Report on Soufriere Hills (United Kingdom) — 27 December-2 January 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 27 December-2 January 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2000. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 27 December-2 January 2001. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Activity at the Soufrière Hills volcano remained at an elevated level during 22-29 December, with continued growth of the lava dome and high levels of rockfall activity. The overall level of seismic activity remained high. Rockfall signals were often immediately preceded by long-period events, indicative of explosive onsets. This was confirmed by visual observations of vigorous ash venting prior to and during rockfall activity. Lava dome growth continued at the summit, producing rockfalls predominately to the E, and to a lesser extent, to the S and W area of the new growth. The spine that was growing on top of the lava dome reached a maximum height of 1,071 m a.s.l. The Washington VAAC reported that throughout the week low-level (below 2.4 km a.s.l.) ash clouds that were produced by rockfalls, and periodic hot spot activity were visible on GOES-8 imagery. Wind conditions during the week resulted in a small amount of ash being deposited in inhabited areas in the N and W of the island.
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.