Exposure-based risk assessment and emergency management associated with the fallout of large clasts at Mount Etna

Abstract

Abstract. Fallout of ballistic blocks and bombs ejected from eruptive vents represents a well-known hazard in areas proximal to volcanoes (mostly <5 km from the vent). However, fallout of large clasts sedimenting from plume margins that extend to medial areas and have the potential to produce severe injuries to people and cause damage to infrastructure, is often overlooked. Recent eruptive events at Mount Etna (Italy) provide a clear example where large-clast fallout from plume margins (>5 cm) has posed a real threat both to the many visitors reaching the summit area and to local infrastructure, and, therefore, has been selected as a case study. To quantify this hazard, a new particle sedimentation model was calibrated with field data and then used for probabilistic hazard assessments. For a fully probabilistic scenario the hazard zone covered 72 km2 and included some 125 km of paths and roads, as well as 15 buildings. Evacuation on foot to a safe area was estimated at almost 4 h, but this could be reduced to less than 3 h if two shelters were provided. Our results show the importance of integrating probabilistic hazard analysis of large-clast fallout within effective strategies of risk management and reduction, especially in the case of volcanoes where visitors can reach the summit areas.

Near-Real-Time Tephra Fallout Assessment at Mt. Etna, Italy

“…The particle sedimentation is obtained numerically from the equation of motion, which takes into account advection by wind, drag, and gravitational forces. The number of particles used in our simulations (500 clasts) is in agreement with previous comparisons between the model results and field data already validated by [53] for the event on 23 November 2013. Two end member reference scenarios are simulated daily based on two well-studied events: (i) the event on 12 January 2011 [36], considered as a low intensity event; and ii) the event on 23 November 2013 [8], which is one of the most explosive events that has occurred in recent years.…”

“…Sedimentation of large clasts is computed with the model described in [52] and applied for the first time at Etna [53]. The model has an approach similar to that presented in [54].…”

“…In our study, fixed scenarios are used to estimate the hazard from the fallout of large clasts. The delimitation of the area having a probability of impact of at least 1% for a 5 cm clast during a single eruptive event can be used as a hazard map [53]. As reported in [53], the evacuation of people from such an area can take several hours for both the eruptive reference scenarios selected.…”

“…The delimitation of the area having a probability of impact of at least 1% for a 5 cm clast during a single eruptive event can be used as a hazard map [53]. As reported in [53], the evacuation of people from such an area can take several hours for both the eruptive reference scenarios selected. There is, hence, the need to give "a priori" information about the area that should be interdicted, and that during an eruption could be exposed to large-clast fallout from plume margins.…”

Evaluating and ranking Southeast Asia's exposure to explosive volcanic hazards

“…Here, we used the model of Rossi et al (2019) that accounts for limited gravitational spreading of the umbrella cloud and the influence of three-dimensional atmospheric conditions on the particles. This model was successfully validated and applied by Osman et al (2019) Here, we considered the threat to human activity in the vicinity of the vent (e.g. hiking activity at the summit).…”