Report on Soufriere Hills (United Kingdom) — 7 November-13 November 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 November-13 November 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, 7 November-13 November 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 increased slightly during 2-7 November, and intensified on the 8th and 9th. The lava dome continued to grow mainly towards the E and at night parts of it were incandescent. Small pyroclastic flows and numerous rockfalls were generated by material avalanching off the flanks of the dome; they traveled mainly down the volcano's eastern flank, and to a lesser extent down the NE flank. On 8 November observations from a helicopter revealed that a shallow, circular depression was located over the summit area of the dome, with ash vigorously venting from it. On several days a low-level plume, with small amounts of ash, drifted to the W or N. Cycles of weak and sporadic seismicity occurred, with periods of more intense seismicity characterized by increased rockfall activity and hybrid earthquakes. Mudflows occurred in the Belham Valley on the morning of 9 November during a period of heavy rainfall.
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.