Report on Soufriere Hills (United Kingdom) — 12 April-18 April 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
12 April-18 April 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Soufriere Hills (United Kingdom). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 12 April-18 April 2006. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
Observations of the lava dome at Soufrière Hills suggested that lava extrusion continued during 7-14 April. Growth occurred over a sector extending E to N, and an eastward-facing lobe developed on the NE side of the dome. Numerous small rockfalls continued from the active eastern flanks of the dome, adding to the talus in the upper reaches of the Tar River valley. Rockfalls were accompanied by minor ash venting. Due to the wind coming from the S in contrast to the normal prevailing wind direction (from the E) during the second half of the report period, ash fell over many parts of Montserrat: notably after a minor pyroclastic flow occurred at 0645 on 14 April. During the report period, the sulfur-dioxide flux averaged 540 metric tons per day. The hydrogen chloride to sulfur dioxide ratio on 12 April was 3.75, higher than 2.64 measured the previous week.
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: Washington Volcanic Ash Advisory Center (VAAC), Montserrat Volcano Observatory (MVO)