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The Yangtze River is the longest watercourse in China, where it flows through the most densely populated and richest regions. The upper course of the River (Jinsha River) has been recurrently blocked over the course of time. The dam-outburst flood process has exerted a significant impact on the river's drainage area. However, the frequency of such events along the course of the Yangtze River remains poorly investigated. In this study, damming chain sediments were identified in the First Bend area of the Yangtze River, and were dated using optically stimulated luminescence (OSL) and 14C techniques. The obtained ages would suggest that the river was dammed by a debris flow during the ~20–7 ka period, with a resulting paleolake covering an area of 40.79 km2 and having a water volume of 0.63 km3. Two outburst megafloods occurred at ~18–20 and ~ 6.0 ka, respectively. The river was re-dammed again during 1.5–0.4 ka, with a lake coverage of 28.20 km2 and water volume of 0.28 km3. The dammed lake may have been gradually breached after ~0.4 ka. The damming events were caused by debris flows triggered by glacial advances on Yulong Mountain. • Fully investigated the paleo- damming chain sediments in the First Bend area of the Yangtze River. • OSL and 14C ages suggest that the river were dammed twice by debris flows during the ~20–7 and 1.5–0.4 ka period, and two outburst megafloods occurred at ~18–20 and ~ 6.0 ka, respectively. • The damming events were caused by debris flows triggered by glacial advances on Yulong Mountain. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau and Indian Plain exhibit the largest altitudinal difference between two geographically contiguous areas on Earth, but the eastern margin of the Plateau has not experienced headward erosion of the Yarlung Zangbo River (YZR) since ~2.5 Ma. In the past, some scientists have argued that moraine dams on Mount Namcha Barwa (in the Eastern Himalayan syntaxis) frequently blocked the YZR, thus keeping the Plateau's margin intact at this point. In this study, three sets of moraines were identified in the Pai Valley alongside Namcha Barwa, and were dated using optically stimulated luminescence (OSL) and 10Be exposure dating. The resultant ages would suggest that three glaciations occurred at ~22.2, 4.7 and 1.3 ka, respectively. Comparison of OSL and 10Be ages for glacial advances with local paleoclimatic proxies would suggest that temperature was the dominant factor controlling glacial change. Because of the paleoglacial advance frequency, coupling with rapid fluvial incision, moraine dams were cut through by the YZR. Thus, any moraine dams that lost their efficacy in impacting upon knickpoint migration. Instead, similarities between rock uplift and fluvial incision, rather than moraine dams, might have been the main control impeding headward erosion of the YZR, thereby keeping this part of the eastern Tibetan Plateau margin intact. • Glacial-fluvial landscape development explored in the Eastern Himalayan syntaxis were mapped and dated in the Pai Valley • OSL/TCN ages cluster to ~22.2, 4.7, 1.3 ka, associated with climate-glacial advances • Glacier extent-timings and knickpoints in relation to river gorge damming explored • Uplift-fluvial incision balance controls eastern Tibetan Plateau margin stability [ABSTRACT FROM AUTHOR]