Permafrost Distribution Temperature

According to its geographical position the cryolithozone is subdivided into subaeral, shelf and subglacial. The subaeral cryolithozone is the most widespread and is usually made up of surface-laying permafrost. The shelf cryolithozone is typical for arctic seas of the Siberian sector of the Russian Federation. The subglacial permafrost underlay glacial covers on the northern islands and in highlands. Strictly speaking permafrost is not restricted to the polar territories, but rather it extends both under glaciers and on iceless mountain ridges in lower latitudes (fig. 5 and also fig.2).

Circumpolar Maps With Latitude
Figure 5. Circumpolar map of permafrost. Eurasian sector.

Alpine permafrost can be found in the Caucasus, in Mongolia and in Tien Shan. In Tien Shan (i.e. at the latitude south of the Caspian Sea and Japan) the alpine permafrost areas are more than the whole Northland. Nevertheless alpine permafrost in low latitudes is rather an exotic event, and thus northern and eastern regions are the dominant areas of permafrost distribution.

Permafrost can be subdivided into 4 types based on unit continuity: i) continuous (frozen rocks occupy 90-100% of the territory); ii) discontinuous (50-90% permafrost); iii) island or sporadic (10-50% permafrost); and iv) isolated patches (0-10% permafrost). Their distribution is controlled by strict latitudinal (for plains and mountains) and altitude (for mountains) zonality (fig. 6). The boundary of the continuous permafrost distribution shifts more and more southward as it moves from west to east. Permafrost temperature decreases in the same direction (from -2 to -100° C and below), while its thickness increases in the plains (from the first tens of meters to 300 - 500 m and more) and in mountain ridges (up to 1500 m).

Mountains t Lowlands

Mountains t Lowlands

Permafrost Distribution
Figure 6. Permafrost in Russia: Space distribution, iciness and temperature at the depths of zero seasonal amplitudes. [by E.S. Melnikov, K.A.Kondratieva, G.F.Gravis].

Local natural and human factors are superimposed on the zonal and altitude regularities of the permafrost distribution, thus highlighting the local changeability of the geocryological conditions. For example, taliks can appear in continuous permafrost in river valleys and lake depressions due to the defrosting effect of the hydrosphere, while frozen sites can disappear completely in the sporadic permafrost zone. Various natural and man-made cooling factors (for instance, wind erosion or snow removal) can cause the formation of permafrost islands even outside the cryolithozone.

The continuous permafrost zone is the largest (fig.6). On the plains of the Russian European north it stretches out along the coast in a 100 to 200 km wide strip. Its southern limit coincides approximately with the polar circle in the ranges of the West-Siberian Lowland, and it reaches the latitude of Lake Baikal in eastern Siberia and Yakutia.

The discontinuous permafrost zone stretches out in a very narrow strip in the European north, and then in western Siberia it widens up to several hundreds of kilometres. Eastward discontinuous permafrost is basically localized to the intermountain troughs or to the coastal plains south of the 60th parallel.

Sporadic permafrost and isolated patches of permafrost extend up to the latitude of the polar circle in Europe and up to the 60th parallel in western Siberia. In the more eastern regions it extends to the southern frontier of the Russian Federation.

Figure 7. The extent and temperature of permafrost in the Timan-Pechora oil and gas province: 1-4 -permafrost types: 1— continuous, 2 - discontinuous, 3 - sporadic, 4 - isolated patches; 5 - non frozen and thawed soils; 6 - permafrost relict contour; 7 - permafrost temperature isograms; 8 -cryopegs.

Figure 7. The extent and temperature of permafrost in the Timan-Pechora oil and gas province: 1-4 -permafrost types: 1— continuous, 2 - discontinuous, 3 - sporadic, 4 - isolated patches; 5 - non frozen and thawed soils; 6 - permafrost relict contour; 7 - permafrost temperature isograms; 8 -cryopegs.

Relict permafrost bedding occurs at a depth of tens to hundreds of meters below the earth's surface, often separated by thawed (lateral) ground horizons from the overlying modern superficial permafrost. The relict permafrost can form a single stratum, layers or separate fragments. The vast lobe of relict permafrost in the south of western Siberia is well seen on fig.6, while the zone of relict permafrost in the European north is well seen on fig.7.

Relict permafrost has been the result of cyclic changes in climate and the alternation of warm and cool epochs, with many being due to the heritage of ancient Upper-Pleistocene cooling epochs. However it would be incorrect to assume that relict permafrost layers are a single dimensional formation. The long-term history of its evolution has resulted in the formation of numerous taliks that have broken down the single whole into many isolated patches (fig.8).

Elevator) S P fi. Isolated natrhGS

Elevator) S P fi. Isolated natrhGS

Permafrost Holocene
Figure 8. Relict permafrost. The thickness of relict permafrost decreases gradually from the north to the south. Local isolated subsurface patches of modern (Holocene) permafrost can be found to the north of Kogalym city. Their thickness could achieve 20-30 m. [by G.V.Malkova].

Continuous permafrost is a good aquiclude, and it is a reliable foundation for construction if the proper technologies are applied. The active exchange between supra- and sub-permafrost ground waters takes place in the zone of discontinuous permafrost, and pre-thawing is required before building at temperatures close to 0°C. Sporadic and island permafrost is also a complicating factor from a hydrogeological and engineering point of view.

The sites of unfrozen rocks in all types of permafrost are referred to as taliks, which can be subdivided into closed, open and lateral taliks. Their formation has been conditioned both by geological and paleoenvironmental evolution and by recent warming factors. So-called "cryopegs" occupy a unique place in talik classification, as they are unfrozen sites and horizons, despite sub-zero temperatures, within rocks hosting saline waters. Predominantly these are either deep horizons of ancient rocks under many-hundred-meters thick permafrost strata saturated with brines, or the shallow-laying bedrocks or sedimentary rocks with marine saline waters along the northern coasts (fig. 7). The presence of cryopegs testifies to the importance of geochemical and hydrogeochemical factors in the distribution of frozen and unfrozen rocks in the cryolithozone.

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