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Modélisation numérique du contrôle climatique sur l'érosion des versants. Développement d'un nouveau modèle et application au dernier cycle glaciaire-interglaciaire dans le Nord-Ouest de l'Europe

Abstract : Hillslope evolution results from the combined action of weathering and sediment transport processes, which are thought to be both influenced by climate. Yet, the strength and nature of the connection between climate and hillslope erosion remain poorly understood at a quantitative level. In this study, we present a new numerical model of soil production and transport, which aims to better represent, at different time scales, the climate control on soil transport. The numerical model operates at the scale of a single hill and predicts the rates of soil thickness and elevation change, by using a simple parametrization of soil production and a multi-process parametrization of soil transport which includes climate-dependent variables (overland flow discharge and active-layer depth). Simple ground heat transfer and water balance models are used for calculating these variables from time-series of precipitation and temperature. The behaviour of the model has been studied through a few simulation examples and sensitivity analysis. The results highlight the importance of considering multi-process parameterization of soil transport when modelling the response of the hillslope system to climate variations, as these results display significant differences on how each transport process behaves under various climatic conditions and on how each process affect the evolution of the system. Our numerical model has also been combined with an inversion scheme (Neighbourhood Algorithm) to extract quantitative information on the evolution of hillslopes in the Ardenne (Belgium, NW Europe) during the Last Glacial-Interglacial Cycle, using a simple climatic scenario and a unique set of topographic and soil thickness data. Model predictions based on inversion results are consistent with independent observations on hillslope morphology and cosmogenic nuclide-derived erosion rates, although the inversion results show that soil production and transport rates under both the cold and warm phases of the last climatic cycle cannot be fully constrained by the present-day soil thickness distribution. The inversion results suggest that soil transport is by far more efficient during the cold climatic phase than during the warm phase, resulting in the succession of weathering-limited (cold phase) and transport-limited (warm phase) systems. Maximum soil transport rates are predicted during the transitions between the cold-warm phases. The results also suggest that a soil thickness dynamic equilibrium has been recently reached on convex regions of the hillslopes, while shallow soils found in convergent areas may be the relics of the soil thickness distribution that formed during the cold phase.
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Submitted on : Monday, July 30, 2012 - 11:47:12 AM
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Benoît Bovy. Modélisation numérique du contrôle climatique sur l'érosion des versants. Développement d'un nouveau modèle et application au dernier cycle glaciaire-interglaciaire dans le Nord-Ouest de l'Europe. Sciences de la Terre. Université de Grenoble; 131 Université de Liège, 2012. Français. ⟨NNT : 2012GRENU007⟩. ⟨tel-00721762⟩

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