Montserrat Volcano Observatory

Chronology of the Eruption of Soufriere Hills Volcano
from January 1992 to Early July 1997

Stage 1: Pre-Eruptive Seismic Activity

• Jan 92 Start of earthquake swarms in southern Montserrat.
• Jun 94 One of the largest precursory earthquake swarms.

• 18 Jul 95 Initial steam and ash venting from the northwest crater. Further vents opened on 28 July, 20, 22 and 28 August. The initial stage of the eruption was wholly phreatic, with small amounts of ash and vigorous steaming.
• 12-13 Aug 95 Strong earthquake swarm beneath St Georges Hill, with over 30 felt events.
• 21 Aug 95 First large phreatic eruption, which blanketed Plymouth in a thick ash cloud and caused darkness for about 15 minutes. First evacuation of southern Montserrat initiated shortly afterwards.

• late Sep 95 First signs of dome growth in English's Crater, and the appearance of a small spine in the southwest of the crater. Accompanied by the first swarm of hybrid earthquakes, from 22 to 29 September.
• 17 Oct 95 Mud flow from the southeast side of the crater.
• 30 Oct 95 Another large phreatic eruption.

• 14 Nov 95 First indication of new dome growth within the 18 July vent. Increased deformation measured by the Castle Peak EDM line.
• 24-25 Nov 95 Intense swarm of hybrid earthquakes, which lasted for several days and developed into low-amplitude volcanic tremor.
• 30 Nov 95 Confirmation of dome growth within the 18 July vent, with incandescent lava seen for the first time.
• 1-2 Dec 95 Evacuation of southern Montserrat, until 1 Jan 96.
• Jan-Mar 96 Continued dome growth in Englishs' Crater, with hybrid earthquake swarms, small rockfalls from the dome, and continued slow deformation.

• 29 Mar 96 First block and ash flows carried material from the crater region into the upper Tar River valley.
• 3 Apr 96 First pyroclastic flow, which travelled about 1.5 miles from the dome, to the road which crosses the Tar River valley. Third evacuation started.
• 6, 8 Apr 96 Further pyroclastic flows caused by collapses of the eastern face of the dome.
• 12 May 96 "Mothers Day" pyroclastic flows reached the sea for the first time.
• May 96 Continued dome growth, concentrated in the northeast sector of the crater. The seismic activity dominated by rockfall signals, and there were few earthquakes. Continued slow deformation measurable only at sites close to the dome (Castle Peak and Chances Peak).
• 9 Jun 96 Switch in dome growth to the northwest. Dome growth in subsequent days lead to the overtopping of Gages Wall.
• 19 Jun 96 Dome growth switched again to the north and southwestern sectors of the dome.
• 20 Jul 96 Increase in the amount of seismic activity, with the occurrence of high numbers of VT earthquakes for the first time since dome growth began. Accompanied by a major increase in the magma production rate, and a switch in dome activity to the eastern side of the crater. Rate of deformation on the eastern side increased to about 6 mm per day.
• 25-29 Jul 96 High rate of magma production of about 10 cubic metres per second, which led to major collapses and pyroclastic flows in Tar River valley. Start of period of intense seismic activity, with repetitive episodes of tremor, and hybrid and VT earthquakes, which lasted until 11 August.
• 11-12 Aug 96 Further dome collapses lead to pyroclastic flows.
• 2-3 Sep 96 More pyroclastic flows
• early Sep 96 Frequent VT earthquake swarms

• 17-18 Sep 96 A series of dome collapses lead to the first magmatic explosion during this eruption, at 23:46? on 17 September. Rocks and pumice fell in the south of the island, and houses were destroyed at Long Ground. A major ash plume rose to about 40,000 ft, and about 600,000 tonnes of ash was deposited in southern Montserrat. About one-quarter of the dome was removed during the dome collapses and subsequent explosion.

• 1 Oct 96 First sign of continued dome growth, with the appearance of a new dome at the base of the scar left by the explosion.
• 21 Oct 96 Restart of VT earthquake swarms, which continued through until 8 December. The earthquakes were accompanied by deformation of the Galway's Wall, the south part of the crater rim. Many landslides occurred from the outside face of the wall, and several cracks opened up across the wall near Chances Peak.
• 11 Dec 96 Restart of dome growth, in the southwest of the crater. The ``December 11'' dome grew rapidly to exceed the height of the October 1 dome, and was soon sending pyroclastic flows down the south side of the Tar River valley.
• 25 Dec 96 Following partial collapse of the December 11 dome on 19 December, dome growth switched back to the October 1 dome. The ``Santa Lobe'' grew rapidly on top of the dome, and between 25 December and 5 January, was extruding at the highest sustained rate seen during this eruption. The dome expanded to the east, over Castle Peak, which started to erode away as rockfalls fell over and around the Peak.
• Jan 97 Steady dome growth, with occasional moderate pyroclastic flows
• 20 Jan 97 Short-duration collapse which excavated part of the south-east dome. Fresh dome growth started immediately, forming the "January 20" dome within the collapse scar.
• 1-2 Feb 97 Further degradation of the Galway's Wall, allowing dome material to collapse over the wall for the first time.
• 30 Mar 97 First sizable pyroclastic flows to the south, over Galway's Wall and into the White River valley. Galway's Soufriere and Great Alps waterfall covered by pyroclastic deposits. Flows reaches 3.6 km down the White River.
• 1-11 April 97 Major pyroclastic flows down White River to within 500 m of the sea at O'Garras

• 14 May 97 Beginning of rock fall activity on north face of dome.
• 19 May 97 First rockfall spills in to Tuitt's Ghaut.
• 29 May 97 First pyroclastic flow activity in northern ghauts
• 2-14 June 97 Pyroclastic flows down Tuitt's Ghaut travelling to 2.9 km from the crater.
• 15 June 97 Significant changes in Mosquito Ghaut. Pyroclastic flow material advanced 500m down the Ghaut. Debris from a small rockfall in Gage's Valley.
• 16 June 97 Pyroclastic flows in Gage's Valley travelling 1.6 km from the crater rim. Smaller pyroclastic flows occurred in Mosquito and Tuitt's Ghaut.
• 17 June 97 Significant pyroclastic flow activity in Mosquito Ghaut to a distance of 4 km. Lesser activity in Gage's Valley with pyroclastic flows travelling 200m further than previously.
• 24 June 97 Small pyroclastic flows down Mosquito Ghaut for the first time since 17 June, travelling 1km from the crater rim. Focus of dome growth confirmed at top of Mosquito Ghaut.
• 25 June 97 Major pyroclastic flows in Mosquito Ghaut reaching to within 50 m of the airport. Surges and flows devastate Streathams, Rileys, Harris, Windy Hill, Bramble, Bethel, Spanish Point, Trants, and Farms. Surge reaches into Belham valley as far as Cork Hill. 7 confirmed fatalities, 19 missing presumed dead.
• 27 June 97 Small explosions from the dome scatter rock fragments to Fox's Bay.
• 28 June 97 Pyroclastic flow over Gages wall as far as Webbs village
• 1 July 97 Pyroclastic flow to Catholic Church, Plymouth
• Early July 97 Continued small pyroclastic flows in Mosquito Ghaut and Fort Ghaut
• Middle July Continued dome growth with rockfall activity Stage 9: Major flows to west and vulcanian explosions
• 31 July Continuous and semi-continuous volcanic tremor and ash venting. Small pyroclastic flows
• 1 August Resumption of cyclical behaviour with hybrid swarms followed by pyroclastic flows
• 3 August Major pyroclastic flows into Plymouth. Burning of buildings on the side of Fort Ghaut
• 4 August Second episode of major pyroclastic flows into Plymouth. Large flow lobe overtops Fort Ghaut into Dagenham as far as the Technical College. Afternoon eruption shows definite explosive behaviour with a dark jet of material to 2000 feet in the north. Pumice fragments to 1.5 cm fall at observatory.
• 5-8 August Explosions on 12 hour cycle with ash clouds to 40000 feet, and pumice clasts to 8 cm at observatory. Column collapse confirmed.
• 9-10 August Hybrid earthquake swarms without explosive activity
• 11-12 August Two small explosions Stage 10: Continued dome growth
• August/Sept Continued hybrid swarms superseded by high level rockfall activity as the dome grows rapidly within the crater excavated by the explosions of early August.
• 7 September Montserrat Volcano Observatory moves from site in Old Towne to new facility at Mongo Hill in the north. Stage 11: Major dome collapse to north-east and resumption of vulcanian explosions
• 21 September Major dome collapse to north-east of the volcano engulfing the area between Trant's Yard and White's Yard, destroying W. H. Bramble airport terminal building and entering the sea at various points along the coast.
• 22 Sept-21 Oct Second series of vulcanian explosions occurring at approximately 10 hour intervals, but with little or no precursory activity. In total 76 explosions occurred and ash clouds were sent up to 40000 feet with pumice fragments falling over all the island. Stage 12: Continued dome growth
• 22 Oct- Continued hybrid swarms superseded by high level rockfall activity as the dome grows rapidly within the crater excavated by the explosions of September and early October. A few large pyroclastic flows occurred to the south of the volcano into the White River valley, reaching the sea at O'Garra's.

Montserrat Volcano Observatory