Report on Soufriere Hills (United Kingdom) — 6 January-12 January 2010
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 January-12 January 2010
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2010. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 6 January-12 January 2010. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
MVO reported that during 31 December-8 January pyroclastic flows from the Soufrière Hills lava dome continued to travel predominantly down areas to the N including Whites Ghaut (NE), Farrells plain (N), and Tyers Ghaut (NW). Observations on 2 January showed that a 40-m-high, 150-m-wide lobe of lava had been extruded northwards onto the N summit of the dome. This lobe was the main source of rockfall and pyroclastic flow activity. On 3 and 4 January ash plumes rose to an altitude of 4.6 km (15,000 ft) a.s.l. and drifted NW. Ashfall occurred in areas to the NW several times during the reporting period.
On 8 January, a large pyroclastic flow event occurred after a collapsing fountain of tephra was observed on the NE side of the volcano. Pyroclastic flows traveled NE down Whites Bottom Ghaut to the sea and down Tuitts Ghaut to within a few hundred meters of the sea. Pyroclastic flows also traveled NW down Tyers Ghaut and into the Belham Valley, W towards Plymouth, and E down the Tar River valley. The event lasted about 11 minutes and seismicity returned to background levels quickly. There was no precursory seismicity associated with the event. Ashfall was reported in inhabited areas in the NW.
Seismic signals indicated that another explosion occurred on 10 January. Pyroclastic flows descended the NE, NW, and W flanks, and ashfall was reported in areas to the NW. Another explosion later that day also caused ashfall in inhabited areas. The Hazard Level remained at 4.
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.