During 28 September to 5 October volcanic activity at Soufrière Hills increased in comparison to the previous week. Numerous pyroclastic flows were produced by material avalanching off the lava dome, which continued to grow in the summit crater at a moderate rate. Most of the pyroclastic flows during the report period were small and confined to the upper reaches of the Tar River Valley E of the volcano, but larger flows occurred on 4 and 5 October. On 4 October a small-scale lava-dome collapse (consisting of 10-15% of the dome's volume) on the N side of the dome produced sustained pyroclastic-flow activity between 0745 and 0915, with at least three flows reaching the sea. Similar activity occurred on 5 October at 0845 until at least midday. Dense ash clouds generated during both periods of elevated pyroclastic-flow activity were visible on satellite imagery rising to ~1.8 km a.s.l. and drifting to the W. Seismicity continued to be dominated by bands of hybrid earthquakes and rockfalls.

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), Montserrat Volcano Observatory (MVO)