Report on Soufriere Hills (United Kingdom) — 21 January-27 January 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
21 January-27 January 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 21 January-27 January 2004. 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 Soufrière Hills remained at low levels during 16-23 January, although there was a slight increase in seismic activity. The seismic network recorded 1 rockfall, 1 volcano-tectonic earthquake, and 38 long-period and 9 hybrid earthquakes. An unusual seismic event began on 18 January around 0600, consisting of a low-amplitude swarm of long-period earthquakes. The swarm continued for 36 hours and was comprised of ~1,000 separate events every ~2 minutes, although only 37 were large enough to trigger the seismic-event detection systems.
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.