These are hot, fast moving mixtures of ash, rock fragments and gas, flowing from a collapsed eruption column or lava dome. Pyroclastic flows travel down valleys and completely devastate the area over which they flow. Pyroclastic surges cause greater devastation since they may also sweep across ridges and hills. Pyroclastic flows and surges have caused most of the destruction in Montserrat during the Soufriere Hills Volcano eruption.
Pyroclastic surges were responsible for the fatalities on the 25th June, 1997 event.