Natural Molecular Hydrogen Seepage Associated with Surficial, Rounded Depressions on the European Craton in Russia

In the Russian part of the European craton, several thousands of subcircular structures ranging in size from a hundred meters to several kilometers in diameter have been identified throughout the region extending from Moscow to Kazakhstan. Generally, these structures correspond to minor morphological depressions. In cultivated areas, the periphery of these structures is often outlined by a ring of soil bleaching associated with growth anomalies of vegetation. The cores of the structures commonly correspond to marshes, sometimes with lakes. Subsoil gas composition of these structures was studied. For this purpose, portable gas detectors were used, and the results obtained were confirmed by gas chromatography analysis. Inside and around these structures, the concentration of molecular hydrogen in soil was much greater inside than outside, up to 1.25% at 1.2 m in soils. The hydrogen is associated with a small quantity of methane. We estimated a daily hydrogen flow seeping out at the surface is between 21,000 and 27,000 m(3) in one of these structures.