Geology

Megafloods from Tibet

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Science  23 Aug 2013:
Vol. 341, Issue 6148, pp. 823
DOI: 10.1126/science.341.6148.823-c
CREDIT: BGABEL AT WIKIVOYAGE SHARED/WIKIMEDIA COMMONS

In between the Tibetan plateau and the Himalaya runs the Yarlung-Tsangpo River. In general, the balance of tectonic uplift and erosion—usually caused by rivers that carry abraded bedrock downstream—controls the elevation of such mountainous regions. Lang et al. used U-Pb dating to record the source of zircon grains in sediments deposited downstream of the Tsangpo Gorge, a steep, narrow canyon cut by the Yarlung-Tsangpo River as it enters the Eastern Himalaya. The ages and composition of these grains suggest they were deposited by large flood events from rapid drainage of glacial lakes in Tibet in the past few million years. Although these historical events may be infrequent, they probably contribute substantially to the overall evolution of the landscape. One megaflood alone could erode more material than the baseline erosion rate typically removes in 1000 to 4000 years.

Geology 41, 1003 (2013).

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