Abstract
At the southeastern margin of the Tibetan Plateau, the Yarlung-Tsangpo River plunges through the Himalaya to drop >2 km through the Tsangpo Gorge. Upstream, relict glacial dams and impounded lake terraces suggest that Quaternary lakes as large as 800 km 3 catastrophically drained through the gorge as megafloods. We report on new megaflood deposits downstream of the gorge and use detrital zircon U-Pb provenance data to demonstrate that these high-magnitude events originated in Tibet, and more effectively focused erosion in the gorge than both the extremely erosive modern peak flows and one of the largest landslide-dam outburst floods ever documented. Our findings support the proposition that in this steep, narrow gorge, where hillslope angles are near the threshold angle of bedrock failure, megafloods provide a mechanism to rapidly evacuate hillslope material and focus erosion on channel-adjacent hillslopes. Although megaflood frequency remains unconstrained, we demonstrate the capability of these events to contribute substantially to rapid exhumation in this region.
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