Fracture of rock and crystal growth in veins and fractures at high temperature are important agents in volcanic system. Rock failure in the volcanic edifice, i.e. the high temperature fracture, leads to the opening of new pathways, which allows pressure to be released. On the other hand rapid crystallization can be the agent for large excess pressures to be maintained by sealing fractures. Competition between the two results in complex behaviour, which controls lava dome eruptions. However the understanding of these controls is poor. This lends itself to an integrated laboratory experimental and fieldwork campaign to ascertain the mechanics and physics of high temperature fracture growth and crystallization. In this project, the student will undertake fieldwork on Mt St Helens and Long Valley Caldera, as a comparison of two different volcanic systems, to analyse and quantify the fracture networks and the crystallization within fractures, and the relationship between fracture and high-temperature deformation, in recently erupted materials. The student will use the high-pressure/high-temperature rock deformation apparatus in the Rock and Ice Physics Laboratory at UCL to perform rock fracture experiments under conditions simulating in the shallow volcanic edifice. Fault healing by crystallization and sealing in the presence of pore fluids will also be investigated. The data generated will provide key input to quantitative geomechanical models of volcano deformation currently being developed.