Report on Soufriere Hills (United Kingdom) — 30 November-6 December 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 November-6 December 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 30 November-6 December 2005. 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 elevated during 25 November-2 December 2005. The seismic network recorded 158 rockfall signals, one volcano-tectonic earthquake, 93 long-period earthquakes, two hybrid earthquakes, and 17 long-period rockfall signals during the reporting period. Measured sulfur dioxide fluxes varied between 600 metric tons per day (t/d) measured on 30 November and 830 t/d on 26 November, with a weekly average of 690 t/d. Dome growth continued on all flanks, although activity was most intense on the S and E; incandescence was observed at night on the SE and E flanks throughout the reporting period. Large rockfalls and small pyroclastic flows collapsed off the E flank of the dome during this period and entered the upper reaches of the Tar River Valley.
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.