Volcanic and seismic activity at Soufrière Hills remained at moderate levels during 11-18 October. Signals associated with rockfalls and pyroclastic flows continued to dominate the seismicity. The NW extrusion lobe of the lava dome continued to grow steadily. Growth remained centralized and there was noticeable bulking up of the lobe's summit area. Rockfalls and small pyroclastic flows traveled mainly down the northern flanks of the volcano, although some also traveled E into the incised channel on the N side of the Tar River Valley, and W into the upper portions of Fort Ghaut. Talus continued to accumulate behind the NW buttress and in the head of Tyre's Ghaut. SO2 emission rates varied considerably during the report period.

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)