Report on Soufriere Hills (United Kingdom) — 22 March-28 March 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
22 March-28 March 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 22 March-28 March 2006. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Observations of Soufrière Hills during 17-24 March revealed that lava-dome growth was focused in the summit area and towards the E and NE. The N side of the lava dome showed little change. Rockfalls and pyroclastic flows were restricted to the Tar River Valley and they were particularly numerous on 19-20 March. The largest pyroclastic flows traveled as far as 2 km down Tar River Valley. There was an increase in gas emission during the report period. The sulfur-dioxide flux averaged 1,034 metric tons per day, with high gas emissions occurring on days of elevated pyroclastic-flow activity. The hydrogen chloride to sulfur dioxide ratio was 2.8 on 22 March. The ground-deformation network continued to indicate deflation across the volcano.
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.
Sources: Washington Volcanic Ash Advisory Center (VAAC), Montserrat Volcano Observatory (MVO)