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Several analytical and numerical eruption models have provided insight into volcanic eruption behaviour^,,,,, but most address plinian-type eruptions where vent conditions are quasi-steady. Only a few studies have explored the physics of short-duration vulcanian explosions^,,, with unsteady vent conditions and blast events^,. Here we present a technique that links unsteady vent flux of vulcanian explosions to the resulting dispersal of volcanic ejecta, using a numerical, axisymmetric model with multiple particle sizes. We use observational data from well documented explosions in 1997 at the Soufrière Hills volcano in Montserrat, West Indies, to constrain pre-eruptive subsurface initial conditions and to compare with our simulation results. The resulting simulations duplicate many features of the observed explosions, showing transitional behaviour where mass is divided between a buoyant plume and hazardous radial …