Report on Soufriere Hills (United Kingdom) — 7 March-13 March 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 March-13 March 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, 7 March-13 March 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 MVO reported that during 2-9 March activity decreased at Soufrière Hills volcano in comparison to the previous week, with the lava dome returning to a steady growth rate. Early in the report week the banded tremor recorded the previous week died away, as did the associated hybrid earthquakes. Rockfall activity increased during the middle of the week, returning to more usual levels. The volcano appeared to have resumed steady dome growth by the end of the week. Observations confirmed that the main area of lava-dome growth had switched to the S of the dome on 25 February, which led to a concentration of rockfall activity in the upper portions of the White River Valley. Light ashfall from activity during the week was blown over the N of the island, although by the end of the week the wind switched back to the more usual direction towards the W. The Washington VAAC reported that throughout the week low-level ash clouds (up to ~3 km a.s.l.), presumably produced by rockfalls, and periodic hot-spot activity were visible on GOES-8 imagery.
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.