Report on Soufriere Hills (United Kingdom) — 25 June-1 July 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 June-1 July 2003
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2003. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 25 June-1 July 2003. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Volcanic and seismic activity at Soufrière Hills remained at low levels during 20-26 June, but increased on 27 June. There were no apparent changes at the summit region since it was last observed several weeks previously. During 20-25 June, rockfalls and sporadic pyroclastic flows occurred on the lava dome's E and N flanks and traveled into the Tar River Valley, and White's, Tuitt's, and Tyre's ghauts. Hybrid earthquake activity developed into a diffuse swarm on 22 and 23 June. Some of the larger hybrid earthquakes were located at depths of about 3 km beneath the lava dome. On 27 June activity was mainly confined to the northern flanks with numerous small pyroclastic flows into Tuitt's and Tyre's ghauts.
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.