Report on Soufriere Hills (United Kingdom) — 10 December-16 December 2008
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
10 December-16 December 2008
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2008. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 10 December-16 December 2008. 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 seismicity from Soufrière Hills lava dome remained elevated during 6-10 December. On 10 December, seven pyroclastic flows traveled W down Gages Valley, at least two reached Plymouth (about 5 km W). A few small pyroclastic flows were detected during 11-12 December. Monitoring data indicated that the volcano continued to inflate.
Based on analysis of satellite imagery and information from MVO, the Washington VAAC reported that on 14 December an ash plume drifted W at an altitude of 1.8 km (6,000 ft) a.s.l. A diffuse gas-and-steam plume possibly containing ash drifted W the next day. On 13 December, a pilot reported that an ash plume rose to altitudes of 4.6-5.2 km (15,000-17,000 ft) a.s.l. On 15 December, ash plumes at altitudes of 2.4-3 km (8,000-10,000 ft) a.s.l. drifted SW. The next day an ash plume drifted S and a thermal anomaly was detected on satellite imagery.
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.
Sources: Montserrat Volcano Observatory (MVO), Washington Volcanic Ash Advisory Center (VAAC)