MVO reported that during 8-15 September, the lava dome at Soufrière Hills continued to grow at a high rate. On 9 and 10 September, ash venting from the Gages wall was vigorous and accompanied by small explosions producing black jets up to 100 m above the vent. Pyroclastic flows from fountain collapse occurred on all sides of the dome and notably reached 1 km W down Gages valley. On 11 September, the collapse of an over-hanging lava lobe produced pyroclastic flows NE down the Tar River valley. On 13 September, one pyroclastic flow in the same area reached the sea. On 14 September, vigorous ash venting resumed.

Based on information from the MVO, pilot reports, and the Piarco MWO, the Washington VAAC reported that continuous ash and gas emissions during 13-19 September produced plumes that reached altitudes of 2.4-3.7 km (8,000-12,000 ft) a.s.l. and drifted predominantly NW, W, and SW. A hotspot was visible on satellite imagery.

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)