Post-glacial entrenchment and knickpoint migration of the Yarlung Tsangpo Gorge, southeastern Tibetan Plateau

Abstract

The formation of the Yarlung Tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago. However, climate change may also play an important role in guiding drainage evolution. Here we reconstruct the drainage history of the Yarlung Tsangpo Gorge using field observations, age constraints from optically stimulated luminescence and radiocarbon dating, paleosalinity reconstruction and grain size analysis of lacustrine deposits, and river valley characteristics. Field observations, clay boron-derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the Yarlung Tsangpo Gorge, implying that cutting of the gorge postdated this paleolake. Optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after ~13 ka. With a shift in global climate following the Last Glacial Maximum, the paleolake drained by river capture, and the gorge entrenchment commenced at the village of Jiala northwest of the Namche Barwa peak, approximately 13–10 ka ago. The evolution of the Yarlung Tsangpo occurred on a remarkably short timescale of just tens of thousands of years. In response to drainage system reorganization, the Yarlung Tsangpo incised at an average rate of at least 26 mm/yr. The rapid fluvial incision initiated at Jiala ~13 ka ago propagated rapidly upstream at ~2.12 m/yr. The Yarlung Tsangpo knickpoint has not stabilized, but will likely continue to migrate upstream.