Report on Soufriere Hills (United Kingdom) — 16 November-22 November 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
16 November-22 November 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, 16 November-22 November 2005. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Seismic and volcanic activity at Soufrière Hills remained at elevated levels during 11-18 November. Clear observations of the lava dome on the morning of 18 November indicated that it continued to grow and was shedding rockfalls to the E, S, W, and NW. A pyroclastic flow was observed in the Tar River valley on 15 November and reached to within a kilometer of the sea. The ash cloud associated with this event rose to ~2.1 km (~7,000 ft) a.s.l. The sulfur-dioxide flux averaged 650 metric tons per day.
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.