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Discussion papers
https://doi.org/10.5194/esurf-2019-31
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-31
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Jun 2019

Research article | 26 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Estimating the disequilibrium in denudation rates due to divide migration at the scale of river basins

Timothée Sassolas-Serrayet1, Rodolphe Cattin1, Matthieu Ferry1, Vincent Godard2, and Martine Simoes3 Timothée Sassolas-Serrayet et al.
  • 1Géosciences Montpellier, Université de Montpellier and CNRS UMR 5243, Montpellier 34095, France
  • 2Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France
  • 3Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France

Abstract. Basin-averaged denudation rates may locally exhibit a wide dispersion, even in areas where the topographic steady state is supposedly achieved regionally. This dispersion is often attributed to the accuracy of the data or to some degree of natural variability of the signal, but it can also be attributed to stochastic processes such as landsliding. Another physical explanation to this dispersion is that of local and transient disequilibrium between tectonic forcing and erosion at the scale of catchments. Recent works have shown that divide migration can potentially induce such perturbations and they propose reliable metrics to assess divide mobility based on cross-divide contrasts in headwater topographic features. Here, we use a set of landscape evolution models assuming spatially uniform uplift, rock strength and rainfall to assess the effect of divide mobility on basin-wide denudation rates. We propose the use of basin-averaged aggressivity metrics based on cross-divide contrasts in channel-head χ, in local slope and in elevation. From our simulations, we show that the metric based on differences in channel-head elevations across divides is the least reliable to diagnose local disequilibrium. For the other metrics, our results suggest a nonlinear relationship with the ratio of basin denudation to uplift, which can reach up to a factor of two, regardless of the imposed uplift rate, diffusivity coefficient and critical hillslope gradient. A comparison with field observations in the Great Smoky Mountains (southern Appalachians, USA) underlines the difficulty of using the metric based on χ, which depends on the – poorly constrained – elevation of the outlet of the investigated catchment. Regardless of the considered metrics, we show that observed dispersion is controlled by catchment size: a smaller basin may be more sensitive to divide migration and hence to disequilibrium. Our results thus highlight the relevance of divide stability analysis from digital elevation models as a fundamental preliminary step for basin-wide denudation rate studies based on cosmogenic radionuclide concentrations.

Timothée Sassolas-Serrayet et al.
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Short summary
The topographic steady state assumption is often used in Geomorphology. However recent studies suggest that drainage network is more mobile than previously thought. Using landscape evolution models, we show that those migrations have a significant impact on basin-wide denudation rates even if an overall topographic steady state is achieved at large scale. Our approach provides new tools to derive minimal uncertainties in basin scale denudation rates due to this topographic disequilibrium.
The topographic steady state assumption is often used in Geomorphology. However recent studies...
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