Report on Soufriere Hills (United Kingdom) — 15 November-21 November 2000
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 15 November-21 November 2000
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2000. Report on Soufriere Hills (United Kingdom). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 15 November-21 November 2000. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
The MVO reported that during 10-17 November, volcanism continued at an elevated level, with the continued growth of the lava dome on the eastern side of the summit region. The level of seismicity was higher than in the previous week, with a marked increase in the number of long-period earthquakes. The lava dome was still dominated by the extrusion of a large lava spine that had an altitude of 1,059 m a.s.l. on 12 November, and 1,077 m a.s.l. by 13 November, which was the greatest height that had been measured throughout the eruption. The spine appeared to be even taller on 17 November, but a direct measurement was not possible. The number of rockfalls and pyroclastic flows increased towards the end of the week. On 15 November a small pyroclastic flow traveled ~1 km to the NW down Tyre's Ghaut. On 17 November pyroclastic-flow deposits were noted in the upper reaches of Tuitt's and White Ghauts on the NE side of the volcano. This represented the first new dome material to have traveled down the notch between the NE and N lobes of the 1995-98 dome. Most rockfall activity occurred across the E face of the dome above Tar River. Ash clouds produced from pyroclastic flows and rockfalls did not exceed 3 km a.s.l and mostly traveled to the W across the exclusion zone. Many of the low-level ash clouds were visible in GOES-8 imagery during the week.
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.