Carbon dioxide degassing from the Albani Hills volcanic region, Central Italy

The Albani Hills are affected by strong CO2 degassing processes. The amount of CO2, which rises from the depths and subsequently dissolves into shallow groundwater, has been estimated to be more than 4.2 x 10(9) mol year(-1). Most of the gas is released in localised anomalous spots (Lavinio. Solforata, and Ciampino-Albano-Nemi areas), generated by fluid leakage processes from buried pressurized reservoirs hosted by structural highs of the calcareous-siliceous marry basement. The groundwater circulating in the anomalous areas becomes CO2 oversaturated, generating observable gas manifestations whose composition is mainly controlled by gas-liquid separation processes. A gas flow rate of 6.1 x 10(8) mol year(-1) has been measured from the two larger manifestations using the accumulation chamber technique. The presence at shallow level of CO2 oversaturated groundwater can explain several episodes of sudden release of gas which was documented by historical chronicles from Roman times, until now. (C) 2001 Elsevier Science B.V. All rights reserved.