Rainstorms Could Trigger Volcanic Eruptions Thursday 5th September 2002 The most dangerous type of volcanic eruption can be triggered by heavy rain, UK researchers have found. This suggests that simply watching the weather forecast could be used to save lives. The type of eruption in question is a "dome collapse". This form of eruption has caused more than 70 per cent of volcano-related deaths over the past century. They tend to be big, violent eruptions. The Mount St Helens eruption on 18 May 1980, for example, sent a cloud of 520 million tonnes of ash 25 kilometres into the air. Rock and debris fell to Earth up to 30 kilometres from the volcano. The build-up to an eruption is often easy to see months or years ahead, as magma pushing from below produces a visible dome on the side of the mountain. Small eruptions of lava add to the bulge, making it more unstable until eventually it collapses, releasing the pressure in a massive explosion. But it is extremely difficult to tell exactly when this will happen. Now researchers studying Soufriere Hills volcano on the Caribbean island of Montserrat have linked the last three eruptions to an unlikely culprit - the weather. The volcano became active on 18 July 1995 after a break of some 300 years. On all three occasions, heavy rain destabilised a dome that was already primed to collapse. Rain may have played a part in triggering other volcanoes too. There is a statistical link between the wettest times of the year and eruptions at Mount Etna and Mount Saint Helens, but the connection is not clear-cut. It is possible that large amounts of water seep into cracks in the dome and are vaporised by the molten rock. The massive increase in pressure as the water heats up and turns to steam then triggers a blast. Factoring rainfall into eruption predictions could improve accuracy, though she cautions that rain will not necessarily be the trigger in every case. Being able to predict any dome collapse would be a major step forward. These events are particularly deadly because of the avalanche of searing toxic gas, hot ash and boulders they send down the mountain. These "pyroclastic flows" - which travel at up to 80 kilometres per hour - are much more hazardous than lava. (Geophysical Research Letters) More on the causes of volcanic eruptions...
