Report on Soufriere Hills (United Kingdom) — 7 August-13 August 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
7 August-13 August 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 7 August-13 August 2002. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 2-9 August, activity at Soufrière Hills continued at a high level. Lava-dome growth remained focussed on the N side of the dome complex, with the development of a massive curved lobe of lava. During the early part of the week, the lobe repeatedly crumbled, producing rockfalls and small pyroclastic flows that reached the upper portion of Tuitt's Ghaut. Limited activity occurred on the NW part of the dome, although one small pyroclastic flow occurred in the notch between the central and north-western buttresses. Over the last 3 days of the report period, rockfall activity decreased substantially. This was due to the lobe becoming more coherent and not collapsing, not due to the activity stagnating. During the report week SO2 mass flux increased.
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.