What caused the Soufrière Hills Volcano to erupt? The Caribbean island of Montserrat is situated on a destructive plate boundary. A plate boundary occurs when two of the plates that make up the surface of the earth meet. Underneath Montserrat the Atlantic plate is slowly being forced under the Caribbean plate. This happens because the oceanic plate is denser than continental plate. Convection currents pull the dense Atlantic plate into the mantle where intense heat and friction cause the rock to melt. This molten rock is lighter than the surrounding rock, forcing it to rise through cracks in the in the rock towards the earth's surface. Molten rock or magma gathers under the volcano until the pressure is so great that it is forced up through a vent towards the surface of the earth. The Soufrière Hills Volcano produces a thick sticky lava called andesite. The lava is so thick that it builds up at the top of the volcano in a dome until it becomes too heavy and the dome collapses. When the dome collapses hot rocks, gases and ash are released from the volcano causing the following hazards. Pyroclastic flows are extremely fast-moving flows of lava, hot rocks and gas that flow down the side of the volcano. Pyroclastic Surges are fast-moving clouds of hot ash that travel with the pyroclastic flow. Tiny pieces of volcanic ash are blasted into the air forming a plume of ash. As it cools down it falls back to the earth, covering vast areas with a layer of ash. The current eruption of the Soufrière Hills Volcano started on 18 July 1995 and is still continuing in 2003. Throughout this time, the volcano has experienced different stages of eruption from earthquake swarms to explosive eruptions. On 25 June 1997 at about 1 p.m. the Soufrière Hills Volcano erupted catastrophically. The dome of the volcano collapsed, sending 5 million cubic metres of hot rocks and gases down the side of the volcano towards the north of the island. This signalled an increased period of volcanic activity and had a significant impact on the island.