High-temperature fracture mechanics of dome lava

Volcanoes that erupt highly-viscous lava domes are amongst the most hazardous, intensely studied and newsworthy of geological phenomena, as the past twenty-five years of activity at Mount St Helens, USA have demonstrated. A key challenge in geological science is how to predict reliably the sudden changes in behaviour that are typical of such domes, from gentle lava effusion to devastating explosive eruptions. Much progress has been made in recent years in studying eruptive behaviour, with the realisation that the material response of magma to applied stresses largely controls eruption mechanisms and the rheology of dome lava changes greatly during shallow degassing and crystallisation. A goal of the current generation of models for dome growth is to identify thresholds in behaviour (e.g. explosive/effusive eruptions, endogenous/exogenous dome growth) that are closely related to the fundamental physical behaviour of whether deforming magma will fracture or flow. We propose to do experiments in the laboratory on lava dome material from the recent eruption of Mt St Helens under simulated volcanic conditions. These expriments will establish the thresholds for dome growth and explosive eruptions. Acoustic emissions will also be measured during these laboratory experiments, so that the laboratory experiments can be related to observed volcano seismicity.These laboratory studies will provide direct input into the development of the current generation of models of volcanic dome behaviour.