Diffuse degassing of carbon dioxide on the NW sector of Colli Albani volcanic complex (Rome, Italy)

systematic CO2 soil flux surveys carried out at cava dei Selci on the Colli Albani volcano (28 seasonal surveys since the year 2000), have shown a significant variation of CO2 diffuse release, with a marked decrease, from 25 to 4 tons/day, from May 2000 to August 2004, followed by a new increase. In the same time CO2 flux halved at S. Maria delle Mole (16.8 tons/day in 2000 and 8.3 tons/day in 2006). Also the total quantity of CO2 dissolved in the deep waters of the Albano crater lake decreased by one order in the period 1997-2006. The high CO2 flux values could represent the “tail” of a strong degassing episode recorded at Colli Albani in 1995 and related to local earthquakes. The following decrease of CO2 release could reflect a permeability decrease caused by hydrothermal calcite precipitation favoured by PCO2 reduction in the deep source