Glaciation's topographic control on Holocene erosion at the eastern edge of the Alps

Abstract

Abstract. What is the influence of glacial processes in driving erosion and uplift across the European Alps? It has largely been argued that repeated erosion and glaciation sustain isostatic uplift and topography in a decaying orogen. But some parts of the Alps may still be actively uplifting via deep lithospheric processes. We add insight to this debate by isolating the role of post-glacial topographic forcing on erosion rates. To do this, we quantify the topographic signature of past glaciation on millennial-scale erosion rates in previously glaciated and unglaciated catchments at the easternmost edge of the Austrian Alps. Newly measured catchment-wide erosion rates, determined from cosmogenic 10Be in river-borne quartz, correlate with basin relief and mean slope. GIS-derived slope–elevation and slope–area distributions across catchments provide clear topographic indicators of the degree of glacial preconditioning, which further correlates with erosion rates. Erosion rates in the easternmost, non-glaciated basins range from 40 to 150 mm ky−1 and likely reflect underlying tectonic forcings in this region, which have previously been attributed to recent (post 5 Ma) uplift. By contrast, erosion rates in previously glaciated catchments range from 170 to 240 mm ky−1 and reflect the erosional response to local topographic preconditioning by repeated glaciations. Together, these data suggest that Holocene erosion across the Eastern Alps is strongly shaped by the local topography relict from previous glaciations. Broader, landscape-wide forcings, such as the widely debated deep mantle-driven or isostatically driven uplift, result in lesser controls on both topography and erosion rates in this region. Comparing our data to previously published erosion rates across the Alps, we show that post-glacial erosion rates vary across more than 2 orders of magnitude. This high variation in post-glacial erosion may reflect combined effects of direct tectonic and modern climatic forcings but is strongly overprinted by past glacial climate and its topographic legacy.

Postglacial to Holocene landscape evolution and process rates in steep alpine catchments

“…Likely, the rates represent maximum rates as the nuclide production at the lower lying fan position is lower compared to the higher elevated source areas. The Guttannen catchment, which has only been limitedly affected by debris flow activity, revealed higher nuclide concentrations [(1.6–2.3) × 10 4 at/g] and, thus, accordingly lower apparent denudation rates of 0.6 to 0.9 mm/yr that are typically found in the Alps (Dixon et al, ).…”

“…Cosmogenic nuclides studies dedicated to deriving alpine regional averaged denudation rates usually assume that large(r) spatial scales (i.e. catchments > 10–20 km 2 ) should sufficiently average perturbations from mass wasting events, despite mixed global results (Portenga and Bierman, ; Dixon et al, ). Similarly, sediment budget studies also suggest sufficient buffering of perturbations in larger catchments due to more effective mixing that allows shredding of episodic signals (de Vente et al, ).…”

“…A high‐resolution sampling approach in space and time seems necessary to improve our understanding of sediment dynamics in alpine headwater catchments. By additionally applying a multi‐method approach we were able to show that early Holocene paraglacial denudation rates (20–30 mm/yr) are an order of magnitude higher than modern rates (2–3 mm/yr) which are still a factor of two to three higher than typically alpine denudation rates (Dixon et al, ). Our conclusions constrain the evolution of the upper Haslital‐Aare area, however, we suggest that similar processes may have been occurring and may be the rule rather than the exception in many other alpine settings.…”

“…Converted into apparent denudation rates, these low 10 Be concentrations provide up to two times higher denudation rates after debris flow events than typical central alpine rates (~0.8 mm/yr; e.g. Dixon et al, ).…”

Denudation systematics inferred from in situ cosmogenic 10Be concentrations in fine (50–100 µm) and medium (100–250 µm) sediments of the Var River basin, southern French Alps

“…For the VAR-16-2, TIN-16-1, and VES-16-2 subbasins, we used subbasin 10 Be denudation rates (Table 2). We used the OCTOPUS database (Codilean et al, 2018) to acquire data from the Alps (Buechi et al, 2014;Chittenden et al, 2014;Delunel et al, 2010;Dixon et al, 2016;Glotzbach et al, 2013;Grischott et al, 2017a;Molliex et al, 2016;Norton et al, 2008Norton et al, , 2011Savi et al, 2014;Wittmann et al, 2007Wittmann et al, , 2016.…”