Permafrost

PERMAFROST, a layer of permanently frozen ground that constantly maintains a temperature below 0° and is located at a certain depth from the earth's surface. The phenomenon of permafrost is caused by a combination of a number of factors. The existence of a permanently frozen soil layer is possible only where a given location ultimately radiates more heat into space over the course of a year than it receives from the sun, i.e., when the average annual temperature of the location is below 0°. Therefore, permafrost is found mainly in regions with a cold climate. The presence of thawed or frozen soil and the thickness of the frozen layer are closely related: 1) to the climatic conditions of a given location—the average annual temperature, the thickness and duration of the snow cover; 2) to soil conditions: the composition of the soil, its thermal conductivity, the degree of moisture, and the presence or absence of soil water; 3) to the character of the vegetation cover; 4) to the topographical data of the terrain: altitude above sea level and slope in relation to the cardinal directions. A higher temperature, greater development of snow cover, relative dryness of the soil, absence of a continuous moss cover, greater absolute altitude of the location, a slope facing south, and the presence of flowing water hinder the formation and preservation of soil permafrost. The thickness of the permafrost layer varies: from 0.4 m to 70 m. Above the permafrost layer lies a layer of summer thawing, which in different places has a different, but usually small, thickness (from 25 cm to 4 m). In a number of places, the upper horizon of permafrost lies relatively deep (from 10 to 30 m), and even in winter, a layer of thawed ground of varying thickness remains between the layer of winter freezing and the permafrost layer. Cases of alternating frozen and thawed ground are encountered. One of the types of permafrost is so-called ground ice. The southern boundary of permafrost is rather indefinite and in the Northern Hemisphere covers large areas of the northern parts of Europe, America, and northeastern Asia. The region occupied by permafrost is divided according to the nature of the distribution of this phenomenon: 1) into an area of continuous distribution (stable permafrost), 2) into an area of permafrost with the presence of more or less significant island sections of thawed soil, and 3) into areas of island distribution of permafrost among vast thawed spaces. Within the USSR, the southern boundary of the area of continuous distribution of permafrost runs from Novaya Zemlya through the mouth of the Ob to Turukhansk, Yakutsk, and further to the northeast to Anadyr. The southern boundary of the island distribution of permafrost goes from Norway through the Kola Peninsula to Arkhangelsk, Turukhansk, then descends to the southeast to Yeniseysk, goes east through Ulaanbaatar, Blagoveshchensk, and further to the northeast through Okhotsk to the northern part of Kamchatka. In this strip in Transbaikalia, a vast island of continuous permafrost distribution is noted. Thus, within the USSR, the area of permafrost distribution is approximately 7 million km², which constitutes one-third of its entire territory. Permafrost exerts a great influence on the physical-geographical features of the terrain, causes the origin of certain forms of microrelief (peat mounds in tundras), and causes waterlogging of the surface, the formation of ice crusts in rivers, anchor ice, etc. With high-rising horizons of permafrost, it exerts an influence on the vegetation cover. Permafrost exerts an influence on mineral springs; especially in Transbaikalia, the extremely low temperature of almost all springs in Transbaikalia is explained by it, which also affects their chemical composition in the sense of a high content of dissolved CO₂. The conditions for the emergence of mineral springs to the surface also depend on the frozen layer: the melting of permafrost causes a change in the location of the springs' emergence (see Transbaikalian resorts). The presence of permafrost causes great difficulties in earthworks, in the construction of roads, water supply, the erection of buildings, etc.