Relating magma dynamics and ground deformation patterns at Mount Etna

Abstract

We adopt a forward model approach to ground deformation through the use of GALES (GAlerkin LEast Squares) to simulate the mixing of magmas of variable compositions and temperatures, coupled with the elastodynamic response of the surrounding medium. GALES is a finite element parallel C++ code which solves for both the fluid and elasto-dynamic equations. Firstly, the mass, momentum and energy conservation equations are solved through GALES to simulate magma transfers across reservoirs connected through dykes. This allows the computation of the space-time stress distributions along the geometrically complex magma-rock boundary. Such stress distributions are then employed by GALES as a set boundary conditions in elasto-dynamic simulations to compute the space-time distribution of rock displacement within the heterogeneous rock system and on the free surface. The computed synthetic time series for surface ground deformation at places corresponding to the position of actual receiver stations are finally analysed and compared to the real observational data at Mount Etna.  The geometry of the plumbing system, the temperature and major oxide composition of the involved magmas, and their water and carbon dioxide contents, are constrained from the bulk knowledge at the highly investigated, highly monitored, well-known Etna volcano. The space-time dependent physical properties of the multiphase magmas are computed on the basis of the local composition and volatile partition between the gas and melt phases. The results highlight the relationships between observations from surface monitoring networks and deep magma dynamics. In particular, they allow an in-depth investigation of ground oscillations with periods from seconds to hours, covering the intermediate range between seismic and geodetic observations which is being increasingly accessed to direct measurements. Such an intermediate frequency range emerges as being rich with new information on underground magma dynamics, potentially opening new perspectives and possibilities to magma monitoring and volcanic forecasts.