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Report on Soufriere Hills (United Kingdom) — 21 February-27 February 2007

Soufriere Hills

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 21 February-27 February 2007
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2007. Report on Soufriere Hills (United Kingdom) (Sennert, S, ed.). Weekly Volcanic Activity Report, 21 February-27 February 2007. Smithsonian Institution and US Geological Survey.

Weekly Report (21 February-27 February 2007)

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)

During 16-23 February, lava-dome growth at Soufrière Hills continued and was concentrated on the E and N sides. Small pyroclastic flows traveled down the Tar River Valley to the E, Gages to the W, and Tyres Ghaut to the NW. Ash venting and roaring noises originated from an area above Gages to the SW, where a new blocky lobe was visible. Moderately-sized pyroclastic flows traveled E down the Tar River Valley during 24-25 and 27 February. Bright incandescence at the dome was observed during the reporting period.

Based on satellite data, pilot reports, and information from the MVO, the Washington VAAC reported continuous ash emissions during 21-27 February. Resultant plumes rose to altitudes of 2.1-6.1 km (7,000-20,000 ft) a.s.l. and drifted mainly NE, NW, and W. A thermal anomaly was detected in the crater on satellite imagery.

Geological Summary. 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.

Sources: Washington Volcanic Ash Advisory Center (VAAC), Montserrat Volcano Observatory (MVO)