Timescales of sediment dynamics, climate and topographic change in mountain landscapes (SedyMONT)
Final Report Abstract
This project was embedded in the European Research Unit SedyMont. The general scope wasto gain an advanced understanding of the timescales and the mechanisms of sediment production and transfer in mountainous landscapes and the role of glacial inheritance, bedrock lithology, and climate. Our project contributed to the overall aims by investigating one of the largest, and presently most active debris flow fan in the Alps: the Illgraben fan in the Upper Rhone Valley in Switzerland. We explored this archive of post-glacial depositional and erosional processes using ground penetrating radar (GPR). In total about 60 km sections of GPR over an area of 6.6 km² were surveyed in a spiderweb pattern down to a depth of ca. 10 m. Radarfacies was classified and calibrated to lithofacies at outcrop walls to derive a 3D model of the sedimentary architecture and identify evolutionary stages of the fan. Of particular interest was to distinguish between debris-flow deposits and alluvial deposits which could be well identified via their characteristic reflection pattern (radar facies). Both represent two different modes of sediment transport, the first showing distinct pulses of gravitative, massive sediment transport, the latter showing roughly continuous transport by flowing water. Over the surveyed upper 10 m of the Illgraben fan, we found an overall decline of debris-flow deposits from ca. 50% to 15% and an increase in stream-flow activity. The uppermost depositional unit forms an incision up to 700 m wide which was subsequently filled up mostly by stream deposits. The pronounced palaeo-surfaces and the specific depositional trend suggest allocyclic controls of the Illgraben fan, making this fan a valuable archive for past sediment fluxes and environmental change in the Alps. The project could show for the first time that GPR can retrieve the depositional history of alluvial fans despite their coarse-grained sediment fabric and weak sorting. Debris-flows play an important role as natural hazards in mountainous regions, hence, the identification of debris-flows activity in the past has important implications for the assessment of future risks and the sensitivity of mountainous regions to climate warming.
Publications
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(2010): 3D architecture, depositional patterns and climate triggered sediment fluxes of an alpine alluvial fan (Samedan, Switzerland). In: Wilford, D., Giles, P. & Nichols, G. (eds): Alluvial fan research and management from reconstructing past environments to identifying contemporary hazards. Geomorphology 115:202-214
Hornung, J., Pflanz, D., Hechler, A., Beer, A., Maisch, M. & Hinderer, M.
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(2012): From gullies to mountain belts: a review of sediment budgets at various scales. Sedimentary Geology 280: 21-59
Hinderer, M.
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(2013): River loads and modern denudation of the Alps – a review, Earth Science Reviews. 118: 11-44
Hinderer, M., Kastowski, M., Kamelger, A., Bartolini, C., Schlunegger, F.
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(2015): A combined quantitative study of radar facies and litho facies over an entire Alpine alluvial fan (Illgraben, Switzerland). Sedimentology 62: 57-86
Franke, D., Hornung, J., Hinderer, M.
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(2021): Postglacial outsize fan formation in the Upper Rhone valley Switzerland – gradual or catastrophic? Earth Surf. Process. Landforms 2022: 1-22
Schoch-Baumann. A., Blöthe, J. J., Munack, H., Hornung, J., Codilean, A.T., Fülöp, R.- H., Wilcken, K., Schrott, L.
