Formation Mechanism and Hummock Development of the River-damming Daipo Landslide and its Impact on the Longitudinal Profile Evolution of Lai'nong River, Southeastern Tibetan Plateau

Large-scale river-damming landslides are widespread in the orogenic regions of the Tibetan Plateau and represent an important feedback between fluvial erosion and hillslope processes, with potential long-term impacts on river longitudinal profile evolution. This study investigates the formation mechanism, depositional characteristics, and geomorphic effects of the ca. 11.0 Mm³ Daipo river-damming landslide in the Lai'nong catchment, southeastern Tibetan Plateau. Remote sensing interpretation, UAV-based photogrammetry, detailed field investigations, and GIS-based analyses were employed to characterize the geological structure of the source area, landslide kinematics, hummock development, landslide mobility, and the stability of the landslide dam. The Daipo landslide originated as a deep-seated compound rockslide on a northeast-facing dip slope composed of highly fractured Triassic Jieza limestone. Three major discontinuity sets, including gently downhill-dipping bedding planes, high-angle NW-trending joints, and steep NE-trending joints, provided the toe, rear, and lateral release surfaces for the initial detachment. Oblique thrusting associated with a prehistoric rupture of the Duolunduo-Mamuqu Thrust, which crosses the toe of the landslide source, is considered the most probable triggering mechanism. The landslide reached an estimated maximum velocity of 30 to 43 m/s based on run-up analysis. A total of 255 hummocks were identified on the landslide deposit, predominantly clustered in the middle and distal depositional areas. The hummocks exhibit a typical size-distance relationship, with their average size decreasing progressively away from the landslide source. Transverse ridges initially formed near the failure scar through extensional faulting and subsequently disaggregated during downslope transport under combined downslope and lateral extension. In the final depositional stage, frontal compression against the opposite valley wall further contributed to hummock formation. The Daipo landslide completely blocked the Lai'nong River and formed a 48 m high stable landslide dam, which generated a pronounced knickpoint along the river longitudinal profile. By burying the channel bed beneath landslide debris and subsequent deltaic sediment deposits, the dam has effectively inhibited local river incision since its formation. This study provides new insights into the formation mechanisms of large river-damming landslides, the development of hummocky deposits, and their long-term geomorphic impacts on mountain river systems.