Estimating the mass of tephra accumulated on roads to best manage the impact of volcanic eruptions: the example of Mt. Etna, Italy

Abstract. During explosive eruptions a large amount of tephra is dispersed and deposited on the ground with the potential to cause a variety of damage and disruption on public infrastructure, such as road networks, which can require a rapid clean-up. The quantification of the tephra load is, therefore, of significant interest to reduce environmental and socio-economic impact, and for managing crises. Tephra dispersal and deposition is a function of multiple factors, including mass eruption rate, tephra characteristics (size, shape, density), top plume height, grain size distribution and local wind field. In this work we quantified the tephra mass deposited on the main road network on the east-southeast flanks of Mt. Etna (Italy), during lava fountains occurring in 2021. We focused this analysis on road connections of municipalities mostly affected by these events such as Milo, Santa Venerina and Zafferana Etnea. First, we analysed a sequence of 39 short-lasting and intense Etna’s lava fountains detected by the X-band weather radar, applying the volcanic ash radar retrieval approach able to retrieve main eruption source parameters, such as mass eruption rate, top plume height, grain-size distribution of those events. When the radar measurements were unavailable for a specific event, we analysed images acquired both by the SEVIRI radiometer and by the visible and/or thermal infrared camera of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (Catania) to derive some ESPs. Second, we used those eruption source parameters as inputs to run two different numerical models, Tephra2 and Fall3D, and reproduce tephra dispersal and accumulation on the road network. Finally, we produce, for the first time, georeferenced estimates of tephra mass deposited on the whole road network of three municipalities, allowing to identify the main roads which have been mostly impacted by significant tephra accumulation, as well as to estimate the total mass of primary tephra that has been removed from roads and disposed. Such information represents a valuable input for quick planning and management of the short-term tephra load hazard for possible future Etna explosive events.