During 28 December-4 January volcanic activity at Soufrière Hills remained high, with vigorous rockfalls travelling down the volcano's E flank. The most notable event during the week was the collapse of several million cubic meters of volcanic material down the volcano's NE flank on 28 December. The collapse, during about 1330-1500, continuously generated pyroclastic flows down the Tar River Valley to the sea. A dense W-drifting ash plume was generated that deposited up to a centimeter of ash in the vicinity of the town of Plymouth. The average flux of SO2 in the volcanic plume was ~460 metric tons on 3 January, in comparison to 851 metric tons measured on 27 December. A 30-minute-long sustained event began on 5 January around 1640 and produced an ash cloud to a height of ~2.4 km a.s.l.

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)