Structures and grain size distribution in surge deposits as a tool for modelling the dynamics of dilute pyroclastic density currents at La Fossa di Vulcano (Aeolian Islands, Italy)

Turbulent, dilute pyroclastic density currents (surges) represent the most common and hazardous type of eruptive event at La Fossa di Vulcano. During the volcanic history these currents have frequently passed over the topographic barrier of La Fossa caldera, maintaining a high velocity. We interpret lateral facies Variation in terms of fluid-dynamic behaviour by analyses of structures, thickness and grain size of correlated surge layers from the Palizzi succession. Using these data we validate a sedimentation model of traction fed by a low concentration, turbulent and stratified current. By the use of a sedimentological model, we have then reconstructed the fluid-dynamic parameters of the current and calculated the maximum horizontal distance that solid particles travelled before deposition. Results have been checked against actual deposit features. Consistency of data indicates that the method used in this study, even if it is approximate, and needs further refinement by specific experimental approaches and numerical simulations, gives a reasonable indication of surge characters such as velocity and density, which are relevant for hazard calculation and risk assessment.