From Crystal Mush to Eruptible Magma: Thermo-Poroelastic Controls on Melt Channelization

The generation of eruptible magma from long-lived, crystal-rich mush reservoirs remains a fundamental challenge in volcanology. Magma stored in the crust commonly resides as a high-crystallinity mush below the eruptibility threshold, yet many volcanoes exhibit frequent eruptions that require rapid remobilization of stored melt. In this study, we investigate the physical mechanisms by which hot melt recharge reorganizes a colder, partially crystalline reservoir to produce localized zones of mobile, eruptible magma. We present a fully coupled three-dimensional thermo-poroelastic model that simulates hot melt injection into a porous magma mush, incorporating Darcy flow, heat transfer with phase change, and poroelastic deformation. Magma properties, including melt fraction, viscosity, density, and mush permeability, evolve dynamically as functions of temperature, pressure, and composition. We utilize thermodynamic models, specifically MagmaSat and MELTS, to simulate decompression-driven H₂O-CO₂ exsolution, melt-crystal phase development, and crystallization processes in magmatic systems. The resulting volatile budgets and phase equilibria are then used to parameterize our coupled finite element model, providing melt fraction, density, viscosity, and compressibility inputs to the fully coupled thermo-poroelastic deformation model. We explore three initial mush storage temperatures (800, 850, and 900 °C) and a range of recharge temperatures from 900 to 1300 °C. These conditions are implemented in a fully coupled 3D finite element model that resolves Darcy melt migration, heat transfer, and thermo-poroelastic deformation within a mush reservoir embedded in a linear elastic half-space. Our results show that low temperature recharge produces only small, isolated melt pockets, while hotter injections generate channels with high melt fraction. These channels grow upward and outward, forming vertically connected networks where melt fractions exceed ~50 vol%, a threshold for eruptibility. We constrain reservoir and injection parameters to yield realistic surface deformation, and we find that incorporating temperature- and volatile-dependent feedbacks does not alter the overall surface deformation pattern. These results provide a physical framework for understanding magma rejuvenation, channelized melt transport, and eruption triggering in crystal-rich reservoirs.