Overview of the Present Eruption

The current eruption of the Soufriere Hills Volcano, which began in July 1995 and continued through to February 2010, has been characterised by the occurrence of activity in five distinct “Phases”, separated by periods of little to no activity termed “pauses”. The eruption is currently in its fifth (and longest) pause since the end of lava extrusion and a major dome collapse event on 11 February 2010.

The eruption began on 18 July 1995 with a phreatic explosion. More explosions followed and a two week-long evacuation of southern Montserrat was ordered in August 1995. Following the commencement of lava extrusion in November 1995, when a new lava dome began growing inside English’s Crater, a second evacuation of Plymouth was ordered in December 1995. By March 1996, small pyroclastic density currents (PDCs) were travelling to the east down the Tar River Valley. In April 1996 a state of emergency was declared by the Governor and Plymouth and southern parts of the island were evacuated for the last time. The first PDCs reached the sea on 12 May 1996.

Dome growth continued through 1996 and 1997. During this time, PDCs descended all flanks of the volcano. The first magmatic explosion occurred on 17 September 1996 following a large dome collapse. PDCs overtopped the south crater wall in February 1997 and the north crater wall in May 1997, reaching Plymouth for the first time in August 1997. This was followed by a series of Vulcanian explosions that showered the island with ash. In June 1997, 19 people were killed when surges hit the village of Streatham, which was in the exclusion at the time, while Bramble Airport was destroyed by PDCs from a large dome collapse on 21 September 1997. Between September and October 1997, a series of 75 Vulcanian explosions generated frequent and extensive ash fall that caused many remaining islanders to leave, reducing the island’s population to 3300. A major dome collapse on 26 December 1997 generated a debris avalanche and violent lateral blast, destroying the village of St Patrick’s.

Pyroclastic Flows on 25 June 1998

Growth stopped suddenly in March 1998, and the following 20 months saw little activity with occasional pyroclastic flows and minor explosions. In November 1999, lava dome growth began once more and the second phase of activity had begun.

The new phase of lava dome growth again resulted in PDCs and explosions that inundated all the flanks of the volcano. By 2003, the lava dome was the biggest than ever previously – more than 200 million cubic metres. It loomed over the Belham River Valley causing the evacuation of Old Towne and all areas in the lower part of the valley. On 12 July 2003, the lava dome began to collapse in a series of massive pyroclastic flows that travelled to the east, down the Tar River Valley. Almost the entire lava dome disintegrated into the sea over just 18 hours generating a tsunami that reached the neighbouring island of Guadeloupe, and resulting in a series of 5 Vulcanian explosions.

Dome growth began again almost immediately, but stopped after a few days. The following 24 month-long pause involved more activity than had occurred during the 1998-99 pause. A number of small explosions occurred in March 2004, while vigorous ash venting occurred in April, June and July 2005. Seismicity was also higher, with numerous swarms of volcano-tectonic and long period earthquakes, including one that saw more than 1000 seismic events within a 36-hour period from 30-31 January 2004.

The Soufrière Hills entered its third phase of activity in August 2005. Growth of the dome began slowly, but in February 2006, a period of rapid extrusion (at around 10 m³/s) began. Although this rate declined over the next few months, the dome reached 90 million m3 by late May 2006 – when a major dome collapse occurred. Within the space of three hours, the whole dome collapsed eastwards in to the sea. Dome growth resumed immediately after the collapse, and continued at an elevated rate of 8-10 m³/s for the next 6 months until the dome finally overtopped the old English’s Crater wall in January 2007. During this time, the focus of dome growth switched direction many times. On 8 January 2007, three explosions occurred in the space of a few minutes just before dawn that were heard as far north as Woodlands on Montserrat. PDCs associated with the explosions reached 5 km down the Belham Valley, further than any previous flows in the valley. Growth continued until April 2007, when it again stopped, leaving behind a dome with a height of 1063 m and a volume of approximately 204 million m³.

The third pause lasted 16 months until August 2008 and saw relatively little activity.

The fourth phase of activity began with a series of eight explosions between 13 May and 26 July 2008 from a well-developed vent on the west flank of the dome. A larger Vulcanian explosion occurred 29 July 2008 from the same vent, which was followed a week later by the resumption of extrusion on the western flank of the dome. Slow extrusion continued until October 2008, when it again stopped. However, this time the pause was very short-lived, and in early December 2008, activity resumed with several explosions. A pyroclastic surge associated with one of these explosions nearly overtopped the south east flank of St George’s Hill. Following these explosions, there was a period of intense dome growth with extrusion occurring high up on the west side of the dome, rapidly filling the area between the dome and Chance’s Peak. Dome growth continued throughout December and was accompanied by PDCs down Tyre’s Ghaut and the Gages gap. On 2 January 2009, there was a dramatic increase in activity that culminated with two large explosions in the early hours of 3 January that sent tephra columns to more than 10 km above sea level. Activity decreased rapidly following the second explosion, and the volcano entered its fourth pause which lasted 10 months and had almost no visible activity associated with it.

Activity resumed in October 2009 with a series of 13 vigorous ash venting events that sent tephra to more than 6 km above sea level. This was quickly followed by rapid lava extrusion from the summit of the dome. New lobes were emplaced in the northern, western and southwestern sectors of the dome, resulting in PDCs down all major drainages. On 8 and 10 January 2010, 3 large Vulcanian explosions occurred. The first, on 8 January, was the largest such explosion to date since the eruption began, and sent at least two pulses of PDC down the Belham Valley to 6 km from the dome, further than the previous longest flows of 8 January 2007. On 10 February 2010, extrusion on the northern flank increased dramatically and on 11 February 2010, a large partial dome collapse occurred. This event removed approximately 50 million m3 of dome rock and talus, leaving behind a 300 m-deep and 1 km long scar. PDCs reached the sea to the NE, adding approximately 1 km2 of new coast and covering the remains of the old Bramble airport with up to 15 m of debris. PDCs inundated the previously unaffected Farm River Valley to the north of the volcano, and also travelled 5.7 km down the Belham Valley. This is the largest event to have occurred on the northern flank since the eruption began, and marked the end of the fifth phase of extrusion.

As of 1 November 2021, the volcano is more than 11 years into its fifth pause, which has seen very little activity apart from some minor ash venting in June and July 2010 associated with some small volcano-tectonic earthquake swarms. There was also some significant seismic activity and surface activity in the form of ash venting and the opening of new craters in March 2012 and to more strong seismicity in March 2014. Overall, the pause has been characterised by persistent low levels of seismicity, continued deformation (inflation) of the island as measured by continuous GPS and consistent, but variable SO₂ flux. All indications are that a resumption of extrusion in the future is likely given the continuing trend of deformation signal recorded by the GPS network and consistent SO₂ flux.