Report on Soufriere Hills (United Kingdom) — 14 March-20 March 2007
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 14 March-20 March 2007
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2007. Report on Soufriere Hills (United Kingdom) (Sennert, S, ed.). Weekly Volcanic Activity Report, 14 March-20 March 2007. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 9-16 March, lava-dome growth at Soufrière Hills continued and was concentrated on the NE side. Intermittent pyroclastic flows, possibly originating from the large blocky spine on the edge of the E lobe, traveled E down the Tar River Valley and produced large ash plumes. One of the plumes on 12 March rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted NW. On 13 March, a steam-rich plume rose to 2.4 km (8,000 ft) a.s.l. and drifted W. By 14 March, the spine was completely shed. On 15 March, heavy rains caused mudflow activity in several drainages. Pyroclastic flows were observed NW in Tyre's Ghaut and ashfall was reported from the Salem /Old Towne areas. On 16 March, pyroclastic flows were observed in Tyre's Ghaut and in the Tar River Valley. A resultant ash plume drifted WNW. Based on satellite imagery, the Washington VAAC reported that diffuse ash plumes drifted NW during 17-18 March.
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.