Volatile degassing at Stromboli Volcano: Continuous soil CO2 fluxes monitoring network and soils discrete measurements. Volcanic implications

The Stromboli volcano, Aeolian Islands, Italy, is characterized by persistent Strombolian activity. It is a perfect case study to investigate the relationship between outgassing activity and paroxysmal events.The discrete soil CO2 degassing measurements, performed with the portable flux meter based on the accumulation chamber method, were carried out in the summit and peripheral zones. These measurements surveys allowed us to individuate the anomalous degassing areas (Scari, Piscità, and Pizzo Sopra La Fossa), coincident with the main structural faults respectively N64° and N41° as preferential paths for the rising of deep fluids.Based on the information resulting from the discrete measurements a near-continuous (hourly frequency) geochemical network was installed on Stromboli Island and consists of three stations, one located in the summit part of the Pizzo Sopra La Fossa area (STR02), and two located in the peripheral zone STR01 and STR03 in the Scari and Piscità areas respectively. This network allowed us to acquire a large amount of soil CO2 flux data to investigate and model the plumbing volcanic system. The analysis of a large dataset of soil CO2 fluxes collected in the summit crater area (STR02), from 2000 to 2023, showed significant changes in degassing values and style before and in coincidence with major volcanic events like paroxysmal explosions caused by the rapid rise of volatile-rich magma and the changes from explosive to effusive eruptions. In particular, the soil degassing processes of CO2 peaks showed three main and peculiar behaviors:A long-lasting modification, characterized by a slow and continuous increase in CO2 flux; Transient changes, characterized by abrupt changes in the rate of CO2 outgassing; Strong Increase in the Natural Daily Variation, highlighting drastic changes in the degassing style, a few months before the major paroxysmal events.