Formation of Longitudinal River Valleys and the Fixing of Drainage Divides in Response to Exhumation of Crystalline Basement

Thomas Bernard,Matthew Fox,Hugh D Sinclair,Boris Gailleton

doi:10.1029/2020gl092210

Thomas Bernard, Matthew Fox + Show 2 more

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https://doi.org/10.1029/2020gl092210

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Abstract

AbstractVariations in rock strength act as a first‐order control on mountain landscapes. However, the transient topographic signal of basement exhumation has not been explored. We use model outputs to demonstrate the mobility of drainage divides in mountain ranges in response to the exhumation of basement rocks and the implications for the morphology of river catchments. The exhumation of harder rocks within a catchment reduces upstream channel steepness and erosion rates in contrast to neighboring catchments. The results are a shift in the orogen‐scale drainage divide toward the harder rocks, and the formation of range parallel longitudinal valleys as neighboring river networks capture the headwaters of catchments impacted by the harder lithology. Our model outputs provide a process explanation for the initiation of many longitudinal valleys in mountain ranges, and for the pinning of drainage divides on rocks of higher strength as seen the Central Pyrenees, Western Alps, or High Atlas.

Highlights

The evolution of drainage networks in mountain ranges is governed by multiple factors in which slope, climate-induced water discharge, rock uplift rate and lithology are the most important (Howard, 1994)
The results are a shift in the orogen-scale drainage divide toward the harder rocks, and the formation of range parallel longitudinal valleys as neighboring river networks capture the headwaters of catchments impacted by the harder lithology
The time evolution of the results demonstrates the impact on drainage divides upstream of the exhumed basement rock, and on the implications for changing erosion rates and modified catchment forms

Summary

Introduction

The evolution of drainage networks in mountain ranges is governed by multiple factors in which slope, climate-induced water discharge, rock uplift rate and lithology are the most important (Howard, 1994). In many mountain ranges such as Taiwan and the Southern Alps of New Zealand, this scaling is expressed by transverse catchments that are spaced at regular intervals along the range with an outlet spacing that approximates half the distance from the range front to the drainage divide (Hovius, 1996). This characteristic catchment geometry is observed during early stages of orogenesis, and reflects an optimal shape for the balance between river incision and hillslope response (Perron et al, 2009).

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