Gas Hazard from Natural CO2 Emissions in Central and Southern Italy.

Details Gas Hazard from Natural CO2 Emissions in Central and Southern Italy. Gas Hazard from Natural CO2 Emissions in Central and Southern Italy.

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.h14a..05c&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #H14A-05

Mathematics

Logic

0468 Natural Hazards, 1000 Geochemistry, 1009 Geochemical Modeling (3610, 8410), 1012 Reactions And Phase Equilibria (3612, 8412)

Scientific paper

Recent studies at regional scale showed that the central and southern Italy are affected by an active and intense process of CO2 Earth degassing. Considering the deeply derived carbon dissolved in the groundwater of large regional aquifers, Chiodini et al. (2004) elaborated a regional map of CO2 Earth degassing, pointing out the presence of two large CO2 degassing structures (62000 km2) a northern one, the tuscan roman degassing structure (TRDS) and a southern one, the campanian degassing structure (CDS). The deeply derived CO2 released by these two structures was estimated in ~ 9.2 Mt/y (Chiodini et al., 2004). This amount, which is globally relevant being ~ 10% of the present-day total CO2 discharge from subaerial volcanoes of the Earth, is of low magnitude with respect to the amount of CO2 that is estimated to be injected in the storage sites. TRDS and CDS are characterized by the presence of many vents of cold CO2 rich gases and areas of anomalous soil diffuse degassing of CO2. The gas manifestations are generally fed by buried carbonate reservoirs, covered by low permeability formations, where the gas produced at depth accumulates before the expulsion at the surface. More than 100 gas emissions are located in the Italian territory and represent a serious hazard for humans and animals. Gas flow rates are very high. For example, the biggest gas emissions daily release into atmosphere hundreds of tons of CO2, amounts similar to those released by diffuse degassing from active volcanoes (CO2 fluxes from 6 t/d to 2800 t/d, mean of 430 t/d, Morner and Etiope, 2002). Under stable atmospheric conditions and/or in presence of topographic depressions, CO2 air concentration can reach high values resulting in lethal effects to humans or animals. The last lethal accident occurred in 2003 in Tuscany, at Mt. Amiata. However, the most dangerous gas emission is Mefite d'Ansanto, located in the Southern Apennine, where three persons were killed during 1990's and historical chronicles describe the death of many other people during the 17^{th} century. Here a gas river is fed by a CO2 vent releasing ~ 1000 ton/d of gas. The numerical simulation of the gas river obtained using a code based on a shallow layer approach (TWODEE) shows that a large area is interested by lethal CO2 concentrations at 1.5 m above the ground for different wind conditions. Geological settings and typical gas flow rates which characterize dangerous situations of gas dispersion are investigated and discussed. References: Chiodini et al., 2004. Geophys. Res. Lett.. L07615, doi:10.1029/2004GL019480; Morner and Etiope, 2002. Glob. and Planet Sci: 33, 185-2003

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