Report on Soufriere Hills (United Kingdom) — 9 October-15 October 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 October-15 October 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 9 October-15 October 2002. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 4-11 October, volcanic and seismic activity at Soufrière Hills remained at moderate levels. The NW extrusion lobe of the lava dome continued to grow steadily; early in the report period it grew to the NW, but later growth was more centralized. There was a noticeable bulking up of the summit area of the lobe. Rockfalls and small pyroclastic flows were shed into the upper portions of Fort Ghaut and Tuitt's Ghaut. Minor mudflow activity occurred during the evening of the 9th. The growth of the lava dome towards the NW increased the probability of pyroclastic flows entering the Belham River system. In order to reduce the level of risk this poses, populated areas along the fringes of the lower part of the Belham Valley (~300 people) were evacuated on 8 and 9 October, and were declared part of the Exclusion Zone. A relatively small pyroclastic flow traveled NNE down the flanks of the volcano on the 13th.
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.