Report on Soufriere Hills (United Kingdom) — 23 November-29 November 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 November-29 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, 23 November-29 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)
Activity at Soufrière Hills increased during 18-25 November in comparison to the previous week. Growth of the volcano's lava dome was focused towards the E and S, with minor activity to the S and W. Continuous incandescence was observed at night on the SE and E sides of the lava dome. A pyroclastic flow was seen in the upper reaches of the Tar River Valley on 22 November. Minor ash emissions occurred from the volcano, including one on the afternoon of 24 November that sent an ash cloud several hundred meters above the volcano's summit. Measurements of sulfur-dioxide emissions were only possible on 2 days due to the wind direction. An average of 1,055 metric tons of sulfur dioxide was measured daily.
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.