Permafrost

approximately with the -5°C mean annual air temperature isotherm in Eastern Siberia. The
lowest temperatures of mountainous permafrost (between -13°C and -15°C) occur in the
subarctic mountains of north-eastern Siberia. Most of the north-east is occupied by the
continuous cryolithozone and only in a limited area on the Okhotsk coast does discontinuous
permafrost occur. In the mountains of north-eastern Asia permafrost exceeds 1000 m in
thickness. The extreme thickness of permafrost is caused by a number of factors, such as high
thermal conductivity of bedrock and paleoclimatic conditions.
The depth of the active layer varies strongly as a function of altitude, aspect, microclimatic,
and hydrological conditions, and vegetation. The maximum depth of the active layer (about 1.5
m) is observed in the low and middle mountains on the southern slopes with poor vegetation
cover, while in peatlands the active layer is no more than 0.5 m deep.
The whole spectrum of cryogenic and slope processes typical of cold climates, such as
frost weathering, sorting, wedging, and solifluction which play an important role in the
formation of landscapes particularly in the upper mountains, is represented in north-eastern
Russia. The extent and intensity of these processes are controlled by various factors including
the type of rocks, presence and .thickness of unconsolidated deposits, and steepness of slopes.
Frost or thermal contraction cracking creates the most typical cryogenic landforms: ice wedge
polygon relief, also known as tundra polygons or fissure polygons.
Ice-wedge formation is ubiquitous in the Chersky-Moma region and the northern
Verkhoyansk mountains while in the southern Verkhoyansk their occurrence is mostly limited to
the northern macroslope of the Suntar-Khayata. The largest ice wedges, which exceed 3 m in
surface diameter and 5-8 m in depth, develop in the Verkhoyansk region in wide valleys and
where mountains merge with plateaux. In the southern Verkhoyansk mountains, northern
Chukchi peninsula, and the Koryak highland thawing of ice wedges has led to the widespread
development of thermokarst.
Thermokarst is among the most important processes shaping permafrost landscapes. It
develops in response to the disruption of the thermal equilibrium of permafrost and is controlled
by such changes in the environment as climatic warming, increase in snow cover, and an
increase in seasonal variation of temperature, deforestation or destruction of vegetation,
presence of standing water, and anthropogenic impacts. Thus in the Koryak highland the
maximum surface subsidence reaches 10-12 m and in the Main basin thermokarst destroys a
layer of ground up to 6-8 m in thick per year. This phenomenon seldom occurs naturally in the
northern Verkhoyansk and Chersky mountains where it is mainly limited to the moraines of
modern glaciers that have a high ground ice content.
Patterned ground is the most common cryogenic form of microrelief. Different varieties of
patterned ground such as spot-medallions, polygonal and hummocky forms, stone circles and
rings occur in the tundra environment. Sorted and unsorted patterned ground can form nets of
circles on flat surfaces and steps or stripes on hillslopes. They are created by different processes
in the active layer: frost cracking, contraction, heave resulting from cryostatic pressure and ice
segregation in winter: ice-melting and dilation subsidence in summer; and frost sorting around
the ear. Patterned ground most often has the following morphology: spot-medallions which may
be surrounded tussocks, flat, curved or convex heaves (which have a size range between 0.5 m
and 2.0 m) and hummocks. Sorted patterned ground (circles, garlands, nets. and polygons) is
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