Abstract

Although volcano instability is increasingly recognised as a societal hazard, understanding and predicting volcanic collapse remains a complex and challenging task. In particular, large-scale, deep-seated catastrophic edifice failure has been successfully modelled in only a small number of cases, despite extensive field evidence that this type of edifice collapse is a common feature. One reason for this may relate to the way in which the instability is initiated. While most studies to date have focused on the role of magma intrusion or seismic activity as the primary cause of edifice failure, we present new data on the destabilising role of deep internal gas pressurisation. Shallow-level pressurisation has been put forward as a potential collapse mechanism where the failure resembles a surficial landslide. Here, pore fluids entering the system from above (e.g. rain water) result in a finite volume and hence a finite pressure so that upon saturation, further surface fluids simply run off. We show that that is unlikely that the pressures developed in this way can lead to deep-seated failure. In contrast, for internally de-gassing magma and/or boiling hydrothermal systems, the internal pressures that arise are constrained only by the strength of the volcano, which under appropriate loading conditions will fail producing giant lateral collapse. Using a combination of two and three dimensional finite element models and physical experiments, we show to a first approximation the effects of deeply sourced internal pressure on the mechanical behaviour of a volcano edifice, and demonstrate its potential to promote large-scale volcanic collapse.