Permafrost

80
Theme 2. Frost hazards and periglacial environments in
mountain/plateau regions
Thermodynamic conditions of the cryopegs formation in the coastal
zone of Russian Arctic
A. Koroteev 1 , Streletskaya I. 2
(1.Lomonosov Moscow State University, Physical Faculty, Leninskie Gory, Moscow, 119992, Russia
(thunderbird@pochta.ru); 2. Lomonosov Moscow State University, Faculty of Geographyl, Leninskie Gory,
Moscow, 119992, Russia)
Abstract: Cryopegs are mineralized groundwater lenses existing at bellow 0 o C temperatures,
which are widespread in the coastal area of west Yamal, for example. They occur at different
depths as isolated lenses, which are not connected with each other or to ground or surface
waters, and have different pressure heads (depending on the depth of location). An examination
of a cross-sectional profile shows that cryopeg lenses occur in multiple layers. Cryopeg water
has a rather constant chloride-sodium composition, however concentrations of SO4 -2 , Mg +2 ,
Ca +2 ions can differ among occurrences, as can salinity.
The process of formation of cryopegs is followed by heat-mass transfer. Physical model of
freezing of a salt dispersed sediments is much more difficult than model of unsalt sediments.
Process of freezing is followed by: a – displacement of ions to the layer of unfrozen water; b –
water and ions migration, caused by diffusion; c – salt crystallization with formation of
minerals; d – adsorption of pore solution on mineral surface of sediments; e – ion exchange and
chemical reactions; f – origin of mechanical stress, caused by moisture phase changes. During
freezing in the body appears mobile border between two zones, and pore solution undergoes
differentiation: small portion of salt stays in the frozen area, but the main part squashed to the
liquid area. As the result of squashing salt by phase border there is a formation of liquid
high-mineralized zones, concentration of their solution can be 200gr/litre or higher, it means
these zones don’t freeze at temperatures bellow 0 o C.
The goal of the investigation is to determine specific features associated with the
occurrence and formation of cryopegs, mainly focusing on those shallowly lying in the coastal
zone of the west Yamal. Cryopegs in this region have been drilled through by boreholes on
several occasions, to different geomorphological levels at depths ranging from 2-3 m to 10-12
m during explorations in the oil- and gas fields of this region, along the lines of trenches
planned for gas utilities and railways. The deep parametric boreholes drilled in the areas of
Kharasavej and Bovanenkovo have detected cryopeg lenses at depths ranging from 30-50 m to
200-250 m.