Modeling the 4D coupled dynamics of magma propagation, ground deformation, and gravity changes

We illustrate GALES, a finite element C++ code that we developed during last >10 years. GALES solves the time-dependent 3D thermo-fluid dynamics (4D space-time) of non-Newtonian multicomponent flows (magma) and 2-way coupled elastic structure (rocks). GALES accounts from incompressible to compressible flow regimes, and it is therefore suited to simulate from under-saturated magma conditions deep into the crust to the rapidly accelerating conditions along volcanic conduits including transonic flow regimes leading to explosive volcanic eruptions. The code is implemented with a suite of models describing the real properties of multi-component multiphase magmas, which are locally (in space and time) computed. Magma dynamics are fully coupled with rock elasto-dynamics, allowing computation of the transient signals (deformation, gravity) associated with magmatic flows by accounting for rock heterogeneities, free surface and real topography. Geometrical complexities associated with multiple magmatic reservoirs, connecting dykes, volcanic conduits etc. can all be accounted for, in separate or individual simulations. Typical computational time steps of 0.01 s and simulation lengths of order hours allow confident computation of signal frequencies in the range 0.001 – 10 Hz, which is still under-investigated for magmatic and volcanic systems. The results illustrate several original aspects of magma dynamics and associated signals, such as the association between magma convection and generation of Ultra-Long-Period ground displacement dynamics; the ground deformation patterns associated with complex distributions of overpressure, both negative and positive, reflecting magma transfer across separate reservoirs; the decoupling of gravity and deformation sources associated with buoyancy-driven ascent of magma; the generation of transient explosive events associated with deep arrivals of gas-rich magmas in basaltic open system volcanoes; and many others.