Advancing volcano surveillance through soil gas monitoring: insights from Stromboli Island, Italy.

Soil gas monitoring proves to be a powerful tool for studying volcanoes and their subsurface dynamics. Various gas species are examined as indicators of volcanic activity, with a focus on understanding the processes governing gas emissions. Carbon dioxide (CO2) is of particular interest due to its significant release during both active volcanic periods and periods of dormancy. Hydrogen (H2) concentration is also analysed to gain insights into the oxygen fugacity of magmatic gases, a parameter that influences the redox state and the distribution of elements among solid, fused, and gas phases. To effectively monitor volcanic gases, automated geochemical stations are deployed to simultaneously measure multiple gas species. This study presents a comprehensive analysis of reducing capacity monitoring data collected at Stromboli during the 2021-2023 time window. This station records data on molecular hydrogen (H2) concentration, CO2 flux, CO2 concentration, soil water content, atmospheric pressure, temperature, and relative humidity. The dataset underwent normalization of variables and filtering processes of spurious data to facilitate Principal Component Analysis (PCA), allowing for the identification of linear dependencies among the variables. The results of the PCA reveal insights into the relationships of the monitored parameters, shedding light on potential factors influencing volcanic activity. These data reveal variations in reducing capacity and soil CO2 flux that correlate with changes in Stromboli's eruptive activity. The delay in CO2 variations following shifts in reducing capacity is attributed to the advective-diffusive transport of gases through the volcanic rock formations. This research contributes to a deeper understanding of the volcanic degassing of Stromboli and shows the efficacy of combining multiple regression analysis methods for filtering geochemical datasets. This research enhances our understanding of volcanic behaviour and aids in volcano monitoring efforts.