Soufrière Hills Volcano - John Seach

john

Montserrat, West Indies
(British Overseas Territory)

16.72 N, 62.18 W,
summit elevation 915 m
stratovolcano

Soufrière Hills is a stratovolcano volcano formed at the junction of the Atlantic tectonic plate and the Caribbean plate. Failed eruptions occurred at Soufriere Hills volcano in 1890's, 1930's, and 1960's.

2010 Eruptions
Large pyroclastic flows occurred at Soufriere Hills volcano at 2:49 pm on 8th January 2010. The pyroclastic flows were caused by a collapsing tephra column, similar to the events in the summer of 1997. The flows traveled northeast down Whites Bottom Ghaut and reached the sea. The flow which moved down Tuitts Ghaut stopped a few hundred metres from the sea. Pyroclastic flows also traveled northwest down Tyers Ghaut and into the Belham valley. The event lasted 11 minutes and was not preceded by seismic activity. Ashfall occurred on the northwestern side of the volcano. Residents said it was one of the largest eruptions they have witnessed at the volcano, since its reawakening in 1995. At 1:28 am on 10th January there was another explosion at the volcano. The seismic signal lasted 7 minutes. The eruption produced pyroclastic flows which traveled rapidly northeast down White Bottom and Tuitts Ghaut. Flows also moved northwest down Tyers Ghaut and down the Gages valley towards Plymouth. A third smaller explosion occurred at 8:27 pm on 10th January. Scientists don't believe there was a major collapse of the dome, but a significant amount of material was lost. Hazard level 4 remains in place around the volcano, which means there is no access allowed in zone C, and only daytime access to zone B.

October 2009 eruptions
Renewed eruptions occurred at Soufriere Hills volcano on Montserrat on 5th October. A swarm of earthquakes began at 9pm on 4th October. Two hours of vigorous ash emission began at 10 pm on 5th October. The eruptions were followed by intermittent ash emissions. This was the first eruptions at the volcano since April 2009.
During the week 9-16 October activity has been high at Soufriere Hills volcano, Montserrat. A new lava dome has been growing at the volcano since 9th October 2009. Seismic activity during the week consisted of 1224 rockfall signals, 382 long period events, and one volcano tectonic earthquake. Pyroclastic flows occurred in all the major valleys that drain the volcano except the Tar River valley. Pyroclastic flows began on 9-10 October and extended south of the volcano. From 11 October pyroclastic flows extended down the Tyers Ghaut. Pyroclastic flows have reached about 3 km down the White River to the south; 1.5 km down the Gages valley to the west; and 3 km down Tuitts and Whites Bottom Ghaut in the east. Dome growth is located at the volcano summit which is responsible for the radial flow of pyroclastic flows. Lahars occurred in Belham valley on 14th October.

April-September 2009
Soufriere Hills volcano on Montserrat has been relatively quiet for six months. There has been no extrusion of new lava, and no explosions in that period. Surface activity was restricted to rockfalls and occasional small pyroclastic flows from the dome, together with mudflows. While gas emission has remained unchanged, the number of earthquakes recorded has fallen to the lowest level seen during the eruption cycle. This suggests the long-term activity has changed at the volcano. It could possibly mean the "beginning of the end" of the eruption cycle. Formal end of eruption criteria have not yet been met. However, the risks to people living near the volcano have not changed, and sudden resumption of explosive and extrusive activity can rapidly pose a threat to adjacent areas.

2008 Activity
Dome growth paused between March 2007 and May 2008. During 25th April to 2nd May the level of volcano-tectonic earthquakes at Soufrière Hills increased, and was the highest since February 2006. On 29 May produced an ash plume to an altitude of 3 km altitude which drifted SW and generated a pyroclastic flow. New lava extrusion from Soufrière Hills started from the west side of the lava dome between the 28th July and 8th August. Lava dome has continued to grow from August to November 2008. On 3rd December 2008, an eruption at Soufriere Hills volcano ejected rocks into the island's abandoned capital Plymouth, setting buildings on fire. Buildings burned for several hours.

1995 Eruption of Soufrière Hills Volcano
The first historical eruption on Montserrat was in 1995 following three years of increased seismicity. On 18 July, villagers around Soufriere Hills volcano reported unusually loud rumbling noises coming from the fumarole areas, light ashfall, and a strong sulfur odour. These phreatic eruptions were the first in recorded history at the volcano.

Since then, the eruption has been characterised by the growth of an andesite lava dome with associated pyroclastic flows, vulcanian explosion and debris flows.

1933 unrest
In 1933 a series of earthquakes occurred at the the volcano, but no eruption resulted.

There have been five distinct phases to the eruption so far.
1) period of extrusion from 1995 to early 1998, during which the dome grew and collapsed on a number of occasions.
2) residual activity, from early 1998 to late 1999, when there was no extrusion of lava, but several collapses of the dome occurred, as well as small to moderate size explosions.
3) November 1999-July 2003. Renewed extrusion and growth of a large lava dome.
4) Three major collapses during the second phase of dome growth: in March 2000, July 2001 and July 2003.
5) August 2005 - current. Third phase of dome growth.

1966-67 Seismic Crisis
Between May 1966 and the end of 1967 a total of 723 earthquakes were recorded at Soufriere Hills volcano, with 32 felt on Montserrat island. Most of the earthquakes were located in an WNW-ESE belt under the volcano at depths less than 15 km. There was a strong seasonal variation with a maximum in May and November-December each year. The earthquakes were caused by upward migration of magma beneath the volcano.

Soufrière Hills Volcano Eruptions

1995-2011, 1646±54