Bedload-to-suspended load ratio and rapid bedrock incision from Himalayan landslide-dam lake record
نویسندگان
چکیده
About 5400 cal yr BP, a large landslide formed a N400-m-tall dam in the upper Marsyandi River, central Nepal. The resulting lacustrine and deltaic deposits stretched N7 km upstream, reaching a thickness of 120 m. C dating of 7 wood fragments reveals that the aggradation and subsequent incision occurred remarkably quickly (∼500 yr). Reconstructed volumes of lacustrine (∼0.16 km) and deltaic (∼0.09 km) deposits indicate a bedload-to-suspended load ratio of 1:2, considerably higher than the ≤1:10 that is commonly assumed. At the downstream end of the landslide dam, the river incised a new channel through ≥70 m of Greater Himalayan gneiss, requiring a minimum bedrock incision rate of 13 mm/ yr over last 5400 yr. The majority of incision presumably occurred over a fraction of this time, suggesting much higher rates. The high bedload ratio from such an energetic mountain river is a particularly significant addition to our knowledge of sediment flux in orogenic environments. © 2007 University of Washington. All rights reserved.
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