Report on Soufriere Hills (United Kingdom) — 18 November-24 November 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 November-24 November 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, 18 November-24 November 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 13-20 November activity from the Soufrière Hills lava dome consisted of ash venting along with semi-continuous rockfalls and pyroclastic flows that were concentrated on the W flank. Ashfall occurred across many areas of the island. Views of the lava dome on 16 November showed that the dome height had decreased because of collapses and that a deep channel had developed NE of Chances Peak. Pyroclastic flows in the Gages Valley (W) continued down Spring Ghaut and Aymer's Ghaut, and spread onto the alluvial fan below St. Georges Hill. On 19 November, heavy ashfall occurred to the NW between Old Towne and Brades. The Hazard Level remained at 3.
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.