Report on Soufriere Hills (United Kingdom) — 27 September-3 October 2006
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 27 September-3 October 2006
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2006. Report on Soufriere Hills (United Kingdom) (Sennert, S, ed.). Weekly Volcanic Activity Report, 27 September-3 October 2006. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Visual observations of Soufrière Hills during 22-29 September showed that the dome continued to grow at a moderate rate. Growth appeared to have occurred predominantly on the domes summit area, and on its eastern side, with a prominent lobe growing in this location. The vents just inside Gage's wall and on the summit of the dome periodically produced both ash and gases. There were also a number of pyroclastic flows during the period, some of which appear to have had explosive onsets in the seismic record. Northerly winds during 28 and 29 September resulted in minor ashfall in inhabited areas. The sulfur dioxide flux for the reporting period averaged around 450 tonnes/day, varying between 850 tonnes/day on 22 September and 190 tonnes/day on 26 September. Aviation ash advisories on 2-3 October described continuous ash emissions reaching 2.4 km (8,000 ft) a.s.l. that eventually extended 140 km W.
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.