New stations to monitor gas hazard in the ongoing volcanic unrest crisis of La Fossa volcano (Vulcano Island, Italy)

Abstract

<p>La Fossa volcano, located in the Vulcano Island of the Aeolian Archipelago, is the type locality of Vulcanian explosive eruptions. It last erupted in 1888-1890 and since then it is affected by an intense fumarolic activity from both the summit crater area and a hydrothermal site (Levante Beach) located very near to the main settlement of the island (Vulcano Porto). In Autumn 2021 a potential volcanic unrest crisis began with a strong increase of steam, CO<sub>2</sub> and SO<sub>2</sub> emission from the high-T crater fumaroles, ground uplift and episodic anomalous seismicity. Vulcano Porto inhabited area is exposed to gas hazard either from the wind dispersed crater fumarolic plume (mostly CO<sub>2</sub> and SO<sub>2</sub>) and from anomalous diffuse soil gas emissions in Levante Beach and other zones of Vulcano Porto village (mostly CO<sub>2</sub> and eventually H<sub>2</sub>S). The gas hazard of the village was considered so high that in December 2021 Civil Protection prohibited residents to stay at home during the night. In order to improve the monitoring of gas hazard we developed new stations continuously measuring the air concentration of CO<sub>2</sub> and SO<sub>2</sub>. Each of these stations is operating with an electrochemical sensor for the measurement of SO<sub>2</sub> and a photoacoustic sensor for the measurement of CO<sub>2</sub>. Moreover, atmospheric pressure, temperature and humidity are monitored in parallel to the gas measurements. The measured data are sent continuously via mobile data connection to a dedicated server. By this means the measured parameters can be monitored remotely, without the need to access the site personally. Three stations were installed (at 1 m from the ground) in mid-December 2021 in three sites of Vulcano Porto; two of them were located at the base of La Fossa cone in the sector most exposed to the crater gas plume, while a third station was located in the heart of the village, near the church. Results show that CO<sub>2</sub> exceeds of few hundreds ppm the normal air value of 400 ppm in all the stations. In some occasions, during night in absence of wind or with light wind blowing from SW, some peaks of both CO<sub>2</sub> and SO<sub>2</sub> were recorded in all the stations (CO<sub>2</sub> max 1500 ppm; SO<sub>2</sub> max 2 ppm). Additionally a future server sided extension to our system is planned, which integrates an early warning system, that can send email alerts, if certain thresholds are exceeded.</p>