Report on Soufriere Hills (United Kingdom) — 12 March-18 March 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 12 March-18 March 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 12 March-18 March 2003. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 7-14 March, volcanic and seismic activity at Soufrière Hills were at moderate levels that were similar to those of the previous 2 weeks. The lava dome continued to grow, but was not focused in any particular direction. Lava extruded into the center of the summit-dome complex, increasing the dome height to just over 1,100 m. Rockfalls and pyroclastic flows occurred down all of the volcano's flanks. Spectacular incandescence was visible at night in the Tar River Valley, NW in Tuitt's Ghaut, and on the N talus slopes. Small rockfalls and pyroclastic flows infrequently descended the volcano's W flank, to the top of Gage's Valley. Ash vented continuously in the dome summit area and sulfur dioxide emission rates were relatively low during the week. The Washington VAAC reported that several low-level ash plumes were visible on satellite imagery.
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.