Sulfur origin and flux variations in fumarolic fluids of Vulcano Island, Italy

Abstract

A sharp increase in volatiles, especially SO2 fluxes from the solfataric plume and diffuse CO2 from the soils of the La Fossa crater area, started in June 2021, and subsequently from the Levante Bay area, suggests renewed unrest at Vulcano Island, Italy. This event has encouraged monitoring activities and stimulated new research activities aimed at understanding the recent evolution of the volcanic system. In this study, the chemical and isotopic composition of fumaroles, thermal waters, and soil gases from the main degassing areas of Vulcano Island with a special focus on sulfur isotopes, are used to investigate the fluid transfer mechanism inside the volcano. Sulfur is one of the most abundant volatile elements present in magmas and volcanic fluids from the La Fossa crater, where it mostly occurs as SO2 and H2S at variable relative concentrations depending on oxygen fugacity and temperature. The isotope composition and the chemical ratio of sulfur species depict a complex hydrothermal-magmatic system. In addition, we utilize the installed SO2 monitoring network that measures the total outgassing of SO2 with the UV-scanning DOAS technique. The SO2 fluxes from the La Fossa crater fumaroles, coupled with the SO2/CO2 and SO2/H2O ratios, were measured to evaluate the total mass of fluids emitted by the shallow plumbing system and its relationship with the status of volcanic activity. Combining the whole chemical composition of fumaroles analyzed with a discrete, direct sampling of high-temperature fumaroles located on the crater summit, the output of discharged water vapor has been estimated (5,768 t·d−1). On the basis of the water output, we estimated the total thermal energy dissipated by the crater during the last enhanced degassing activity (167 MW). This strong and sharp increase in energy observed during the current crisis confirms the long-growing trend in terms of mass and energy recorded in recent decades, which has brought the surface system of Vulcano Island to a critical level that has never been recorded since the last eruptive event of 1888–91.

Multi‐Temporal InSAR, GNSS and Seismic Measurements Reveal the Origin of the 2021 Vulcano Island (Italy) Unrest

“…The overall results presented here indicate that the investigated unrest phase (September‐December 2021), that is, inflation and seismicity, together with anomalies in gasses emissions (Aiuppa et al., 2022; Federico et al., 2023; Inguaggiato et al., 2022, 2023), is compatible with the expansion of the hydrothermal system located within the La Fossa Caldera. Thermal anomalies also show a similar trend, with a peak again in October 2021 (Coppola et al., 2022; Corradino et al., 2023; Pailot‐Bonnétat et al., 2023).…”

“…Since September 2021, Vulcano has undergone a new phase of unrest. Fumarolic activity increased in the latter half of September, accompanied by intensified seismic activity (Coppola et al., 2022; Corradino et al., 2023; Federico et al., 2023; Inguaggiato et al., 2023). Notably, Very Long Period (VLP; frequency peak ∼ 0.3 Hz) seismic events were recorded for the first time, with the source area located at 950 ± 270 m below sea level, North of La Fossa cone (Federico et al., 2023).…”

Heat transport process associated with the 2021 eruption of Aso volcano revealed by thermal and gas monitoring

“…In magmatic-hydrothermal systems, which are responsible for phreatic eruptions, thermal energy is discharged in various forms, such as fumarole fields (Inguaggiato et al 2023), geothermal anomalies (Harris et al 2009), gas plumes (Matsushima et al 2003), and hot water ponds and crater lakes (Hurst et al 1991;Tajima et al 2020). In recent years, satellite-based thermal infrared (TIR) imagery has become a powerful tool for monitoring such thermal phenomena in hydrothermal systems (Gaete et al 2020;Coppola et al 2022).…”