Report on Soufriere Hills (United Kingdom) — 17 October-23 October 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 October-23 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, 17 October-23 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 12-19 October activity at Soufrière Hills remained at an elevated level, although there was a reduction in seismicity compared with the previous few weeks. The cyclical nature of the seismic activity, which had been a dominant feature over recent months, also weakened. The active lava dome continued to grow at a moderate rate, producing pyroclastic flows on most days into the upper reaches of the Tar River Valley. Two significant collapse events occurred during the reporting period involving residual material from the dome that formed prior to the 29 July dome. On 14 October, after a day of torrential rainfall, several million cubic meters of unconsolidated talus was destabalized on the SE flank of the pre-July 29 dome. This material produced sustained pyroclastic flows E down the Tar River Valley, reaching the sea. Seismic data suggested that the event began at about 1715, peaked at 2245, and ended at about 2300. Ash from the event drifted to the NW and fell in residential areas between Iles Bay and St Peter's. On the morning of 16 October a collapse occurred on the S flank of the dome complex, producing numerous pyroclastic flows W 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.
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.