Report on Soufriere Hills (United Kingdom) — 26 January-1 February 2022
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 26 January-1 February 2022
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2022. Report on Soufriere Hills (United Kingdom) (Sennert, S, ed.). Weekly Volcanic Activity Report, 26 January-1 February 2022. Smithsonian Institution and US Geological Survey.
16.72°N, 62.18°W; summit elev. 915 m
All times are local (unless otherwise noted)
MVO issued a statement about Soufrière Hills on 28 January explaining overall trends observed in monitoring data since lava extrusion ended in 2010. They noted that although activity at the volcano had been low when analyzed on a week-to-week basis, subtle trends have emerged in the data in recent months that indicate an overall but small increase in unrest. The number of volcano-tectonic earthquakes were low, averaging one per day since the last eruption ended, though during 2018-2021 the average increased from 0.4 to 1.2 per day. Fumarolic temperatures which initially showed a cooling trend during 2013-2017 began to rise in 2018. The increase was most notable at one specific fumarole that had a temperature increase from 200 to 500 degrees Celsius; the high temperature was similar to those last recorded in 2013. Sulfur dioxide gas flux during 2020-2021 averaged 100-200 tonnes per day higher than the fluxes recorded 2018-2019, though remained below 2012-2013 levels. Slow inflation of the whole island had continued since 2010, with no changes to the patterns of deformation; changes associated with volcano-tectonic swarms were only observed in areas close to the dome. An increase in rockfall activity was also noted. MVO reiterated that these changes since about 2018 were minor and did not merit an increase in the Hazard Level, which remained at 1 (on a scale of 1-5).
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.