Rapid Decompression of Bubble-Bearing Magma and Implications for Eruption Style and Explosive Potential: An Experimental Study With Analogue Fluids

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One of the most important unresolved problems in physical volcanology is understanding what controls the style of volcanic eruptions, and in particular, the transition between effusive and explosive eruption styles. Currently, this transition is thought to be controlled by two key processes: fragmentation and degassing. Through fragmentation, magma is broken into discrete pieces. The viscous magma containing melt and bubbles is thus transformed into a much less viscous gas flow that can erupt rapidly and explosively. Degassing refers to the loss of dissolved and exsolved volatiles from the magma. Because the driving force of eruptions is often dominated by the expansion of exsolved gases, degassing should act to suppress explosive eruption. The main goal of the project is to determine experimentally the relationship between fragmentation and degassing during the rapid decompression of magmas. The experiments will be done in a shock tube apparatus, designed and built at the University of California, Berkeley. Analogue fluids will be used in order to control properties of the fluids, bubbles, and bubble growth. The experimental study will allow the determination of the relative importance of 1) preexisting bubbles, 2) exsolution, 3) conduit geometry, and 4) decompression rate on the processes that lead to explosive eruption. The experimental results will be interpreted in the context of theoretical models, which will then allow the scaling of laboratory results to volcanoes. The most important long-term impact of this work will be a better physical basis for estimating hazard. As a specific example, one implication of the experimental results obtained so far is that the bubble content of magmas is the primary control on whether rapid decompression will lead to explosive eruptions. Determining the vesicularity of domes or subsurface magma bodies (using some remote method) can thus be used to estimate the hazard posed by these magma bodies. This project will provide a training opportunity for a graduate student, a postdoc, and an introduction to research for undergraduates. Outreach will take place through classes at UC Berkeley, scientific conferences and refereed publications. It is expected that this project to lead to new interdisciplinary collaborations between the engineering and volcanology communities.