During 6-12 September, lava-dome growth at Soufrière Hills was substantial and concentrated on the W part of the edifice. A vent that had opened above Gage's Wall on 31 August vigorously emitted plumes of hot gases. A second vent near the summit of the dome emitted ash-and-steam plumes.

Based on information from the MVO, pilot reports, and the Piarco MWO, the Washington VAAC reported that ash, gas, and steam emissions on 6 and 7 September produced diffuse plumes that drifted WNW. On 10, 11, and 12 September, ash-and-gas plumes reached altitudes of 3 km (10,000 ft) a.s.l. and drifted E and SW. A hotspot was detected on satellite imagery on 6, 7, and 10-12 September.

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)