No abstract

We present the first regional map of CO2 Earth degassing from a large area (most of central and south Italy) derived from the carbon of deep provenance dissolved in the main springs of the region. The investigation shows that a globally significant amount of deeply derived CO2 (10% of the estimated global CO2 emitted from subaerial volcanoes) is released by two large areas located in western Italy. The anomalous flux of CO2 suddenly disappears in the Apennine in correspondence to a narrow band where most of seismicity concentrates. Here, at depth, the gas accumulates in crustal traps generating CO2 overpressurized reservoirs which induce seismicity.

Abstract. In the •?resent period of quiescence, the Solfatara volcano, 1 km far from Pozzuoli, releases 1500 t d-of hydrothermal CO2 through soil diffuse degassing from a relatively small area (0.5 krn2). This amount of gas is comparable to that released by crater plume emissions of many active volcanoes. On the basis of the CO2/H20 ratio measured in high-temperature fumaroles inside the degassing area, we computed a total thermal energy flux of 1.19 x 1013 J d -1 (138 MW). Most of this energy is lost by shallow steam condensation and transferred to the atmosphere through the hot soil of the degassing area. The thermal energy released by diffuse degassing at Solfatara is by far the main way of energy release from the whole Campi Flegrei caldera. It is 1 order of magnitude higher than the conductive heat flux through the entire caldera, and, during the last 20 years, it was several times higher than the energy associated with seismic crises and ground deformation events. It is possible that changes in the energy flux from a magma body seated underneath Solfatara and/or argillification processes at relatively shallow depths determine pressurization events in the hydrothermal system and consequently ground deformation and shallow seismic swarms, as recorded during the recent episodes of volcanic unrest centered at Pozzuoli.

No abstract

[1] Conditional sequential Gaussian simulations (sGs) have been applied for the first time to the study of soil diffuse degassing from different volcanic and nonvolcanic systems. The application regards five data sets of soil CO 2 fluxes measured with the accumulation chamber methodology at the volcanic areas of Solfatara of Pozzuoli (Italy), Vesuvio cone (Italy), Nisyros (Greece), and Horseshoe Lake (California) and at the nonvolcanic degassing area of Poggio dell'Olivo (Italy). The sGs algorithm was used to generate 100 realizations of CO 2 flux for each area. Probabilistic summaries of these simulations, together with the information given by probability plots, were used (1) to draw maps of the probability that CO 2 fluxes exceed thresholds specific for a background flux, i.e., to define the probable extension of the degassing structures, (2) to calculate the total CO 2 output, and (3) to quantify the uncertainty of the estimation. The results show that the sGs is a suitable tool to model soil diffuse degassing, producing realistic images of the distribution of the CO 2 fluxes that honor the histogram and variogram of the original data. Moreover, the relation between the sample design and the uncertainty of estimation was investigated leading to an empirical relation between uncertainty and the sampling density that can be useful for the planning of future CO 2 flux surveys. Citation: Cardellini, C., G. Chiodini, and F. Frondini, Application of stochastic simulation to CO 2 flux from soil: Mapping and quantification of gas release,