Coupling UV Camera‐Derived SO2 Emission Rate and Thermal Output at Mount Etna: A Decadal Analysis Across Eruptive Phases

At persistently degassing open-vent volcanoes, SO2 emissions are especially useful to capture the transition from quiescence to eruption, though accurate quantification is challenged by complex volcanic plume dynamics and limited resolution of observations. Here, we present an exceptionally long (~10–years) record of SO2 emission rates from Etna volcano in Italy, obtained using a permanent UV Camera system. We combine these data with satellite-derived thermal fluxes, to explore links between SO2 degassing, thermal output, and eruptive behaviour. We initially use the thermal flux to identify the main eruptive phases during 2015–2024. For each of these phases, we identify a typical increasing pattern in time-averaged SO2 fluxes, from ~2000 t/d during inter-eruptive periods, to ~2500 t/d in the days before (and after) eruptions, to ~3800 t/d during eruptions. Coupling thermal-derived magma output rates with SO2-derived magma supply rates, we quantify the volumetric imbalance between supplied and erupted magma. Results shows that only ~28% of the eruptible magma (i.e., the volume of magma in excess to that sustaining background activity) is discharged during eruptions, with the remaining magma fraction (~72%) being stored intrusively. We additionally calculate that ~120 Mm3 of magma (or more, considering that the UV-Camera derived SO2 emission rates are likely minimum estimates) may have accumulated during the 2015–2021 interval, contributing to volcano deformation. Our analysis underscores the importance of integrated gas and thermal observations for improved interpretation of monitoring data.