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Physical Geography of Northern Eurasia
Permafrost
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Distribution, Geothermal Regime, and Thickness of Permafrost
Permafrost occurs in various environments: polar, subarctic, middle latitudes, and
alpine (Baranov, 1959; Kudryavtsev et al., 19786; French, 1996). In Northern Eurasia,
permafrost is found in polar and temperate zones, in the mountains, and on the Arctic
shelf. Permafrost is classified according to its territorial extent, mean annual
temperature at the depth of zero annual amplitude, and thickness of frozen ground. In
terms of its territorial extent, permafrost is classified into one of the following
categories: continuous, discontinuous, massive-island (scattered). [In this chapter, the
terms 'massive-island' and 'island permafrost' will be used — synonymous terms are
'scattered permafrost' and 'sporadic permafrost'] and island (sporadic) (Kudryavtsev et
al., 1978a). The continuous permafrost zone is often referred to as the 'northern
geocryological zone' while the discontinuous, massive-island and island zones are known as
the 'southern geocryological zone' (Permafrost Science, 1981). In general, the spatial
extent and severity of permafrost conditions in Russia increase northwards and eastwards.
In the south, permafrost is young and its extent and thickness depend mainly on
contemporary climatic conditions; in the north, permafrost conditions are an imprint of
the Pleistocene climate (Kudryavtsev et al., 1978b). The regional distribution and
thickness of permafrost vary in response to changes in climate, relief, bedrock, extent of
water bodies, and vegetation. Mean annual temperature of permafrost is a function of heat
exchange in the contemporary landscapes (Kudryavtsev, 1965; Kudryavtsev et al., 1978a).
The southern permafrost boundary extends across Russia from the Kola peninsula in the
west to the Russian-Chinese border in the Far East. It crosses different landscapes:
tundra in the Kola peninsula, northern taiga, in the European north, northern, and central
taiga in Western Siberia, central and southern taiga in Eastern Siberia, steppe near the
Mongolian border, and the forest-steppe in the Russian Far East. Within Russia, permafrost
reaches its southernmost extent at 49°N in Transbaikalia. To the west of the Yenisey
river, the southern boundary has a sub-latitudal direction which is consistent with
climatic zonation (Figure 6.1).

Fig. 6.1 Distribution, temperature, and thickness of permafrost
To the east of the Yenisey, the boundary takes a sub-meridional direction and sharply
deviates to the south. There are two main reasons for this deviation: (1) an orographical
contrast between the low depositional plain of Western Siberia where the maximum height
does exceed 250 m, and the denuded tableland of the Central Siberian plateau with an
average elevation of 600 m; (2) the increasing continentality of climate. The domination
of the Siberian anticyclone over Eastern Siberia in winter leads to intensive radiational
cooling, which results in extremely low air temperatures, and ensures a small depth of
snow cover (see above). Along the southern boundary of permafrost in Western Siberia, the
mean winter air temperatures are about -20°C with snow depth in excess of 0.6 m, whereas
at the Central Siberian plateau the average winter temperatures vary between -23°C and
-27°C and snow depth does not exceed 0.5 m (Gavrilova, 1981). The southern limit of
permafrost lies between the -1°C and -3°C mean annual air temperature isotherms in the
European part of Russia, between the -2°C and -5°C isotherms in Western Siberia, and
coincides with the -3°C isotherm in Eastern Siberia and the Far East (Gavrilova, 1981).
The percentage of area underlain by permafrost increases northwards from 5-10 per cent
(island permafrost) at the southern edge to over 90 per cent (continuous permafrost) along
the Arctic coast and in the high mountains (Figure 6.1). Mean annual ground temperature
decreases and typical thickness increases from island to continuous permafrost.
The Continuous Permafrost Zone
Continuous permafrost occupies about 50 per cent of the total area of Russia's
cryolithozone. It occurs in the arctic, subarctic, and temperate climatic zones; in the
landscapes of polar desert, tundra, forest-tundra, northern, and central taiga; on the low
depositional and high eroded plains, and in the mountains. The southern limit of the
continuous permafrost coincides approximately with the -5°C mean annual air temperature
isotherm in European Russia, with the -7°C isotherm in Western Siberia, and with the
-8°C isotherm in Eastern Siberia (Gavrilova, 1981). Mean annual ground temperature (MAGT)
varies between -5°C and -15°C; thermal conditions are particularly diverse in the south.
The lowest MAGT is observed the Arctic islands and the Arctic coast of Sakha-Yakutia.
Conditions are milder southwards and westwards: both insolation and air temperature
increase, particularly in summer, as well as snow depth and the area occupied by lakes and
bogs which provide better insulation. Denser vegetation cover assists the accumulation of
snow in winter. These factors lead to an increase in permafrost temperature to -10°C
through to -5°C in the Western Siberian and Taymyr tundras and in the lowlands of
northern Sakha-Yakutia. The highest MAGT (between -5°C and -3°C) within the continuous
permafrost zone is observed in the northern tundra of European Russia, in the
forest-tundra zone of Western Siberia and in the taiga of the Lena-Vilyuy plain (Figure
6.1).
The lowest temperatures of mountainous permafrost (between -13°C and -15°C) occur in
the subarctic mountains of north-eastern Siberia3 (Geocryology of the USSR: Eastern
Siberia and the Far East, 1989). In the tundra and taiga regions of the mountains and
uplands of Central Siberia MAGT ranges between -10°C and -5°C; frequent and intensive
temperature inversions and cold air drainage are important controls over permafrost
temperatures in these regions. In the sparse forests of the inner and eastern parts of the
Central Siberian plateau, MAGT is higher and ranges between -5°C to -3°C. It should be
pointed out, that permafrost temperature in the mountainous regions varies greatly in time
and space as a result of the great variety of local controls such as aspect and steepness
of slopes (Kudryavtsev, 1965).
In the continuous zone, the thickness of permafrost varies from 100 m to more than 1000
m not only with latitude and altitude as a function of climate, but also in response to
variations in bedrock and Quaternary history. On the plains, frozen ground reaches a
maximum thickness of 400-600 m on the Arctic islands and in the narrow zone of the Arctic
coastal plain in northern Sakha-Yakutia (Geocryology of the USSR: Eastern Siberia and the
Far East, 1989). In tundra, the average thickness of frozen ground ranges between 300 and
500 m though sometimes it can be less, about 100 m as, for example, on the young marine
terraces of the Yamal peninsula (Figure 6.1), (Geocryology of the USSR: Western Siberia,
1989). The thickness of mountainous permafrost is often much greater than that on the
plain as a result of higher thermal conductivity of rocks (Feldman et al., 1988; French,
1996). In the mountains of northeastern Asia, in the northern part of the Central Siberian
plateau, and in the nival belt of Transbaikalia, permafrost exceeds 1000 m in thickness.
The thickest known permafrost exists on the Anabar tableland in the north-eastern Central
Siberian plateau where it extends to a depth of 1200-1470 m. [An estimated value of 1600 m
reported by Nekrasov (1976) and quoted by French (1996) is not supported by factual
evidence (Geocryology of the USSR: Eastern Siberia and the Far East, 1989)]. The extreme
thickness of permafrost is caused by a number of factors, such as high thermal
conductivity of bedrock, low geothermal flux which does not exceed 13-27 MW m-2
(Geocryology of the USSR: Central Siberia, 1989), and paleoclimatic conditions. In these
regions, which had never been glaciated, perennial freezing began in response to the very
low air temperatures in the Neogene and continued throughout the Pleistocene, lasting in
total about 15 million years. Westwards, permafrost thickness becomes smaller and in the
Polar Urals it ranges between 300 m and 500 m, while in the taiga regions permafrost
develops to a depth of 100-300 m (Geocryology of the USSR: European Territory of the USSR,
1989).
The Discontinuous Permafrost Zone
In the discontinuous zone, bodies of frozen ground exist alongside areas of thawed
ground (taliks) which occupy about one-third of the entire territory. The extent of
unfrozen ground increases westwards and southwards in response to climatic factors: the
increasing amount of received solar radiation, higher summer temperatures, longer summers,
and greater depth of snow cover (in the western part of the cryolithozone). In the western
regions, discontinuous permafrost occurs in the forest-tundra zone and at places extends
to the northern taiga regions. Typical MAGT ranges between -1°C and -3°C. Permafrost
thickness increases eastwards from 100-150 m in the north-eastern European Russia to
200-300 m in Western Siberia. In Eastern Siberia, discontinuous permafrost underlies the
northern taiga and forest belt in the mountains. Here, the average thickness is about
150-200 m while in the mountains of the Far East it is about 100 m (Figure 6.1).
Taliks are a characteristic feature of the discontinuous permafrost zone. They differ
in their origins and may form in response to the presence of surface and underground water
bodies, the heat effect of increasing solar radiation, and the insulating effect of deep
snow cover. Accordingly, two major types of talik are distinguished: hydrothermal and
thermal (Kudryavtsev et al., 1978a). The majority of taliks develop in response to the
local heat sources, such as water bodies. Taliks located under rivers and large lakes
which do not freeze to the bottom in winter are typical of the flat terrain of the western
cryolithozone. The intensive accumulation of snow, which protects soils from deep
freezing, causes the formation of thermal taliks under depressions and gullies. As a rule
these taliks are closed (i.e., entirely surrounded by permafrost) (Brown and Kupsch,
1974). In the eastern part of the discontinuous permafrost zone, hydrothermal taliks form
due to the heat supplied by ground water. The release of subpermafrost waters forms open
taliks along the cracking zones and in river valleys in the mountains and tablelands of
southern Central Siberia, Transbaikalia and the Far East (Geocryology of the USSR:
Southern Mountains of the USSR, 1989). In the monsoon regions of the Far East, warm
rainwater creates taliks by penetrating coarse-grained filtering sediments. On
south-facing slopes of Southern Siberia and the Far East mountains the formation of taliks
is controlled by solar radiation.
The Massive-island Permafrost Zone
In the massive-island permafrost zone, terrain conditions are a particularly important
control over the formation and distribution of frozen ground, which has a patchy
character. It is the variations in terrain that are primarily responsible for the
massive-island occurrence of permafrost as well as its temperature and thickness.
Peatlands are especially conducive to the formation of frozen ground and about 70 per cent
of the total peatland territory is underlain by permafrost. This is a higher share than in
the adjacent terrain (Regional Cryolithology, 1989). Peatlands have unique thermal
properties due to which, soils, underlying peat, cool faster in winter than they warm in
summer. Therefore, MAGT is lower (Feldman et al., 1988; French, 1996). In addition to
seasonal variability in thermal conductivity of peat, the insulating effect of moss cover
causes mean summer temperatures of soils to decrease by 4-6°C in comparison to
temperatures of the moss-free soils (Kudryavtsev, 1959; Feldman et al., 1988). The
formation of permafrost in peatlands is a typical feature of the northern taiga of
European Russia and especially of the forested wetlands of Western Siberia where peatlands
occupy between 50 per cent and 80 per cent of the land surface. In these regions, MAGT
usually varies between -1°C and -1.5°C and permafrost thickness reaches 70-100 m (Figure
6.1). In the southern taiga of the Far East, peatlands (called mary) also promote a broad
extent of permafrost. Forests are another important control over local permafrost
conditions. In the west of the cryolithozone, permafrost islands form under the spruce
forests which provide shade in summer and intercept snowfall in winter causing additional
cooling of the ground. In the mountains of the Far East, permafrost is typical of the
tree-covered northern slopes. Under forests, MAGT is higher than in peatlands and vary
between 0°C to -0.5°C and thickness does not exceed 50 m (Geocryology of the USSR:
Eastern Siberia and the Far East, 1989).
The Island Permafrost Zone
Island permafrost occupies the southernmost part of the cryolithozone. Frozen ground
accounts for as little as 5-10 per cent of the total territory of the island permafrost
zone. Terrain conditions are by far the most important control over the formation of
permafrost here. In northern European Russia, Western Siberia, southern Eastern Siberia,
and the Far East, permafrost forms in peat, peaty soils, and under the thick surface moss
cover in wetlands. Here, peaty permafrost mounds mark the southern limit of the permafrost
zone (Popov, 1962c).
In southern Central Siberia on the watersheds of the Yenisey, Angara, and Lena rivers
the agents of permafrost formation are more varied and include geo-morphology. Cold air
drainage is typical of the deep river valleys where permafrost forms in response to the
lower temperatures. It is also found on the northern slopes covered with mossy forests.
Along the eastern frontier of Russia, island permafrost occurs in the mountains of
Kamchatka (from an altitude of 1000-1500 m), Sakhalin and the Sikhote-Alin (from 1500 m).
MAGT varies within narrow limits from 0°C to -0.5°C (Regional Cryolithology, 1989) and
the permafrost thickness is 10-20 m in soils, reaching 50 m in rocks (Figure 6.1).
Subsea Cryolithozone
The spatial distribution of the thickness and thermal regime of the submarine
cryolithozone depends on a variety of factors, such as climate, the ratio between the
thickness of sea ice and sea depth, sea hydrology, salinity and temperature of water and
bottom sediments, and sea level oscillations (Mackay, 1972a; Hunter et al., 1976; Rogers
and Morack, 1980; Solovjev, 1983). Two types of permafrost develop on the Arctic
continental shelf: typical ice-bearing permafrost and the saline unfrozen sediments with
temperature below -1.8°C (Solovjev, 1983), with both frozen and unfrozen marine deposits
containing cryopegs (highly saline solutions) which form lenses and layers under and
within the marine sediments (Kononova et al., 1971). Both relict and contemporary
permafrost are found on the Arctic shelf. Contemporary freezing of subsea deposits occurs
only in shallow seas, which remain frozen to the bottom for up to eight or nine months per
year (Solovjev, 1983). The perennially frozen sediments form under the ice cover which is
approximately 0.5 m thick; when thickness of sea ice reaches 1.0-1.5 m, frozen layers
develop on a seasonal basis (Geocryology of the USSR: Western Siberia, 1989). The subsea
cryolithozone is characterized by the following features: widespread saline unfrozen
sediments and an alternation between perennial frozen layers, saline unfrozen layers, and
cryopegs. The area occupied by subsea permafrost and permafrost thickness both decrease
northwards. Subsea permafrost is in a condition of thermal disequilibrium (Mackay, 1972a;
Solovjev, 1983).
The major area of subsea permafrost, both relict and contemporary, occurs beneath the
waters of the Laptev and East Siberian Seas (Baranov, 1959). Relict permafrost developed
during the Quaternary marine regressions when areas of the present sea floor were exposed
to cold subaerial conditions. Later, during the transgression of 19 000-18 000 BP,
permafrost was degraded by thermo-abrasion and geothermal heat (Geocryology of the USSR:
Eastern Siberia and the Far East, 1989), and at present continuous relict permafrost
occurs only in those parts of the shelf where sea depth does not exceed 10 m. In the East
Siberian Sea, relict sub-sea permafrost forms a narrow zone of about 30 km, which extends
along the coast, with the permafrost table laying at a depth of 1-8 m beneath the sea
floor. The island relict permafrost occurs between the isobaths of 10 m and 60 m, though
at these depths the shelf is mainly occupied by unfrozen saline deposits. The contemporary
subsea permafrost forms under the shallower waters near the shore and in the shallow
deltas of the large rivers (the Lena, Yana, Indigirka, and Kolyma), where the depth does
not exceed 2.5 m (Grigoriev, 1966a; French, 1996). Permafrost thickness decreases from
150-200 m near the shore to about 10 m at a distance of 200 m from the coast while the
depth at which the permafrost table occurs beneath the sea floor increases from 2 m to 100
m (Geocryology of the USSR: Eastern Siberia and the Far East, 1989). The area occupied by
subsea permafrost diminishes westwards. In the Kara Sea continuous relict permafrost,
which formed in the late Pleistocene and Holocene, occurs only in the nearshore areas
where the sea depth does not exceed 20 m (Geocryology of USSR: Western Siberia, 1989). In
the nearshore areas of the Yamal peninsula subsea permafrost may have originated as result
of extensive coastal retreat (Grigoriev, 1966b). Subsea permafrost in the Kara Sea lies
either straight beneath the sea floor or at a depth of 30-50 m under the floor, with
layers of saline unfrozen deposits and lenses of cryopegs underlying or alternating with
layers of typical permafrost (Geocryology of the USSR: West Siberia, 1989). Permafrost
temperatures normally vary between -1°C and -3°C in the southern part of the shelf and
-0.5°C and -2°C in its northern sector, though in places temperatures may be as low as
-10°C (Geocryology of the USSR: European Territory of the USSR, 1989). Its thickness
ranges from 100 m to 200 m along the eastern coast of Novaya Zemlya and the eastern sector
of the Kara Sea to less than 100 m in the central sector of the sea. Further west, under
the Barents Sea, only sporadic islands of permafrost occur near the Frantz Joseph Land and
between the islands of Kanin and Vaygach with unfrozen saline deposits predominating in
other areas (Geocryology of the USSR: European Territory of the USSR, 1989). At present,
subsea permafrost on the Arctic continental shelf remains poorly researched. Further
investigations present a challenging and important task, particularly with respect to the
development of natural resources which are abundant on the Arctic shelf.
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