DEM AND GIS BASED MORPHOMETRIC ANALYSIS OF DANXIA LANDFORM IN LONGHUSHAN, CHINA

Danxia is a kind of landform consisting of terrestrial red beds, featuring steep cliffs. It is also recognized as a type of erosional landform widely located in China. Previous studies mostly focus on qualitative description of its definition, geomorphologic features, and slope morphometry. A model of erosional stages of Danxia landform geomorphic development, and tectonic/lithologic controls on its formation have been suggested but rarely verified by rigorous quantitative analysis. Statistical study of the Earth's surface through morphometric parameters is found useful for understanding landform evolution. In this paper, Longhushan, an archetypal Danxia landform site, is selected to study the morphometric features using DEM- and GIS-based analysis. Dimensionless geomorphologic parameters are adopted including normalized stream length-gradient index (SLK), hypsometric integrals (HIs) and hypsometric curves (HCs) as well as river longitudinal profiles. The SLK anomalies for the seven streams across the study area are found to positively correlate with the presence of faults and changes in rock erodibility, reflecting tectonic and lithologic controls on the formation of topography. Hypsometric analysis of the 26 subwatersheds in Danxia landform areas yield low HIs (<0.42, mean=0.21) with concave up hypsometric curves, suggesting Danxia landforms in Longhushan are in an old erosional stage. The findings in this research are in accordance with the previously proposed, but invalidated, old geomorphic stage of Longhushan that is based on estimated eroded land mass. This work developed a quantitative approach for evaluating the erosional status of Danxia landforms and for validating lithological and tectonic controls on its surface topography in relation to bedrock channels. The parameters used in this research are dimensionless, thus can be applied in other Danxia landform areas for future comparison.