underground ice deposits, accompanied by the change in properties, consolidation and soaking of soils when thawing.

The second group comprises fluvial, abrasion and water balance processes arising from mechanical and thermal effects of water masses over frozen and thawing soils, annual variations of heat exchange over the soil surface and long-term variations of water balance over the surface. This group includes thermal abrasion, thermal erosion and waterlogging. For all these there are analogous processes outside the permafrost regions. However, these processes should be included in an independent group with regard to the specific nature of their occurrence in the permafrost. Development of all the above processes is always preceded by thawing of soils accompanied by disturbance of structural relations in the soils and changing of their physical-mechanical and thermal-physical properties. The specific nature of the processes is revealed in the particular forms of meso- and microrelief, in the transformation of the cover of loose deposits and in the formation of specific genetic types of new geological units (for example, in appearance of syn-cryogenic lacustrine and coastal-marine deposits, diluvial and talus deposits, in the accumulation of peat, etc.).

The third group of processes integrates gravitational processes, such as solifluction, sliding, slipping, talus, deserption, rock stream formation and the like. Some of the processes have analogies beyond the cold regions. However, all the gravitational processes without exception that occur within the cold regions are characterized by a specific nature of manifestation leading to the formation of specific shapes of meso- and microrelief such as rock streams, rock fields, solifluction terraces or covers, streams and terraces. Besides, these processes in the cryolithic zone are responsible for the formation of a specific composition and structure of slope wash (solifluction, talus, colluvial sliding and similar deposits); they are associated with burial of firn, ice bodies and glacier ice in these deposits, with the formation of cave and golets ice; and with cryogenic grading of the material and other special characteristics.

0 0

Post a comment