Grain-size distribution of surface sediments of climbing and falling dunes in the Zedang valley of the Yarlung Zangbo River, southern Tibetan plateau

Climbing and falling dunes are widespread in the wide valleys of the middle reaches of the Yarlung Zangbo River. Along a sampling transect running from northeast to southwest through 10 climbing dunes and two falling dunes in the Langsailing area, the surface sediments were sampled to analyse the grain-size characteristics, to clarify the transport pattern of particles with different grain sizes, and to discuss the effects of terrain factors including dune slope, mountain slope, elevation and transport distance to sand transport. Sand dunes on both sides of the ridge are mainly transverse dunes. Fine and medium sands were the main particles, with few very fine and coarse particles in the surface sediments. Particles {>}4.00Φ were blown upslope by suspension, particles 1.00{-}4.00Φ were mainly transported upslope by saltation with opposite change tendency, and particles {<}1.00Φ mainly moved by creep were found almost exclusively at the bottom of the slopes. As terrain factors, elevation and transport distance were more important factors influencing the distribution of grain size and particle fraction on dunes. Local winds observation might be helpful for the transport mechanism study of particles on climbing and falling dunes, while the wind data from nearby weather station was hardly helpful.