Unique strainmeter observations of Vulcanian explosions, Soufrière Hills Volcano, Montserrat, July 2003



[1] Five Vulcanian explosions were triggered by collapse of the Soufrière Hills Volcano lava dome in 2003. We report strainmeter data for three explosions, characterized by four stages: a short transition between the onset of disturbance and a pronounced change in strain; a quasi-linear ramp accounting for the majority of strain change; a more gradual continued decline of strain to a minimum value; and a strain recovery phase lasting hours. Remarkable ∼800 s barometric gravity waves propagated at ∼30 m s−1. Eruption volumes estimated from plume height and strain data are 0.32–0.42 × 106, 0.26–0.49 × 106, and 0.81–0.84 × 106 m3, for Explosions 3–5 respectively, consistent with quasi-cylindrical conduit drawdown <2 km. The duration of vigorous explosion is given by the strain signature, indicating mass fluxes of order 107 kg s−1. Conduit pressures released reflect static weight of porous gas-charged magma, and exsolution-generated overpressures of order 10 MPa.