A mechanical model for lava dome deformations using the visco-poroelastic damage rheology 

Abstract

The eruption style and structural stability of lava domes are determined by the mechanical strength (rigidity), porosity and temperature of their constituent magmas and the stress (pressure) and strain rates acting on them. Both rigidity and porosity of dome materials evolve with time as a result of (1) formation of new micro-fractures (damage) due to cooling and/or increasing strain rates (causing rigidity decrease and porosity increase) and (2) large effective pressures (causing porosity decrease and compaction) in lava domes. The interaction between damage and porosity may lead to different deformation modes including transition between brittle or ductile behavior in the same material even at constant temperature, pressure and strain rate. We use a visco-poroelastic damage model to quantify the evolution of damage and porosity and their interactions in lava domes. The model is based on thermodynamic principles and uses a non-linear continuum mechanics formulation which predicts different effective elastic moduli for a solid when the loading changes from tension to compression. The model accounts for the temporal evolution of damage and porosity, damage-porosity interaction and gradual accumulation of irreversible deformation due to damage-related viscosity. Thus, the model can simulate a wide range of deformation mechanisms including local damage increase and strain localization leading to brittle failure, and cataclastic flow characterized by homogeneous damage increase and porosity decrease (inelastic compaction). We apply this continuum damage-porosity model to lab experiments on lava samples form Volcán de Colima (Mexico) and Galeras volcano (Colombia). We show that the model allows us to distinguish the contributions of different deformation mechanisms in the course of each experiment. For each volcano, we compare the model parameters constrained by the lab experiments and discuss the implications of the results for up-scaling the model and performing natural-scale simulations of lava dome deformations.