From 12 June to at least 15 June volcanic activity increased at Soufrière Hills in comparison to the previous week. There was a larger number of rockfalls, and hybrid and long-period earthquakes. Sulfur dioxide flux markedly increased (770 metric tons on 11 June and 1410 metric tons on 14 June). New growth was substantial in the southern sector of the lava dome and there was a large accumulation of new dome material SW of the dome in the upper reaches of the White River. The daytime entry zone was open for limited periods during the week. The Washington VAAC reported that at 0510 on 14 June a small ash cloud rose 3-4.5 km a.s.l. and drifted to the W and that low-level ash was emitted throughout the week. In addition, moderate rockfall activity produced ash to ~2 km a.s.l. and a hot spot was occasionally 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)