Slope height and slope gradient controls on the loess slide size within different slip surfaces

Based on intensive landslide surveys and interpretation of remote sensing images, we established a loess slide inventory map of the Yan'an region in northern Shaanxi province, China. According to their slip surfaces, we grouped loess slides into three categories: landslides in loess, red clay contact landslides, and bedrock contact landslides. Results indicate an obvious power law relationship among loess slide length, area, and volume. Moreover, landslide size depends remarkably on the slip surface. The average area and length of red clay contact landslides are 5.52 and 2.45 times larger than those of landslides in loess. Intermediate-slope relative height and slope gradient have a prominent role in landslide formation. The size distribution of loess slides was examined with respect to the slope height and slope gradient. The analysis revealed that slope height and slope gradient were the most dominant controlling factors for loess slide size. The loess slide became larger with the increasing relative height of the slope, and there is an obvious linear or power law relationship between loess slide size and slope relative height. On the contrary, landslide size gradually decreases as the slope gradient increases at a certain level.