The exhalations of CO₂ in the Poprad River valley (Polish Inner Carpathians)

The Krynica tectonic-facies zone within the Magura Unit of the Polish Inner Carpathians contains a region rich in carbonated mineral waters and in moffettes, i.e., dry exhalations of carbon dioxide. The lithostratigraphic profile spans the strata from the Upper Cretaceous to Upper Eocene. The region of the moffettes studied is situated in the Poprad River valley between Muszyna and Tylicz. The exhalations have been found in the Złocki stream and Jastrzębik stream valleys near Muszyna, in the Szczawiczny stream valley near Krynica and in Tylicz. The largest and most beautiful exhalation with an area of about 25 m² occurs in the bottom of the Złocki stream valley. Both this exhalation and the smaller, adjacent exhalations and the springs of carbonated waters are associated with the Szczawnik-Złocki-Jastrzębik antiform structure and with a system of discontinous dislocations, i.e., a thrust and faults. The emanating gas represents almost pure CO₂ (about 99.3%) with minor admixtures of CH₄, N₂, Ar and other noble gases.
   The upper surface of the basement of the Carpathian orogen in the Poprad subregion rests at a depth of about fifteen kilometers. The origin of the gaseous components – particularly of CO₂ – is usually attributed to metamorphism of carbonates rocks under the thick cover of overthrusted flysch strata and/or to Tertiary volcanism. The volume of carbon dioxide emanating from the moffette in question is about 15,000 m³ CO₂/day. The maximum content of CO₂ in the soil air close to the moffette reaches 94%. The temperature of the emanating gases is around +10ºC, both in the Złockie site and in other moffettes of the region.
   The moffette is partly covered by the water of the stream and also by the water flowing out of submerged springs of carbonated mineral waters, thus the emanations are manifested by smaller or larger bubbles of carbon dioxide. They are accompanied by rusty-coloured, gelatinous floccules of colloidal hydrohematite and goethite, the minerals originating by oxidation and hydrolysis of hydrated ferrous carbonate contained in the mineral waters mentioned. The process is a result of metabolism of the green plants populating this habitat (forest bulrush Scirpus silvaticus is a dominating species), and also of ferruginous bacteria Ferribacterium sp., cyanide plants (Cyanophyceae), euglenines (Euglenophyceae), diatomeae (Bacillariophyceae) and green algae (Chlorophyceae).
   In the year 1998 the moffette in Złockie was declared a legally protected site as the Professor Henryk Świdziński monument of inanimate nature and later placed on a proposed European list of protected geosites (European List of Geosites).
   Acknowledgements: Research has been supported by AGH – University of Science and Technology in Cracow, grants no. 11.11.140.447 and no. 11.11.140.598.