Stable isotope surveys reveal variations in the air CO2 during the unrest event at Vulcano, Italy, in 2021

Monitoring volcanic gases have provided valuable information in recognizing variations of the magma outgassing at depth. The increase of magmatic volatile compounds in either crater plumes or fumarole emissions can help in tracking transitions from dormancy to unrest which can progress further in a volcanic eruption. The volcanic degassing has renewed at Vulcano since September 2021 as the result of an increase of the magma degassing at depth. This event created concerns among civil defense authorities because the CO₂ concentration rose in the air, although the unrest has not produced an eruption.

This study examines the air CO₂ at Vulcano Porto from the early summer to autumn of 2021, when the volcanic degassing achieved the climax at La Fossa volcano. Five surveys enabled exploring lateral variations for CO₂ in the air at Vulcano Porto based on measurements for stable isotope compositions of both oxygen and carbon. In addition, the continuous stable isotopes surveying at a fixed point of interest (i.e., the Centro Carapezza - INGV) enabled studying the time variations for CO₂ in the air.

The surveys captured a remarkable increase of the volcanic CO₂ in the air throughout the settled zone of Vulcano Porto from October to November 2021. At Vulcanello, which lies a few kilometers far from the crater cone, the isotopic signature of the air CO₂ revealed also an increased volcanic degassing. Several variations for the volcanic CO₂ in the air occurred during the same period and some estimations of the CO₂ flux from the crater plume were obtained through continuous stable isotope surveying.
The results of this study represent a step forward in providing volcano monitoring techniques that enable estimating the CO₂ emission in the air from active vents.