Report on Soufriere Hills (United Kingdom) — 10 October-16 October 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 10 October-16 October 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 10 October-16 October 2001. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 5-12 October volcanic activity at Soufrière Hills remained at elevated levels, although there was a marked reduction in the number of hybrid earthquakes compared with the previous few weeks. Numerous pyroclastic flows were produced by material avalanching off of the lava dome, which continued to grow in the summit crater at a moderate rate. The flows were relatively small, but energetic, and were confined to the upper and middle reaches of the Tar River Valley to the E of the volcano. Associated ash clouds drifted to the W and NW, occasionally depositing small amounts of ash on inhabited areas on the N part of the island. According to the Washington VAAC, ash clouds did not rise over ~2 km a.s.l. Avalanching talus on the S flank of the previous lava dome produced a pyroclastic flow that traveled SW down the White River approximately two-thirds of the distance to the sea. Mudflows occurred in the Belham Valley during several days with periods of torrential rainfall. The daytime entry zone was reopened on 11 October, following its temporary closure the previous week.
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.