Morphometrics of China's Loess Plateau: The spatial legacy of tectonics, climate, and loess deposition history

Abstract

The Loess Plateau in China is the largest and deepest loess deposit in the world. The surficial geology is dominated by Quaternary loess deposits of varying thicknesses, which exhibit some of the fastest erosion rates in the world. Although the plateau has been traditionally thought of as morphologically homogenous, river network morphometrics in this area are spatially variable, suggesting that landscape evolution processes across the plateau are sensitive to variability in local conditions. We divided the plateau into sub-basins and examined six DEM-derived morphometric parameters: Aspect Ratio, Anisotropic Coefficient Variation (ACV), Bifurcation Ratio, Concavity, Steepness, and Mean Junction Angle. The sub-basins exhibited low aspect ratios, high bifurcation ratios and large junction angles relative to landscapes around the world, however they varied intra-regionally relative to each other. Through the use of Principal Component Analysis and Cluster Analysis, we observed specific spatial variation in morphometrics attributable to differences in climate, lithology and tectonics along a NW-SE transect through the plateau. Sub-basins in the elevated plateau regions are more oval with higher aspect ratios and lower ACV values while those located in down-dropped valley regions have smaller junction angles, lower concavity and steepness index. Sub-basins in the transition area between down-dropped and elevated parts of the plateau are distinguished by their high bifurcation ratios and elongated shape. We propose a conceptual model to explain the relationship between these morphometrics and the local environmental conditions.