Classification of processes and phenomena

Exogenous geological processes and phenomena in the permafrost regions are often referred to as cryogenic (frozen ground) geological processes and phenomena. They are due to the development of the thermal-physical, physico-chemical and mechanical processes that occur in freezing, frozen and thawing soils, which were considered in the previous chapters. The specific features of exogenous geological processes in the permafrost zone are determined by the cyclic recurrence of freezing and thawing, cooling and heating, by the properties of frozen, perennially frozen and thawing soils, by the variability with time of ground stresses etc. These lead to the different cryogenic phenomena (formations) that contribute to the geological structure of loose Quaternary deposits and manifest themselves in the topography and micro-terrain within the area of permafrost as well as in the area of deep seasonal freezing. With regard to the basic agencies of the environment which are the driving forces for the processes and phenomena, all the exogenous processes in the cryolithic (permafrost) zone may be subdivided into three major groups (Table 5.1).

The first group comprises the cryogenic processes proper (frozen ground geologic processes) caused by seasonal and long-term variations of heat and mass exchange over the ground surface and in the underlying materials. These are frost cracking and frost weathering caused by multiple recurrence of freezing and thawing, and cooling of frozen soils in the layer of annual temperature variations (the layer of seasonal freezing and thawing included) together with the dynamics of the state of stress in the variable temperature field; frost heaving of soils and icings conditioned by seasonal and long-term freezing of soils, ground and surface water (in icings), with the enlargement of soil volume during segregation of ice; thermokarst associated with seasonal and long-term thawing of soils with a high ice content and of

Table 5.1 Classification of the principal exogenous geological processes in the permafrost regions (according to E.D. Yershov and L.S. Garagulia)

Manifestations of the process

Group of processes

Kind of process in the relief in the deposits

I. Cryogenic processes proper

Frost cracking and formation of ice-wedge polygons

Cryogenic weathering of rocks

Frost heaving of rocks

Icing

Perennial ice and snow formation over rock surfaces

Polygonal fissured micro-relief

Polygonal and polygonal-dike relief

Disintegrated polygon blocks, block fields

Areas of heaving

Seasonal and perennial mounds, hydro-laccoliths Round spots and cryoturbations Stone rings and stone wreaths

Thufurs (small frost mounds) Mounds (formed with participation of frost cracking)

Seasonal and perennial ice bodies Glaciers

Open vertical fractures

Systems of ice wedges, ice-ground, ground and sand veins in deposits of alluvial, slope, eolian and other origins

Fragmental-block formations of the upper layer of eluvial materials (golets eluvium) Cavities and ice interlayers over soil bed

Ice inter-layers and ice cores in frost mounds

Pot-holes of mixed ground (folded) Soil-rock waste and rock waste-block veins

Peaty deposits of mounds Mineral soil in mounds divided by open fractures, soil or peat veins Alluvium with icings and ice sills Glacial ice

Table 5.1 (continued)

Group of processes

Kind of process

Manifestations of the

process

in the relief

in the deposits

0 0

Post a comment