Quantification of tephra impact on the road network: the example of lava fountains at Etna volcano in 2021-22

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 to residential buildings and infrastructure, including road networks. The quantification of the tephra ground load is, therefore, of significant interest to reduce environmental and socioeconomic impact, and for managing crisis situations during volcanic eruptions. Tephra dispersal and deposition is a function of multiple factors, including mass eruption rate (MER), degree of magma fragmentation, vent geometry, top plume height (H_TP), particle size distribution (PSD) and wind velocity and pattern.In this work we quantify the tephra load deposited on the road network of the eastern flank of Mt. Etna, in Italy, during the sequence of lava fountains occurred between February 2021 and 2022. In particular we analyse those events generating volcanic plumes mostly dispersed towards the east-southeast direction and focus our study on the main road networks of some municipalities which are found in this section of Mt. Etna as Milo, Santa Venerina, Fleri.We applied the volcanic ash radar retrieval (VARR) approach to a large dataset of short-lasting and intense lava fountains detected by the X-band weather radar, located at about 32 km from the Etna summit, to retrieve the eruption source parameters. When the radar data were unavailable, we analysed images of the SEVIRI satellite and of the visible calibrated camera images of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo.

Two numerical models (TEPHRA2 and FALL3D) were used to simulate tephra ground accumulation. The model calibration was performed using data collected during an eruptive event in 2021. Tephra load was calculated for areas of particular interest as e.g., building roofs, infrastructure and road networks, requiring clean-up.We compute a cumulative in time of deposited tephra on some locations of the road network obtaining values ranging from 40-140 kg/m², and from 110-480 kg/m² in function of model considered and selected location.As a result, we produce fast estimates of total tephra deposited on specific infrastructures (e.g., roads) during sequences of eruptive events; such information can be a valuable input for quick planning and management of the short-term tephra fall hazard.