Evidence for Holocene megafloods down the Tsangpo River gorge, southeastern Tibet

LacustrineandalluvialterracesandsedimentsrecordtheextentofatleasttwoHoloceneglaciallydammedlakesimmediatelyupstreamofthe Tsangpo Rivergorge at the eastern syntaxis of the Himalaya. The larger lake covered 2835 km 2 , with a maximum depth of 680 m and contained an estimated 832 km 3 of water; the smaller lake contained an estimated 80 km 3 of water. Radiocarbon dating of wood and charcoal yielded conventional radiocarbon ages of 8860 F 40 and 9870 F 50 14 C yr B.P. for the higher set of lake terraces, and 1220 F 40 and 1660 F 40 14 Cy r B.P.forsedimentsfromthelowerterraces.Catastrophicfailureoftheglacialdamsthatimpoundedthelakeswouldhavereleasedoutburstfloods down the gorge of the Tsangpo River with estimated peak discharges of up to 1 to 5 10 6 m 3 s 1 . The erosive potential represented by the unit stream power calculated for the head of the gorge during such a catastrophic lake breakout indicates that post-glacial megafloods down the Tsangpo River were likely among the most erosive events in recent Earth history. D 2004 University of Washington. All rights reserved.