Procesy mrozowe w dnach dolin dorzecza Sugnugurin-goł

Abstract

Within the Valley bottoms in the Sugnugurin-gol Basin a permafrost is present (fig. 1). In summer, the ground unfreezing is differentiated and it ranges from 1 m in the bottom to 1,5 m and sometimes to 2 m in insolated sites. In the longitudinal profile, morphology of the Sugnugurin-gol valley is fluctuating. Its various sections are located in different landscape zones. As a consequence of the permafrost occurence and of the varying bottom morphology, they are modelled by different groups of frost processes. Basing on this criterion, four types of the valley bottoms were distinguished (fig. 6). The first type are higher sections of trough valleys within the higher portion of South-Siberia taiga. At present, an important role in modelling the river beds is played by the processes associated to icing occurrences and in summer the trough bottoms are modelled by mechanical suffosion. The second type are taiga valleys. Their longitudinal profiles are levelled and the river beds are winding. The valley bottoms are overgrown with scrub birches and single larches. The whole bottoms are covered by the permafrost, the occurrence of which is most often associated to big hydrolakolites arising. The biggest ones are located at the lateral valley outlets. Icing crusts in winters are deposited on the flat valley bottoms and the processes associated to their occurrence dictate the present bottom morphology. The third type of valleys has a system of well developed bottom terraces. Wide, braided troughs are present accompanied by numerous petrified shoals, flood terraces and higher terraces which are best preserved at the lateral valley outlets as cones. Frost effects, tuffurs mainly, are present within lower terraces at the bases of taiga-overgrown slopes exposed to the north and north — east. In these valleys an evident asymmetry is existing in the associated effects permafrost. The valley beds are modelled by processes connected with icing formations. The fourth valley type is featured by wide flood terraces, having often a form of vast talus and it includes also the flood terrace of the Chara-gol valley in the Batsumber Valley. Numerous old river-beds in various development stages are present here indicating often alterations of the river-bed. The permafrost is of insular type here and the forms associated to its occurrence are related to the old river-beds which are shaped by frost heave processes and by thermal erosion.