Carbon dioxide and radon emissions from the soils of Pantelleria island (Southern Italy)

Abstract In the period July 2005–October 2006 several soil gas prospections were performed on the island of Pantelleria, an active volcanic/geothermal system at present in a quiescent state. Measured parameters were CO 2 concentrations and 220 Rn and 222 Rn activities at 50 cm depth and CO 2 fluxes from the soil. The whole island was covered with a measurement density of 3.5 points/km 2 for CO 2 (flux and concentration) and 1.6 points/km 2 for Rn. Further three main and seven minor areas of previously ascertained or expected exhalative activity were covered with a measurement density up to 100 points/km 2 . The obtained results ranged from 0.038 to 95%vol for CO 2 concentration, from 10 Bq/m 3 to 164,000 Bq/m 3 from 10 Bq/m 3 to 750,000 Bq/m 3 for 220 Rn and 222 Rn activities, respectively and from 2  day for CO 2 fluxes. Probability plots evidenced for all measured parameters the presence of three populations (background, mixed and hydrothermal). All anomalous values were found in the central part of the island within the youngest caldera. Flux data allowed us to estimate a total CO 2 output of the volcanic/geothermal system of Pantelleria in 24.2 tons per day. Some new exhaling area, significantly contributing to the total output and characterised by stunted or absent vegetation, were evidenced on the southern flank of Mt. Grande. At one of these areas the relationships between the measured parameters and vegetation cover were studied in detail along a 140 m long transect of 15 points. Finally, a first evaluation of the gas hazard related to the geogenic degassing evidenced some high risk area at the mofette along the shores of the Lake Specchio di Venere (CO 2 ) and in the village of Rekale (CO 2 and Rn).