Hazardous Changes in Soil CO2 Emissions at Vulcano, Italy, in 2021

The La Fossa volcano on the Island of Vulcano, Italy, showed signs of more energetic fumarolic–solfataric activity during 2021. Several increases in volcanic gas emissions and seismicity, namely, “crisis,” punctuated the passive degassing at Vulcano that had ensued after the last 1888–1890 vulcanian eruption. Most of the gases (i.e., up to 90%) were emitted at the crater cone while the diffuse degassing of CO2 at Vulcano Porto accounted for more than 10% of the volcanic emissions. Two anomalous degassing zones at the base of the volcanic cone (i.e., Palizzi and Faraglione) showed notable changes in the gas output during the volcanic crisis. In these zones, increases of soil CO2 flux (φCO2) had several practical implications other than of volcanological interest, owing to the risk related to people's exposure to volcanic gas emissions. The results of this study reveal variations of the average φCO2 from 74 g m−2 d−1 during September 2021 to 370 g m−2 d−1 in November 2021, which were 27% and 538% higher than the statistical background since 1988 (φCO2 ≈ 58 g m−2 d−1), respectively. These observations helped in volcanic surveillance at Vulcano. The soil CO2 partitioning determined using both φCO2 and carbon isotope measurements, helped track changes in the volcanic CO2 output from 9.97 · 104 to 101.15 · 104 kg d−1. Estimates for volcanic CO2 suggest that the instability of a magmatic body caused a transition from background fumarolic–solfataric activity toward an unrest event after September 2021.