Controls on bedrock hillslope erosion in the European Alps

Erosion rates in cold, bedrock hillslopes where temperatures are below freezing for a considerable portion of the year are believed to be set by frost-cracking. Nevertheless, numerous studies from the European Alps have shown that permafrost thaw-induced rockfalls can contribute non-trivially to long-term erosion rates.

Here, we report 27 new bedrock hillslope erosion rates from across the European Alps estimated using in-situ cosmogenic ¹⁰Be. Samples were collected from bedrock hillslopes as well as talus slopes with identifiable (steep, bedrock) source areas using amalgamated sampling techniques. Our sites range in elevation from 2700 m to 4040 m, and consist of a range of lithologies, bedrock temperature conditions, and deglaciation histories. Furthermore, several of our selected sites include hillslopes wherein erosion rates have been previously estimated by others using methods other than in-situ cosmogenic nuclides. We explore how our rates vary against these previously derived rates, which may integrate over shorter (or, in exceptional cases, longer) timescales.

Preliminary calculations yield ¹⁰Be-based erosion rates ranging from 0.1 mm yr^-1 to 2.7 mm yr^-1 and show no apparent correlation with elevation, aspect, or bedrock thermal conditions. In addition to erosion rates, we likewise calculate site-specific frost-cracking intensities using modern ground surface temperatures and modelled paleoclimatic conditions. Comparing the calculated frost-cracking intensities against our erosion rates inferred using ¹⁰Be suggests that frost-cracking alone is likely not the rate-limiting erosion rates in cold, high-Alpine bedrock hillslopes.