Study area Lancang River (Upper Mekong) Grand Canyon, situated on the southeastern Tibetan Plateau, represents a high mountain canyon of Three Parallel Rivers Region. Research focus This study integrates sedimentary, geomorphic, chronological, and hydraulic evidence from outburst flood events in the Lancang River Grand Canyon. Our investigation identified three primary palaeoflood records: fine-grained slackwater deposits, gravel bar deposits, and boulder deposits. These flood deposits with similar geochemical composition implies a same flood source. Outburst floods induced by the upstream two landslide dams were dated to 11.9–6.4 ka. New hydrological insights for the region Holocene outburst flood magnitudes were estimated to 39,500–45,900 m³ /s, exceeding the largest observed flood by 7.5–10 times. Such discharges were generated by partial landslide dam failures that eroded more than 50% of the dam height. Hydrodynamic variations and channel morphology result in lateral accretion and backwater-eddy effects during floods. Bedrock channel erosion occurred preferentially at local topographic features within narrow meander bends. High-magnitude outburst floods generate high shear stress (0.4–1.1 kPa) and unit stream power (4.5–10.5 kW/m²) and play a critical role in the geomorphic evolution of the upper Lancang River. Depth-velocity (DV) metrics from palaeoflood‑based worst‑case scenarios indicate highest hazards (DV> 240 m 2 /s) for bridges versus backwater flooding (DV< 65 m 2 /s) for roads/villages. This study provides valuable insights into the assessment of similar cascading flood hazards in the southeastern Tibetan Plateau.
Guo et al. (Fri,) studied this question.