ИСТИНА

The area of permafrost at the end of the Valdai era occupied in Eurasia a wide belt from the edge of the drained shelf in the north to about 39 N. in south. In this area, on the plains (Great Poland, Pannonian, East European, West Siberian), fragments of meandering paleochannels 16-19 thousand years old are widely developed. The width and depth of these paleochannels, as well as meander wave-lengths, are significantly larger than that of modern rivers with the same catchment areas. It is assumed that large rivers in cold climates were formed due to atmospheric precipitation, without the runoff from melting continental glaciers. Significant water discharge was generated during the spring flood due to melting snow, which accumulated over the long winter. Losses of spring runoff due to evaporation and infiltration were minimal. During the transition to the Holocene, snow depth decreased, and the losses increased. This led to a decrease in the size of river channels (up to 15 times in width). At the same time, sediments washed away from the catchments were accumulated in the over-deepened channel network. As a result, the geometry of large channels of the end of the Valdai era largely control the modern morphology of river channels and floodplains, as well as the sediment budgets.