SGER: Extent and Impact of Distal Ash Fallout From the May 2008 Eruption of Chaiten, Chile

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This Small Grant for Exploratory research will support the travel of a team of scientists from the University of South Florida (USF) to collaborate with an international group of volcanologists in Argentina that are currently studying the new volcanic deposits from the ongoing eruption of Chaitén volcano in Chile. Chaitén volcano began erupting on May 2, 2008, apparently after approximately 9,500 years of quiescence. This ongoing eruption is already the largest in South America since the 1991 eruption of Hudson volcano, and creates a unique opportunity to sample tephra fallout from the eruption in detail, particularly because the tephra fallout is distributed primarily eastward, across Argentina. The team from USF, together with their international collaborators, plan a rapid response to this event by sampling tephra fallout across southern Argentina, the most distal and easily eroded parts of the deposit, in June and early July, 2008. The primary goal of this excursion will be to measure the variation of thickness, grain-size, and mass loading across a widespread tephra fall deposit. Such data will allow the determination of the volume of erupted material; and will provide a test of the current models of tephra dispersal and deposition. In addition, they will work with colleagues to determine the physical and chemical characteristics of the readily-soluble salts associated with freshly-fallen tephra. Such data provide essential information for determining the potential geochemical impact of ash fallout. It is also planned to measure the grain-size characteristics of fine airborne-ash (both freshly falling, and re-suspended), using actively-pumped filters, an essential input for models of the potential health impacts of volcanic ashfall. Ultimately, they plan to use the TEPHRA2 numerical model developed over the past decade to model tephra fallout from the Chaitén eruption. Although this and other fallout models have been widely used to forecast volcano hazards there has not yet been an opportunity to validate these models for large explosive volcanic eruptions that have been directly observed and sampled soon after tephra deposition. Thus, the Chaitén eruption provides a rare opportunity to collect data to validate and improve the TEPHRA 2 numerical model. For example, the ability to forecast deposition of very fine ash hundreds of kilometers from the erupting volcano has not yet been adequately tested yet represents a major health and economic impact. With the data collected in the field, the team will use TEPHRA2, coupled with nonlinear inversion techniques, to estimate eruption parameters (column height, duration, mass flow), and compare with observations of the eruption. All results will be available to the volcanology community via the IAVCEI Tephra Working Group website.