1. Department of Geological Sciences, University of California, Santa Barbara, California 93106, USA
2. Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA
3. Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA
4. Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
5. Himalayan Experience, 659-1 Mhepi, Kathmandu 3, Nepal

Correspondence to: D. W. Burbank¹ Email: burbank@crustal.ucsb.edu

Abstract

The hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks^{1, 2, 3}. Most such models invoke a 'stream-power' rule, in which either increased discharge or steeper channel slopes cause higher erosion rates. Spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain. Here we combine observations from a meteorological network across the Greater Himalaya, Nepal, along with estimates of erosion rates at geologic timescales (greater than 100,000 yr) from low-temperature thermochronometry. Across a zone of about 20 km length spanning the Himalayan crest and encompassing a more than fivefold difference in monsoon precipitation, significant spatial variations in geologic erosion rates are not detectable. Decreased rainfall is not balanced by steeper channels. Instead, additional factors that influence river incision rates, such as channel width and sediment concentrations, must compensate for decreasing precipitation. Overall, spatially constant erosion is a response to uniform, upward tectonic transport of Greater Himalayan rock above a crustal ramp.