Volcanic and seismic activity at Soufrière Hills remained elevated during 16-23 December. Images revealed that the lava dome continued to grow during the report period. Growth occurred over a broad sector extending from the SW around to the NE. Vertical growth was focused to the S and SW, with lateral growth in the E and SE sectors. Numerous small rockfalls traveled down the S, E, and NE flanks of the lava dome, adding to the talus in the upper reaches of the Tar River Valley to the NE. The sulfur-dioxide flux averaged 415 metric tons per day.

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)