Hydrothermal alteration of andesitic lava domes can lead to explosive volcanic behaviour

Dome-forming volcanoes are among the most hazardous volcanoes on Earth. Magmatic outgassing can be hindered if the permeability of a lava dome is reduced, promoting pore pressure augmentation and explosive behaviour. Laboratory data show that acid-sulphate alteration, common to volcanoes worldwide, can reduce the permeability on the sample lengthscale by up to four orders of magnitude and is the result of pore- and microfracture-filling mineral precipitation. Calculations using these data demonstrate that intense alteration can reduce the equivalent permeability of a dome by two orders of magnitude, which we show using numerical modelling to be sufficient to increase pore pressure. The fragmentation criterion shows that the predicted pore pressure increase is capable of fragmenting the majority of dome-forming materials, thus promoting explosive volcanism. It is crucial that hydrothermal alteration, which develops over months to years, is monitored at dome-forming volcanoes and is incorporated into real-time hazard assessments

Controls on explosive-effusive volcanic eruption styles

One of the biggest challenges in volcanic hazard assessment is to understand how and why eruptive style changes within the same eruptive period or even from one eruption to the next at a given volcano. This review evaluates the competing processes that lead to explosive and effusive eruptions of silicic magmas. Eruptive style depends on a set of feedbacks involving interrelated magmatic properties and processes. Foremost of these are magma viscosity, gas loss, and external properties such as conduit geometry. Ultimately, these parameters control the speed at which magmas ascend, decompress and outgas en route to the surface, and thus determine eruptive style and evolution

A review of tectonic, elastic and visco-elastic models exploring the deformation patterns throughout the eruption of Soufrière Hills volcano on Montserrat, West Indies

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