Report on Soufriere Hills (United Kingdom) — 14 October-20 October 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 October-20 October 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 14 October-20 October 2009. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
MVO reported that during 9-16 October activity from the Soufrière Hills lava dome was at a high level; a new lava dome first reported on 9 October continued to grow. Over 1,200 rockfalls were detected by the seismic network. Pyroclastic flows traveled down every major drainage valley except the Tar River valley to the E. Brief views of the lava dome revealed that the new lava dome summit was about 60 m above the old dome structure. Heavy rainfall caused a lahar in the Belham Valley to the NW on 14 October. On 16 October, several large pyroclastic flows descended the White River to the S and reached the sea. Moderate-sized pyroclastic flows traveled 3 km NE down Tuitts Ghaut and White Bottom Ghaut, and a few smaller pyroclastic flows descended Tyers Ghaut to the N. Extensive ash clouds rose to an altitude of 6.1 km (20,000 ft) a.s.l. and drifted WNW, resulting in minor ashfall in inhabited areas. During 18-19 October, rockfalls and small pyroclastic flows continued to be detected.
Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.