The paroxysm of Etna (Italy) on 23rd November 2013: Ballistics shower and hazard zones implications

On 23rd November 2013, a paroxysmal eruption occurred at Etna's New SE Crater (NSEC). A powerful eruptive column was developed and reached several km high, leading to the fallout of material on the NE flank. The ash reached as far as the S coast of Italy. During the climax phase there was a huge shower of dense ballistic clasts >0.2 m. These covered a distance of >5 km between the Rif. Citelli, Mt. Sartorius and Due Monti, where they destroyed roofing tiles, solar panels, windows of cars and slightly injured some hikers; the pyroclastic material with a diameter up to 2 cm reached about 30km. We studied 30 samples from sites ranging between 5-25 km from NSEC. For the >5 km range, it is impossible to distinguish the clasts falling from the eruptive column from the clasts erupted from the vent following ballistic trajectories. The trajectories of smaller blocks (d<0.1m) are not purely ballistic, since these can be carried in the eruptive column. They are then dispersed by the finger-like projections from the jet-thrust region of the column from where they fall or produce gravity currents in the surrounding region of the eruptive column. Furthermore, the gas expansion in the column reduces the drag force on particulates and assists their vertical-lateral transport. The composition of magma erupted proves to be more primitive than that emitted during the 2011-2013 paroxysms. This aspect could be important factors to explain the highly explosive paroxysm of 23rd November, 2013. Finally, compared with 180 paroxysms in the past 15 years, this event has generated one of the most significant pyroclastic deposits in terms of thickness, amount of material on the ground, particle size and dispersion of products erupted and raises some significant implications regarding hazard zones