Ascent rates and volatiles of explosive basaltic volcanism

Abstract: Explosive volcanic eruptions are propelled to the surface by the exsolution of vapour bubbles from magma due to decompression. A long-held view is that the amount of H2O dissolved in the magma at depth controls the intensity of an explosive eruption. Growing evidence from studies reporting H2O concentrations of melt inclusions (MIs) do not support this view. Instead, the rate at which magma ascends to the surface may play an important role in modulating the eruption style. Slow magma ascent allows the vapour bubbles to rise ahead of the magma, thereby diffusing the driving force for an explosive eruption, whereas for fast magma ascent, the bubbles remain essentially trapped within the magma, causing acceleration and the potential for an explosive eruption. This talk will highlight some new tools that we have developed for estimating magma decompression rate and their application to several notable eruptions of different intensities at Cerro Negro Volcano, Nicaragua, and Etna Volcano, Sicily. I will end with some remaining mysteries and suggest possible avenues for future experimental and modeling work.