Report on Soufriere Hills (United Kingdom) — 31 December-6 January 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 31 December-6 January 2004
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, 31 December-6 January 2004. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Volcanic activity at Soufrière Hills was low during 26 December to 2 January, with low counts of all seismic signals. The seismic network recorded 2 rockfalls, 9 hybrid earthquakes, and a swarm of small hybrid earthquakes during 31 December to 2 January. A sulfur-dioxide flux rate of 500 tons per day was measured at the beginning of the report period, but instrument problems and unfavorable wind directions hampered measurements during the rest of 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.