During 4-11 January volcanic activity remained high at Soufrière Hills. Observations on 10 January revealed that the summit region had increased in volume considerably over the past several weeks and that the lava dome was broad with several spines sticking out from it. The highest spine reached 1,015 m a.s.l. on the 12th. The western side of the zone appeared to be inactive. A large extrusion lobe was active on the upper E flank of the dome, just below the summit. The E flank of the dome was very active, producing numerous rockfalls and pyroclastic flows. On 5 January a series of pyroclastic flows traveled down the Tar River Valley to the sea. This event was accompanied by vigorous venting of ash from the summit, producing a pulsating ash-laden plume that drifted to the W. Seismicity remained at a similar level in comparison to the previous week. SO2 and HCl emissions were high; 898 and 1,122 metric tons of SO2 were measured on 1 and 10 January, respectively. Low-level ash emissions occurred throughout the 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: Montserrat Volcano Observatory (MVO), Washington Volcanic Ash Advisory Center (VAAC)