The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat.  The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone.  English's Crater, a 1-km-wide crater breached widely to the east, was formed during an eruption about 4000 years ago in which the summit collapsed, producing a large submarine debris avalanche.  Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits at Soufrière Hills.  Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but with the exception of a 17th-century eruption that produced the Castle Peak lava dome, no historical eruptions were recorded on Montserrat until 1995.  Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.