The formation of hydrogen-emitting “fairy circle”

Natural hydrogen is emerging as a promising sustainable energy source with a negligible carbon footprint. Among the most striking surface indicators of subsurface hydrogen production are “fairy circles”, distinctive, sub‑circular features marked by anomalous vegetation patterns and subtle topographic depressions, often with depth‑to‑diameter ratios as low as 1:100. While previous numerical studies have examined soil‑gas hydrogen anomalies associated with active fairy circles, the mechanism responsible for the observed surface subsidence has remained unclear.

Here, a geomechanical model grounded in soil‑mechanics principles is developed to explain the formation of these depressions. Using coupled simulations of two‑phase flow and volumetric deformation driven by changes in effective stress, the model reproduces surface expressions consistent with those observed in natural hydrogen‑emitting fairy circles. These results provide a physically plausible mechanism for the development of fairy‑circle topography and offer a framework for interpreting surface indicators of subsurface hydrogen generation.