Report on Soufriere Hills (United Kingdom) — 27 May-2 June 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
27 May-2 June 2009
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2009. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 May-2 June 2009. 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 22-29 May activity from the Soufrière Hills lava dome was at a low level. On 23 May, a rockfall was detected by the seismic network and contained some low-frequency energy at the onset that may have indicated a small explosion. A small pyroclastic flow on 24 May traveled 1 km E towards the Tar River valley; a resultant ash plume drifted W over Gages Mountain and Plymouth. 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.