Spatial Variations Of Glacial Erosion And Its Influential Factors In The Qilian Shan

The glacier is one of the most dominant and active exhumation agents responsible for the evolution of the mountain topography. Researchers have been focusing on studies of the processes of glacial erosion, the mechanisms of glacial erosion topography formed and the spatial and temporal variations of glacial erosion landforms, etc. Internationally, researchers deduce the impacts of glacial erosion on topography through analysing the differences between glacial and fluvial landforms or simulating the evolution of glacial landforms based on numerical models. The studies of the interactions among climate, topography and glacial erosion were limited owing to the lack of enough quantitative data of glacial erosion.Qilian Shan, located on the northeastern margin of the Tibetan Plateau, had experienced several glaciations and resulted in the great changes of topography since the Pleistocene. A variety of lithologies, nature of glaciers, climate made Qilian Shan an ideal place to discuss the interactions among climate, topography and glacial erosion. Therefore, we selected the glacial troughs of Qilian Shan as the study object(about 616 glacial troughs and 1845 cross-profiles), and acquired the quantitative data of the degree of glacial erosion by fitting the cross-profiles usig power law model(y=axb), then the distribution of the degree of glacial erosion was obtained. As the glacial troughes could not cover all glacial zones, we also used the Hkr method to analysis the the distribution of the degree of glaciations in the Qilian Shan. Furthermore, we analysis the impacts of glacial dynamic conditions, topography and lithology on the degree of glacial erosion by using qualitative and quantitative analysis methods, and make sure the main control factor that leads to the distribution of the degree of glacial erosion. Finally, based on the summary of the morphology parameters of glacial cross-profiles in the global mountains, we further disscussed the reason that might cause the different development of glacial troughs in mountain ranges. The main conclusions were as follows:(1)The longitudinal variations of the glacial erosion along the glacial troughs closely related to the location of ELA, the general characteristics was that the degree of glacial erosion increase from the upstream to the ELA and decrease from ELA to the downsream, a tributary joins could cause the change of ice volume along the valley and which would leads to the distribution of glacial erosion along the valley.(2)The distribution of the glacial erosion degee among the Qilian Shan shows that the erosion degree is largest in southwest mountain, such as the glacial erosion degree is the largest in Chaidamu Shan and Tuergendaban, the larger in Lenglongling, Shule South Shan and Tuolai South Shan, the less larger in Zoulang South Shan, Danghe South Shan and Tuolai Shan, the smallest in Daxue Shan and Datong Shan.(3)The distribution of the glacial erosion degee among the Qilian Shan might be attributed to the combined effect of glacial dynamic conditions, topography and lithology. However, the average glacier size indicated by the topography especially the slope above ELA might be the control factor among them. In addition, glacial erosion in the Qilian Shan also limits its elevation.(4)There are two opposite types of glacial valley cross-profile development in mountain ranges, which were caused by the nature of glacier. For example, the marine glaciers focus on an overdeepening process of glacial valley, while the continental glaciers focus on a widening development of glacial valleys. Besides, we also find the extreme continental glaciers present less overdeepening than continental glaciers in Qilian Shan.