LONGITUDINAL PROFILES OF LARGE RIVERS DRAINING ALL EDGES OF THE TIBETAN PLATEAU

River long profile has been used extensively to test bedrock incision models or to deduce the style of regional tectonic uplift. Rivers draining from the Tibetan plateau are among world’s longest rivers with largest drainage basin relief and sediment loads. Incision of these rivers and thus erosion of the plateau is an important process, which has been largely overlooked in geodynamic models of Tibetan plateau deformation. We analyze long profiles of rivers that drain all edges of the plateau, to gain perspective on recent studies on fluvial incision of the plateau, which have mainly focused on certain parts of the Himalayas and southeastern Tibet: regions currently under monsoonal influence with relatively higher modern day precipitation than the rest of the plateau. Our preliminary results show that most rivers with their headwaters on the plateau have a stepped or convex-up long profile: flat in the upper reach on the plateau and steep in the middle reach across the plateau edge. The knickpoints are not far inside from the edge, especially on those draining the Himalayas, which suggests limited knickpoint retreat, or even pinning. In southeast Tibet, Salween, Mekong, Jinsha and Yalong have wider knick zones. The lower elbows of the knick zones are aligned roughly northeasterly between 25 - 27°, parallel to the Yalong thrust belt. The locations of upper elbows, however, vary. The widths of knickzones are positively correlated to the sizes of drainage basins and discharge. In addition, rivers in dry regions have more prominent convex shapes, and less valley-ridge relief than in wetter regions. In general, the degree of down-cutting and headwords extent of Tibetan plateau rivers is strongly modulated by climate/climate change, and the steepness of plateau edge. If so, river incision can lag considerably, perhaps tens of millions years, behind regional surface uplift under dry conditions. Our observations have implications for numerical modeling of the rate of knickpoint retreat, particularly in the context of eroding regionally extensive “flat” paleo-surface.