Permafrost

Investigation results showed that the Prilensko'e plateau is an area of wide karst formation
linked with Lower Cambrian carbonaceous strata. Wide distribution of karst processes and
phenomena are determined by the following conditions: low (up to 200 m a.s.l.) location of
local basis of erosion, big thickness (up to 300 m) of aeration zone, intensive physical
weathering and discontinuity of permafrost. The thickness of frozen strata is ranged between 0
to 200 m, and in single cases reaches 700 m. The temperature at the depth of zero annual
amplitude comprises in most cases -2°C.
By character of exposure, the karst is related to the type of mantled karst, bedding under a
cover of disperse, 1-3 m in thickness, ground. By geomorphologic position, an under-river bed
and river bed karst is observed here. By time of development, modern, ancient and renewed
karst is separated. Primary development of vertically-orientated channels of discharge and
limited development of horizontal channels of discharge is character for the karst of the region.
By type of permeability, this karst may be named crevassed. The forms of surface-exposed karst
are divided into micro-, meso-, and macroforms. For the first time, sink holes are separated
among the karst microforms of the region. By form, sink holes are divided into crevasses,
furrows, grooves, rills, etc. Karst mesoforms are presented by corrosion, corrosion-suffosion,
corrosion-erosion cones and cup-like depressions. Karst megaforms are presented by large
(many hundreds of meters in diameter) karst-erosion and karst-subsidence depressions.
Hydrodynamic zonation, peculiar to karst areas of the Earth, expressed in interval of
influation (aeration) and interval of intensive underground discharge is clearly presented in the
region limits. Surface waters bear a big heat supply in the depth of the carbonate rocks massive
and destroy cryolithozone. A zone of surface circulation is spatially coincides with a
thermoactive cryogenic zone, the thickness of which reaches 4 meters. Intensive cryogenic
weathering, and in particular frost cracking, occurs here, that is also favourable for development
of surface karst phenomena. The zone of vertical descending circulation in the region limits is,
probably, linked by subvertical or inclined lots of thawed ground. Small, by their debit, hanging
springs located in the upper parts of slopes are linked with this zone. The zone of periodical
fluctuation of karst water level and horizontal circulation is linked with lateral taliks. The
surface of horizontal circulation zone crosses different age layers, including salt-bearing ones.
In this connection, the salt content of ground waters and their mineralization are considerably
changing by area. An important peculiarity of the region karst waters is the presence of a siphon
circulation zone. Of big importance for appearance of this zone are the character and form of
the lower cryolithozone surface. Investigations were conducted in the scopes of the Integration
program #13, SB RAS.
Key words: karst, permafrost, cryolithozone, cryogenic processes
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