The island of Montserrat lies in the northern Antilles, a group of islands sitting on the junction of the Atlantic and Caribbean tectonic plates. Montserrat, which is only 16 km long and 10 km wide is almost exclusively formed from volcanc rock and has three volcanic centers.
Of these, the Soufriere Hills volcano remains active and its last major eruption in 1995, destroyed the capital city, Plymouth, and forced an evacuation of the island´s southern parts.
-
Soufriere Hills is stratovolcano with a lava dome, typical of a subduction volcano formed by the subduction of the Atlantic tectonic plate under the Caribbean plate. The volcano is andesitic, which is a gray, fine-grained volcanic rock, compared with the much darker basalt volcanic rock. The summit consists of a series of lava domes sitting along an ESE-trending zone, referring to the fault line directions East to Southeast. The 1 km wide English's Crater, formed during an eruption 4,000 years ago, when the summit collapsed to form it, is the largest crater on the eastern edges of the volcano.
The volcano's summit is at about 3,300 feet (1,050 meters) although this changes with volcanic activity. The eruption of 1995 is actually still ongoing with minor to medium ash eruptions accompanied by lava dome growth and some pyroclastic flow. The Castle Peak lava dome was formed during an eruption around 1630 and between then and 1995, the volcano has only had a series of failed eruptions, which means non eruptive seismic events.
Between 1992 and 1995, geologists recorded a series of pre-seismic events including 18 earthquakes in the south part of the island. From July to November 1995 there were a number of phreatic explosions from the volcano. A phreatic eruption is one powered by steam. Water beneath the Earth is heated by the volcano's magma to boiling point turning to steam that then erupts from the volcano bringing water, ash and rocks with it. The largest phreatic eruption was on August 21, 1995, which
Since 1995, monitored events at the Soufriere Hills volcano show several major lava dome collapses. On Christmas Day 1997 a seismic tremor causes the collapse of a lava dome with a height of 1030 meters, and the debris swept down the White River valley destroying 10 square kilometers of south Montserrat on Boxing Day. In 2006, another major dome collapse caused a small tsunami and the sulphur dioxide released was traced right across the Pacific Ocean.
