Experimental Pyroclastic Density Currents

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Pyroclastic flows are poorly understood, hazardous mixtures of expanding gas and hot ash that can move tens of kilometers at velocities in excess of 100 km/sec. Pyroclastic flows are dangerous to observe and rarely coincide with researchers'timing. This project, therefore, will begin a multi-disciplinary study to investigate how pyroclastic flows work. Pyroclastic density currents can be produced in the laboratory by pouring 600oC. ash down an inclined surface that is moistened with water. Preliminary experiments successfully produce flows with many of the features of natural pyroclastic flows. A moving flow has three parts; a sediment-rich basal avalanche, an overriding ash cloud surge and a convecting ash cloud. The environmental conditions of experimental flows can be easily controlled individually and the effects on the flow noted. Of principle concern are the factors that affect the mobility of pyroclastic flows because of the obvious importance of runout in hazard assesment. The results of such a study are likely to improve the assesment of hazards due to pyroclastic flows, which is a serious societal responsibility for volcanologists.