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by Vladimir Kotlyakov and Tatyana Khromova
Copyright 2002, International Institute for Applied Systems Analysis and the Russian Academy of Sciences
The rigorous continental climate of Siberia and the north half of the Far East is the reason for permafrost formation. These territories occupy an area greater than 10 million square kilometers (km2). In the European part of Russia, permafrost occurs only in the tundra and the forest-tundra zone. Its southern boundary goes from the Kola Peninsula to the mouth of the Mezen River and further on almost along the Arctic Circle to the Urals. In West Siberia, the permafrost border runs along the Enisei River near the River Podkamennaya Tunguska, where it sharply turns to the south and goes along the right bank of the Enisei River. To the east of the Enisei, the permafrost is spread almost everywhere, except for south Kamchatka, Sakhalin Island, and Primorjie.
Three types of permafrost are distinguished on the basis of how they are propagated.
Continuous permafrost is distributed throughout the northern part of the Bolshezemelskaya tundra; on the Polar Urals; in the tundra of West Siberia; in the northern part of the Middle-Siberia tableland, on Taimyr Peninsula, Severnaya Zemlya, Novosibirskie Islands, Yano-Indigirka and Kolyma lowlands; in the mouth of the river Lena; on the plain of Central Yakutiya and on Prilenskoe plateau; on the Verkhoyanskii, Cherskii, Kolymskii, and Anadyrskii ranges, on the Yukagirskii tableland, and on Anadyrskaya plain. The thickness of perennially frozen layers is around 300-500 m and greater; a maximal thickness of 1,500 m was recorded in the basin of the river Markhi, which is one of tributaries of the Vilyui River. As a rule, the rock temperature varies from -2 down to -10 deg. C, but sometimes it can be lower.
Discontinuous or sporadic permafrost occurs in the Bolshezemelskaya and Malozemelskaya tundras; on the Middle-Siberian tableland between the rivers Nizhnyaya and Podkamennaya Tunguskas; in the south part of the Near-Lena plateau, and in Zabaikaljie. The thickness of the layers here varies from 10 to 150 m, but sometimes reaches 250-300 m. The temperatures are usually from -2 up to 0 deg. C.
Insular permafrost occurs on the Kola Peninsula; on the Kanin Peninsula; and in the Pechora River basin; in the taiga zone of West Siberia; on the south of the Middle-Siberian tableland, along the coast of the Sea of Okhotsk; and on Kamchatka. The thickness of the layers are from several meters to several tens of meters, and the temperatures are close to 0 deg. C. Insular permafrost occurs in the mountains, frequently along the periphery of regions of contemporary glaciation.
The perennially frozen rocks always contain ice in their mass. These can be loose clusters of sublimation ice in caves and other underground cavities; lenses and veins of ice inside the rocks; or continuous ice bodies in the ground mass. Large ice masses form recurrent-fissure ices. The formation of ice bodies lasts for hundreds and thousands years; as a result, they grow up to 50 m in height and 5 m in width.
On Russia's territory, the mass of the recurrent-fissure ices amounts to approximately 1 thousand km3. The best conditions for their formation were developed on the plains of the north of Eurasia during the last Ice Age, 17-20 thousand years ago. To this day, grandiose ice exposures in scarps of the northern seas, and along banks of rivers and lakes remain. On Novosibiskie Islands and on the East Siberian Sea coast the ice wedges have joined into an almost continuous ice massif.
Perennial mounds of cryogenic heaving occur in the regions of the perennially frozen rocks. The so-called bulgunyakhis (or boolgoonyakhs, which is the local Yakut name for hydrolaccoliths) are formed on the bottoms of dried and drying lake depressions, they reach 40-70 m in height, measuring several hundreds meters at the base. When outcrops or underground waters freeze, hydrolaccoliths with an ice core inside appear. These are mounds from 25 to 40 m high with a base of tens, and sometimes hundreds, of meters. They most frequently occur on Taimyr, in the north of West Siberia, in Zabaikaljie, and in Yakutiya.
Under persistent melting through of the icy rocks, special forms appear on the surface, forms like sinks, hollows, craters (cones), depressions with lakes and without lakes, and original sink-mound relief which is called a thermokarst. In Central Yakutiya, i.e., on the Lena-Amra and Lena-Vilyui interstream areas, the underground ice melting results in formation of alases. These are spacious, often forestless, flat-bottom depressions with areas of several square kilometers. Alases are occupied with lakes, mires, and meadows.
Two types of ice content (iciness) are possible in perennially frozen rocks: cryptic (invisible) (latent) ice and visible (evident) ice. When melting down, the first type remains in the ground as a bound water, while the second transfers (transforms) into a free gravitational water, i.e., it becomes involved in water circulation. The thickness of the icy horizon depends on the composition and moisture of the rock before it freezes, as well as on hydrological and geological conditions, the manner of formation, and a history of the permafrost layer development. The thickness varies from 1 to 60 m and greater; however, the main mass of ices is concentrated in the upper 10 to 20-meter layer of perennially frozen rocks. The total amount of underground ice is inversely proportional to its concentration in the Earth's crust, i.e., the larger the ice bodies (deposits) of underground ice, the more rarely they occur.
On Russia's territory, the total mass of underground ice amounts to approximately 19,000 km3, and of prime importance here are the recurrent-fissure ices and stratified deposits of underground ice. The recurrent-fissure ices have a dominant role in the north of West Siberia, in Central Yakutiya, and on coastal lowlands of North Yakutiya. Stratified ice deposits occur especially frequently on the north of West and Middle Siberia, and on coastal lowlands of Chukotka. The greatest volumetric ice content (iciness) of perennially frozen rocks (more than 40%) is noticed on the Arctic coastal lowlands of Russia, in the Central Yakutiya, and on individual areas of mountain regions to the north of East Siberia and Zabaikaljie.
Naled is a stratified ice mass on the surface of the Earth; one is formed as natural or technogenic waters are repeatedly forced out and freeze. They mainly occur in zones of perennially frozen mountain rocks, which occupy almost half of Russia's territory. The volume of underground or river water frequently turns out to be larger than that which can be retained underground or within rivers covered with ice. The result is that a part of the water pours out onto a surface and freezes.
On Russia's territory, about 94 km3 of water is accumulated in naleds of river (45%) and underground waters (55%). This is approximately equal to a volume of annual runoff from two rivers like the Indigirka. The total area of naleds of both types amounts to about 128,000 km2.
On the whole, the number and areas of naleds increase as one moves from the southern boundary of perennial permafrost to the north. They also increase with a growth of absolute altitude in the mountains, except for the most northerly and highest territories, where hydrological and geological structures and watercourses are strongly frozen through. In mountains, average thickness of naleds of underground waters is about 2-2.5 m; the maximal value reaches 10-12 m; and the area, tens of square kilometers.
In the northeast of Russia, the portion of naleds in an annual river runoff generally ranges from 1%-3% to 10%-15%. In basins with a great number of naled massifs, the coefficient of the naled nourishment of rivers reaches 30%-40%.