HR: 1330h
AN: V42B-0360    [PDF]
TI: The Collapse of the Lava Dome at Soufriere Hills Volcano, 12-13 July 2003
AU: * Herd, R
EM: richard@mvo.ms
AF: Montserrat Volcano Observatory, Fleming, Salem, 664 Montserrat
AU: Edmonds, M
EM: marie@mvo.ms
AF: Montserrat Volcano Observatory, Fleming, Salem, 664 Montserrat
AU: Strutt, M
AF: British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Ottermeiler, L
AF: British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA United Kingdom
AB: A large dome collapse took place at the Soufriere Hills Volcano, Montserrat, on 12 July 2003. Around 120 million m$^{3}$ of lava dome and talus collapsed to the east, generating large pyroclastic flows in the Tar River Valley. The collapse took place after a three-day-long hybrid earthquake swarm, which merged into a continuous tremor in the early morning of 12 July 2003. A period of brief but intense period of rainfall occurred between 6:30 and 9:30 am, which coincided with the onset of pyroclastic flow activity. Pyroclastic flows continued throughout the day, slowly increasing in volume and energy as the hotter interior of the talus and dome were exposed, this stage being similar to the evolution of dome collapses on 20 March 2000 and 29 July 2001. At 18:00 phreatic explosions began to take place where the block and ash flows were hitting sea on the Tar River Fan, sending black jets 50-100 metres vertically above the Fan. By 20:00 the pyroclastic flows were associated with energetic surges that were observed to be traveling 2-3 km over the surface of the sea at the mouth of the Tar River Valley. From 22:30 to 01:30 13 July the most energetic sequence of events took place, with one very large vulcanian explosion from the exposed upper conduit and dome remnants and 3-4 smaller explosive events. These explosions took place shortly after large volumes of dome material slumped into the sea down the Tar River Valley, the largest occurring at 23:34. This event caused a 1 metre high tsunami in Guadeloupe. The subsequent explosions were recorded by pressure sensors both on Montserrat and on the island of Martinique, 260 km to the south. This large single flow in the Tar River was associated with a block and ash flow that was confined to the Tar River valley and a powerful surge component derived from the lower reaches of the Tar River valley, which spread northwards, covering 10 km$^{2}$ and reaching as far as Spanish Point, Bethel Village and White's Yard. This surge was immensely destructive and its deposit reached over 1 m thick in places. Animals were killed 4 km northwards of the Tar River Valley and a GPS receiver and remote camera at White's Yard were destroyed (the last data recorded at 23:35 12 July). An explosion occurred shortly after 01:00 13 July and thereafter the seismic signal decreased in amplitude over the next three hours, reaching background levels by 06:00 13 July. At 09:12 13 July a vulcanian explosion occurred, with a vertical eruption column 12 km high. This event deposited highly vesiculated pumice up to 6.5 cm in dimension in inhabited areas and up to 30 cm on the southwestern flanks of the volcano. Two more vulcanian explosions took place thereafter, the first at 01:10 14 July and the second at 01:15 15 July. On 16 July 2003 at 09:10 a strong SO$_{2}$ degassing event took place, reaching 70 kg/s before decaying exponentially throughout the rest of the day. A new dome began to grow in the scar 22-25 July, but then stagnated. On 1 August 2003 a sustained water degassing and ash venting event took place throughout the day, from 06:00 to 17:00, sending a thick plume of steam and ash to the west of the volcano. Seismicity decreased dramatically after 1 August and up to 3 September, there was no eruptive activity at Soufriere Hills Volcano.
DE: 8414 Eruption mechanisms
DE: 8419 Eruption monitoring (7280)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting