Report on Soufriere Hills (United Kingdom) — 16 December-22 December 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 December-22 December 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, 16 December-22 December 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 11-19 December activity from the Soufrière Hills lava dome continued at a high level. Night-time incandescence and observations with a high resolution thermal camera showed that activity was concentrated on the NW flank. Pyroclastic flows and semi-continuous rockfalls traveled down the NE, N, and NW flanks, channelling NE directly into Whites Ghaut and continuing into Whites Bottom Ghaut. Pyroclastic flows also traveled as far as 2 km NW down Tyers Ghaut multiple times a day, occasionally as far as 2 km W down Gages valley, and rarely E down Tar River valley. Fresh deposits from small pyroclastic flows moving S were seen at the head of the White River and Gingoes Ghaut. On 19 December heavy ashfall occurred in several areas in NW Montserrat. The Hazard Level remained at 4.
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.