基于面积-高程积分值的喀斯特地貌演化动力机制研究

Dynamic mechanism of karst geomorphology evolution based on Hypsometric Index

洼地是喀斯特地形分化的元地形,定量化阐述洼地与整体地貌之间的协同演化对于揭示喀斯特地貌空间结构差异及其差异演化的动力学机制具有重要意义。将地理信息系统的数字地形分析与戴维斯地貌循环论、面积-高程法结合,以盘龙河-泸江喀斯特流域为研究对象,探讨从古夷平面向阶梯状地形格局转变背景下喀斯特地貌的分异规律及其动力学机制。结果显示:1)从上游、中游到下游,洼地的数量分别为8145个、5636个、1883个,平均密度分别为1.96个/km^(2)、1.23个/km^(2)、0.61个/km^(2),平均深度分别为22.6 m、34.9 m、12.8 m;峰丛数量分别为9094个、7281个、5710个,平均密度分别为2.19个/km^(2)、1.59个/km^(2)、1.86个/km^(2),平均高度分别为29.3 m、47.8 m、26.1 m。2)从流域汇口到源头可划分为堆积孤丘平原、构造侵蚀花岗岩中山、斜坡峰丛谷地、溶原缓丘-断陷盆地和构造溶蚀亚高山这5个地貌区,对应的平均坡度分别为16.8°、23.5°、22.4°、12.5°、19.8°,平均起伏度分别为311 m、605 m、393 m、170 m、323 m。3)流域平均面积-高程积分值为0.352,洼地平均积分值为0.508,属溶原背景下的回春型壮年晚期地貌,5个地貌区的区域面积-高程积分值分别为0.147、0.425、0.510、0.355、0.397,洼地面积-高程积分值分别为0.116、0.302、0.598、0.481、0.278。反映高原隆升形成的梯级坡降奠定了盘龙河-泸江流域差异性喀斯特地貌发育的基础,即海拔梯度上的结构动力学和水系发育带来的流域汇流、侵蚀溶蚀顺水力坡度变化,具体过程是洼地的发育和合并。从区域积分值和洼地积分值的大小关系,结合各地貌区内的海拔、坡度、起伏度特征和野外地质地貌调查,认为当洼地面积-高程积分值大于区域面积-高程积分值时,洼地强烈新生和扩张,地貌向起伏度增大的青年期发展;反之洼地发育减弱或停滞,地貌向夷平蚀低的准平原化发展。由此可见,洼地面积-高程积分值可作为喀斯特区地貌演化动力增强或减弱的定量化指标。

Depression is the meta-topography of karst topography differentiation.It is of great significance to quantitatively explain the co-evolution between depression and whole landform for revealing the spatial structure of karst landform and its dynamic mechanism of differential evolution.Panlong-Lujiang River Basin is located in the transition area from Yunnan Plateau to Vietnam Hilly Plain.Controlled by the uplift of Qinghai-Tibetan Plateau,this area changes from ancient leveling to stepped topography pattern,and the distribution of carbonate rocks in this area is close to 87%,which is a typical karst basin.The unique tectonic history and topographic structure provide a rare test site for studying the evolution and differentiation of karst landforms.In this study,the digital terrain analysis of GIS is combined with Davis geomorphology cycle theory and Hypsometric Index to discuss the differentiation law and dynamic mechanism of karst geomorphology under the background of changing from ancient leveling to stepped terrain pattern.The results show that:(1)The number of depressions is 8145,5636 and 1883,the average density is 1.96/km^(2),1.23/km^(2) and 0.61/km^(2) depressions,the average depth is 22.6 m,34.9 m and 12.8 m;The number of peak clusters is 9094,7281 and 5710 respectively,the average density is 2.19/km^(2),1.59/km^(2) and 1.86/km^(2) respectively,and the average height is 29.3 m,47.8 m and 26.1 m respectively.(2)From the confluence to the source of the basin,it can be divided into five geomorphic areas:accumulation solitary hill plain,tectonic erosion granite mountain,slope peak cluster valley,lysogenic gentle mound-fault basin and tectonic erosion subalpine.The corresponding average slopes are 16.8,23.5,22.4,12.5 and 19.8 respectively,and the average undulations are 311 m,605 m,393 m,170 m and 323 m respectively.(3)The average watershed integral value is 0.352 and the depression integral value is 0.508,which belongs to the late mature landform of rejuvenation type under lysogenic background.The regional area-elevation integral values of the five landform areas are 0.147,0.425,0.510,0.355 and 0.397 respectively,and the depression area-elevation integral values are 0.116,0.302,0.598,0.481 and 0.278 respectively.Cascade gradient reflecting the formation of plateau uplift lays the foundation for the development of differential karst landform in Panlong-Lujiang River basin,that is,structural dynamics on altitude gradient and watershed confluence,erosion and dissolution along hydraulic gradient change caused by water system development,and the specific process is the development and merger of depressions.According to the size relationship between regional integral value and depression integral value,it is considered that when the HI of depression is greater than that of region,the karst geomorphology evolves in reverse combined with the characteristics of elevation,slope and undulation in each geomorphic area and the field geological and geomorphological investigation.That is,the karst geomorphology develops towards the young and middle-aged period with the increase of topographic undulation and hydraulic slope,which corresponds to the deepening of depression,the increase of peak cluster and the development of surface zone;On the contrary,it is a positive evolution,that is,the karst landform develops towards the lysogen of the residual mound with low leveling and erosion,and the erosion power is mainly lateral leveling and widening,which shows that the depressions become shallow,merged and widened,and the dissolution plain and peak cluster change to peak forest and isolated peak,and its basic power is controlled by the difference between the above-ground and underground erosion datum levels.