Experimental studies of particle-laden plumes

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Experiments are described in which buoyant plumes of fresh water and solid particles are generated in a tank of salt water. Dependence of the behavior of the plumes on particle concentration and grain size was studied. At low concentrations, behavior was similar to single-component plumes, and the principal effect of the particles was to reduce the buoyancy flux. Plumes with high particle concentration exhibit several kinds of convective instability, which generated gravity currents and rapid sedimentation. When the plume density was close to but less than the density of the ambient fluid, a fountain forms high in the plumes which collapsed asymmetrically to generate a gravity current on one side of the plume. When the density of the particle-laden flow was greater than the ambient fluid, a symmetrical fountain formed, and gravitiy currents moved across the tank floor, depositing sediment. All the experimental plumes ascended to the top of the tank and spread out as gravity currents beneath the upper surface. Observations indicate that sedimentation is enhanced by convective instabilities when particle-rich fluid is emplaced above particle-free fluid. The experiments indicate that there may be several different mechanisms of generating pyroclastic flows and surges from the collapse of volcanic eruptions columns. The experiments also demonstrate that the sedimentation of particles from a plume has an important influence on dynamical behavior. -from Authors

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Journal of Geophysical Research