Diffuse CO_2 soil degassing and CO_2 and H_2S concentrations in air and related hazards at Vulcano Island (Aeolian arc, Italy)

摘要

La Fossa crater on Vulcano Island is quiescent since 1890. Periodically it undergoes "crises" characterized by marked increase of temperature (T), gas output and concentration of magmatic components in the crater fumaroles (T may exceed 600 ℃). During these crises, which so far did not lead to any eruptive reactivation, the diffuse CO_2 soil degassing also increases and in December 2005 an anomalous CO_2 flux of 1350 tons/day was estimated by 1588 measurements over a surface of 1.66 km2 extending from La Fossa crater to the inhabited zone of Vulcano Porto. The crater area and two other anomalously degassing sites (Levante Beach and Palizzi) have been periodically investigated from December 2004 to August 2010 for diffuse CO_2 soil flux. They show a marked variation with time of the degassing rate, with synchronous maxima in December 2005. Carbon dioxide soil flux and environmental parameters have been also continuously monitored for over one year by an automatic station at Vulcano Porto. In order to assess the hazard of the endogenous gas emissions, CO_2 and H_2S air concentrations have been measured by Tunable Diode Laser profiles near the fumaroles of the crater rim and of the Levante Beach area, where also the viscous gas flux has been estimated. In addition, CO_2 air concentration has been measured both indoor and outdoor in an inhabited sector of Vulcano Porto. Results show that in some sites usually frequented by tourists there is a dangerous H_2S air concentration and CO_2 exceeds the hazardous thresholds in some Vulcano houses. These zones should be immediately monitored for gas hazard should a new crisis arise.