Report on Soufriere Hills (United Kingdom) — 5 September-11 September 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 September-11 September 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 5 September-11 September 2001. 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 remained at similar levels as during the previous week. Bands of tremor, associated with rockfalls and ash venting, occurred at irregular intervals. The active lava dome appeared to be growing rapidly and was well-formed, with steep sides and a rugged summit area. Rockfalls and small pyroclastic flows that originated from the new dome were observed in the upper reaches of the Tar River Valley. On the night of 3 September incandescence was visible at the dome. According to the Washington VAAC, rockfalls generated ash clouds that did not rise above ~1.5 km a.s.l.
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.