Controls on valley width across active structures

Beveled folds in the foreland of the Tian Shan.

In the foreland of the Tian Shan, folds that are uplifting several millimeters per year have been completely planed off by rivers. How do such wide erosion surfaces form? And why do most rivers at the modern-day incise deep and narrow canyons into the folds? We have shown that, in order to explain these geometries, the rate at which rivers erode bedrock laterally must have varied by orders of magnitude.

A model for valley width

Motivated by the observations from the Tian Shan foreland, we used physical experiments to show that the width of valleys across active structures is controlled by the competition between the uplift rate and the lateral mobility of channels. In turn, lateral channel mobility is controlled by water and sediment discharges. Therefore, our model yields a framework to use the width of valleys as a proxy for tectonics and climate.

Testing the framework

Ongoing work is aimed at testing this framework. For example, we are working at a compilation of river widths in active mountain ranges for which uplift rates and sediment and water discharges are known. Moreover,  we are currently measuring modern and paleo-erosion rates (as a proxy for sediment and water discharges) in the foreland of the Tian Shan across times where valley width changed by orders of magnitude.