Report on Soufriere Hills (United Kingdom) — 18 July-24 July 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
18 July-24 July 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 18 July-24 July 2001. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
The number of rockfalls increased (719) during 13-20 July in comparison to the previous week (297), although most of them were very small. Near-continuous rockfalls occurred on the S side of the lava dome, where dome growth was concentrated. Numerous pyroclastic flows originated from the S flank of the dome and moved eastward down the Tar River Valley. Several pyroclastic flows also originated from the W side of the dome and traveled short distances into the upper part of the Gages area. On 23 July at 1145 a pilot reported spotting an ash cloud approximately 800 m above the volcano. Satellite imagery at that time detected a faint ash-and-steam plume and an occasional hot spot.
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.