Mixing of endogenous CO and meteoric HO causes extremely efficient carbonate dissolution.

Karst corrosion of carbonate rocks by water with dissolved gases proceeds in most cases along two major scenarios: (i) meteoric water absorbs CO from soil and atmosphere, or (ii) ascending water of deep circulation carries with it dissolved endogenous gases, mainly CO and HS. We have observed a peculiar variant where meteoric water absorbs ascending endogenous gases at a natural gas vent on a travertine mound in Slovakia. Carbonate dissolution's extreme effectiveness is demonstrated by mineralization of rainwater ponded at a gas vent, rising to 3.2 g/L of dissolved solids shortly after the rainfall. One liter of water ponded at the vent and mixing with the venting gas, dissolved up to 800 mg of calcium at a rate exceeding 5.8 mg/L·min. Limestone tablets placed at the vent show signs of significant corrosion, at rates up to 126 mm/ka. The rate is comparable to those in coastal karst, where freshwater is mixing with seawater and to those in sulfuric acid speleogenesis (SAS), both the highest hitherto known rates of karst corrosion in carbonates. The geomorphic effects of the process described are depressions on the surface of travertine near the vents of endogenous CO This type of corrosion seems to be universal and probably occurs everywhere where endogenous CO is exhaled to the surface from carbonate rocks.