Report on Soufriere Hills (United Kingdom) — 8 June-14 June 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 8 June-14 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, 8 June-14 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)
On 13 June at 0600 there was an increase in volcanic and seismic activity at Soufrière Hills. A series of volcano-tectonic earthquakes was accompanied by low-level tremor and a period of ash venting. An ash plume reached a height of ~2.4 km (7,900 ft) a.s.l and drifted NE, depositing light ash in Lookout, Geralds, and St. Peters. Activity decreased significantly after 0900.
Prior to the activity increase, during 3-10 June, the seismic network at Soufrière Hills recorded 17 volcano-tectonic earthquakes and one rockfall. Steam venting continued on the NW side of the crater. The daily recorded sulfur-dioxide flux varied from a low of 142 metric tons per day (t/d) on 4 June to a maximum of 671 t/d on 7 June, with an average of 399 t/d for the week. This was below the eruption's long-term average of 500 t/d.
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.