Fallout of ballistic blocks and bombs ejected from eruptive vents representsa well-known hazard in areasproximal to volcanoes (mostly <5 km from the vent). However, fallout of large clasts sedimenting fromplume margins that extend to medialareas and have the potential to produce severe injuries to people and causedamage to infrastructure, is often overlooked. Recent eruptive events atMount Etna (Italy) provide a clear example where large-clast fallout fromplume margins (>5 cm) has posed a real threat both to the manyvisitors reaching the summit area and to local infrastructure, and,therefore, has been selected as a case study. To quantify this hazard, a newparticle sedimentation model was calibrated with field data and then used forprobabilistic hazard assessments. For a fully probabilistic scenario thehazard zone covered 72 km2 and included some 125 km of paths androads, as well as 15 buildings. Evacuation on foot to a safe area wasestimated at almost 4 h, but this could be reduced to less than 3 h if twoshelters were provided. Our results show the importance of integratingprobabilistic hazard analysis of large-clast fallout within effectivestrategies of risk management and reduction, especially in the case ofvolcanoes where visitors can reach the summit areas.
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