Pressure changes in the magmatic system during the December 2008/January 2009 extrusion event at Soufriere Hills Volcano, Montserrat (W.I.), derived from strain data analysis

In December 2008/January 2009 a 4-week episode of lava extrusion characterised by rapid dome growth and ground deflation occurred at Soufriere Hills Volcano (SHV), Montserrat W.I. Recorded strain dilatometer data show strain changes up to -3500 ns during this event. Modelling the collected data assuming existing structural models of the magmatic system, best-fit solutions are obtained for a simultaneous decompression of the shallow and the mid-crustal magma chambers together with a dilation of the shallow dyke-conduit. We interpret our model results as magma ascending from the two chambers into the eruption feeding dyke-conduit and partly extruding at the surface. Dome growth volume estimations from visual observations at SHV fit the extrusion volume inferred from our best-fit model and support our results. The reported data is the first set of geodetic data that documents the dynamic coupling within the entire crustal magmatic system of SHV. (C) 2012 Elsevier B.V. All rights reserved.