The degree of glacial modification controls non-glacial erosion in alpine landscapes

Alpine topography of many high- and mid-latitude mountain ranges gives the qualitative impression that glaciers have been highly efficient erosive agents during the Quaternary. Glacial retreat leave slopes in an unstable state, highly susceptible to modification as new geomorphic processes take over. The glacially induced transience of the topography may however last considerably longer than the redistribution and clearance of most of the glacigenic sediments. Response times to fully erase the glacial signature of an orogen must exceed an interglacial and rather is on the order of 10⁵ to 10⁶ years, depending on climate conditions, rock type, and tectonic uplift. Considering multiple cycles of glacial erosion during the Quaternary, the glacial-topographic signature will tend to become more dominant in low to medium uplifting mountain ranges. It is generally accepted that changes in hillslope relief have a first order impact on the type and magnitude of denudation, but the glacial history of a mountain range might be critical in setting the long-term pace on the magnitude of denudation rates. In order to investigate the long-term effects of the glacial-topographic overprint on non-glacial (postglacial) erosion of watersheds we analyze catchment-wide denudation rates (CWDR) inferred from the in-situ produced cosmogenic nuclide¹⁰Be of basins showing a high variation in glacial modification. We found the High Tatra Mts. (Western Carpathians, Slovakia) a suitable site to evaluate our hypothesis given i) its uniform, granitic (quartz bearing) lithology, ii) the presence of basins with a varying degree of glacial perturbation iii) the well-known glacial history, with the absence of glaciers at least for the Holocene, iv) the similar hillslope steepness distribution across analyzed catchments and v) a spatially close distribution of basins where strong climatic gradients (acting on postglacial erosion) can largely be ruled out. In this context, our study represents the first attempt to derive ¹⁰Be-inferred CWDR in the entire Carpathian Mountain range.

Analyzed catchments involve basins that show intense, slight, and no glacial impact on topography (Klapytia and Zazdni 2018; Salcher et al., 2021). Those with a high glacial impact were occupied by ice during glacial maxima (i.e. LGM and equivalents) but also during less cold stadials (i.e. younger dryas and equivalents). Those with medium perturbation, at lower elevation, experienced glacial erosion likely only during glacial maxima, while the latter have never been glaciated. We follow a nested sampling strategy to assess whether denudation rates scale with the degree of glacial imprint on topography. Derived rates range from around 60 mm/kyrs (no impact) to more than 300 mm/ka (high impact).

Even tough investigations remain at a local scale, our results point to a positive relationship between the degree of glacial perturbation and the magnitude of CWDR. To better understand the geodynamic impact of glaciation on mountain range dynamics the knowledge of such dependences is highly relevant and especially critical during the Late Cenozoic cooling climate.

Zasadni,J. Kłapyta,P., 2014. The Tatra Mountains during the Last Glacial Maximum. Journal of Maps, 10, 3. https://doi.org/10.1080/17445647.2014.885854.

Salcher,B., Prasicek,G., Baumann,S., Kober,F., 2021. Alpine relief limited by glacial occupation time. Geology, 49, 10. https://doi.org/10.1130/G48639.1.