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Discovering Clues to Impending Explosive Volcanic Eruptions Through Geochemical Microanalysis and Magmatic Process Modeling: Heather Wright
Project Title: Discovering Clues to Impending Explosive Volcanic Eruptions Through Geochemical Microanalysis and Magmatic Process Modeling
Mendenhall Fellow: Heather Wright, (650) 329-4143, hwright@usgs.gov
Duty Station: Menlo Park, CA
Start Date: March 1, 2010
Education: Ph.D. (Geology), University of Oregon, Eugene, 2006
Research Advisor: Charles Bacon, (650) 329-5246, cbacon@usgs.gov; Alan Koenig, (303) 236-2475, akoenig@usgs.gov; Wendy Bohrson, Central Washington University, bohrson@geology.cwu.edu
  Heather Wright

Project Description: Large caldera-collapse style volcanism forms the greatest natural volcanic hazard on earth.  Though infrequent, explosive eruptions that are large enough to generate roof-block collapse have the potential to cause extensive damage, immediately affecting life, human and otherwise, devastating the economy in the short term, and potentially affecting global climate in an even longer term.  The range in magnitude of volcanic eruptions that lead to caldera collapse is huge: over 4 orders of magnitude in volume (Lipman, 2001). Furthermore, a single volcano can vary in eruptive style and volume with time, in some cases evolving towards creation of a larger magma chamber.  For the largest eruptions, we are prompted to ask: what are the necessary requirements to develop large volumes of magma in the shallow crust?  And moreover, how is eruptibility of this magma maintained?  The eruption sequence at Mount Mazama (Crater Lake), Oregon is a classic example of evolution from small central vent-style eruptions to a large, caldera-collapse event.  The eruption history at Mount Mazama is well characterized and sample suites exist for eruptions spanning hundreds of thousands of years, culminating with the climactic caldera-forming eruption approximately 7,700 years ago.  Therefore it provides the ideal focus for a case study of magma chamber evolution (growth) at a single volcano. 

This project will involve two distinct parts:

    1. Micro-scale geochemical measurements of eruptive products from the eruptive sequence at Crater Lake.  Volcanic deposits contain variable proportions of several key physical components: melt, crystals, bubbles, and accidental fragments of rocks that are not in equilibrium with the melt.  Key targets of the geochemical analyses will be phenocrysts and melt inclusions within phenocrysts. Melt inclusions trapped in phenocrysts act can preserve the chemistry of the melt at the time of crystallization (including volatile contents).  The inclusions become isolated from the melt, thereby acting as a time capsule that allows us to determine chemical changes in the magma chamber (for example, Wallace and others, 1999). Volatile analyses will be performed using recently developed analytical techniques with the U.S. Geological Survey-Stanford SHRIMP RG ion microprobe.  These data will be complemented by geochemical analyses of rare, accidental fragments of highly crystallized magma, which may be the intrusive, non-erupted counterpart of erupted volcanic material. 
    2. Computational modeling, using Magma Chamber Simulator software to constrain the relative role of magma chamber evolution processes including: fractionation, assimilation, and magma recharge, and constraining the relative timing of these processes.  Models will consist of a stepwise series of simulations that recreate the chemical, physical, and energetic characteristics of the magmatic system through time.  The results of the simulations will help us test current predictive models that use the same input parameters to forecast future explosive eruptions.

The goals of this project are to better understand:

References:

Lipman, P.W., 2001. Calderas, in Sigurdsson, H., Houghton, B.F., McNutt, S.R., Rymer, H. and Stix, J., eds., Encyclopedia of volcanoes: San Diego, Academic Press, p. 643–662.

Wallace, P.J., Anderson, A.T.J., and Davis, A.M., 1999, Gradients, in H2O, CO2, and exsolved gas in a large-volume silicic magma system: Interpreting the record preserved in melt inclusions from the Bishop Tuff: Journal of Geophysical Research, vol. 104, no. B9, p. 20097–20122.


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