Pressure changes in the magmatic system during the December 2008/January 2009 extrusion event at Soufrière 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 Soufrière 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 yke-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.