High-impact low-probability events: Exposure to potential large-magnitude explosive volcanic eruptions

Due to their rarity, large-magnitude hazards are often ignored in disaster risk analysis, leaving societies with unmitigated exposure and limited preparedness. Volcanic eruptions of VEI 7 magnitude occur once or twice per millennium, with the last in 1815. Due to increasing populations and interdependent infrastructure, such an event happening today would be catastrophic. Assessing exposure is challenging due to the lack of past event data, limiting hazard modelling potential. We have developed a framework to assess exposure of populations, buildings, infrastructure, and cropland to VEI 7 eruptions. We assessed exposure within 100 km of 136 VEI 7 potential volcanoes, the likely extent of caldera collapse and pyroclastic density currents. We find that approximately 312 million people live within 100 km of these volcanoes. Laguna Caldera, Taal, and Wilis have the highest exposures. For tephra fall, we quantified exposure within isopach footprints from five past VEI 7 eruptions, and rotated these around the volcano to account for wind-direction variability. Among case studies, Ilopango has the highest exposure in the direction of current and future wind direction, with 115 million people, 3.2 million buildings, ~4,000 km2 cropland exposed. Our results show that exposure is highly sensitive to wind direction and highlight the scale of potential exposure. These findings can help prioritise preparation for catastrophic eruptions by integrating VEI 7 scenarios into disaster risk analysis.