First author

The Tibetan Plateau, sometimes called the 'roof of the world', is thought to be the largest and highest flat area ever to exist on Earth. We know how it formed — through a massive collision between the Indian and Asian continental plates — but how it is maintained in the face of erosion and incision by the powerful rivers that flow along its fringes is much less clear. On page 786, Oliver Korup of the Swiss Federal Institute for Snow and Avalanche Research in Davos and David Montgomery at the University of Washington in Seattle propose that glacial advances over at least the past 10,000 years preserved the plateau's southeastern edge by blocking and weakening the flow of water through much of the river network. Korup tells Nature more.

Why is the Tibetan Plateau's magnitude such a mystery?

According to widely accepted theory, the plateau margin should erode rapidly, and the plateau itself should be sliced to bits by some of Asia's largest rivers. Yet the plateau surface and its edges are prominent. Classic explanations for this mainly invoke aridity and highly localized rock uplift as limits to the plateau's dissection.

What made you think that glaciers might be involved instead?

Satellite images of the area showed a surprising number of large moraine dams — river-blocking piles of debris formed by glaciers. The way these dams cluster together is unusual, so we decided to reconstruct how much ice once occupied the drainage network. Just as you can figure out somebody's shoe size from their footprint, the extent of past glaciers can be calculated from moraine dams.

How do glaciers help to preserve the plateau margin?

The glaciers act a bit like bulldozers: they collect a lot of sediment and push it into the larger river valleys, where it sits like used coffee grounds in a sink, and blocks up the drainage network. We argue that a similar mechanism is shutting down the incision into bedrock along the plateau edge. Meanwhile, aggressive river incision below the dams helps to accentuate the steep plateau margin.

How might climate change affect the Tibetan Plateau's landscape?

If most of the remaining glaciers in this area dwindle away, the rivers' stream power, and so erosion potential, could increase as the glaciers melt. But eventually, with little or no ice left, the erosion potential of the smaller rivers will decrease, thereby slowing down incision into the plateau edge.