Abstract
Since the eruption began in 1995, Soufrière Hills volcano on Montserrat has been characterised by five phases of magma extrusion and corresponding pauses. Despite a lack of eruptive surface activity since 2010, the volcano continues to show signs of unrest in the form of ongoing outgassing, and inflation of the entire island of Montserrat. Using numerical modelling, we compare a set of contrasting deformation models in an attempt to understand the current state of Soufrière Hills volcano, and to gauge its future eruption potential. We apply a suite of deformation models including faults and dykes, and an ellipsoidal source geometry to all phases and pauses covering the entire eruptive history from 1995 through 2020. Based on recent petrological evidence suggesting no recent injection of magma from depth after an initial magma intrusion, we test the hypothesis that the ongoing inflation of Montserrat could be explained by a visco-elastic, crustal response to the initial magma intrusion without a renewed pressurisation due to magma injection. In contrast to previous modelling attempts, we focus on conceptual models and compare elastic- with several visco-elastic models taking temperature-dependent viscosity models, tectonic components, mass balance, magma compressibility and outgassing data into account. We explore a wide parameter space in a Generalised Maxwell Rheology to explain the observed deformation patterns, and demonstrate that a realistic, depth-dependent distribution of visco-elastic parameters does not allow an interpretation of the deformation signal without any magma influx or further pressurisation. Within the range of large uncertainties attached to the visco-elastic model parameters we show that visco-elasticity reduces the degree of ongoing pressurisation or magma influx into a crustal reservoir by a few percent. We conclude that magma influx at a rate of 0.10 to 0.57 m3/s is the most likely explanation of the current deformation pattern and is also in agreement with mass balance considerations and current SO2 flux observations.
Keywords
Deformation, GPS, Magma compressibility, Maxwell rheology, Soufrière Hills, Visco-elastic response