Volcanic activity rapidly declined after the lava dome at Soufrière Hills partially collapsed on 29 July. Observation flights after the collapse revealed that the general summit region had been lowered by about 150 m. There was also a complex amphitheater-shaped scar several hundred meters deep incised into the core of the dome at the head of the Tar River Valley. A new dome was growing within the scar. The Washington VAAC reported that a minor eruption occurred on 4 August at 0300. The eruption produced ash that traveled in two different directions; the first ash cloud rose to ~4.6 km a.s.l. and drifted NW; the second cloud rose to ~9.7 km a.s.l. and drifted NE.

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), Associated Press, Montserrat Volcano Observatory (MVO), Reuters