TRACKING MAGMATIC PROCESSES THROUGH SO2 FLUX MEASUREMENTS AT OPEN-VENT VOLCANOES

Volcanic gas monitoring plays a central role in modern volcano surveillance, offering critical insights into magmatic processes and contributing to the forecasting of eruptive events. Among volcanic gases, sulphur dioxide (SO2) is widely recognized as a key tracer of shallow degassing dynamics and magma transport within the upper portion of a volcano’s plumbing system. This thesis investigates the utility of high-resolution SO2 flux records acquired from permanent Ultraviolet (UV) Camera systems to monitoring the activity of Mount Etna and Stromboli, two persistently active, open-vent volcanoes in Sicily. Particular emphasis is placed on the interpretation of SO2 degassing trends in relation to magma dynamics and eruptive phases, and on the assessment of the uncertainties affecting SO2 flux measurements.The two volcanoes exhibit a wide range of eruptive behaviours and associated hazards, making them ideal sites for testing and refining gas-based monitoring techniques. Stromboli’s persistent activity is characterized by mild-to-moderate Strombolian explosions recurring at regular intervals, with occasional more violent major and paroxysmal explosions that can affect inhabited areas and trigger slope instabilities and tsunamis. Etna’s activity is dominated by continuous degassing from its summit craters, usually accompanied by mild Strombolian explosions, which is often interrupted by effusive eruptions and powerful lava fountain episodes, which can produce high eruptive columns. These eruptive phenomena pose significant hazards, including destructive lava flows, ash emissions that compromise air traffic and health, and the potential for pyroclastic density currents and lahars with severe impacts on populations and infrastructure.The decadal SO2 flux records analysed here allow a variety of topics to be analysed with unprecedented detail and temporal resolution. At Stromboli, I undertake the first long-term (nine years) systematic comparison between near-vent SO2 fluxes derived from UV Cameras and those obtained from a network of distal scanning spectrometers coupled with the DOAS technique. A large SO2 flux mismatch between the two time series is observed. This offset is attributed to plume coverage limitations and radiative transfer effects in UV Camera data, and to overestimation in DOAS-derived fluxes using wind speed without accounting for plume dilution from source to the analysis section. A novel integrated SO2 flux is developed to address these issues, combining DOAS column amounts with UV Camera-derived plume velocities. In parallel, multi-year datasets of SO2 and CO2 concentrations are analysed to identify gas-based precursors to explosive events. Statistical results indicate that periods of reduced SO2 concentrations and fluxes and elevated CO2/SO2 ratios consistently precede major explosions. Based on this, a gas-based composite indicator is proposed, which retrospectively forecasts over 70% of events on timescales of weeks. The Stromboli’s July 2024 eruption is also examined in detail, with particular focus on the differing behaviour of SO2 and CO2 fluxes as indicators of shallow and deep magmatic degassing, respectively. Results show that the eruption was preceded and accompanied by a large escalation in the CO2 flux relative to the SO2 flux, suggesting a deeper magmatic gas source, consistent with the involvement of gas-rich magma ascending from greater depths. These findings highlight the diagnostic value of elevated CO2 fluxes in detecting deep gas release preceding explosive activity that may not be immediately evident from SO2 measurements alone.At Mount Etna, ~10 years of UV Camera data are used to characterise SO2 flux variations associated with a wide range of eruptive style, from variable effusive eruptions, differing in volume and duration, to paroxysmal lava fountain events. These data have been analysed in combination with geophysical and satellite thermal data, to obtain a more comprehensive understanding of eruptive mechanisms and involved magma volumes. A particular focus was placed on the paroxysmal sequences of 2020-2021, during which the highest SO2 fluxes and erupted volumes were recorded. The results point to rapid injections of volatile-rich magma into a shallow reservoir located at ~3-4 km depth as the main driver of these intense eruptive phases, causing a sharp increase in magma supply rate above the sulphur exsolution threshold (~150 MPa).Taken together, these findings advance our understanding of degassing dynamics at open-vent systems and contribute to a deeper insight into eruptive mechanisms. By addressing key methodological uncertainties and integrating multiple datasets, these studies contribute to refining monitoring strategies and strengthening interpretations of gas-based eruption precursors at active volcanoes.