Report on Soufriere Hills (United Kingdom) — 29 June-5 July 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 June-5 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, 29 June-5 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)
During 24 June to 1 July, seismic and volcanic activity at Soufrière Hills was elevated in comparison to the previous week. Periodic episodes of intense ash venting continued during the report period, culminating in an explosive event beginning on 28 June at 1306. During the event, ballistics were ejected onto the Farrell's plain (to the NW) and a column collapse produced pyroclastic flows. The pyroclastic flows reached the sea at the Tar River delta (to the NE) and a smaller volume of material flowed into the top of Tyre's Ghaut (to the N). Ash analyses from a venting episode on 13 June did not indicate the presence of fresh magma.
Preliminary analysis of recent ground deformation data from the GPS network at the volcano showed that deflation during April to mid June 2005 had later reversed, and the volcano appeared to be inflating. The daily recorded sulfur-dioxide flux varied from 300 metric tons per day (t/d) on 28 June to 700 t/d on 29 June, with an average of 470 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.