Periglacial processes and deposits

Periglacial environments experience cold-climate nonglacial conditions and ground freezing. Some are underlain by permafrost, whereas others experience seasonal, intermittent or shorter periods of freezing. Their ground thermal regime is influenced by a dynamic buffer layer of snow, vegetation, organic material and water that thermally modulates the interactions between the atmospheric and ground climate. Three groups of processes, structures and deposits characterize periglacial environments. (1) Ground cooling and freezing processes comprise thermal contraction, volumetric expansion (of freezing liquid water), ice segregation, and syngenetic permafrost growth. (2) Ground warming and thawing processes consist of thermal expansion, thaw consolidation and thermal erosion. (3) Recurrent freeze-thaw processes involve cryoturbation and solifluction. These processes produce a variety of distinctive periglacial and permafrost structures and deposits. The most important relate to the growth and thaw of ground ice, which denotes all types of ice contained in freezing and frozen ground, irrespective of the form of occurrence, or origin of the ice. Collectively, the overall effects of periglacial processes in modifying the landscape are term periglaciation. Periglaciation is clearest in thermokarst landscapes that develop where ice-rich permafrost thaws and in unglaciated lowlands underlain by frost-susceptible soil and brecciated bedrock.