Frost Sorting

Frost sorting refers to the differential movement of particles of different sizes during frost heave and subsequent settling. Sorting involves a combination of frost-related processes, including needle ice development and frost heaving. The complexity of frost sorting is reflected in the diversity of patterned ground forms observed in the Arctic landscape. The sorting mechanism is most comprehensively understood from the work of Corte (1966), who recognizes three fundamental sorting mechanisms. First, sorting by heave when freezing and thawing occurs from the top. Large particles move upward and fine particles move down, giving rise to vertical sorting. Coarse particle migration is enhanced by the combined effects of frost pull in which the fragments fail to return to their points of origin, and by frost push resulting from preferential growth of segregated ice beneath coarse fragments due to their higher thermal conductivity. Secondly, sorting by migration ahead of a moving freezing plane in which freezing and thawing may take place from either the top or the sides. Under these conditions, fine particles migrate away from the freezing front and coarse particles remain in proximity to the cooling site. This results in lateral sorting. The third mechanism involves mechanical sorting in which mounds and frost heaved structures are produced. Coarser particles migrate, forming borders around finer particles. The regularity and perpetuation of these sorted forms is best explained by the development of convective cells associated with density differences within thaw water of the active layer during the thaw season.

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