High Temperature Fracture Mechanics of Dome Lava (Standard NERC grant)
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.

To meet these goals, I am conducting experiments in the fracture mechanics laboratory at UCL with Prof Peter Sammonds , Dr Hugh Tuffen, and Prof Philip Meredith, in collaboration with the Cascades Volcano Observatory (CVO).

CVO have provided samples of dacite and fault gouge from the dome currently growing at Mount St Helens. I will deform these samples under simulated volcanic conditions (stress, pressure, temperature, and pore fluid conditions) whilst recording acoustic emissions (AE) and stress-strain relationships using recently modified apparatus shown (insert technical overview diagram). These experiments address the role of fracture, friction and the brittle-ductile transition during volcanic lava dome growth and in magma conduit dynamics. Characteristics of AEs recorded during these laboratory experiments are compared to those of seismic events recorded during the emplacement of the lava dome from which the samples were taken in order to aid interpretation of volcanic seismicity. These laboratory studies will provide direct input into the development of the current generation of models of volcanic dome behaviour, which hinge upon whether deforming magma will flow, slip or fracture.