Report on Soufriere Hills (United Kingdom) — 23 March-29 March 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
23 March-29 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 March-29 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 March activity at the Soufrière Hills lava dome was at a low level. A small lahar occurred in the Belham valley (NW) on 19 March. A relatively large pyroclastic flow traveled likely in excess of 2 km down the Tar River valley to the E and a resulting ash plume drifted W over uninhabited areas. The pyroclastic flow was related to the degradation of the lava dome on the E side as recent observations noted undercutting and overhanging areas on that side. 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.