Seismic and volcanic activity at Soufrière Hills remained at elevated levels during 22-29 July. The seismic network recorded 29 volcano-tectonic, four hybrid, and five long-period earthquakes. It also recorded one explosion and 23 rockfalls. An explosion on 27 July at 0114 deposited ash between Plymouth on the island's W side, and Brades on the island's NW side. The explosion was similar to, but smaller than, an explosion on 18 July. Occasional ash venting also occurred during the report week. The daily recorded sulfur-dioxide flux averaged 510 metric tons per day (t/d), slightly above the long-term average of 500 t/d.

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.

Source: Montserrat Volcano Observatory (MVO)