Report on Soufriere Hills (United Kingdom) — 16 February-22 February 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 February-22 February 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 16 February-22 February 2011. 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 on 15 February clear views of the Soufrière Hills lava dome allowed scientists to conduct a thermal survey, the first since 2 December 2010, and compare the results to identify changes. A warmer area on the W side of the lava dome (Gages) had moved upslope. This area had been the source of a number of pyroclastic flows and rockfalls since February 2010. The second difference was the apparent increase in the number of fumaroles inside the collapse scar and around the 2006-2007 dome. One of the most obvious areas of increase was on the NE side of the lava dome.
MVO also reported that in total 18 volcano-tectonic earthquakes from Soufrière Hills were detected in two swarms that occurred on 12 and 16 February. Brief clear views of the lava dome revealed no significant morphological changes. Fresh pyroclastic-flow deposits on the E side of the dome at the head of the Tar River valley were noted. 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.