When the frozen ground reaches very low temperatures, it contracts, splitting up to form a pattern of polygonal cracks. Anderson (1998) Arct. & Alp. Res. 30, 4 defines the frost cracking window—the optimal thermal range for frost cracking—as between –3º and –10º C. See also Grab, Geografiska A 89, 3. Vegetation and accumulations of organic matter may reduce the likelihood of frost cracking by creating a layer of lower thermal conductivity relative to bare soil, provided the area is not water saturated (Murton and Kolstrup (2003) PPG26, 2).
Subjects: Earth Sciences and Geography.