Preprints
https://doi.org/10.5194/esurf-2021-50
https://doi.org/10.5194/esurf-2021-50

  28 Jun 2021

28 Jun 2021

Review status: this preprint is currently under review for the journal ESurf.

Generation of autogenic knickpoints in laboratory landscape experiments evolving under constant forcing

Léopold de Lavaissière1, Stéphane Bonnet1, Anne Guyez1, and Philippe Davy2 Léopold de Lavaissière et al.
  • 1GET, Université de Toulouse, CNRS, IRD, UPS(Toulouse), France
  • 2Univ Rennes, CNRS, Géosciences Rennes - UMR 6118, 35000 Rennes, France

Abstract. The upward propagation of knickpoints in the long profiles of rivers is commonly related to discrete changes in tectonics, climate or base-level. However, the recognition that some knickpoints may form autogenically, independently of any external perturbation, may challenge these interpretations. We investigate here the genesis and dynamics of such autogenic knickpoints in laboratory experiments at the drainage basin scale, where landscape evolved in response to constant rates of base-level fall and precipitation. Despite these constant forcing, we observe that knickpoints regularly initiate in rivers at the catchments’ outlets throughout experiments duration. Their propagation rate does not decrease monotonically in relationship with the decrease in drainage area as predicted by stream-power based models, but first increases with a peak retreat rate in the mid-part of catchments. Their initiation coincides with rivers narrowing and increasing their shear stress. Then, rivers widening leads to a decrease in shear stress and incision rate below the base-level fall rate once knickpoints have propagated upward, creating an unstable situation that ends up with the formation of a new knickpoint. We propose a new model of cyclic generation of autogenic knickpoints controlled by river width dynamics. It illustrates the need to consider autogenic processes in the generation of knickpoints and for deciphering variation of tectonic and climatic processes from landscape records.

Léopold de Lavaissière et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2021-50', Anonymous Referee #1, 27 Jul 2021
  • RC2: 'Comment on esurf-2021-50', Laure Guerit, 05 Aug 2021

Léopold de Lavaissière et al.

Léopold de Lavaissière et al.

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Short summary
Rivers are known to record changes in tectonic or climatic variation through long adjustment of their longitudinal profiles slope. Here we describe such adjustments in experimental landscapes and show that they may result from the sole effect of intrinsic geomorphic processes. We propose a new model of river evolution that links long profiles adjustment to cycles of river widening and narrowing. This result emphasizes the need to better understand control of lateral erosion on rivers width.