Research drilling at Inyo Domes, Long Valley Caldera, California

While a great deal of attention has been focused on inferring conditions within deep magma reservoirs, much of the action in terms of magmatic processes such as degassing, explosive fragmentation, and fluid/melt interaction occurs at depths of a few hundred meters to a few kilometers. Our understanding of what happens to magma in this important subvolcanic regime is primitive and inconsistent. For example, eruption models assume that magma is a chemically closed system during ascent, but geochemical models tacitly assume it is an open system (but only to H2O and perhaps a few other volatile components). Thermal models are well developed but untested. The extent of magma/wallrock/fluid interaction is unknown. Yet we must understand the processes in this regime not only to understand the mechanisms of explosive eruption and hydrothermal circulation but to correctly interpret evidence of the deep plutonic conditions as well.