Catastrophic outburst floods along the middle Yarlung Tsangpo River: Responses to coupled fault and glacial activity on the Southern Tibetan Plateau

Abstract

The immense outburst floods that have occurred on the Tibetan Plateau during the Late Quaternary are closely linked to tectonic and climatic factors. These floods likely induced very rapid, short-term geomorphic impacts on the evolution of mountain drainage systems and patterns of sedimentary movement. In this study, four glacially-dammed lake outburst flood events that occurred along the middle reaches of the Yarlung Tsangpo River since the Middle Pleistocene were reconstructed by combining comprehensive geomorphic, stratigraphic and geochronologic investigations. The most recent outburst flood sequence occurred at ∼10.5 ka, with a peak discharge of ∼5 × 105 m3/s. The tilted uplift of the Cona Normal Fault has resulted in localized topographic lift and the formation of river knickpoints, contributing to the development and stabilization of glacial dams. River damming and outburst events have also been influenced by glacial-interglacial climate fluctuations since the Middle Pleistocene. The focused erosion and extensive mobilization of sediment by these low-frequency, high-energy floods have resulted in a repeated pattern of material transport and deposition from the Tibetan Plateau interior to its exterior. Coupled with glacial activity, the primary factor impacting the sustained stability of knickpoints on the Yarlung Tsangpo River along the Tibetan plateau's southern margin has been differential rock uplift, which results in a distinct geomorphic pattern characterized by knickpoints, glacial dams and alternating wide valleys and deep gorges.