Activity at Soufrière Hills during 5-12 January remained elevated with continued growth of the lava dome and rockfalls. The broadband seismic network recorded 1,076 rockfall signals during the reporting period. Growth continued in the summit area with a large amount of debris being shed down the E face of the dome, although the focus of activity seemed to be on the SE side of the dome later in the week. A small amount of rockfall activity occurred down the S side, entering the upper reaches of the White River Valley. The results from a recent dome survey revealed that about 64 million cubic meters of lava have been extruded since 20 March 2000, an extrusion rate for March-December 2000 of about 3 m3/s. On 10 January, a series of static COSPEC scans of the volcanic plume gave SO2-flux values of 400-700 metric tons per day. On 11 January, measurements from a helicopter averaged 640 metric tons per day.

GOES-8 visible infrared and multispectral imagery interpreted by the Washington VAAC showed a low-level plume on the late afternoon to early evening of 9 January that was 9 km wide and extended 41 km WNW. An occasional hot spot was also detected on the 10th.

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)