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 P omezia (Alban Hills, Italy) has been investigated by the application of U-s eries disequilibrium methods. Chronological data of sulphide mineralization and of a phreatomagmatic deposit close to Solforata fit with a temporal wi ndow (26-47 ka BP) of intense volcanic activity which occurred during the f inal hydromagmatic phase (180-11 ka BP) of the Alban Hills volcano. Radon m easurements have allowed an estimation of fluxes of the main gases presentl y released at Solforata. A model combining Darcy's law and modified Stoker- Kruger equations has been used in order to predict the upper limit of the g as pressure (19 atmospheres) at the base of the volcanic succession and of the rising time (35 days) of the gas through the volcanic pile. Geochronolo gical and geochemical constraints, obtained by U-series disequilibrium meth ods, have proved useful in comparing the volcanic and geochemical risks in this area. The comparison shows that, under normal conditions of gas disper sion, the geochemical risk associated with Rn and H2S exposure is high and it must be tackled immediately with particular surveillance and interventio n methods. (C) 2000 Elsevier Science Ltd. All rights reserved.