The micromechanics of strain localization in partially - molten silicic magma chambers: keys for understanding the origin, and dynamics of "supervolcanic" eruptions

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Catastrophic caldera-forming eruptions during which thousands of cubic kilometers of very viscous and crystal-rich magma is erupted explosively over a time scale of days to weeks are among the most awesome natural phenomena on Earth. Such events have occurred intermittently throughout Earth's history in places such as the Yellowstone caldera, USA and in the Taupo volcanic zone, New Zealand. Magmas feeding these so-called "supervolcanic eruptions" are thought to be driven from high-level chambers, in part, by a time-dependent piston-like foundering of a dense chamber roof into an underlying laterally-extensive molten or partially-molten magma chamber of lower density. Whereas the volumes of such eruptions are perhaps not surprising, as they are expected to proceed until most or all buoyant magma is expelled, an explanation for the extreme rate of eruption remains one of the most compelling problems in volcanology. In detail, the physical problem governing the rate of eruption is analogous to the rapid compaction and disaggregation of a strong, deformable porous medium constructed of a solid crystalline matrix and a viscous interstitial pore fluid. The inherent mechanical difficulty with disrupting and expelling such a material places restrictive demands on the underlying magma chamber processes. This proposal uses a novel combination of field observations, laboratory fluid dynamics experiments, theoretical work and numerical simulations to identify and understand the magma chamber dynamics that enable such a large volume of crystal-rich material to be erupted so quickly.