Report on Soufriere Hills (United Kingdom) — 2 March-8 March 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 2 March-8 March 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 2 March-8 March 2005. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
MVO reported that during 25 February to 4 March, seismic activity at Soufrière Hills remained at low levels. The sulfur-dioxide flux remained fairly stable, averaging 672 metric tons per day. FTIR (Fourier-Transform Infrared Spectroscopy) measurements on 3 March yielded a hydrogen chloride to sulphur dioxide mass ratio of 0.35, showing no significant change since the last measurement in February. Views of the entire summit on 3 March revealed that there were no surficial changes at the volcano. There was still a small pond in the 3 March 2004 explosion pit.
A news article reported that hazy skies over St. Martin (NE of Soufrière Hills) and the surrounding islands on 6 March were the result of increased activity at Soufriere Hills. Several people in the eastern section of St. Martin reported a thin film of "dust" on their homes and vehicles. According to the Washington VAAC, a very faint area of possible ash was visible on satellite imagery on 6 March extending NE.
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.