Non-volcanic CO_2 Earth degassing: Case of Mefite d'Ansanto (southern Apennines), Italy

摘要

Mefite d'Ansanto, southern Apennines, Italy is the largest natural emission of low temperature CO_2 rich gases, from non-volcanic environment, ever measured in the Earth. The emission is fed by a buried reservoir, made up of permeable limestones and covered by clayey sediments. We estimated a total gas flux of ～2000 tons per day. Under low wind conditions, the gas flows along a narrow natural channel producing a persistent gas river which has killed over a period of time people and animals. The application of a physical numerical model allowed us to define the zones which potentially can be affected by dangerous CO_2 concentration at breathing height for humans. The geometry of the Mefite gas reservoir is similar to those designed for sequestering CO_2 in geological storage projects where huge amounts of CO_2 should be injected in order to reduce atmospheric CO_2 concentration. The approach which we have used at Mefite to define hazardous zones for the human health can be applied also in case of large CO_2 leakages from storage sites, a phenomena which, even if improbable, can not be ruled out.