Report on Soufriere Hills (United Kingdom) — 19 September-25 September 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 19 September-25 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, 19 September-25 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)
There was a moderate increase in volcanic activity at Soufrière Hills in comparison to the previous week. A marked increase in hybrid earthquake events was recorded and banded tremor events were slightly more intense. In addition, the number and strength of hybrid events associated with the banded tremor increased. The active lava dome continued to grow at a moderate rate, producing rockfalls and small pyroclastic flows that traveled E to the upper reaches of the Tar River Valley. The dome's volume was estimated to be 12 million cubic meters, therefore, the average growth rate has been ~2.6 cubic meters per second since the partial dome collapse on 29 July. Episodes of vigorous ash venting and increased rockfall activity occurred during periods of tremor. Low-level ash plumes from this activity were visible in 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.