Activity at the Soufrière Hills volcano during 29 December to 5 January was similar to the previous week, with continued growth of the summit lava dome and high levels of rockfall activity. The overall level of seismic activity remained high. In addition, at 0406 on 5 January a regional earthquake was felt on Montserrat. According to the volcano observatories on Martinique and Guadeloupe, the earthquake's epicenter was about 40 km E of the island of Marie Galante, and had a provisional magnitude of 4.6. Marie Galante lies ~200 km SE of Montserrat. Lava dome growth continued, producing rockfalls predominately to the E, and to a lesser extent, to the S and W areas of the new growth. The spine growing atop the lava dome reached a maximum height of 1,052 m a.s.l. by the end of the report week. The Washington VAAC reported that throughout the week low-level (up to ~3 km a.s.l.) ash clouds, presumably produced by rockfalls, and periodic hot-spot activity were visible on GOES-8 imagery. Winds blew small amounts of ash to inhabited areas in the N and W of the island.

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)