Computer simulations of pyroclastic flows on Somma–Vesuvius volcano

Abstract

We describe a numerical simulation of pyroclastic flows on Somma–Vesuvius consisting of two integrated parts: forward and inverse approaches. The forward approach consists of the numerical generation of radial, one-dimensional flow lines from the vent, over a digitised topographic model of the Somma–Vesuvius area. The numerical flows are generated sampling a multi-dimensional matrix of dynamic and rheological parameters based on data from real eruptions. Analysis of the simulated flow patterns suggests that the pyroclastic flows of Vesuvius are compatible with a relatively dense flow model. The acceptable parameter values are confined within a relatively small range (moderate flow thickness and viscosity and initial velocity near 50 m/s). The diffusion of most of the pyroclastic flows, even with high initial velocity was mainly restricted to the southern sectors of the volcano by the Mt. Somma rim. The range of flow patterns generated by the direct approach was sampled for inverse analysis of eruptive conditions and rheology of the historical pyroclastic flows associated with the A.D. 79 and A.D. 1631 Plinian and sub-Plinian eruptions. The results of inversion suggest that flows were compatible with Bingham rheology (yield strength=600 Pa), initial velocity ranging between 50 and 100 m/s, viscosity ranging between 30 and 700 Pa s, and flow thickness ranging between 2 and 10 m.