Lava fountains at Etna volcano deciphered in real-time by high precisions borehole strainmeters data and implications on hazard mitigation: the 21 May 2023 case

In recent decades, Etna's main eruptive activity  was characterized by prolonged sequences of lava fountain episodes. In particular, the sequence from December 2020 to February 2022 was characterized by 65 lava fountains. After the conclusion of the last sequence in February 2022, preceded a few days earlier by a shallow seismic swarm, a powerful fountain occurred on May 21, 2023. This lava fountain was unexpected since it was far from the previous sequence and did not even  belong to a new sequence. The greatest criticality was the difficulty in monitoring this eruptive event using conventional remote sensing devices due to the bad weather conditions characterized by thick cloud cover.

In this study we present the strain data recorded by the borehole dilatometers network on Etna. The high precision strain changes make it possible to follow all the recent lava fountains providing a valuable interpretative contribution. Through new approaches recently implemented, the analysis of the strain data allowed us to identify the correct timing of the events, evaluate the ‘size’ of the fountain (i.e. its eruptive power) and estimate the erupted volumes in near real-time. In particular, during the 21 May 2023 event, the quantification of these features provided a useful support during the Civil Protection meeting convened in emergency at the Prefecture of Catania, where the evolution of these features was presented and updated in near real-time. The experience gained on the 21 May 2023 lava fountain demonstrates the contribution that the real-time high precision strain may provide to define and evaluate the hazard associated with a lava fountain even in unfavorable weather conditions, when the remote sensing systems may not be able to provide helpful information on the ongoing phenomenon.