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

Lacustrine and alluvial terraces and sediments record the extent of at least twoHolocene glacially dammed lakes immediately upstream of the Tsangpo River gorge at the eastern syntaxis of the Himalaya. The larger lake covered 2835 km, with a maximum depth of 680 m and contained an estimated 832 km of water; the smaller lake contained an estimated 80 km of water. Radiocarbon dating of wood and charcoal yielded conventional radiocarbon ages of 8860F 40 and 9870F 50 C yr B.P. for the higher set of lake terraces, and 1220F 40 and 1660F 40 C yr B.P. for sediments from the lower terraces. Catastrophic failure of the glacial dams that impounded the lakes would have released outburst floods down the gorge of the Tsangpo River with estimated peak discharges of up to 1 to 5! 10 m 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.