The rise of high mountain peaks: Feedbacks between orographic precipitation, fluvial erosion and flexural isostasy

The majority of the highest mountain peaks on Earth is located at the dissected rim of large orogenic plateaus such as the Tibetan Plateau or the Altiplano. The striking spatial coexistence of deep, incised valleys and extraordinary high peaks located at the interfluves led to the idea of a common formation even a hundred years ago: focused erosion in valleys triggers the rise of mountain peaks due to erosional unloading and isostatically driven uplift. Ridgelines rise at the interfluves parallel to major rivers, but an additional ridgeline forms perpendicular to the principal flow direction separating the dissected rim from the undissected center of the plateau. As major rivers originate within the plateau and bypass the highest peaks, the latter rigdeline does not form a principal drainage divide. However, it forms a strong orographic barrier with wet conditions at the windward and dry conditions towards the plateau center at the leeward side. The height of the ridgeline is controlled by valley incision via erosional unloading and isostatic uplift.  If the precipitation pattern responsible for localized valley incision is controlled by the geometry of orographic barriers, a series of complex feedbacks between precipitation, erosion and ridgeline uplift (including the evolution of the highest peaks) occurs.

In this study, we present first results of a novel numerical model, which couples (a) fluvial erosion based on the stream power law, (b) flexural isostasy including viscous relaxation and (c) orographic precipitation based on the advection and diffusion of moisture and its reaction on topographic barriers. Originating from a simple model setup with a plateau in the center of the model domain and moisture transported along a predominant wind direction, we explore the co-formation of valleys and the rise of ridgelines including the growth of extraordinary high peaks. As the evolving topography controls the precipitation pattern, erosion rates are high at the wet windward side of the ridgeline, which parallels the plateau rim, while the leeward side towards the plateau center is characterized by low precipitation and very low erosion rates. As it prevents elevated low-relief areas from dissection, we suggest that this mechanism is a principal cause for the longevity of orogenic plateaus.