| Baimaxue Shan，watershed of the Jinsha River and the Lancang River with latitude of27°24′~28°36′N and longitude of98°57′~99°25′E, is located in the inner part of theHengduan mountain range and is situated between the Deqin County and Weixi County of inthe northwest of the Diqing Tibetan Autonomous Prefecture. The study of the physicalgeographical features here has the significant meaning about both reconstructing theenvironmental change of the southwest monsoon and the glacial development. The definitelypreserved glacial landforms and deposits indicate here was once glaciated during the lateQuaternary, especially the glacial erosive landform such as the trough valleys. Using themethods of the shape ratio, gradient ratio of wide and depth, parameters of the parabolic curve,we analysis the geomorphologic features of the simple glacial trough valleys distribute in thenortheastern side of the main peak of Zhalaqueni (5429m)and the affected factors. Adoptedthe shape parameters of the seven profiles of these trough valleys and contrasted with otherregions with well developed trough valleys, the possible reasons influenced the glacial troughvalleys such as the glacial extent, type, the local climate, time span and the base rock type etcwere discussed herein. The results show that the mean value of b is1.750in the troughvalleys of Baimaxue Shan is lower than that in the trough valleys developed in the Luoji Shan(1.835) due to the different precipitation condition. However, the value of B is different fromthe head water of the Urumqi (1.825) indicates that the effect factors may be the glacial type,basement rock type and the time span ets. The glacial trough valley not only affected by theglacier nature but also affected by the climate condition, glacial extent, time interval and thelithology. The parameter change of the gradient ratio of wide and depth along the troughvalley can reflect the dynamic change during the course of the glacial flow. The parameters ofthe b-FR in Baimaxue Shan show that the characteristic of the glacial trough valley is notconsistent with the mountainous pattern put forward by the Hiran and Aniya even in theregion of maritime glacier. However, the feature of the b-FR can reflect the procedure of theglacial erosion well. The glacial erosion is mainly the lateral erosion, so the steepness of the glacial trough valley is small and the bottom of the trough valley is relative flat and wide andshows tha perfect U shape. Meanwhile, the shape ratio (b-FR) can also verify the ancientsnow line altitude. In comparison of c values of quadratic polynomial model in BaimaxueShan with the values in Tian Shan, it indicates that the shape feature of glacial trough valley iswider in Baimaxue Shan, which is in accordance with the feature of the b-FR reflected.Based on research of the glacial remains in the Baimaxue Shan,there exists sixglaciations during Quaternary. Using geomorphology method and the lab Electron SpinResonance (ESR) dating of glacial periods,in this paper we confirm that there were threeglacial advances occurred during Pleistocene which are the Zhonglianggan glaciation(MIS12)and the penultimale glaciation (MIS6) during the Middle Pleistocene, the late glaciationduring the Late Quaternary. Especially, it included the early stage(MIS4), the middlestage(MIS3b) and the Last Glacial Maximum(LGM)(MIS2) during the late glaciation. Inaccordance with morphology and research made by predecessors, there were the neoglaciationand Little Ice Age during the Holocene. And present glacier exists above5000m a.s.l. in thisarea. The glacial extent of the early stage was larger than that of the middle stage during thelast glaciation. According to the shoulder location of the early stage of the last glacial cycle,we estimate that the glacial equilibrium line altitude is consistent with the height confirmedby the geomorphology methods with the cirque floor altitude. So the ancient snowline canalso be determined by the altitude of the shoulder of the glacial trough valley. |
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