Report on Soufriere Hills (United Kingdom) — 20 March-26 March 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 March-26 March 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 20 March-26 March 2002. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
The level of volcanic activity at Soufrière Hills remained high during 15-22 March. Lava-dome growth continued to be focused on the E side of the summit region. Throughout the report period large (50-70 m high), fast-growing, spines developed on the dome's summit. These spines periodically collapsed, producing pyroclastic flows down the volcano's E flank that sometimes reached the Tar River fan. Small ash clouds produced from these events reached ~1 km above the volcano and drifted westward over Plymouth and Richmond Hill. Ash predominately fell into the sea. SO2 emission rates remained high. Theodolite measurements of the dome taken on 20 March yielded a dome height of 1,039 m.
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.