During 25 April to about 6 May, volcanic activity was at moderate levels at Soufrière Hills, with pyroclastic flows and rockfalls mainly traveling NE. During about 6-9 May there was a general increase in the size of pyroclastic flows, some of which were among the largest and most energetic seen for several months. Most flowed along the N side of the Tar River Valley, and a few also flowed into White's and Tuitt's ghauts. Sulfur-dioxide emission rates were low during about the first week of the report period, then fluctuated from moderate to high levels. The Washington VAAC reported that low-level ash plumes were sometimes 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: Montserrat Volcano Observatory (MVO), Washington Volcanic Ash Advisory Center (VAAC)