Volcanic activity at Soufrière Hills increased slightly during 28 March to 4 April and for the last 2 days of the report period activity was at moderately high levels. A prominent extrusion lobe was established on the E and SE sides of the lava dome's summit. A large vertical spine was extruded at the back of this lobe during the night of 1-2 April. During the report week, activity was dominated by rockfalls and pyroclastic flows mainly in the Tar River Valley. Rockfall activity also continued on the dome's S side. Some pyroclastic flows also occurred on the NE flanks in White's Ghaut and Tuitt's Ghaut, and on most days rockfalls and small pyroclastic flows initiated on the NW flanks, often moving into the upper reaches of Tyre's Ghaut. Sulfur dioxide emission rates fluctuated during the report period. 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)