Controls on the effect of impact scraping on high-position and long-runout landslides

Landslides in mountainous areas act as an important control on morphological landscape evolution and represent a major natural hazard. The dynamic characteristics of a landslide directly relate to the distance it traveled and its scale. Based on extensive field investigations, we explored the effect of impact scraping on high-position and long-runout landslides. During a rapid landslide, impact scraping amplifies the volume of the landslide and the size of the affected area. Without acknowledging this effect, it is easy to underestimate the risk presented by a given potential landslide. In this study, we investigate the impact scraping of landslides that travel significant distances both vertically (high-position) and horizontally (long-runout). There are four developmental stages of high-position and long-runout landslides: high-position shearing, gravitational acceleration, impact scraping, and debris deposition. Impact scraping amplifies the scale of a landslide by drastically increasing the volume. After accounting for the effect of impact scraping, the total volume of the landslide exhibits a strong correlation with its travel distance. Additionally, the material properties of the erodible layer influence landslide mobility. High-position and long-runout landslides have multiple scraping modes, including the embedding and excavation mode, the entrainment mode, the pushing and sliding mode, and the impact and splashing mode. In this study, we aim to provide insight that will improve the dynamic modeling and risk assessment of high-position landslides and to offer theoretical support for high-position and long-runout landslide dynamics research, prevention and mitigation and first responder rescue operation planning.