Report on Soufriere Hills (United Kingdom) — 23 October-29 October 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
23 October-29 October 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, 23 October-29 October 2002. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Volcanic and seismic activity at Soufrière Hills remained at a similar level during 18-25 October to that of the previous week. Occasional clear views of the lava dome revealed that the active extrusion lobe in the NW continued to grow steadily, increasing in height and bulging out on the N and W sides. The most notable event of the week occurred on the afternoon of 22 October when intense rainfall at midday produced large mudflows NW in the Belham Valley where residents had recently been evacuated. At the peak of flow, the entire width of the valley floor at Belham Bridge was flooded and standing waves up to 2.5 m high were observed. By 1430, pyroclastic-flow activity began. For several hours, pyroclastic flows were generated off of the N flank of the dome and were channeled northeastwards into the upper parts of Tuitt's Ghaut, from where they crossed over into White's Bottom Ghaut. Flows also occurred on the dome's E flank in the Tar River Valley. SO2 emission rates were low at the beginning of the report period and increased towards the end of the week.
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.