Thursday, April 28, 2011, 12:00PM - 1:00PM
Peter van der Beek
Université Joseph Fourier, Grenoble
Full title: "Erosion rates and relief development in the Western European Alps in response to late Quaternary climate change."
The Ecrins-Pelvoux massif (French Western Alps) was extensively glaciated during Quaternary glaciations, leading to a ~100 % increase in relief through glacial valley carving and leaving a strong imprint on the morphology of the massif1. Here, I aim to address the efficiency of erosion processes in relief evolution in response to deglaciation of the massif 15-17 ka ago. Denudation rates inferred from in-situ produced 10Be concentrations in stream sediments, obtained from 12 catchments throughout the Ecrins-Pelvoux massif, correlate with mean catchment elevation in the absence of significant relationships with other morphometric parameters2. We have proposed that present-day (millennial-timescale) denudation of Ecrins-Pelvoux massif is climatically driven through increasing efficiency of frost-controlled processes with elevation, providing a mechanistic link for the inferred feedback between uplift, elevation and denudation rates observed in the European Alps3, 4.
However, cosmogenic isotope measurements in stream sediments do not allow distinguishing the intrinsic spatial variability of denudation within a catchment. Therefore, we have sought to verify our previous conclusions on a smaller scale within a single catchment, from exhaustive measurements of 10Be concentrations carried by different sources feeding the high-altitude sediment routing system, in order to develop a 10Be budget at the catchment scale. 10Be concentration measurements at a single catchment scale suggest the processes within a catchment to be more complex than our initial interpretation based on catchment-wide erosion rates on the massif scale. In particular, the roles of attrition of scree material, transient storage of scree deposits on slopes leading to non-steady state conditions on Holocene timescales, and strongly localised glacial and fluvial erosion need to be taken into account.
1. van der Beek, P. & Bourbon, P. A quantification of the glacial imprint on relief development in the French Western Alps. Geomorphology 97, 52-72 (2008).
2. Delunel, R., van der Beek, P. A., Carcaillet, J., Bourlès, D. L. & Valla, P. G. Frost-cracking control on catchment denudation rates: Insights from in situ produced 10Be concentrations in stream sediments (Ecrins-Pelvoux massif, French Western Alps). Earth Planet. Sci. Lett. 293, 72-83 (2010).
3. Wittmann, H., von Blanckenburg, F., Kruesmann, T., Norton, K. P. & Kubik, P. W. The relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the Central Alps of Switzerland. J. Geophys. Res. 112, F04010, doi:10.1029/2006JF000729 (2007).
4. Champagnac, J.-D. et al. Erosion-driven uplift of the modern Central Alps. Tectonophysics 474, 236-249 (2009).