Strain field analysis on Montserrat (W.I.) as tool for assessing permeable flow paths in the magmatic system of Soufrière Hills Volcano

Abstract

Strain dilatometers have been operated on the volcanic island of Montserrat (West Indies) for more than a decade and have proven to be a powerful technique to approach short-term dynamics in the deformational field in response to pressure changes in the magmatic system of the andesitic dome-building Soufrière Hills Volcano (SHV). We here demonstrate that magmatic activity in each of the different segments of the SHV magmatic system (shallow dyke-conduit, upper and lower magma chambers) generates a characteristic strain pattern that allows the identification of operating sources in the plumbing system based on a simple scheme of amplitude ratios. We use this method to evaluate strain data from selected Vulcanian explosions and gas emission events that occurred at SHV between 2003 and 2012. Our results show that the events were initiated by a short phase of contraction of either one or both magma chambers and a simultaneous inflation of the shallow feeder system. The initial phase of the events usually lasted only tens to hundreds of seconds before the explosion/gas emission started and the system recovered. The short duration of this process points at rapid transport of fluids rather than magma ascent to generate the pressure changes. We suggest the propagation of tensile hydraulic fractures as viable mechanism to provide a pathway for fluid migration in the magmatic system at the observed time scale. Fluid mobilization was initiated by a sudden destabilization of large pockets of already segregated fluid in the magma chambers. Our study demonstrates that geodetic observables can provide unprecedented insights into complex dynamic processes within a magmatic system commonly assessed by theoretical modeling and petrologic observations.

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

“…Recent observations of degassing and deformation at volcanoes demonstrate that transport can be rapid in igneous mush systems. For example, episodes of magmatic fluid transport from depths of at least 10 km are illustrated by volumetric strain data and SO 2 gas fluxes associated with eruptive activity at the andesitic Soufrière Hills volcano on Montserrat (Gottsmann et al, 2011;Hautmann et al, 2014;Christopher et al, 2015). Transport speeds of several meters per second are indicated within the Soufrière Hills volcano mush region and are consistent with transport through transient fracture systems.…”

Assimilation of Deformation Data for Eruption Forecasting: Potentiality Assessment Based on Synthetic Cases

“…This progress allows to characterize the geometry of magmatic plumbing systems underlying volcanoes in terms of reservoir shapes, depths and numbers. In particular, at some specific volcanoes, deep magmatic reservoirs, which had been ignored so far, are evidenced (e.g., Elsworth et al, 2008;Chadwick et al, 2011;Bagnardi and Amelung, 2012;Hautmann et al, 2014;Tiampo et al, in press). However, most of the models used to interpret geodetic data are kinematic and cannot provide information on the pressure within the magmatic system, which is the key parameter to control the timing of magma reservoir rupture as well as the ability of magma to reach the surface and thus to feed an eruption.…”

Shallow crustal mechanics from volumetric strain data: Insights from Soufrière Hills Volcano, Montserrat

“…A typical conduit radius of around 15 m has been inferred from the size of extruded andesitic spines [Voight et al, 1999;Sparks et al, 2000;Melnik and Sparks, 2002] though spines of 25 m radius have also been reported . Volumetric strain data have provided important insights on plumbing system dynamics beneath SHV during explosive activity [Chardot et al, 2010;Linde et al, 2010;Voight et al, 2010;Hautmann et al, , 2014.…”

“…Volumetric strains induced by pressure transients in the conduit are thought to be masked when lower sections of the plumbing system are involved in explosions; this has been shown by strain modeling of the various system components of the Soufrière Hills Volcano [Hautmann et al, 2014;Odbert et al, 2014]. Consequently, the conduit dimensions consistently used in the literature have not been tested by strain modeling [Chardot et al, 2010;Linde et al, 2010;Voight et al, 2010;Gottsmann et al, 2011].…”

“…This eruption has been interpreted as having been triggered and fed exclusively by dynamics in the shallowest part of the plumbing system, i.e., the conduit [Chardot et al, 2010;Hautmann et al, 2014]. Extensive strain modeling of the entire SHV plumbing system has isolated and identified the individual signatures of almost every component; conduit signals typically demonstrate a low-amplitude strain change on the order of tens of nS with the same polarity at all sites [Chardot et al, 2010;Hautmann et al, 2014]. This renders it an ideal candidate for a study on the effects of topography and heterogeneity.…”