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Report on Soufriere Hills (United Kingdom) — 16 July-22 July 2003

Soufriere Hills

Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
16 July-22 July 2003
Managing Editor: Gari Mayberry

Please cite this report as:

Global Volcanism Program, 2003. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 16 July-22 July 2003. Smithsonian Institution and US Geological Survey.

Weekly Report (16 July-22 July 2003)

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)

After a lava-dome collapse at Soufrière Hills on 12 July volcanic activity was at relatively high levels until 13 July when it slowly subsided. On the 13th activity had declined to very low levels, then the following morning a sudden vulcanian explosion occurred at the lava dome. Two more explosions occurred during the next 2 days. Pumice from these explosions reached 15 cm in size at Richmond Hill, declining to 4 cm in Olveston. Heavy ashfall from the collapse occurred over all the inhabited parts of Montserrat. The greatest ash thickness was recorded at the Vue Pointe Hotel, where it exceeded 15 cm in depth. After an explosion on 15 July, volcanic and seismic activity were relatively low, with only a few hybrid earthquakes and rockfalls each day. Scientists saw an open explosion crater in the collapse scar, with no new lava extruded. The bulk of the lava-dome structure was removed during the collapse. Pyroclastic flows impacted the area between Tar River Valley and Spanish Point.

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)