Experience of comparative morpholithological analysis of hill forms in Upper Dnieper valley

One of the features of morphological structure of the Upper Dnieper valley along its sublatitudinal section from Dorogobuzh to Orsha is the series of specific hill forms, which have a big elevation above the valley bottom and are separated from the interfluves by alluvial surfaces of floodplain and first terrace levels. There are two hills in the centre of attention of this research - near village Korovniki and near village Katyn-Pokrovskoe, which are 100-km away one from the other (along the valley) and have surprising morphological resemblance. Firstly, this is resemblance of hill plan shapes (including elongation of both forms along the Dnieper valley) and elevations above the low stage of the Dnieper (about 30 m). Secondly, there are sudden turns of modern channel in these points, which is the evidence of important influence of hills on morphodynamics of the Dnieper. Thirdly, each of these hills is rounded by a modern stream bed from the one (right, if to look down the stream) side, and by a wide hollow, which has morphological indications of a big, but non-functioning at present paleochannel, from the other (left) side. The results of alluvial surfaces boring demonstrate a difference between the thickness of alluvium of modern floodplains and paleochannels rounding the hills: near v. Korovniki the floodplain alluvium is more than twice thicker than the paleochannel alluvium, and paleochannel alluvium is almost twice thicker than the floodplain alluvium thickness near v. Katyn-Pokrovskoe. At the same time the paleochannel near v. Korovniki and the floodplain near v. Katyn-Pokrovskoe are of socle type (alluvium is bottomed by moraine, whose top lies above the low stage of the Dnieper). Based on the results of morpholithological analysis we can conclude, that the ''jump'' of the Dnieper over the hill near v. Korovniki took place before the beginning of the Late Valdai (after which this paleochannel could only be an additional channel of melt water run-off from the Late Valdai glacier), and by the hill near v. Katyn-Pokrovskoe that ''jump'' occurred in the Late Valdai period. Such ''jumps'' were most likely conditioned by features of redistribution of the river run-off in the Late Glacial period: multibranch channels of powerful run-off of melt glacial waters were formed in the river valley, and after the fall of water-the level separate branches in these channels dried, overgrew and changed into segments of the floodplain and later - into terraces above the floodplain. Hills near v. Korovniki and near v. Katyn-Pokrovskoe formed by moraine covered by a rather thin (1-5 m) layer of sand, rounded extensively by modern channels and paleochannels and elongated along the river valley can be characterized as erosion cut-off hills separated from the surrounding interfluves by river flows.

Keywords

Authors

References