Seasonally Frozen Rock

rock that contains ice inclusions in its cavities and pores but does not remain frozen during the entire year. Seasonally frozen rock makes up the uppermost (active) layer of the cryolithozone—a layer that each year is warmed above 0°C—except for those areas of the layer in which the seasonal cooling of the rock is not accompanied by the crystallization of water; these areas include cryic areas, the shelf of polar seas, and outcroppings of massive rocks on the surface. On the margins of the active layer, the seasonally frozen rock gives way to briefly or periodically frozen rock (in middle and low latitudes) and to permanently frozen rock and underground ice, which may be exposed at the surface (in higher latitudes).

Seasonally frozen rock can be as much as 5 m thick in areas with an annual mean surface temperature of 0°C. It is thickest in the continuously permeable thaw areas of the permafrost zone. In higher latitudes, a number of specific cryogenic phenomena are closely related to the existence of seasonally frozen rock.