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| Titel |
Geomorphological response of a landscape to long-term tectonic and glacial processes: the upper Rhône basin, Central Swiss Alps |
| VerfasserIn |
Laura Stutenbecker, Fritz Schlunegger |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105688
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| Publikation (Nr.) |
 EGU/EGU2015-5225.pdf |
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| Zusammenfassung |
| The Rhône River in the Central Swiss Alps drains a 5380 km2 large basin that shows a high
spatial variability of bedrock lithology, exhumation rate, glacial conditioning and climate. All
of these factors were recently discussed to control erosion rates in orogenic settings in
general, and particularly in the Alps (e.g. Wittmann et al. 2007, Vernon et al. 2008,
Norton et al. 2010a). Thanks to various and densely distributed data, the upper
Rhône basin located between the Aar massif and Lake Geneva is a suitable natural
laboratory to analyze the landscape’s geomorphological state and controlling factors at a
basin-scale.
In this study, we extract geomorphological parameters along the channels of ca. 50 tributary
basins of various sizes that contribute to the sediment budget of the Rhône River either
through sediment supply by torrents or debris flows. Their catchments are located in either
granitic basement rocks (External Massifs), oceanic meta-sedimentary and ophiolitic rocks
(Penninic nappes) or fine-grained continental-margin sediments (Helvetic nappes). The
analysis of longitudinal river profiles from DEMs and slope/area relationships show that all
tributary rivers within the Rhône basin are in topographic transient state that is expressed by
mainly convex or concave-convex channel shapes with several knickpoints of either
tectonic-lithological or glacial origin. Furthermore, the frequency distribution of elevations
(hypsometry) along the river channel allows identifying glacially inherited morphologies and
the recent erosional front. The combination of those different geomorphological data
yields to a categorization of the tributary rivers into three endmember groups: (1)
streams with highly convex profiles, testifying to a strong glacial inheritance, (2)
concave-convex channels with several knickzones and inherited morphologies of past
glaciations, (3) predominantly concave, relatively steep rivers with minor knickpoints and
inner gorges. Assuming that increasing concavity is an expression of advancing
topographic equilibration (Wobus et al. 2006, and others), tributaries within the
Rhône basin are in different states of equilibrium. Interestingly, the three groups
correspond with distinct litho-tectonic units: Tributaries of group 1 are frequently
found in the External Massifs, whereas channels of group 2 and 3 are located in
the Penninic and Helvetic nappes, respectively. Fission-track data from the Alps
(Vernon et al. 2008) also suggest a spatially variable exhumation history closely
related to the different litho-tectonic units, ranging from youngest exhumation in
the External Massifs, intermediate in the Helvetic units and oldest in the Penninic
units.
Non-equilibrated river profiles in the External Massifs can be explained by a combination of
recent glaciation and exhumation. In contrast, river profiles in the Helvetic nappes appear to
be closer to topographic steady state. Rivers located in the Penninic nappes, which show
much older exhumation ages, were probably perturbed mainly by multiple glaciations and
have not equilibrated yet. These observations suggest that differences in response times of
river channels are probably conditioned by the differences in lithologies and tectonic histories
of the three litho-tectonic domains.
Norton, K.P., Abbühl, L.M. and Schlunegger, F., 2010a, Glacial conditioning as an erosional
driving force in the Central Alps: Geology, v.38, p. 655-658
Vernon, A.J., van der Beek, P.A., Sinclair, H.D., Rahn, M.K., 2008, Increase in late Neogene
denudation of the European Alps confirmed by analysis of a fission-track thermochronology
database. EPSL, v. 270, p. 316-329.
Wittmann, H., von Blanckenburg, F., Kruesmann, T., Norton, K.P., and Kubik, P.W., 2007,
Relation between rock uplift and denudation from cosmogenic nuclides in river sediment in
the Central Alps of Switzerland: J. Geophys. Res., v. 112, p. F04010
Wobus, C., Whipple, K.X, Kirby, E., Snyder, E., Johnson, J., Spyropolou, K., Crosby, B., and
Sheehan, D., 2006, Tectonics from topography: Procedures, promise, and pitfalls, in Willett,
S.D. et al., eds., Tectonics, climate, and landscape evolution: GSA Spec. Paper 398, p. 55–74 |
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