Report on Soufriere Hills (United Kingdom) — 6 August-12 August 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 August-12 August 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, 6 August-12 August 2003. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 25 July to 1 August, volcanic activity at Soufrière Hills was low, with only a few seismic events triggering the network. Activity increased at the end of the report week, on 1 August, with episodes of powerful ash venting from the explosion crater. There were many strong bursts of gas and jets of ash; an ash plume rose to over 3 km. During 1-8 August, activity fluctuated, with a period of relative quiet separating episodes of intense degassing and hybrid-earthquake activity. Occasional rockfalls and hybrid earthquakes occurred during most of the report week. The lava dome was visible on 5 August; there was a small southerly-directed lobe in the dome that was growing extremely slowly, if at all. Sulfur-dioxide emission rates were high for most of the report week.
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.