Spatio-temporal evolution of the fumarolic field of La Fossa cone (Vulcano Island, Italy) in 2021–2024.

Monitoring the spatio-temporal evolution of fumarolic activity is key to understanding volcanic unrest at dormant volcanoes. Here, we present the results of periodic gas surveys conducted at La Fossa (Vulcano Island, Italy) between 2021 and 2024, in which a portable Multi-GAS instrument is used to map the spatial variations in gas composition across the fumarolic field. We identify substantial spatio-temporal changes in gas composition. The crater rim fumaroles exhibit the highest CO2, SO2, H2S, H2 concentrations and stable, relatively low CO2/SO2 ratios (around 20–30), all indicative of a larger magmatic contribution. In contrast, the inner crater fumaroles display more variable and generally higher CO2/SO2 ratios, indicating a larger hydrothermal influence. These data, combined with infrared thermal imaging and SO2 flux results, are indicative of a volcanic unrest that, after having reached its climax in late 2021, has gradually vanished since, although not fully returning to pre-unrest conditions