Report on Soufriere Hills (United Kingdom) — 29 August-4 September 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 August-4 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, 29 August-4 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 weeks. Following the partial dome collapse on 29 July bands of tremor, which indicate rapid magma ascent, occurred at 13-27 hour intervals. During these banded-tremor events rockfall activity and ash venting increased, sending ash up to ~2 km above the volcano, drifting to the W. A weak swarm of volcano-tectonic earthquakes (less than M 1) began on 29 August. Observations revealed that the new lava dome had a well-formed dome-like morphology and appeared to have rapidly grown in the scar produced by the 29 July collapse. Rockfalls and small pyroclastic flows that originated from the new dome were observed in the upper reaches of the Tar River Valley. The daytime entry zone was re-opened on 29 August.
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.