Diffuse CO2 degassing at Vesuvio, Italy

Abstract

At Vesuvio, a significant fraction of the rising hydrothermal volcanic fluids is subjected to a condensation and separation process producing a CO2 rich gas phase, mainly expulsed through soil diffuse degassing from well defined areas called diffuse degassing structures (DDS), and a liquid phase that flows towards the outer part of the volcanic cone. A large amount of thermal energy is associated with the steam condensation process and subsequent cooling of the liquid phase. The total amount of volcanic hydrothermal CO2 discharged through diffuse degassing has been computed through a sequential Gaussian simulation (sGs) approach based on several hundred accumulation chamber measurements and, at the time of the survey, amounted to 151 td1. The steam associated with the CO2 output, computed assuming that the original H2O/CO2 ratio of hydrothermal fluids is preserved in fumarolic effluents, is 553 td1, and the energy produced by the steam condensation and cooling of the liquid phase is 1.471012 Jd1 (17 MW). The location of the CO2 and temperature anomalies show that most of the gas is discharged from the inner part of the crater and suggests that crater morphology and local stratigraphy exert strong control on CO2 degassing and subsurface steam condensation. The amounts of gas and energy released by Vesuvio are comparable to those released by other volcanic degassing areas of the world and their estimates,through periodic surveys of soil CO2 flux, can constitute a useful tool to monitor volcanic activity.