Growth of the lava dome and extrusion rates at Soufrière Hills Volcano, Montserrat, West Indies: 2005–2008

Abstract

The third episode of lava dome growth at Soufrière Hills Volcano began 1 August 2005 and ended 20 April 2007. Volumes of the dome and talus produced were measured using a photo‐based method with a calibrated camera for increased accuracy. The total dense rock equivalent (DRE) volume of extruded andesite magma (306 ± 51 Mm 3 ) was similar within error to that produced in the earlier episodes but the average extrusion rate was 5.6 ± 0.9 m 3 s −1 (DRE), higher than the previous episodes. Extrusion rates varied in a pulsatory manner from <0.5 m 3 s −1 to ∼20 m 3 s −1 . On 18 May 2006, the lava dome had reached a volume of 85 Mm 3 DRE and it was removed in its entirety during a massive dome collapse on 20 May 2006. Extrusion began again almost immediately and built a dome of 170 Mm 3 DRE with a summit height 1047 m above sea level by 4 April 2007. There were few moderate‐sized dome collapses (1–10 Mm 3 ) during this extrusive episode in contrast to the first episode of dome growth in 1995–8 when they were numerous. The first and third episodes of dome growth showed a similar pattern of low (<0.5 m 3 s −1 ) but increasing magma flux during the early stages, with steady high flux after extrusion of ∼25 Mm 3 .