Report on Soufriere Hills (United Kingdom) — 24 March-30 March 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
24 March-30 March 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 24 March-30 March 2004. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
During 19-26 March, activity remained elevated at Soufrière Hills. The seismic network recorded four long-period and seven hybrid earthquakes. Continuous low-level tremor was interrupted by several periods of moderate-level tremor lasting from less than 1 hour to 12 hours. Sulfur-dioxide flux ranged between 550 and 700 metric tons per day. On 29 March at 0745, the Washington VAAC reported that a ~9-km-wide ash plume was observed at a height of ~1 km a.s.l. The plume initially drifted SW until about 1015 the same day when it was observed in satellite imagery drifting NE. On 30 March an ash plume was observed that reached a height of ~2 km and drifted NE.
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.