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Origine, variabilité spatio-temporelle et signature morphologique de l'incision fluviatile dans les Alpes dauphinoises (SE France)

Abstract : the processes of fluvial erosion and transport constitute the main controls on continental morphology and sediment flux. A quantification of these processes on large scales is therefore essential for our understanding of the interaction between tectonics and long-term landscape development. We present a case-study from the French Western Alps where river long-profile and floodplain development are studied on different temporal scales (103 – 106 y), on rivers that experienced varying amounts of climatic (glacial) disturbances. Paleo-river profiles are reconstructed using abundant terrace remnants dates using in-situ produced cosmogenic 10-Be. The Drac River long-profile evolution is controlled by rapid km-scale base-level fluctuations due to glacial damming of its lower valley and subsequent ice-dam disappearance. Its post-glacial long profile has developed by rapid knickpoint retreat at exceedingly high incision rates. Relaxation is about to be achieved and would have lasted 15-20 ky. The contiguous Buëch River experienced limited glacial influences. Its short-term (103 y) incision rates are sensitive to climatic forcing whereas its long-term (105 y) incision rates (0.8 mm y-1) are consistent with regional denudation rates, suggesting long-term equilibrium between uplift and incision. Geomorphic analysis of relief shaped by rivers is achieved through DEM analysis of surrounding rivers. It shows that, beyond a threshold value of the yield of river power vs. bedrock strength, the river long profile is no longer sensitive to external forcing. Lithology and uplift rate then control the width of river meandering belt (valley flat). Further calibrations are required, however, to convert morphometric parameters into uplift rates.
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Submitted on : Wednesday, September 28, 2005 - 4:41:57 PM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
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  • HAL Id : tel-00010314, version 1

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Gilles Brocard. Origine, variabilité spatio-temporelle et signature morphologique de l'incision fluviatile dans les Alpes dauphinoises (SE France). Géologie appliquée. Université Joseph-Fourier - Grenoble I, 2002. Français. ⟨tel-00010314⟩

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