Revealing spatio-temporal variations of soil CO2 flux at Mt. Etna volcano

Abstract

Over the past two decades, significant advances in the geochemical monitoring of volcanoes have shown how crucial the observation of specific geochemical tracers is for understanding and evaluating eruptive processes. Among these, the monitoring of soil CO2 flux is one of the most important and widely employed geochemical parameters used in volcanic monitoring. At Mt. Etna volcano (Italy) long-term soil CO2 time series (2011–2019) are available from a network of 14 monitoring sites located around the volcano. Although variations in the exhalative regime of soil CO2 flux are recognized as possible proxies for potential emergent eruptive activity, little has yet been explored regarding the significance of the spatial variation of soil CO2 over time. In this paper, we look for possible dependence of CO2 flux on the altitude of the monitoring sites, their distances from the main craters, and their azimuthal positions on the volcano flanks. While for the first two elements there seems to be no evidence of dependence, we found evidence of long-term azimuthal variations in the soil CO2 flux that could depend on the structure of the volcano. In particular, the sites in south-eastern flank behave somehow differently from the ones located in other flanks. At yearly time scale, marked variations affect the CO2 flux at various sites. Such variations can be ascribable to volcano dynamics during the observation period characterized by a sequence of effusive and strombolian activities. Variations within a single eruptive episode also emerge investigating the 2018–19 flank eruption with bi-monthly windows.