SE Solid Earth SE Solid Earth 1869-9529 Copernicus Publications Göttingen, Germany 10.5194/se-3-161-2012 New developments in the analysis of column-collapse pyroclastic density currents through numerical simulations of multiphase flows Lepore S. 1 Scarpati C. 1 Dipartimento di Scienze della Terra, University of Naples Federico II, Largo San Marcellino 10, 80138 Naples, Italy 08 06 2012 3 1 161 173 Copyright: © 2012 S. Lepore 2012 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://se.copernicus.org/articles/3/161/2012/se-3-161-2012.html The full text article is available as a PDF file from https://se.copernicus.org/articles/3/161/2012/se-3-161-2012.pdf

A granular multiphase model has been used to evaluate the action of differently sized particles on the dynamics of fountains and associated pyroclastic density currents. The model takes into account the overall disequilibrium conditions between a gas phase and several solid phases, each characterized by its own physical properties. The dynamics of the granular flows (fountains and pyroclastic density currents) has been simulated by adopting a Reynolds-averaged Navier-Stokes model for describing the turbulence effects. Numerical simulations have been carried out by using different values for the eruptive column temperature at the vent, solid particle frictional concentration, turbulent kinetic energy, and dissipation. The results obtained provide evidence of the multiphase nature of the model and describe several disequilibrium effects. The low concentration (≤5 × 10<sup>&minus;4</sup>) zones lie in the upper part of the granular flow, above the fountain, and above the tail and body of pyroclastic density current as thermal plumes. The high concentration zones, on the contrary, lie in the fountain and at the base of the current. Hence, pyroclastic density currents are assimilated to granular flows constituted by a low concentration suspension flowing above a high concentration basal layer (boundary layer), from the proximal regions to the distal ones. Interactions among the solid particles in the boundary layer of the granular flow are controlled by collisions between particles, whereas the dispersal of particles in the suspension is determined by the dragging of the gas phase. The simulations describe well the dynamics of a tractive boundary layer leading to the formation of stratified facies during Strombolian to Plinian eruptions.

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