Report on Soufriere Hills (United Kingdom) — 15 June-21 June 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 June-21 June 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, 15 June-21 June 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 at Soufrière Hills were at elevated levels during 10-17 June. The seismic network at the volcano recorded 17 hybrid earthquakes, 20 long period earthquakes, 46 volcano-tectonic earthquakes, and 7 rockfalls. A period of ash venting that began on 13 June at 0600 declined in intensity during the report week. The ash venting was caused by the rapid release of steam and other volcanic gases, possibly triggered by intense rainfall on the night of 12 June. The daily recorded sulfur-dioxide flux varied from 170 metric tons per day (t/d) on 10 June, to a maximum of 750 t/d on 14 June, with an average of 460 t/d for the week.
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.