白马雪山冰川槽谷发育的形态特征及其影响因素探讨

白马雪山地处横断山脉腹地,对于重建西南季风影响区的环境变迁以及探讨冰川作用特点具有重要科学意义。这里保留着典型的晚第四纪冰川侵蚀地貌,其中冰川槽谷发育特征明显。本文运用抛物线形态参数、梯级宽深比、形态比率等定量分析冰川槽谷的研究方法,对保存在白马雪山主峰扎拉雀尼(5429m)东北坡的两条简单冰川槽谷的形态特征进行分析。采用7个典型剖面的形态特征参数与其他地区对比,探讨冰川槽谷发育的可能影响因素如水热条件、冰川性质、冰川规模、岩性特点、冰川作用时间等。结果显示: 白马雪山冰川槽谷抛物线形态参数b值为1.779,明显小于冰川性质相同的螺髻山(1.835),主要是由于区域降水条件的不同所造成的差异,而与冰川性质不同天山乌鲁木齐河源区(1.825)冰川槽谷的形态特征的差异,可能与冰川规模、作用时间以及岩性条件密切相关; 梯级宽深比中槽谷形态参数沿程变化可以反映冰川流动过程中的动力变化,梯级宽深比中的形态参数Af和Bf值最大处对应的谷肩位置接近雪线位置。根据槽谷谷肩的位置确定末次冰期早期/中期的雪线高度为4140m,这与用地貌法如冰斗底部高程法、侧碛堤最大高度法和冰川末端至冰斗后壁最大高度法等综合确定的雪线高度4092m基本一致。因此,在冰川槽谷发育的冰川作用区,用槽谷谷肩的海拔高度估算雪线高度可以成为一种比较可靠的确定古雪线方法; 白马雪山的冰川槽谷形态参数b-FR的特征表明,即使是海洋性冰川作用区也不符合Hiran和Aniya提出的山地冰川模式,但运用b-FR相关关系可以很好的反映冰川的侵蚀过程。白马雪山地区冰川侧蚀作用导致槽谷坡降值较小,底部较平坦宽阔,呈现出相对完整的U型形态。此外,用形态比率FR值也可以验证雪线的位置高度。

ANALYSIS OF THE GEOMORPHOLOGY FEATURES OF THE GLACIAL TROUGH VALLEYS AND THE INFLUENCE FACTORS IN THE BAIMAXUE SHAN,NORTHWEST OF YUNNAN PROVINCE

Baimaxue Shan,watershed of the Jinsha River and the Lancang River with latitude of 27°24'~28°36'N and longitude of 98°57'~99°25'E,is located in the inner part of the Hengduan Mountain Range and is situated between the Deqin County and Weixi County of in the northwest of the Diqing Tibetan Autonomous Prefecture,northwest of Yunnan Province.The study of the physical geographical features here has the significant meaning about both reconstructing the environmental change of the southwest monsoon and the glacial development.The definitely preserved glacial landforms and deposits indicate here was once glaciated during the Late Quaternary,especially the glacial erosive landform such as the trough valleys.Using the methods 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 the northeastern side of the main peak of Zhalaqueni (5429m) and the affected factors.Adopted the shape parameters of the seven profiles of these trough valleys and contrasted with other regions with well developed trough valleys,the possible reasons influenced the glacial trough valleys such as the glacial extent,type,the local climate,time span and the base rock type etc were discussed herein.The results show that the mean value of b is 1.779 in the trough valleys 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 from the head water of the Ürümqi(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 the glacier nature but also affected by the climate condition,glacial extent,time interval and the lithology.The parameter change of the gradient ratio of wide and depth along the trough valley can reflect the dynamic change during the course of the glacial flow.According to the shoulder location of the early stage of the last glacial cycle,we estimate that the glacial equilibrium line altitude is about 4140m,and this value is consistent with 4092m confirmed by the geomorphology methods such as the cirque floor altitude,maximum altitude of the lateral moraine and the ratio of the toe to headwall.So the ancient snowline can also be determined by the altitude of the shoulder of the glacial trough valley.The parameters of the b-FR in Baimaxue Shan show that the characteristic of the glacial trough valley is not consistent with the mountainous pattern put forward by the Hiran and Aniya even in the region of maritime glacier.However,the feature of the b-FR can reflect the procedure of the glacial 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 and shows the perfect U shape.Meanwhile,the shape ratio (b-FR) can also verify the ancient snow line altitude.