The VOL-CALPUFF model for atmospheric ash dispersal. II. Application to the weak Etna plume of July 2001

The application of the VOL-CALPUFF model (\cite{barsotti}, this issue) to a weak plume erupted from Mt. Etna in July 2001 is here presented and discussed. The reconstruction of the explosive event was obtained by using high-resolution weather forecasts, produced by a mesoscale non-hydrostatic model, and volcanic source data coming from observations and analytical studies. The plume rise and atmospheric dispersal models were investigated over five days of eruption mostly in terms of column height, aerial ash concentration and ground deposition. Modeling results are shown as a function of various source conditions and compared to independent observations derived from satellite images and deposit mapping. The application of VOL-CALPUFF clearly highlights the crucial role played by meteorological conditions in determining dispersal dynamics. Some of the most important effects described by the model are: a) the large wind field influence on the plume height determination and tilting, b) the contrasting dispersal patterns of ash particles of different sizes, c) the complex and somehow non-intuitive distribution of ash on the ground resulting in preferential directions of dispersal and quite irregular deposit patterns, d) the impossibility to reproduce both the column height and the deposit accumulation pattern by adopting a steady-state vent mass flow rate over the investigated four-day period due to observed temporal changes in eruption dynamics. Modeling results also suggest the need for further integration of simulation outcomes with remote sensing and field reconstructions on ash dispersal processes in future