Report on Soufriere Hills (United Kingdom) — 20 August-26 August 2008
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 20 August-26 August 2008
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2008. Report on Soufriere Hills (United Kingdom) (Sennert, S, ed.). Weekly Volcanic Activity Report, 20 August-26 August 2008. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
MVO reported that during 15-22 August, evidence suggested that the W side of the Soufrière Hills lava dome continued to grow. Cloud cover prevented visual observations. Rockfalls and long-period seismicity increased. Most of the rockfalls occurred on the W side of the lava dome in a new channel that developed below Gages Wall. Ash plumes occasionally generated by the rockfalls were most noticeable on 16 and 17 August. On 19 August a pyroclastic flow descended the Tar River Valley. According to news reports, on 25 August a rainfall-induced pyroclastic flow occurred on the W flank, split into two parts, and caused ashfall and a strong scent of gases in areas N. The event enlarged and steepened the rockfall gully below Gages Wall. The Hazard Level remained at 3.
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.