Cirque Extraction And Regional Characteristics In Different Climatic Regions Of High Mountain Asia

Cirques are typical erosion landforms of glaciers and can be used as one of the important indicators of the occurrence of ancient glaciers in an area.The size and shape of cirques have been used to reconstruct paleoenvironment and paleoclimate.With the development of remote sensing and geographic information systems(GIS),automated methods have been developed to delineate cirques and extract cirque parameters,promoting the research of large-population cirque analysis.Most studies have focused on the cirques in a same mountain range,whereas few studies have been conducted to compare the cirques in different regions.Quantifying and comparing cirque metrics in different climate regions can help reconstruct paleoclimate information and improve the understanding of the interaction between mountain topography and climate in High Mountain Asia.This paper first compares the cirque boundaries delineated by different professionals and determines the stability of cirque metrics.Then,both manual and automated methods are used to delineate cirque boundaries for High Mountain Asia that is mainly controlled by Indian monsoon or westerlies.In total,2269 cirques are delineated from the western part of Himalayas,the middle part of Tian Shan,and the southern and northern part of Altai Mountains.The cirque data delineated by Zhang Qian et al.(2020)in the Gangdise Mountains are also included for the further analysis.The parameters,such as the size,shape,and terrain of these cirques,are extracted for the quantitative analysis.The spatial distribution and morphological characteristics of the cirques are analyzed for different climatic regions to derive the palaeoclimate and Palaeoenvironmental conditions.The major findings are summarized below:(1)Due to the potential differences in cartographer's understanding of the cirques and the development degree of the cirques,delineated cirques parameters are slightly different from different professionals.For the well-developed cirques with clear boundary characteristics,the coefficient of variation of cirque parameters,including length width ratio,roundness,minimum elevation and mean aspect,is less than 10%,representing low variability and high stability.For the cirques with poor development and unclear boundary characteristics,the coefficient of variation of mean aspect and plane closure extracted may be greater than 10%,representing medium variability and medium stability;The coefficient of variation of roundness,minimum elevation and other parameters is less than 10%,representing weak variability and high stability.(2)From the Himalayas to Gangdise,the length,width and height of the cirques tend to decrease under the influence of the Indian monsoon;From the Gangdise Mountains to Tian shan and then to the southern Altai,the lengths,widths and heights of the cirques tend to increase with the increase of latitude and the decrease of temperature;From the southern to the northern part of Altai,the temperature further decreases,which makes it easier to form valley glaciers,and the length,width and height of the cirques group tend to decrease.(3)There is a strong positive correlation between the length,width,height,volume and perimeter of the cirques in different climate areas,indicating that the elongation,widening and deepening of the cirques generally occur at the same time in the process of formation and development.(4)Cirque floor altitudes indicates the position of the Equilibrium Line Altitude(ELA)during the formation of the glacier.Cirque floor altitudes shows an upward trend from the Himalayas to the Gangdise Mountains,and a downward trend from the Gangdise to Tian Shan to the southern Altai and then to the northern Altai Mountains.This trend is consistent with the temperature and precipitation characteristics of glacier development;The temperature in the northern hemisphere gradually decreases from south to north,resulting in the overall downward trend of ELA.However,because the Gangdise Mountain is located in Tibetan Plateau and the precipitation is much lower than that of the Himalayas,higher ELA is required,resulting in the upward trend of the bottom elevation of the cirques from Himalayas to Gangdise Mountain.(5)During the Quaternary period,the Himalayas and Gangdise regions were mainly controlled by the Indian monsoon,and the southern and northern Altai Mountains were mainly controlled by westerlies.