Report on Soufriere Hills (United Kingdom) — 14 November-20 November 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 November-20 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, 14 November-20 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)
Volcanic activity at Soufrière Hills during 9-16 November was generally diminished compared to the previous week. The lava dome continued to grow mainly towards the E and its highest point was measured on 9 November to reach 876 m a.s.l. Small pyroclastic flows and rockfalls were generated by material avalanching off the flanks of the dome. The largest of these events was a pyroclastic flow on the night of 14 November, which traveled E and reached the lower parts of the Tar River Valley. The seismicity cycles, which had been a dominant feature since early August, appeared to have stopped. Rockfall seismicity was most intense on 9 and 10 November, but then declined significantly and remained low after 12 November. The Washington VAAC reported that ash was visible in satellite imagery on 17 November at 0845 below 6.1 km a.s.l. and on 18 November at 0845 below 3 km a.s.l., extending ~42 km NE towards Antigua. The satellite imagery showed that a thin portion of the ash cloud may have reached Antigua.
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.