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

Abstract

Fallout of ballistic blocks and bombs ejected from eruptive vents represents a well-known hazard in proximal areas.However, fallout of large clasts sedimenting from plume margins extending to medial areas with 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, 15 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 km 2 and included some 125 km of paths and roads, and 15 buildings; evacuation on foot to a safe area was estimated at almost 4 hours, but this could be reduced to less than 3 hours 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 20 areas.

Remotely assessing tephra fall building damage and vulnerability: Kelud Volcano, Indonesia

“…Reducing the thickness of tiles by 3 mm slightly decreases the load they place on a roof, presumably increasing the load of tephra the roof frame can support by an equal amount. However, 15 mm thick clay tiles are already exceptionally vulnerable to shattering under impact from large clasts (with a threshold of 20 joules), and making tiles thinner will have reduced the impact energy and associated minimum clast size required to exceed damage thresholds (Osman et al, 2018;Williams et al, 2019). Secondly, vulnerability is also likely to have been increased in the many cases where repairs have markedly enlarged overhanging and veranda sections of roofs.…”

Reducing uncertainty in building vulnerability and impact assessment for tephra hazards

“…Reducing the thickness of tiles by 3 mm slightly decreases the load they place on a roof, presumably increasing the load of tephra the roof frame can support by an equal amount. However, 15 mm thick clay tiles are already exceptionally vulnerable to shattering under impact from large clasts (with a threshold of ~ 20 joules), and making tiles thinner will have reduced the impact energy and associated minimum clast size required to exceed damage thresholds (Williams et al 2019;Osman et al 2019). Secondly, vulnerability is also likely to have been increased in the many cases where repairs have markedly enlarged overhanging and veranda sections of roofs.…”