Report on Soufriere Hills (United Kingdom) — 4 February-10 February 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
4 February-10 February 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, 4 February-10 February 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 at Soufrière Hills during 30 January to 6 February increased slightly in comparison to the previous week. The seismic network recorded 15 rockfalls, 1 volcano-tectonic earthquake, 7 long-period earthquakes, and 9 hybrid earthquakes. In addition, a weak long-period earthquake swarm began on 30 January. The swarm was comprised of ~1,000 separate events occurring over a ~30-hour period, although only four events were large enough to trigger the seismic-event detection systems. The sulfur-dioxide flux peaked on 1 February at 1,017 tons per day before decreasing to 439 tons on 5 February.
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.