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

Five Vulcanian explosions were triggered by collapse of the Soufrire 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 × 10 ⁶ 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.