Report on Soufriere Hills (United Kingdom) — 22 October-28 October 2003
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 22 October-28 October 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, 22 October-28 October 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 activity at Soufrière Hills remained at low levels during 17-24 October. The lava dome was visible on 23 October when a volume survey was carried out. The small lava dome that extruded in July had not grown further, appearing to be stagnant with alteration and degradation causing it to break apart. The pit crater associated with the July 2003 explosions widened slightly, although MVO believes this is due to passive slumping of material rather than volcanic activity. Sulfur-dioxide emission rates remained high during the report week. Low-level ash clouds were sometimes visible on satellite 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.