GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.2 GNGTS 2024 How multple observatons tracked the onset and evoluton of the 2021-2023 unrest at Vulcano Island (Southern Italy), and unveiled the processes behind it C. Federico 1 , A. Paonita 1 , S. Bellomo 1 , R. M. R. Di Martno 1 , A. Gatuso 1 , L. La Pica 1 , G. Lazzaro 1 , M. Longo 1 , G. Pecoraino 1 , A. F. Pisciota 1 , F. Sortno 1 . 1 Isttuto Nazionale di Geofsica e Vulcanologia, sezione di Palermo, Italy In September 2021, the La Fossa volcano entered a new phase of unrest. The monitoring system recorded a sudden variaton in seismicity, ground deformaton, fumarole temperatures, and soil and plume degassing. These variatons were ascribed to the fast vaporisaton and expansion of the central hydrothermal system (Federico et al., 2023), strongly impacted by the input of heat and chemicals from the magmatc source. By the onset of the unrest, fumarole chemistry showed clear-cut variatons, related to the dominant contributon of the magmatc gas over the hydrothermal one. The CO 2 content and the He isotopes of the magmatc gas revealed the appearance of a more primitve magma during the climax of the unrest. The increased contributon of magmatc gases was already evident since 2018, so the 2021 unrest could have been the outcome of a long-lastng preparatory phase. The anomalous outlow of magmatc gases gradually extended northwest of La Fossa cone and involved the thermal area of Baia di Levante, where several low-temperature (100°C) fumaroles emit a vapour coming from a local hydrothermal aquifer. The gas compositon had been typical of hydrothermal systems, with equilibrium temperatures close to 200°C but, by the onset of the crisis, it was gradually modifed by the magmatc gas. In May 2022, a sudden and likely explosive release of gas occurred in the Baia di Levante, which was testfed by the whitening of the seawater in the bay, and by the appearance of typical pockmark structures on the seafoor. At that moment, the gas compositon of the monitored fumarole on the beach closely approached that of crater fumaroles. This episode drove the atenton of the scientfc community to this area, for several months afected by a signifcant input of magmatc vapour, because of the risk related to the huge CO 2 emission and the eventual overpressurizaton of the local hydrothermal aquifer. The magmatc contributon is persistently high in the fumaroles of La Fossa crater by the tme of this communicaton, whereas it is declining in the Baia di Levante. The gas output in the crater area, and at the base of the cone is declining as well.