Long-term hazard of pyroclastic density currents at Vesuvius (Southern Italy) with maps of impact parameters

Abstract. The hazard of pyroclastic density currents (PDCs) at Vesuvius is investigated basing on past eruptions. Analysis is extended to all the eruptions that left substantial deposits on the ground.

The currents are bipartite, with a basal highly-concentrated part, which was fed from the impact of the eruptive fountain on the ground, and an overlying part generated by the squeezing of the collapsed material that fed a dilute and turbulent shear flow.

Dynamic pressure, particle volumetric concentration, temperature and flow duration are hazardous characteristics of PDCs that can impact buildings and population and are defined here as impact parameters. They have been calculated by means of an implementation of the PYFLOW code, which uses the deposit particle characteristics as input. The software searches for the probability density function of impact parameters. The 84th percentile has been chosen as a safety value of the expected impact at long term (50 years). Maps have been constructed by interpolation of the safety values calculated at various points over the dispersal area, and show how impact parameters change as a function of distance from the volcano. The maps are compared with the red zone, which is the area that the National Department of the Italian Civil Protection has declared to be evacuated in the impending of an eruption. The damaging capacity of currents over buildings and population is discussed both for the highly concentrated part and the diluted one.