Numerical Simulation of Flow and Deposition of a Pyroclastic Flow

Abstract

To contribute for delineation of the hazardous area by the Merapi type pyroclastic flows, a theory for the mechanics of the flow and deposition is presented. In this model, the flow mechanism transits from the granular flow upstream to the fluidized one downstream associated with the crush of the particles caused by inter-particle collisions. In the granular flow the particles are mainly sustained by the inelastic collisions, whereas in the fluidized flow, the particles are sustained by the large scale turbulence and up-lifting force of the upward gas flow emitted from the material itself. The flow continues to run down leaving the base layer in which the driving force due to gravity does not exceed the resistance force. Using this model, the 1991 pyroclastic flow at Mt. Unzen-lake were reproduced by the 2-D numerical simulation. The results of calculation well explain the actual phenomena.