Potential impacts of tephra fallout from a Plinian eruption at Sakurajima volcano, Japan

We present an exposure analysis to tephra fallout for a future Plinian eruption scenario at Sakurajima volcano developed based on a new field characterization of the last Plinian eruption and a review of reports of the eruptions that occurred in the past 6 centuries. A scenario-based probabilistic hazard assessment is performed using the Tephra2 model, considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions. A quantitative exposure analysis of infrastructures and lifelines is presented primarily using open-access data. Observations drawn from a detailed impact assessment after the 2011 VEI 2 eruption of Shinmoedake (Magill et al. 2013), providing a unique illustration of the impacts from tephra fall in a similar socio-economic context, are used in parallel of the hazard and exposure analyses to identify and discuss potential vulnerable and resilient infrastructures for a future eruption of Sakurajima. Results indicate a main eastward dispersal, with higher eruption duration increasing the hazard in proximal and reducing it in distal areas. The exposure analysis reveals that 2300 km of road network, 18 km2 urban areas and 306 km2 of agricultural lands have a 50% probability to be affected by an accumulation of tephra of 1 kg/m2 and identifies the municipalities of Kagoshima, Kanoya and Tarumizu as the most likely impacted. Finally, the 2011 eruption of Shinmoedake demonstrated that a range of mitigation measures are implemented, increasing the resilience and improving the recovery of the affected infrastructures. Nevertheless, the extent to which these mitigations actions will perform during the VEI 4 eruption presented here is unclear, and our hazard assessment indicates very high hazard levels on the Sakurajima peninsula and the neighboring municipality of Tarumizu.