Report on Soufriere Hills (United Kingdom) — 9 December-15 December 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
9 December-15 December 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, 9 December-15 December 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 4-11 December activity from the Soufrière Hills lava dome continued at a high level and pyroclastic flow activity was concentrated on the N side. Pyroclastic flows traveled as far as 2 km NW into Tyers Ghaut and NE in abundance down Tuitt's Ghaut, and sometimes Whites Bottom Ghaut, continuing onto Farrell's plain. A few small pyroclastic flows also descended the Tar River valley to the E. On 10 December, a large seismic signal was associated with a relatively large pyroclastic flow in Tyers Ghaut that traveled 3.5 km, stopping just beyond the W end of Lee's village. The event prompted the National Disaster Preparedness and Response Advisory Committee (NDPRAC) to raise the Hazard Level to 4, restricting the hours residents can enter certain pre-designated hazard areas.
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.