Ground deformation measurements at the Soufriere Hills volcano, Montserrat:II: Rapid static GPS measurements June 1996 June 1997

We describe measurements of ground deformation around the erupting Soufriere Hills volcano made between June 1996 and June 1997 using Rapid Static GPS. The measurements define a lateral displacement field which is approximately radially symmetrical about the growing dome. No significant sustained vertical displacements have been identified. Radial displacements have generally increased steadily during this period of observation. The rate of displacement decreases from 43 cm per year at a distance of 0.6 km from the centre of the dome to about 1 cm/year at a distance of 3.8 km. Strains within one km of the dome itself are greater than 10(-3). The rate of variation of strain with distance indicates a causative centre of pressure at a depth of not greater than 750 meters below the summit of the dome