Stress and Strain in Magma‐Mush Reservoirs: Implications for Reservoir Failure and Magma Propagation

Abstract Investigating the mechanical stability and failure of magma reservoirs following magma supply is critical for volcanic hazard assessment. While magma reservoirs were traditionally modeled as melt‐filled cavities, they are now more often described as crystal mushes where melt flows and is stored in porous networks. Little attention has been devoted to stress changes within and outside magma‐mush reservoirs, which ultimately dictate their failure and the transport of magma toward the surface. Here, we address this gap by developing Finite‐Element numerical models of magma supply in gravitationally loaded, poroelastic magma reservoirs embedded in an elastic crust. We explore the stress changes and volumetric strain rate within the reservoirs during and after magma supply, and perform sensitivity tests on different poroelastic and magma supply parameters. Contrarily to melt‐dominated, static models, we find that regions where failure is promoted, both within and around the mush, evolve through time and are localized in the surroundings of the magma injection site. However, melt diffusion eventually leads to failure being promoted at the top of the reservoir. We also highlight how pore pressure compensates gravity‐induced compressive stresses, so that smaller magma overpressures are required to reach failure‐likely conditions. Finally, we find that tensile stresses due to magma supply within the mush itself may be large and lead to diffuse mush failure or destabilization. Further modeling developments, combining our approach with fracture propagation, and better constrained magma and mush properties will improve our understanding of reservoir stability and how volcanic eruptions are triggered.