High-elevation, low-relief surfaces are generally believed to be uplifted old landscapes, preserving former, more moderate tectonic conditions. In the current study, published in Nature last week, Dr. Liran Goren of the Department of Geological and Environmental Sciences at BGU and Dr. Rong Yang and Prof. Sean Willet of The Geological Institute, Swiss Federal Institute of Technology tested this view of landscape formation in the southeastern margin of the Tibetan Plateau, where three immense rivers, the Salween, Mekong and Yangtze form up to three kilometer deep gorges with scattered low-relief four kilometer high surfaces in between the gorges.
“Relief refers to differences in topography along an area. Low-relief indicates relatively flat,” says Goren, “Normally, in high mountain ranges, surface slopes are steep and as a result the relief is high, creating the typical impressive morphology we all imagine when we think about the peaks of the Alps for example. In some places, however, it is possible to find low-relief surfaces at high elevations. This is unexpected because rivers that drain high elevations normally have steep gradients and so do the hillslopes that grade to the rivers. So one can ask the following question: what conditions are responsible for the formation of these counter-intuitive low-relief high elevation surfaces?”
So far it has been believed that these are remnants of old, relatively flat, topography that formed during a tectonically quiet period, which was elevated by tectonic uplift. According to this view, low-relief high elevation surfaces along the southeastern margin of the Tibetan Plateau preserve to some degree the local topography before India collided with Eurasia and the Himalayas rose, about 50 million years ago.
The authors demonstrate that this view is not consistent with the drainage network of the southeastern margin of the Tibetan Plateau and offer a different explanation: that these surfaces are forming continuously during more recent geological history (for the Himalayas, for instance, from 50 million years ago and continuing into the present day) due to drainage network reorganization that leaves some tributaries without enough drainage area to collect water, erode the surface, and balance the tectonic uplift, thus forming low-relief surfaces at high elevations.
