Numerical modeling of erosion processes in the Himalaya of Nepal: effects of spatial variations of rock strength and precipitation

Abstract: The interplay between tectonics and erosion has a predominant control on the evolution of the morphology of mountain belts. Here we investigate the modalities of defor-mation in Central Nepal on a c. 100 ka time scale in response to tectonic and external for-cings, through the use of a finite-element thermomechanical model coupled with an integrative denudation formulation that accounts for fluvial incision and hillslope land-sliding. We study the complex coupling existing between tectonics and erosion, with special emphasis on the influences of rock strength and rainfall distributions. Our results underline the key role played by lithologic variations in the elevation of both rivers and mean topogra-phy. We show that the location of the Main Frontal Thrust is mainly controlled by the low erodability of the unconsolidated sandstone in the Siwaliks Hills. As previously suspected (Burbank et al. 2003), our simulations demonstrate that the pattern of uplift in Nepal is mainly dependent on both erodability and fault geometry, rather than on rainfall distribution. It has long been understood that the landscape of mountain belts is the result of the balance between tectonic uplift and surface processes, as modulated by denudation and sedimentation (Molnar 2003). Outside glaciated regions, river incision into bedrock has been recognized as a primary agent in both landscape evolution and large-scale surface mass transport (e.g., Burban