealand. Christchurch. Field Trip 1 21st to 23rd November 2013 Jim Cole Field Symposium: Taupo Volcanic Zone Leaders: Ben Kennedy1, Rose Turnbull2, Paul Ashwell1, Jim Cole1, Darren Gravley1, Sam Hampton1 & Graham Leonard3 1Department of Geological Sciences, University of Canterbury, 2 GNS Science, Dunedin 3GNS Science, Lower Hutt Cover photo: The 1886AD fissure through Wahanga dome and looking towards Whale Island and White Island (which is background centre left, and barely visible in the photograph). Bibliographic reference: Kennedy, B.M., Turnbull, R., Ashwell, P., Cole, J.W., Gravley, D.M., Hampton, S.J. & Leonard, G.S., (2013). Jim Cole Field Symposium: Taupo Volcanic Zone. In: Reid, C.M. & Hampton, S.J. (compilers). Field Trip Guides, Geosciences 2013 Conference, Christchurch, New Zealand. Geoscience Society of New Zealand Miscellaneous Publication 136B, 27 p. ISBN 978‐1‐877480‐34‐8, ISSN 2230‐4487 (print) ISSN 2230‐4495 (online) Jim Cole Field Symposium: Taupo Volcanic Zone Geosciences 2013 Jim Cole Symposium Taupo Volcanic Zone Trip Ben Kennedy, Rose Turnbull, Paul Ashwell, Darren Gravley, Sam Hampton and Jim Cole We also acknowledge a significant contribution on information from the 1886 Tarawera eruption from B.F. Houghton, C.J.N. Wilson and R.J. Carey This trip celebrates Professor Jim Cole’s 50 year contribution to volcanology in New Zealand. We aim to visit a range of volcanological field sites that span some of Jim’s research and to use these sites to promote scientific discussion and the telling of volcanlogical yarns that celebrate Jim’s career. -
Hammer, JE, Cashman, KV, Voight, B. (2000)
Journal of Volcanology and Geothermal Research 100 (2000) 165–192 www.elsevier.nl/locate/jvolgeores Magmatic processes revealed by textural and compositional trends in Merapi dome lavas J.E. Hammera,*, K.V. Cashman, B. Voight aDepartment of Geological Sciences, 1272 University of Oregon, Eugene, OR 97403-1272, USA bDepartment of Geosciences, Pennsylvania State University, 303 Deike Building, University Park, PA 16802-2712, USA Abstract Syn-eruptive degassing of volcanoes may lead to syn-eruptive crystallization of groundmass phases. We have investigated this process using textural and compositional analysis of dome material from Merapi volcano, Central Java, Indonesia. Samples included dome lavas from the 1986–88, 1992–93, 1994 and 1995 effusive periods as well as pyroclastic material deposited by the November 1994 dome collapse. With total crystallinities commonly in excess of 70% (phenocrysts ϩ microlites), the liquids present in Merapi andesites are highly evolved (rhyolitic) at the time of eruption. Feldspar microlites in dome rocks consist of plagioclase cores (Ab63An29Or8) surrounded by alkali feldspar rims (Ab53An5Or42), compositional pairs which are not in equilibrium. A change in the phase relations of the ternary feldspar system caused by degassing best explains the observed transition in feldspar composition. A small proportion of highly vesicular airfall tephra grains from the 1994 collapse have less evolved glass compositions than typical dome material and contain rimless plagioclase microlites, suggesting that the 1994 collapse event incorporated less-degassed, partially liquid magma in addition to fully solidified dome rock. As decompression drives volatile exsolution, rates of degassing and resultant microlite crystallization may be governed by magma ascent rate. -
The Origin and Evolution of Breakouts in a Cooling-Limited Rhyolite Lava Flow
Breakouts in a cooling-limited rhyolite lava flow The origin and evolution of breakouts in a cooling-limited rhyolite lava flow Nathan Magnall1,†, Mike R. James1, Hugh Tuffen1, Charlotte Vye-Brown2, C. Ian Schipper3, Jonathan M. Castro4, and Ashley Gerard Davies5 1Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK 2The Lyell Centre, British Geological Survey, Edinburgh EH14 4AP, UK 3School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand 4Institute of Geosciences, University of Mainz, Becherweg 21, Mainz D-55099, Germany 5Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA ABSTRACT and inflation. The extended nature of some sessment, as well as for interpreting prehistoric breakouts highlights the role of lava supply deposits, improving our understanding of silicic Understanding lava flow processes is im- under a stationary crust, a process ubiqui- lava emplacement processes may be more press- portant for interpreting existing lavas and tous in inflating basalt lava flows that reflects ing than previously considered. for hazard assessments. Although substantial the presence of thermally preferential path- Lava flows initially advance in the direction of progress has been made for basaltic lavas ways. Textural analyses of the Cordón Caulle steepest gradient and their preliminary paths are our understanding of silicic lava flows has breakouts also emphasize the importance of thus relatively easy to forecast. However, after seen limited recent advance. In particular, late-stage volatile exsolution and vesicula- the lava flow front advance ceases, secondary the formation of lava flow breakouts, which tion within the lava flow. -
Small-Volume Volcanism Associated with Polygenetic Volcanoes, Taupo Volcanic Zone, New Zealand
Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. Small-volume volcanism associated with polygenetic volcanoes, Taupo Volcanic Zone, New Zealand A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand Szabolcs Kósik 2018 Panoramic view of the west shore of Lake Taupo with three lava domes from the Motuoapa Peninsula “Each volcano is an independent machine—nay, each vent and monticule is for the time being engaged in its own peculiar business, cooking as it were its special dish, which in due time is to be separately served. We have instances of vents within hailing distance of each other pouring out totally different kinds of lava, neither sympathizing with the other in any discernible manner nor influencing other in any appreciable degree.” Clarence Edward Dutton PREFACE i Abstract In the past 350 ky, the Taupo Volcanic Zone (TVZ) has been the most productive silicic volcanic region in the world, with 12 silicic large-volume (35-2200 km3 DRE) caldera- forming eruptions and hundreds of predominantly silicic smaller-volume eruptions. These spatially and temporally scattered small-volume events are characterised by relatively short-lasting single eruptive episodes that may have been strongly influenced by location-specific environmental factors. The aim of this study is to evaluate the volcanic hazards associated with the activity of these small-volume volcanoes using two different approaches. -
Compositional Gradients Surrounding Spherulites in Obsidian and Their Relationship to Spherulite Growth and Lava Cooling
Bull Volcanol DOI 10.1007/s00445-012-0642-9 RESEARCH ARTICLE Compositional gradients surrounding spherulites in obsidian and their relationship to spherulite growth and lava cooling James E. Gardner & Kenneth S. Befus & James Watkins & Marc Hesse & Nathan Miller Received: 28 February 2012 /Accepted: 30 June 2012 # Springer-Verlag 2012 Abstract Spherical masses of crystal fibers (spherulites) Attributes of those gradients and the behaviors of the other crystalize from rhyolitic melt/glass mainly in response to elements are in accord with their experimentally constrained significant undercooling while lava cools. Spherulite growth diffusivities. Spherulites appear to have grown following should induce compositional gradients in the surrounding radial, rather than volumetric, growth. The observed gra- glass from expulsion of incompatible constituents and dif- dients (and lack of others) are more consistent with growth fusion of those constituents away from the spherulite. mainly below the glass transition, which would necessitate Finite-difference numerical modeling of one-dimensional the dome cooling at ca. 10−5 to 10−7 °C s−1. Such slow diffusion, in which diffusivities are allowed to vary with cooling is consistent with the relatively large volume of the temperature, is used to investigate how compositional gra- dome. dients reflect spherulite growth and lava cooling. Overall, three forms of gradients are identified. Elements that diffuse Keywords Obsidian . Spherulite . Tequila volcano . quickly are expelled from the spherulite but then migrate Diffusion . Crystallization away too quickly to become enriched at the boundary of the spherulite. Elements that diffuse slowly are trapped within the growing spherulite. Between those endmembers are Introduction elements that are not trapped, yet diffuse slow enough that they become enriched at the contact. -
Obsidian Source Localities in the North Island of New Zealand [1973]
OBSIDIAN SOURCE LOCALITIES IN THE NORTH ISLAND OF NEW ZEALAND [1973] G. K. Ward Department of Anthropology University of Otago New Zealand Archaeological Association Newsletter 16(3): 85-103 Previous research has shown the potential of analyses of artefact obsidian, especially source identification, to contribute to knowledge of New Zealand prehistory. As part of an investigation which sought to characterize obsidians by trace element analysis, deposits of raw material in northern and central regions of the North Island were located and sampled. The localities of these potential sources of artefact obsidian are listed along with brief hand specimen description of the material. INTRODUCTION Obsidian is a natural volcanic glass, usually of rhyolitic composition. Its vitreous or non- crystalline character is produced by the rapid cooling of a highly siliceous molten magma, often by quenching in a body of water, as when a lava flow runs into the sea. Thus mineral formation is effectively prevented and a supercooled liquid, a glass, results. The amorphous or extremely fine grained structure of the glass permits the phenomenon of conchoidal fracture, so that wherever in volcanic areas of the world obsidian was located it as sought after as a raw material for artefacts, particularly where metals were scarce or unknown. The homogeneity of obsidian has allowed investigators to apply geochemical techniques to source obsidian artefacts. Because of its method of formation a geological deposit of volcanic glass is likely to have firstly, a uniform chemical composition – or, at least, to be much more homogeneous than crystalline rocks – and, secondly, to differ from other discrete deposits of obsidian, so that a source may be distinguished by its unique chemical composition.