Mechanisms of pressure buildup in magma reservoir: insights from numerical experiments

Abstract

Understanding mechanisms leading to volcanic eruptions are of fundamental importance in geology and volcanology. A prerequisite to a volcanic eruption is the generation of sufficient overpressure in a magma reservoir, enough to exceed the strength of the rock, potentially triggering the volcanic eruption. In geological models, the pressure buildup in magma reservoir is often linked to magma recharge and volatile exsolution. Another mechanism, that is often overlooked in conventional geological models, is related to the isochoric rise of gas bubbles in almost incompressible magma saturated with volatiles. Predicting volcanic eruptions using numerical models is complicated by the need to solve coupled physical processes spanning multiple temporal and spatial scales.We present a coupled thermo-chemo-hydromechanical mathematical model for predicting the pressurization of a magmatic reservoir. The model predicts porous and free convection of partially crystallized magma due to thermal and compositional heterogeneities, and compaction of crystals due to density difference between solid and liquid phases. We describe thermodynamic equilibrium and thermo-mechanical properties of phases using the nonlinear equation of state obtained through direct Gibbs energy minimization. We resolve the multi-scale processes within the magma reservoir using high-resolution numerical modeling based on supercomputing.We demonstrate through numerical experiments that the two mechanisms, volatile exsolution due to retrograde boiling, and rising of gas bubbles in a  nearly isochoric system, could lead to pressure buildup in a magma reservoir, sufficient to exceed rock strength. We study systematically the relative importance of these mechanisms in a simplified problem setup.