Abstract
Field surveys and radiocarbon dating of detrital materials provide evidence that repeated landslides dammed the Yigong Tsangpo River ca. 3500 bc, 1300 bc, 1000 bc, 600 bc, and twice more recently. Together with historical slides in 1900 and 2000, these six older slides make for a total of eight known channel-damming landslide events at the same location over the past six millennia, indicating sub-millennia recurrence intervals over this time period. Together with the likely incomplete nature of the sedimentary record of past channel-damming episodes uncovered to date, our findings indicate late Holocene multi-century-scale recurrence intervals for large landslides at this location. Hence, the riverbed at and immediately upstream of this location may have been inundated by sediment, and therefore not incising, for much of the post-glacial period. Together with the location of this landslide complex at the head of the major knickzone defining the fluvial edge of the Tibetan Plateau, our findings support the hypothesis that repeated glacial and landslide damming in this region inhibited headward propagation of river incision into the Tibetan Plateau.
Highlights
Landslides can be important erosional processes in upland landscapes with moderate to steep hillslopes[1]
Korup and Montgomery proposed that frequent glacial damming in the eastern Himalayan syntaxis (EHS) during the Quaternary inhibited headward incision of major rivers, thereby retarding dissection into the edge of the Tibetan Plateau[2]
Our findings show that repeated failures of large landslides at this location both present a recurrent hazard and help retard headward propagation of fluvial knickpoints, thereby affecting the development of river profiles in the EHS13
Summary
Landslides can be important erosional processes in upland landscapes with moderate to steep hillslopes[1]. Korup and Montgomery proposed that frequent glacial damming in the eastern Himalayan syntaxis (EHS) during the Quaternary inhibited headward incision of major rivers, thereby retarding dissection into the edge of the Tibetan Plateau[2] While this hypothesis was rooted in evidence for repeated glacial damming of the Yarlung Tsangpo immediately above its gorge through the Himalaya[9], similar glacial and landslide blockages occur on other major tributaries upstream of the deeply incised bedrock gorges in the E HS2. Like the glacial dam at the head of the Tsangpo Gorge, and the landslide dam on the Lulang River, the Yigong landslide is located immediately upstream of the knickzone defining the headward limit of river incision into the edge of the Tibetan Plateau. The flood down the gorge produced sustained high bed shear stresses capable of plucking meter-scale blocks from the r iverbed[19]
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