Report on Soufriere Hills (United Kingdom) — 23 February-1 March 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
23 February-1 March 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, 23 February-1 March 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 during 18-25 February activity from the Soufrière Hills lava dome was at a low level. Of 31 volcano-tectonic earthquakes detected by the seismic network, 18 occurred in a small swarm on 23 February. On 24 February a pyroclastic flow that traveled less than 1.5 km on the N flank originated from one of the highest parts of the dome, and traveled down the collapse scar formed on 11 February. The event produced an extensive pyroclastic surge and a relatively strong ash plume that rose to an altitude of about 1.5 km (5,000 ft) a.s.l. The Hazard Level remained at 3.
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.