The Influence Of Glacier Erosion On Topographic Evolution And Its Controlling Factors In The Nianbaoyuze Shan,Northeastern Tibetan Plateau

Glacial and fluvial processes are the two most important surface processes in high latitude and high altitude regions,which have a profound impact on the topographic evolution of these regions.Differences in the landforms produced by the interaction between the two processes are obvious,but compared with fluvial erosion,the research on the methods and mechanisms of glacial erosion and its impact on topography is still inadequate.In particular,the huge differences in the nature and types of glaciers in various regions are not fully considered.As a result,there is still a great deal of controversy about which factors are dominant for glacial erosion and how erosion dominates the evolution of the topography.Outside of the polar regions the largest concentration of glaciers today is located on the Tibetan Plateau.It is also unclear how does glacial erosion affect the topographic evolution of these areas,and whether the nature and type of glaciers will also contribute to the diversity of the influencing factors of glacial erosion and their impact on topographic evolution.Therefore,based on the quantitative description of the glacial erosion topography of the plateau mountain,to carriy out research on the related factors of glacial erosion and its impact on the topography.This work can not only more comprehensively and systematically recognize the impact of the surface process on the evolution of the plateau mountain landform,but also enrich the understanding of the interaction between mountain topography,climate and erosion in middle and low latitudes.The Nianbaoyuze Shan in the northeastern part of the Tibetan Plateau has experienced extensive glaciation since the late Pleistocene.Among glacial eroded topography,the area of the glacial valley is the largest,followed by the cirque.In this work,firstly,the quantitative data and spatial distribution characteristics of glacial erosion are obtained based on the power function fitting of 144 cross-sectional profiles in the 29 glacial valleys,and the main controlling factors were revealed by combining qualitative and quantitative analysis;Secondly,the spatial distribution characteristics and influencing factors of the cirque were obtained through quantitative analysis of the positions,shapes and scales of 230 cirques.Finally,through the spatial distribution and development pattern of two types of glacial erosion topography,the longitudinal distributions of glacial erosion,and the comparative analysis of the distribution of the area-elevation and slope-elevation in various regions,we reveal the impact of glacial erosion on the topography evolution and mountain height.The main conclusions are as follows:(1)The glacial erosion in the Nianbaoyuze Mountain is mainly controlled by temperature.Although it is consistent with the main controlling factors at high latitudes,the mechanism of its function is different.In high latitudes,the ice temperature is low,and and higher temperatures can bring more meltwater to them,thereby promoting bottom sliding and increasing erosion(basal sliding);While in the middle and low latitudes,where the ice temperature is high and the meltwater is abundant,so temperature changes will only affect the size of the glacier,that is,the increase in temperature can only lead to more ablation and thus less erosion(ice volume or ice flux).(2)The distribution of the cirques is mainly controlled by the orientation and ELA height.In the northern hemisphere,the north-facing cirques that receive the least solar radiation are the most developed,with the largest proportion of north-facing cirques,and the largest average area and average size of the northeast cirques;The altitude of the bottom of the cirques is mainly concentrated at the ELA(4350 m)in the north of the mountain and the ELA(4500 m)in the south of the mountain during the local last glacial maximum.(3)The development pattern of the cirque morphology is dominated by widening process and headward erosion,and the glacial valley cross-section morphology of the glacial valley is also dominated by widening process.This is consistent with the characteristics of sub-continental glaciation in the northeast of the Plateau,and also leads to the reduction of the topographic relief of the glacial valley bottom and the cirque bottom.(4)The Hypsometric maxima and average elevation of the northern part in the Nianbaoyuze Shan appeared around 4350 m,and that of the southern part around 4500 m,which was consistent with the elevation of ELAs in the local last glacial maximum of the respective regions.This indicates that the topography evolution of the Nianbaoyuze Shan was affected by the glacial buzzsaw effect,which also indicated that the subcontinental glacier developed on the Plateau still have the effect of limiting the height of the mountain.In addition,although the glacier buzzsaw effect has played a role on the both sides of the north and south of the mountain range,there are differences in the way and process.The topography in the north of the mountain is generally higher,and a larger-scale valley glaciers are developed.The distribution of glacier erosion is greatest along the ELA and its slightly downward position.These factors cause the topograpgy above ELA to converge towards ELA,and the slope decreases accordingly.As a result,a Hypsometric maxima occurred near ELA,and the slope above ELA could not increase indefinitely,thus limiting the mountain height.The cirque glacier or the cirque valley glacier is mainly dominated in the south of the mountain range.Under the condition that the cirque near ELA was kept relatively stable at the back wall height,the headward erosion and the lateral erosion were carried out,which resulted in the slope being reduced and the area proportion increased,thus limiting the height of the mountain.