Report on Soufriere Hills (United Kingdom) — 17 February-23 February 2010
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
17 February-23 February 2010
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2010. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 17 February-23 February 2010. 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 12-19 February activity from the Soufrière Hills lava dome was at a low level. Rockfalls originated from the inner walls of the 300-m-wide collapse scar on the N flank, formed from the 11 February event, and from the dome summit. Gas measurements on 17 February and seismicity were consistent with lava-dome growth, but growth was unconfirmed.
Inspection of the deposits from the 11 February collapse event revealed that the NE coastline had extended into the sea an additional 650 m. Pyroclastic flows razed many buildings in both Harris (3 km N) and Streatham (2 km NNW), and destroyed trees in the Gun Hill area (2 km NNW). Pyroclastic-flow deposits were approximately 15 m thick in the Trants region of the coast (near the old Bramble airport, about 5 km NE). A deep crater, similar in diameter to the collapse scar, was seen in the summit of the lava dome. The Hazard Level remained at 4.
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.