Permafrost and periglacial research in Tien Shan continues both with borehole monitoring and research on periglacial processes. Within the discontinuous permafrost zone of the Zusalykezen Mountain Pass area (3300 m asl) the borehole temperature observations show significant variation of permafrost thickness within a short distance.
These differences depend on topography, slope aspect, geology, snow cover and other microclimatic conditions. At a north-facing slope the permafrost thickness varies from 15 to 90 m within the distance of 250 to 300 m. On the west, east and south facing slopes there is no permafrost for the same altitudes and similar ground composition. The greatest differences in ground temperatures of 1.5 to 2.2°C were observed between north (–0.4°C) and south (1.8°C) slopes.
The long-term observation started in1974 continues on the thermal regime of coarse block slopes in comparison with fine-grained ground. Specific heat transfer by convection inside the coarse debris occurs as a result of its high porosity. The mean annual temperature of coarse blocky materials is 2.5 to 4.0°C cooler than the MAAT. As a result, permafrost can exist inside such deposits even under a positive MAAT. Near the Big Almatian Lake (Transili Alatau Range) at an altitude of 2550 m asl (permafrost with isolated patches) with a MAAT of 1.4°C, the frost penetration is more than 6 m in the coarse block slope. Normally, at the same elevation in the fine-grained soils the seasonally frozen layer does not exceed 1.2 m. The large coarse blocky massifs have a cooling influence for distances of up to 15 m on adjacent sites with fine-grained soils.
The periglacial research includes measurements using geodetic survey on the development of thermal depressions on moraines and rock glaciers. A thermokarst lake began to form a few years ago on the surface of the rock glacier “Perevalny.” The rock glacier is located at the divide of Big Almatian and Chong-Kemin Valleys at the elevation of 3500 m asl. The thermokarst lake developed at the location of the ice-saturated moraine and the rock glacier (see photo). Aerial photos show that the lake did not exist in 1990. During the last decade the thermokarst lake has reached a diameter of 35 m.
The book Permafrost of Northern Tien Shan: Past, Present and Future (106 p.), by S.S. Marchenko, was published with the support of Siberian Branch, Russian Academy of Sciences. Aldar Gorbunov ([email protected])
Sergei Marchenko ([email protected])