Violent but short-lived Vulcanian explosions have been associated with the growth of the viscous lava dome at the Soufrière Hills volcano. Each explosion ejects a slug of ash and rocks at initial speeds of hundreds of metres per second.
Pumice-rich pyroclastic flows are formed on all flanks of the volcano (below). Ash plumes rise rapidly in the atmosphere, sometimes as high as 15 kilometres (right).
The first magmatic explosion of the eruption occurred on 17 September 1996. In early August 1997, 12 explosions occurred approximately 10 hours apart. A further 75 explosions occurred between 22 September and 21 October 1997 at between 3 and 33 hour intervals.
A lateral blast (a type of horizontal explosion) occurred on 26 December 1997. This was similar to the eruption of Mt St Helens, USA, in 1980, but much smaller. It was caused by the collapse of the south-west flank of the volcano at Galway's Soufrière. About 60 million cubic metres of dome and crater wall travelled to the south as a debris avalanche and pyroclastic density currents. The villages of St. Patrick's and Morris were swept away in less than thirty minutes.