Mobility of pyroclastic flows and surges at the Soufriere Hills Volcano, Montserrat

The Soufriere Hills Volcano on Montserrat has produced avalanche-like pyroc lastic flows formed by collapse of the unstable lava dome or explosive acti vity. Pyroclastic flows associated with dome collapse generate overlying di lute surges which detach from and travel beyond their parent flows. The lar gest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas. Different kinds of pyroclastic density currents display contrasting mobilities indic ated by ratios of total height of fall H, run-out distance L, area inundate d A and volume transported V, Dome-collapse Flow mobilities (characterised by either L/H or A/V (2/3)) resemble those of terrestrial and extraterrestr ial cold-rockfalls(Dade and Huppert, 1998). In contrast, fountain-fed pumic e flows and fine-grained, secondary pyroclastic flows travel slower but, fo r comparable initial volumes and heights, can inundate greater areas.