Report on Soufriere Hills (United Kingdom) — 28 February-6 March 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 28 February-6 March 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, 28 February-6 March 2001. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
The MVO reported that during 23 February to 2 March activity at the Soufrière Hills volcano increased with a marked change in the character of the seismicity, a change in the direction of lava dome growth, and moderate levels of pyroclastic flow activity. An unusually large number of hybrid earthquakes (388) were recorded during the week. On 24 February dome growth was concentrated on the NE side of the lava dome, but the next day the area of growth changed to the S side of the dome. After the change in activity, a small collapse occurred towards the SW down the White River Valley and produced small pyroclastic flows that stopped just short of the sea and started fires in Shooters Hill. Throughout the rest of the week rockfalls and small pyroclastic flows traveled to the top of the White River Valley, with only occasional ones traveling in other directions. This activity was accompanied by banded tremor and weak hybrid earthquakes. The Washington VAAC reported that throughout the week low-level ash clouds (up to ~3 km a.s.l.), presumably produced by rockfalls, and periodic hot-spot activity were visible on GOES-8 imagery.
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.