Report on Soufriere Hills (United Kingdom) — 7 October-13 October 2009
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 October-13 October 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, 7 October-13 October 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 ash-venting events from Soufrière Hills lava dome, which had begun on 4 October, ceased in the early hours of 7 October; there were a total of thirteen events. The last three were associated with small pyroclastic flows that traveled about 500 m down Tyers Ghaut to the NNW. Observations on 7 October revealed tongues of rockfall and small pyroclastic-flow deposits at the heads of Tyers Ghaut to the NNW, Tar River valley to the E, White River to the S, and Gages to the W. A small area of incandescence from the N flank of the lava dome was seen during 7-8 October.
Geologic Background. 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.