Report on Soufriere Hills (United Kingdom) — 25 February-2 March 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 February-2 March 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, 25 February-2 March 2004. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Volcanic and seismic activity remained at low levels at Soufrière Hills during 20-27 February. A period of low-level tremor began on 21 February around 0600 that continued for ~36 hours and consisted of many small long-period earthquakes. On 24 February around 0915 mudflows swept down the Belham valley (NW of the volcano) for ~40 minutes during intense rainfall. Signs of mudflows were also seen in the city of Plymouth (SW of the volcano). The sulfur-dioxide flux reached a peak daily value of 920 metric tons on 23 February.
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.