QUATERNARY GLACIATION AND ITS INFLUENCE ON ENVIRONMENT IN THE HIGH MOUNTAINS OF CENTRAL SIBERIA

High mountain ridges surround Siberia from the south and east and form a continuous belt reaching from Altay to Yakutia. The ridges are characterized by a comparable height and cold continental climatic conditions. The mean annual temperatures gradually drop along the belt from -3°C in West Altay to -17°C in northeastern Yakutia. Such a difference is comparable to the temperature change during the Pleistocene Cooling, when climatic continentality promoted the spreading of permafrost under arid conditions ('cryoaridization'). Thus the range of climatic differences today is comparable to the range of climatic changes between glacial and interglacial conditions. We used these characteristics for environmental reconstruction.

The environments along the belt differ in their degree of interaction of glaciers and cryogenic ice. Both of them characterize the certain type of glaciation by their proportion. Deep-reaching permafrost occurred along the belt throughout the Quaternary. Permafrost cannot occur when there is high precipitation. A drop in temperature would have triggered glacier growth under these conditions. An increase in precipitation, which would have also caused an increase in glaciation, we leave out in such a situation.

At present only southwestern end of the mountain belt receives more than 1000 mm of annual precipitation, whereas other ridges receive 500-700 mm, declining to 100-200 mm in the intramontane basins. Therefore the largest modern glaciers are found in Altay, whereas the maximum volumes of cryogenic ice occur in the coldest parts of Yakutia. As the Pleistocene cryoaridization progressed, the difference has been smoothed. The temperature effect became dominant and the largest Quaternary glaciers occurred in the mountains of Yakutia. However, glaciation was restricted to valley glaciers, because the limited moisture supply did not allow the formation of ice sheets. At the certain stage of the glaciation another form of surface ice, so-called icings, could turn into perennial features comparable to glaciers both with regard to ice volume and as landscape-forming agents.