An overview of lava dome evolution, dome collapse and cyclicity at Soufriere Hills Volcano, Montserrat, 2005-2007

The third episode of lava dome growth at Soufrière Hills Volcano, Montserrat was characterised by higher average magma discharge rates than either previous dome growth episode at this volcano and yet fewer collapses. During sustained dome growth at moderate‐high average rates (>6 m3/s), we identified 2–6 week discharge pulses that each supplied c.20 Mm3 magma from depth. Our observations are consistent with some existing models but we explain discrepancies by a combination of higher volatile contents and higher ascent rates. Cycles of c. 11–16 days were evident in rockfall, LP rockfall and shallow LP earthquake counts related to dome growth and degassing. We speculate that degassing at the conduit margins together with stick‐slip conduit flow may drive these cycles. Only one major collapse >10 Mm3 occurred during the third episode (on May 20, 2006) as a new magma pulse entered the dome and coincided with heavy rainfall.