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

Jean L Dixon,Friedhelm Von Blanckenburg,Kurt Stüwe,Marcus Christl

doi:10.5194/esurf-4-895-2016

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.

Highlights

The climatic control on erosion in mountain belts remains a longstanding and active debate in geomorphology
Considering that both erosion rates and catchment mean slope correlate with the proportion of the catchment that exceeds 35◦ (Fig. 2b) and that these steep slopes generally are void of soil cover, it is likely that local slopes > 35◦ within catchments undergoing erosion rates of ∼ 200 mm ky−1 correspond to thresholds for soil cover in this landscape
Our study provides multiple lines of evidence that Holocene erosion in the Eastern Austrian Alps is driven by glacial legacies that set local topographic forcing and hillslope morphology

Summary

Introduction

The climatic control on erosion in mountain belts remains a longstanding and active debate in geomorphology. Some of this debate has focused on whether spatial gradients in precipitation can be invoked to drive gradients in erosion or whether these rates are more strongly controlled by their tectonic setting (e.g., Burbank et al, 2003). Glacial erosion may increase mountain relief and cause isostatic uplift of rocks (e.g., Champagnac et al, 2007; Molnar and England, 1990). Through an erosional “buzzsaw”, glaciers have been suggested to set the limit on mountain range height and relief

Results

Discussion

Conclusion