Activity at the Soufrière Hills volcano during 12-19 January was similar to the previous week, with continued growth of the summit lava dome and high levels of mostly low-energy rockfalls. The overall level of seismic activity remained high. Activity was concentrated on the SE side of the lava dome, although some new pyroclastic-flow deposits were seen to the NE of the volcano. The Washington VAAC reported that low level ash, presumably produced from rockfalls, was occasionally visible on GOES-8 imagery. Less ash fell across the N portion of Montserrat than during the previous 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)