Drainage reorganization driven by strike-slip faulting along the Xiaojiang Fault, Southeastern Tibet: A new explanation for geohazards in the Xiaojiang River watershed

The Xiaojiang River, located at the southeastern margin of the Tibetan Plateau, is among the world’s most landslide- and debris-flow-prone regions. The main trunk of the Xiaojiang River is basically aligned with the Xiaojiang Fault, a major block-boundary fault at the southeastern Tibet characterized by sinistral strike-slip motion. However, it is still unclear how the strike-slip faulting governs the long-term drainage evolution of the Xiaojiang River and, in turn, impacts the geohazards in the Xiaojiang River watershed. Here we investigate the drainage evolution of the Xiaojiang River using high-resolution topography and quantitative geomorphic analyses, with a focus on drainage-divide migration and river captures. Our results reveal that most tributaries within the Xiaojiang River watershed are expanding, primarily driven by bedrock weakening due to fault fracturing. The expansion of the Xiaojiang River watershed further promotes soil erosion and landslides in the basin. We further identify a river-capture event controlled by the strike-slip faulting, which caused the ~400 m lowering of the base level and the subsequent extreme concentration of debris flows within the Jiangjia Ravine. These findings demonstrate that tectonics-induced drainage reorganization is one of the primary regulators of regional geohazard distribution. Incorporating dynamic drainage evolution into hazard-assessment frameworks is therefore essential for improving long-term risk mitigation in tectonically active mountain belts.