Late-Pleistocene catchment-wide denudation patterns across the European Alps

Romain Delunel (1) , Fritz Schlunegger (1) , Pierre Valla (2, 1) , Jean Dixon (3) , Christoph Glotzbach (4) , Kristina Hippe (5) , Florian Kober (6) , Stéphane Molliex (7) , Kevin Norton (8) , Bernhard Salcher (9) , Hella Wittmann (10) , Naki Akçar (1) , Marcus Christl (5)

1 Institute of Geological Sciences [Bern]
2 ISTerre - Institut des Sciences de la Terre
3 MSU - Montana State University
4 Institut für Geowissenschaften [Tübingen]
5 Ion Beam Physics [ETH Zürich]
6 Nagra - National Cooperative for the Disposal of Radioactive Waste
7 LGO - Laboratoire Géosciences Océan
8 Victoria University of Wellington
9 Universität Salzburg
10 GFZ - German Research Centre for Geosciences - Helmholtz-Centre Potsdam

We compile detrital 10Be concentrations of Alpine rivers, representing the denudation rates pattern for 375 catchments across the entire European Alps. Using a homogeneized framework, we employ state-of-the-art techniques for inverting in-situ 10Be concentrations into denudation rates. From our compilation, we find that (i) while lithologic properties and precipitation/runoff do influence erosion mechanisms and rates at the scale of individual catchments and in some specific Alpine regions, such controls do not directly stand for the entire Alps, (ii) as also previously suggested, catchment-wide denudation rates across the entire European Alps closely follow first-order Alpine topographic metrics at the scale of individual catchments or selected Alpine sub-regions. However, in addition to previous local-scale studies conducted in the European Alps, our large-scale compilation highlights a functional relationship between catchment-wide denudation and mean catchment slope angle. Catchment-wide denudation positively correlates with mean catchment slope up to a threshold angle (25–30°). Above this threshold, any correlation between catchment-wide denudation and slope as well as other catchment metrics breaks apart. We can reconcile these systematic patterns by proposing a regional erosion model based on diffusive-transport laws for catchments located below the slope threshold angle. In oversteepened catchments situated above-threshold slopes, erosion is stochastic in nature, as glacial carving likely caused a partial decoupling between hillslope and fluvial domains with complex topographic relationships and sediment connectivity patterns. Finally, we identify a first-order positive relationship between modern geodetic rock uplift and catchment-wide denudation for the European Alps. The observed spatial pattern is highly variable and possibly reflects the surface response to deep geodynamic mechanisms prevailing in the different Alpine regions. We conclude that today's topography and geomorphic features of the entire Alps are the result of a millenial-scale geomorphic response to past glacial processes and active rock uplift, highlighting a link between external and internal drivers for mountain erosion.

Domaines: Sciences de l'environnement; Planète et Univers [physics]

Romain Delunel, Fritz Schlunegger, Pierre Valla, Jean Dixon, Christoph Glotzbach, et al.. Late-Pleistocene catchment-wide denudation patterns across the European Alps. Earth-Science Reviews, 2020, 211, pp.103407. ⟨10.1016/j.earscirev.2020.103407⟩. ⟨hal-02998130⟩