Brief note on several notable features in the periglacial zones

There are characteristic geomorphic processes and landforms in the areas, which are adjacent to those polar and subpolar regions, as well as high mountains of lower latitudes, which are covered with permanent ice sheets, snowfields and glaciers.

There are two kinds of periglacial zones. One type is those of the present times. The other type is those of the Pleistocene Ice Age. Then the ice-sheets of the higher latitudes and Polar Regions and the snowfields of the high mountains were more extensive than now. The periglacial zones were more extensive. Periglacial geomorphology concerns itself both with the present-day and Pleistocene periglacial zones. Obviously, the landforms of the Pleistocene periglacial zones are of ‘fossil’ type belonging to such areas where the conditions causing the formation of the then landforms have disappeared.

There are several notable features in the periglacial zones:

(i) Permafrost, i.e., a soil or rock which is permanently frozen. Any water that occurs amidst the particles of soil or in the pore spaces in rocks is in the form of ice.

(ii) Above the permanently frozen ground there is a layer below the surface of the ground, which undergoes thaw during summer and freeze during winter. This freeze-thaw layer is called active layer and is responsible for important geomorphic processes and forms. Its thickness is variable but usually it ranges from a fraction of a meter to 4 meters or so. It is usually thickest where the permafrost is the thinnest.

(iii) One of the notable features of periglacial regions is the occurrence of several patterns on the ground, e.g., polygons, circles, steps and stripes. Such phenomena are designated as patterned ground and are believed to be due to such processes as contraction and expansion associated with freeze-thaw, contraction of ice under extremely low temperatures and migration of water in the rocks and soils. Patterned ground be seen in lower latitudes also. Thus, we frequently see polygons developed in the clayey fields or on the floors of lakes, ponds and in chaurs (depressions waterlogged during rains). These patterns are due to the cracks formed owing to the reduction of volume after a good deal of water has evaporated. In the periglacial regions, the processes and factors for patterned ground are different.

(iv) Solifluction, i.e., slow movement of soil mass owing largely to the freeze-thaw action of water contained therein produces several characteristic forms.

(v) During arid periods the sediments comminuted into clay and silt by various processes in the glacial regions and brought to the periglacial zones are blown out and deposited as loess, which form one of the characteristic landforms of the periglacial regions.

(vi) In the areas of well-jointed rocks the ground in the periglacial zone may be occupied with fractured rock mass called felsenmeer or blockfield. On sloping land, adjoining blockfields there may be stone rivers. There may be pieces of flat surfaces on the hillsides. These are known as altiplanation terraces.

Various workers have assigned different causes for their origins, e.g., constructional features due to rock waste or intensive frost action in slight depressions developed in well-joined rocks.

Tors, which occur in most regimes ranging from high to low latitudes, are believed to be a characteristic geomorphic feature of periglacial areas. These rock masses occurring singly or in groups, usually marked by steep sides, and cleared of debris from the tops, slopes as well as the base are one of the controversial topics of geomorphology but one view is that freeze-thaw action succeeded by solifluction may account for them.

Nivation, i.e., freeze-thaw, solifluction and avalanches wherever they occur, are among the major landscape-forming processes of the periglacial regions. But as will be apparent from the foregoing introduction, as regards relief, the periglacial landforms are of minor nature.

Demek has emphasized the applied aspects of periglacial geomorphology. He points out that there is an intimidate relation between the reservoirs and dams that are now being constructed in periglacial zones and the permafrost. Water in the reservoirs may cause melting of the ice in permafrost and escape of reservoir water. Gas and oil pipelines or railways and roads are also related to permafrost regarding the firmness of their base.