Cryomorphogenesis within the lower Tom basin

Thelower Tom basin is situated within the Uray-Novosibirsk geocryological subzone, where frost rocks evolve and the formation ofeternal-frost rocks is potentially possible in the result of the anthropogenic impact. In this area the prolonged seasonal frost develops.On the territory of Tomsk Region, the covering deposits occur on the top. These are mainly silt loams: they are without lamination,usually macroporous in the top of the section, with significant water-permeability and are readily washed out. The average yearly airtemperatures are subzero (-0.5 . - 0.6°С), the absolute minimum temperatures of the air and soils reach -58°С and -54°С respectively.The average yearly soil temperatures change from 0оС to -2.5 . -4.5°С. The stable soil freezing comes in November; themaximum depth of soil freezing is observed in the third ten-day of March to the first ten-day of April, and in some years it may shiftto the second and even third ten-days of April. The average frost depth in the subtypes of the grey forest soils in the Tom-Yaya interfluveis 108-116 cm. The 1977-1985 observations demonstrated that in cedar forests the soil frost depth reached 0.8 m, in birch andaspen forests frost penetrated into 0.25-0.4 m. On arable lands the frost depth varies within a substantial range: from 0 cm undersnow banks to 2.0 m and more on the relief microelevations, where the snow thickness is insignificant (0-40 cm) in the result ofeolation. The seasonal frost accounts for such dangerous natural processes and phenomena as the soil frost heave, frost cracking. Allsites of the studied area, where the highly moistened clays occur on the surface, refer to heave-hazardous. The construction of roads,bridges, buildings, land ploughing, etc. change the character of the snow cover distribution and vegetation, thus affecting the temperatureand the ground humidity. As a result, the seasonal heave strengthens involving the rise in expenses for the roads maintenance.In the construction of buildings, the thawing of the foundation grounds results in their additional subsidence. The additionalprecipitation reaches its greatest value after the first cycle of the seasonal frosting-defrosting. On ploughed fields, the depth of thesoils frost increases, the time of their thawing and warming-up to active temperatures is retarded; on large arable massifs, the deepfrost centres are formed, promoting the common cooling of croplands. In some areas, winter crops are destroyed by frost. In earlyspring, on the most drained sites of the land surface the frost cracking reveals itself as the formation of seasonal-crack polygons:mostly quadrangles to octagons. The dimensions of the polygons are 3x5 to 10x15 cm, rarely larger. The width of cracks changesfrom 1-3 to 15-20 mm, rarely larger, and the visible depth is up to 4.5-5 cm.

Keywords

Authors

References