Monserrat’ Soufriere Hills Volcanic eruption

 

                                    Figure.1 The Soufriere Hills Volcano in Montserrat (USGS, 2015)

Montserrat is located in the Lesser Antilles volcanic island arc. The arc is caused by the sinking of the Atlantic oceanic lithosphere beneath the Caribbean plate to the west. Montserrat is the summit of a compound volcanic edifice that stretches from 1 km above sea level at Soufri6re Hills Volcano to 700-900 m below sea level, with a basal diameter of around 25-30 km. (Kokelaar, 2002).

A series of eruptions of Montserrat's Soufriere Hills Volcano began in June 1995 and continued through to 1997. It started with phreatic explosions, which were accompanied by seismic activity and significant ground deformation. (Sparks et al., 1998). In 1997, there were two dome collapses – on the 25^th of June and the 21^st of September.

On June 25, at 12.55 p.m., a major and prolonged collapse of the lava dome began, with three large pyroclastic flows overwhelming an area of 4 km2 on the volcano's north and northeast flanks. A widespread ash cloud surge broke out from the third pyroclastic flow on the volcano's northern slope and rushed across Streatham village, climbing 70 metres on Windy Hill at an average rate of around 35 metres per second.

Flows also engulfed Plymouth, the capital city, whose 5,000 residents had been evacuated months before in preparation for such an occurrence (USGS, 2022).

Many houses were destroyed in the pyroclastic flow, and the remaining severely damaged houses were surrounded by thick deposits, but in the surge area, there were thin deposits and little evidence of raised dynamic pressure, while fences around properties remained mostly intact, and utility poles and wires were unharmed by the blast. Nineteen individuals were killed and seven were injured, with six bodies recovered from inside the surge area as the hot cloud pursued them as they fled to their homes. The temperature of the surge was in the 400°C range. (Baxter et al., 2005).

 

Map of Montserrat's southeast shows the Soufrière Hills volcano and regions damaged by pyroclastic flows. (Baxter et al., 2005).

On December 26, 1997, a debris cascade filled much of the White River to within 100 metres of the sea, followed by high-intensity Pyroclastic currents that devastated 10 km2 of southern Montserrat all the way to the sea. Under tremendous internal pressure, the lava dome shattered explosively, and the produced material collapsed under gravity to flow down the southwest flank towards St Patrick's settlement. Approximately 60% of the island was declared dangerous for human occupancy, including the most densely inhabited sections. 92% of the original population of around 10 500 people was evacuated, and many families were relocated twice or three times. At the height of the crisis, in 1997, about 1600 people were housed in rudimentary temporary shelters, and by early 1998, roughly 70% of the island's inhabitants had fled. From March 1998 until November 1999 there was a pause in magma ascent accompanied by reduced seismic activity, substantial degradation of the dome, and considerable degassing with the venting of ash (Kokelaar, 2002).

Despite significantly increased awareness of the hazards of volcanism in the Caribbean region, largely due to the efforts of the Seismic Research Unit in Trinidad, it is clear that the Montserrat governing authorities were unprepared for the Soufriere Hills eruption. Montserrat had reconstructed its critical infrastructure in Plymouth with UK assistance. In 2022, work started on a £28m project funded by the UK and Caribbean Development Bank on a new town and port at Little Bay on the northwest coast of the island (BBC, 2022).

 

Videos:

https://youtu.be/GeghNYm_03A

 

References:

Baxter, P.J. et al. (2005) “The impacts of pyroclastic surges on buildings at the eruption of the Soufri�Re Hills Volcano, Montserrat,” Bulletin of Volcanology, 67(4), pp. 292–313. Available at: https://doi.org/10.1007/s00445-004-0365-7.

Kokelaar, B.P. (2002) “Setting, chronology and consequences of the eruption of Soufrière Hills Volcano, Montserrat (1995-1999),” Geological Society, London, Memoirs, 21(1), pp. 1–43. Available at: https://doi.org/10.1144/gsl.mem.2002.021.01.02.

Montserrat profile (2022) BBC News. BBC. Available at: https://www.bbc.com/news/world-latin-america-20256517 (Accessed: October 31, 2022).

Soufrière Hills volcano in Montserrat. (no date) Soufrière Hills volcano in Montserrat. | U.S. Geological Survey. Available at: https://www.usgs.gov/media/images/soufri-re-hills-volcano-montserrat (Accessed: November 1, 2022).

Sparks, R.S. et al. (1998) “Magma production and growth of the Lava Dome of the Soufriere Hills Volcano, Montserrat, West Indies: November 1995 to December 1997,” Geophysical Research Letters, 25(18), pp. 3421–3424. Available at: https://doi.org/10.1029/98gl00639.

Volcano Watch - update on Soufriere Hills, Montserrat (no date) Volcano Watch - Update on Soufriere Hills, Montserrat | U.S. Geological Survey. Available at: https://www.usgs.gov/news/volcano-watch-update-soufriere-hills-montserrat (Accessed: October 31, 2022).