Use of Distinct Element Method Models for Interpreting Volcano Deformation

Deformation characterized by large discontinuous (i.e. fault- or fracture-related) strains is typical of several volcano-tectonic processes, such as flank spreading, sector collapse, and caldera collapse. Continuum-based numerical or analytical modelling approaches have an inherent difficulty in simulating fracture or fault system development, but are nevertheless routinely used to model geodetic data from actively-deforming volcanoes. The effects of fracturing (particularly in the sub-surface) on deduced finite deformation sources may therefore be underestimated and misinterpreted. Here we outline the development of numerical models of volcano deformation based on the Distinct Element Method (DEM), a numerical approach that can simulate in an emergent fashion a progressive evolution from continuum to discontinuum mechanics. We highlight how these DEM models can successfully replicate the development of host-rock fracturing during drainage of a magma body, with subsequent collapse of the overburden and development of a surface depression (caldera). The DEM models further show how development of fracture systems can progressively change the shape, volume and depth of a continuum-based elastic-deformation source as estimated from displacements of the ground surface. As shown by applications to Bardarbunga volcano, Iceland, and Piton de la Fournaise volcano, La Reunion, DEM models can thus enable a better interpretation of geophysical and structural observations during volcano deformation.