Report on Soufriere Hills (United Kingdom) — 3 November-9 November 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 3 November-9 November 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 3 November-9 November 2004. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 29 October to 5 November, volcanic and seismic activity at Soufrière Hills remained elevated. The seismic network recorded one rockfall, 33 hybrid earthquakes, and 39 volcano-tectonic earthquakes. The increased hybrid and volcano-tectonic activity was thought to be related to rainfall. In association with the rainfall, minor mudflow activity was recorded on 1 and 3 November. The sulfur-dioxide flux averaged about 290 metric tons per day, with a high of 440 metric tons on 30 October. An observation flight over the volcano on 4 November revealed the continued existence of standing water in the explosion pit produced by the 3 March 2004 event and no evidence of a re-start of lava-dome growth.
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.