Abstract
Abstract. The development of topography depends mainly on the interplay between uplift and erosion. These processes are controlled by various factors including climate, glaciers, lithology, seismic activity and short-term variables, such as anthropogenic impact. Many studies in orogens all over the world have shown how these controlling variables may affect the landscape's topography. In particular, it has been hypothesized that lithology exerts a dominant control on erosion rates and landscape morphology. However, clear demonstrations of this influence are rare and difficult to disentangle from the overprint of other signals such as climate or tectonics. In this study we focus on the upper Rhône Basin situated in the Central Swiss Alps in order to explore the relation between topography, possible controlling variables and lithology in particular. The Rhône Basin has been affected by spatially variable uplift, high orographically driven rainfalls and multiple glaciations. Furthermore, lithology and erodibility vary substantially within the basin. Thanks to high-resolution geological, climatic and topographic data, the Rhône Basin is a suitable laboratory to explore these complexities. Elevation, relief, slope and hypsometric data as well as river profile information from digital elevation models are used to characterize the landscape's topography of around 50 tributary basins. Additionally, uplift over different timescales, glacial inheritance, precipitation patterns and erodibility of the underlying bedrock are quantified for each basin. Results show that the chosen topographic and controlling variables vary remarkably between different tributary basins. We investigate the link between observed topographic differences and the possible controlling variables through statistical analyses. Variations of elevation, slope and relief seem to be linked to differences in long-term uplift rate, whereas elevation distributions (hypsometry) and river profile shapes may be related to glacial imprint. This confirms that the landscape of the Rhône Basin has been highly preconditioned by (past) uplift and glaciation. Linear discriminant analyses (LDAs), however, suggest a stronger link between observed topographic variations and differences in erodibility. We therefore conclude that despite evident glacial and tectonic conditioning, a lithologic control is still preserved and measurable in the landscape of the Rhône tributary basins.
Highlights
1.1 Motivation for this studyThe world’s topographies have been formed by rock uplift, which is initiated by lithospheric processes such as plate convergence, collision and crustal thickening (England and Molnar, 1990)
In this study we focus on the upper Rhône Basin situated in the Central Swiss Alps in order to explore the relation between topography, possible controlling variables and lithology in particular
Several studies have illustrated that denudation and landscape form are highly variable in space and time and that the related topographies depend on a large number of variables, such as climate, glaciation, tectonics and lithology
Summary
1.1 Motivation for this studyThe world’s topographies have been formed by rock uplift, which is initiated by lithospheric processes such as plate convergence, collision and crustal thickening (England and Molnar, 1990). In order to understand this interplay, it is crucial to explore the mechanisms controlling erosion in an area In this context, several studies have illustrated that denudation and landscape form are highly variable in space and time and that the related topographies depend on a large number of variables, such as climate, glaciation, tectonics and lithology. Glacial carving was found to be even more efficient than fluvial erosion, where glaciers have relatively high sliding rates and high basal shear stresses and where subglacial water pressure gradients are large (see, e.g., Hallett et al, 1996; Montgomery, 2002; Norton et al, 2010a, b; Spotila et al, 2004; Shuster et al, 2005; Valla et al, 2011; Jansen et al, 2014; Dürst Stucki et al, 2012) This seems to be especially valid for the Quaternary period, when multiple glacial advances and retreats formed the mountainous landscapes in many orogens (see, e.g., Kelly et al, 2004). Lithology and related rock-mass strengths have been considered as additional factors controlling denudation and landscape forms, since soft lithologies like marls are eroded faster than hard lithologies such as granites or gneisses and since mechanically stronger rocks can sustain steeper slopes (see, e.g., Molnar et al, 2007; Korup and Schlunegger, 2009; Korup and Weidinger, 2011; Korup, 2008; Morel et al, 2003; Cruz Nunes et al, 2015; Scharf et al, 2013)
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