U-series disequilibrium study on a gaseous discharge area (Solforata of Pomezia, Alban Hills, Italy): implications for volcanic and geochemical risk

The age and environmental impact of the gaseous discharge at Solforata of Pomezia (Alban Hills, Italy) has been investigated by the application of U-series disequilibrium methods. Chronological data of sulphide mineralization and of a phreatomagmatic deposit close to Solforata fit with a temporal window (26–47 ka BP) of intense volcanic activity which occurred during the final hydromagmatic phase (180–11 ka BP) of the Alban Hills volcano. Radon measurements have allowed an estimation of fluxes of the main gases presently released at Solforata. A model combining Darcy’s law and modified Stoker–Krüger equations has been used in order to predict the upper limit of the gas pressure (19 atmospheres) at the base of the volcanic succession and of the rising time (35 days) of the gas through the volcanic pile. Geochronological and geochemical constraints, obtained by U-series disequilibrium methods, have proved useful in comparing the volcanic and geochemical risks in this area. The comparison shows that, under normal conditions of gas dispersion, the geochemical risk associated with Rn and H2S exposure is high and it must be tackled immediately with particular surveillance and intervention methods.