The combined surveying of soil CO2 flux and air CO2 concentration for gas hazard mitigation at Vulcano, Italy

Among extreme geological events, people feel the effects of volcanic eruptions through fear and wonder. Several volcanoes erupt across the world with sheer physical power, but a large part of them is either dormant or quiescent. Risks for explosions at active volcanoes are well-recognized, while the gas hazard which is correlated with almost continuous gas emissions from either the crater cone or the soils is still a masked risk. Volcanic gas emissions impact people at settled zones which lay around the main quiescent volcanic structure. In addition, the level of the gas hazard correlates with changes in the gas emissions, which agrees with variations of the magmatic degassing at depth.

This study reports on the results of the continuous monitoring for soil CO₂ flux, air CO₂ concentration, and some weather variables (i.e., temperature, pressure, relative humidity, wind speed, and wind direction). Tailored monitoring stations were deployed in an anomalous degassing zone of the island of Vulcano, Italy (i.e., Faraglione) for mitigating the gas hazard. This area hosts many infrastructures and several tourist facilities. The deployment of the monitoring network occurred in June 2021 in the framework of the agreement between the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, and the Dipartimento Regionale di Protezione Civile (DRPC – Sicilia).

Since late September 2021, the volcanic degassing increased at Vulcano due to a probable increase of the magmatic degassing at depth. The results of this study show a distinct increase in the soil CO₂ flux at Faraglione which correlated with the high CO₂ concentration in the air. These variations caused increases in the gas hazard at Vulcano. Besides various evidence points to the climax of the volcanic unrest in autumn 2021, redundancy for monitoring stations in the anomalous degassing zone allowed capturing of some minor variations of the magmatic activity at depth. Some remarkable increases occurred in soil CO₂ emissions during spring 2022, which culminated in the whitening of the seafloor at Baia di Levante. Minor variations are reported for both summer and early autumn 2022. These results point out as both the accurate monitoring of the air CO₂ concentration and the weather variables complement efficiently the continuous monitoring of the soil CO₂ flux resulting in a suitable strategy for mitigating the gas hazard at Vulcano.