GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.2 103 CHEMICAL ANOMALIES IN THE GAS PHASE RELEASED FROM THE SANTA VENERA AL POZZO THERMAL SPRING (MT. ETNA, SICILY, ITALY): POSSIBLE INFLUENCE FROM LOCAL TECTONIC ACTIVITY F. Sortino 1 , S. Giammanco 2 , P. Bonfanti 2 , C. Bottari 2 1 Istituto Nazionale di Geofisica e Vulcanologia, sez. Palermo 2 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania Introduction. Among the many thermal manifestations that occur in Sicily (Carapezza et al. , 1977; Grassa et al. , 2006), that of Santa Venera al Pozzo (hereinafter referred to as SVP) is the only one, in mainland Sicily, that occurs in a volcanic area, namely that of Mt. Etna. In this area, the outcropping volcanic rocks are typically basalts, which constitute the majority of the rocks (Branca et al. , 2011). Furthermore, this site is located in an area marked by the crossing of some of the most important and seismically active tectonic faults of southern Italy (Bottari et al. , 2020). The name of SVP refers to the site (likely the Greek Akis, later Roman Acium) , located on the lower eastern slope of Mt. Etna volcano, next to the harbor of Capo Mulini and to the town of Acireale, in the province of Catania. Near-continuous monitoring both of gas emissions (CO 2 , CH 4 and H 2 S) and of water temperature at Santa Venera al Pozzo thermal springs (SE foot of Mt. Etna volcano, Sicily, Italy) was conducted fromDecember 2017 to April 2019, using a novel and cheaper Chromatography Monitoring System (CMS) coupled with a water temperature sensor. Methods. Free gases monitoring. The CMS method used in this study is an automatic chromatographic system designed and built to allow a micro-gas-chromatograph (mod. Agilent490) to analyze natural gases, in our case free gas collected from the well headspace at the top of a water well. The micro-gas-chromatograph (µ-GC) used is set with a user-specified sampling frequency controlled by the instrument management software and it is a system made up of individual modules, each provided with an injector, a detector (Micro-TCD) and a chromatographic column that can be changed according to which gas species has to be determined. For the analysis of natural gases, two modules are normally used: one allows detecting He, Ne, O 2 , N 2 , CH 4 , CO with a molecular sieve column (MS5A), whereas the other allows detection of air, CO 2 , H 2 S, SO 2 , CH 4 and some light hydrocarbons with a Poraplot Q column (PPQ). The µ-GC is powered with 12V batteries recharged by electric power. The instrument is controlled through the Galaxie software program installed on the embedded computer. This allows the remote control and maintenance of the system via internet connection, using Remote Desktop Protocol software. Computers, µ-GC, routers, batteries and bottle-carrier have been assembled inside a hermetic suitcase. The CMS needs an automatic sampling system that is activated simultaneously with the start of the analytical procedure. Sampling is controlled by the µ-GC, which activates an external pump, just before the start of the analysis, to suck the gas directly from the gas source. Our system is designed in order to act as a complete field laboratory and our data have accuracy similar to that of a laboratory gas-chromatograph, thus better than 2%. Furthermore, repeated calibration of the system during a one-year period using standards showed an instrumental drift close to 2% for all measured parameters. For the purposes of our work, we set the CMS near the main thermal spring at SVP, pumping the gas out of a 30m-deep small well that was drilled in the 1980s. Water temperature monitoring. In order to monitor the temporal changes of water temperature in the same borehole where gas measurements were carried out, we installed a temperature sensor with built-in data-logger (Gemini Dataloggers, mod. Tinytag Plus2) into water, close to the top of the borehole (about 2 m below water surface), whose total depth