Declining magma supply to a poroelastic magma mush explains long-term deformation at Soufrière Hills Volcano

Abstract

Volcano deformation studies traditionally consider melt-dominated magma reservoirs, often overlooking the significant role of poroelastic mush in modifying surface deformation. Here, we analyze the deformation of Soufrière Hills Volcano (SHV) with a focus on a mush-dominated, poroelastic magma reservoir, drawing on temporal deformation data from 14 continuous GPS stations during the ongoing intra-eruptive unrest period. We implemented a 3D Finite Element model and optimization to simulate the observed deformation. Our results reveal that the deformation is likely driven by ongoing, melt injection (Q = 1.1 m³ sec⁻¹) into a low permeability (k = 4.7 × 10⁻¹⁰ m²) reservoir with the injection to the base of the reservoir at 16.5 km depth below sea level. Our findings highlight temporal variations in the melt injection rate to fit the decreasing GPS-recorded deformation rates. An initial injection rate Qi = 1.9 m³ sec⁻¹ inferred at the start of our study period decreases to Qf = 0.3 m³ sec⁻¹ over a 12-year period (2010–2022). Exploratory forward modeling suggests that if current trends continue, the end of magma supply to our modelled reservoir could occur around June 2024 ± 2 years. However, this does not imply the end of associated volcanic hazards at SHV, as the poroelastic diffusion of melt will continue, causing redistribution of melt, surface deformation, and potentially initiating reservoir rupture. While our models offer new insights, inherent limitations in our simulations include interdependencies among our explored model parameters that would benefit from further refinement. Despite these limitations, the study offers crucial guidance on understanding and forecasting volcano deformation dynamics, particularly for volcanoes like SHV with crystal-rich magma reservoirs.