Report on Soufriere Hills (United Kingdom) — 27 March-2 April 2013
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
27 March-2 April 2013
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2013. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 27 March-2 April 2013. 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 22-29 March activity at the Soufrière Hills lava dome was at a low level. A pyroclastic flow traveled down the Tar River Valley (E) at about 0500 on 28 March. The flow was not observed directly, but the deposits indicated that it traveled halfway down the valley, 1-1.5 km from the dome. There were no reports of ashfall; any ash was probably blown over Plymouth and out to sea. The source of the flow was not known due to cloud cover, but was likely from the failure a large slab that had been slowing moving away from the dome. Heavy rainfall during the evening of 28 March generated large lahars in several valleys around the volcano, including in the Belham Valley (NW). These started at about 1900 and lasted for several hours. The Hazard Level remained at 2 (on a scale of 1-5).
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.