Phreatoplinian Signatures of the 1991 Explosive Eruptions of Hudson Volcano, Chile

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"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Many large volcanoes are ice-covered and, consequently, when they erupt there is the potential for the interaction of high temperature magma and melt-water, such as in the Pacific Northwest region of the United States. This may result in the generation of catastrophic floods or explosive activity that poses significant hazards to communities in the surrounding area. The 1991 eruption of the ice-covered Hudson volcano in Chile was one of the largest explosive eruptions of the twentieth century. It caused over $8.5 million dollars worth of damage in Argentina and Chile as a result of extensive fallout of volcanic ash and flooding. This proposed research seeks to examine the potential role of glacial melt-water in affecting the nature of explosive volcanic eruptions using the 1991 Hudson event as a case study. The interaction of magma with glacial melt-water produces distinctive characteristics in the products of the eruption that can be studied by analytical geochemistry and scanning electron microscopy. Characteristics of the widespread dispersal of the Hudson volcanic products suggest that significant interactions of magma and water took place in addition to primary degassing of the magma. A principal objective of the research will thus be to try to identify the signal of magma/water interactions in the 1991 Hudson deposits and assess its importance to the overall eruption. The findings of the study should have broader significance for the recognition of magma/water interactions in the ancient deposits of large stratovolcanoes and will thus contribute to more precise assessments of future eruption styles and their potential volcanic hazards. The research plan includes the analysis of the volatile content of juvenile particles from the 1991 eruptions using FTIR to assess the potential for arrested degassing during the eruption, SEM imaging of particle surfaces to search for features of 'wet' versus 'dry' phreatomagmatic activity, and crystal size distribution analysis to evaluate the thermal and staging histories of magmatic components from the initial basaltic phase of the eruption. In addition, grain size analysis and pumice vesicularity measurements will be carried out to evaluate the potential role of magma/water interactions on fragmentation efficiency. The project will fund a one-year post-doctoral position.