DEM and GIS based morphometric and topographic- profile analyses of Danxia landforms

“Danxia landform” is a landform type originally defined in China, characterized by red-colored sandstones and steep cliffs, and developed through long-term erosion. In recent years, Danxia landforms have been receiving international attention, and six examples in China became a UNESCO World Natural Heritage in 2010. However, morphometric studies of Danxia landforms in China have been very limited. We conducted DEM-based geomorphometric analyses for 45 watersheds and 319 second-order subwatersheds of Mt. Danxia, a typical Danxia landform in China. Investigated properties include drainage basin area, basin relief, relief ratio, slope, and hypsometry. Mountains and hilly lands dissected by fluvial processes including Danxia landforms can also be characterized by stream longitudinal profiles and valley transverse profiles. Therefore, both profiles for the watersheds in Mt. Danxia were extracted from a DEM and the former was used to analyze the stream length gradient index (SL index), the stream concavity index, and the slope–area relationship. A series of morphometric analyses were conducted to infer lithologic and tectonic influences on the landforms. The results indicate that localized erosion has enhanced deepening of existing fractures rather than lateral erosion to form deep and narrow valleys, while long-term erosion provided large and gentle watersheds. Anomalously higher SL values often occur with knickpoints where bedrock incision is affected by lithology and faults. The results indicate that studied watersheds exhibits high spatial variations in the morphometric properties and some of them resulted from lithologic control.