Patterned ground

Patterned ground in periglacial environments is developed through repeated freezing and thawing of moist, frost-susceptible soil, typically forming circles, polygons, irregular nets and stripes. Sorted patterns are defined by fine cells with coarse borders, and nonsorted patterns by vegetation or microrelief. Most patterns evolve though differential frost heave that develops a stable wavelength through self-regulating feedback processes and/or buoyancy-driven soil circulation. Large sorted patterns and nonsorted circles (frost boils) mainly form above permafrost; small sorted patterns are produced by needle-ice heave. Earth hummocks and nonsorted circles may be initiated by differential frost heave, though buoyancy-driven soil circulation and diapirism may contribute to their subsequent development.