Report on Soufriere Hills (United Kingdom) — 20 July-26 July 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
20 July-26 July 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, 20 July-26 July 2005. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Seismic and volcanic activity remained at elevated levels at Soufrière Hills during 15-22 July. The seismic network recorded 19 volcano-tectonic, 16 hybrid, and 13 long-period earthquakes. It also recorded 11 rockfalls and one explosion. The explosion occurred on 18 July at 0301 and deposited ash between Fogarty Hill in the NW of the island and Brodericks Yard in the SW. The deepest ash deposits were recorded at Weekes. An ash plume rose to at least 6.1 km (20,000 ft). The explosion was similar to, but slightly larger than, an explosion on 3 July. Analysis of ash from an explosion on 28 June showed no evidence for the involvement of fresh magma. The sulfur-dioxide flux reached an average of 608 metric tons per day during the report period.
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.