Report on Soufriere Hills (United Kingdom) — 9 April-15 April 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 April-15 April 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 9 April-15 April 2003. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Activity at Soufrière Hills was generally at moderate levels during 4-11 April, although there were short periods of more elevated activity. Rockfalls and pyroclastic flows mainly occurred on the E side of the lava dome in the Tar River Valley. Pyroclastic flows were also observed on the NE flank in White's and Tuitt's ghauts. Torrential rainfall late in the evening of 10 April produced mudflows in the Belham River and triggered pyroclastic flows on the E, N, and NW flanks of the lava dome. The Washington VAAC reported that low-level ash plumes were sometimes visible on satellite imagery.
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.