Sediment Records Indicate Outburst Events of Gega Dammed Lake at Yarlung Tsangpo River in the Tibetan Plateau

Abstract

Outburst floods from glacial-dammed lakes are the main source of megafloods on earth (Baker, 2013). Outburst floods not only cut deep gorges, but also heavily impacted prehistoric human society deeply because they were the main sources of the great floods described in many legends(Baker, 2009). Outburst floods have even caused global climate change by changing ocean circulation after flowing into the sea (Clarke et al.,2003). The Gega paleo-dammed lake is, located at the entrance of the Yarlung Tsangpo gorge, and is the only paleo-glacial dammed lake found in the eastern Tibetan Plateau. However, no detailed analyses of its outburst floods have been carried out (Liu et al., 2015; Montgomery et al., 2004). The sediments from outburst floods, such as gravel dunes and slack-water deposits, were stored in limited amounts because downstream of the dam often consisted of gorges. In addition to forming downstream deposits, outburst floods can also cause a sudden decline in the dammed lake’s water levels, or even cause the lake to dry up. The sediment from dammed lakes can therefore be used to reconstruct the outburst events (Liu et al., 2014), as has been done for the Missoula dammed lake (Hanson et al., 2012). In previous work, we studied the feasibility of using lacustrine sediment from the Gega paleo-lake to reconstruct outburst events (Liu et al., 2018; Liu et al.,2014). In the present study, we selected the 28.5 m Guoruo (GR) lacustrine section of the Gega paleo-dammed lake for detailed analysis. We carried out detailed multiple proxy analysis and investigated the sand layers that indicated three outburst events.