Report on Soufriere Hills (United Kingdom) — 8 March-14 March 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 March-14 March 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 8 March-14 March 2006. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 3-10 March, lava-dome growth continued at Soufrière Hills in a northerly direction and the dome reached a height of ~950 m. The active lava lobe shed rockfalls and small pyroclastic flows to the W, N, and E. A very vigorous gas vent was seen on the W side of the lava dome on 8 March, above Gages valley. Small fumaroles were visible at the top of Gages valley and below the lava dome remnant that stands at the top of Gages Valley. The shortening monitored by Electronic Distance Measurement (EDM) on the NE flank of the volcano between Jack Boy Hill and Hermitage Estate since mid-February appeared to have eased. Recently processed Global Positioning System (GPS) baseline data suggested continued deflation, with the distance between Mongo Hill and South Soufrière Hill (N/S baseline) reducing, and E/W baselines remaining largely unchanged. The sulfur-dioxide flux varied greatly, but produced an overall average of 454 metric tons per day for the week.
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.