During 16-22 April, dome extrusion continued at Soufrière Hills. Poor visibility prevailed for parts of the week, but seismicity and SO2 fluxes remained significant. Numerous rockfalls and pyroclastic flows have occurred on the eastern flanks of the dome in the Tar River Valley. An observation flight indicated that rockfalls were beginning to spill southwards into the head of the White River. Observers noted that a very large spine had extruded on the dome=s summit. Despite frequent cloud cover during the week, satellite infrared sensors sometimes detected the thermal radiation from the dome, and other sensors continued to detect plumes from the volcano, typically tens of kilometers in length and blowing W.

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)