Lava dome growth and evolution with an independently deformable talus

Subduction zone volcanism occurs due to partial melting from subducting slabs, which generally results in high-viscosity magma containing a large amount of volatiles. Such volcanic eruptions can form a lava dome, from which collapse events are a common and important part of their evolution. Collapse events can have devastating consequences; in the form of block and ash avalanche deposits, pyroclastic flows, surges and the generation of tsunamis if they enter the sea. In addition to this, once a mass of lava dome has been removed during a collapse event, this results in a drop in pressure in the remaining volatile-rich magma, which may then erupt explosively. The internal structure of a lava dome and the extent of the surrounding carapace/talus is unknown, but likely to be critical for hazard assessment, and is the motivation for this research. Presented is a computational model for the growth and evolution of an endogenous lava dome, including an independently deformable talus, using the Finite Element Method. Dome growth is modelled to occur under two timescales: continuous dome expansion via the addition of new magma into the molten core interior, and relatively instantaneous talus readjustments due to rockfalls and the disintegration of the solid surface. The continuous deformation of the dome is modelled as a fluid with a yield strength in the talus region. While talus deformation is modelled as a granular material that rests at angles below its angle of repose. Both surfaces, dome and core/talus interface, are displaced using the level-set method. The model is axisymmetric and assumes that solidification, and therefore talus growth, occurs due to gas exsolution which promotes crystallization, rather than from surface cooling, appropriate for intermediate composition lava flows. For the purpose of this paper we consider and apply the model to the Soufrière Hills Volcano, Montserrat, but the techniques used are generic, allowing the model to be applied to other dome forming eruptions. The model provides information on the shape of the dome, with the growth and extent of the talus and core found to be predominantly governed by the lava extrusion rate, degree of solidification (i.e. a solidus pressure), the friction angle associated with the talus, and lava dome viscosity. © 2008 The Authors Journal compilatio