Report on Soufriere Hills (United Kingdom) — 31 December-6 January 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 31 December-6 January 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 31 December-6 January 2003. 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 was at high-to-very-high levels during most of 27 December to 3 January, but decreased during 3 January. Activity escalated to very high levels on the night of the 27th. For the first 5 days of the report period continuous rockfalls and numerous pyroclastic flows spalled off the active extruded lobe on the NNE side of the lava dome. Most of the pyroclastic flows occurred in White's Ghaut and the Tar River Valley, and to a lesser extent in Tuitt's Ghaut. Small flows and rockfalls also spilled off the N and NW flanks of the dome onto Farrell's Plain and into Tyre's Ghaut. Activity decreased considerably on the night of 2 January to moderate levels on the 3rd, with rockfalls and small pyroclastic flows confined to the NNE and to a lesser extent the N flanks of the dome. The large spine that grew on the summit at the end of the previous week was observed on several days at the beginning of the current reporting period, but was not present when the summit was next seen on 2 January.
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.