Abstract
Mountainous topography reflects an interplay between tectonic uplift, crustal strength, and climate-conditioned erosion cycles. During glaciations, glacial erosion increases bedrock relief, whereas during interglacials relief is lowered by rockwall erosion. Here, we show that paraglacial, frost cracking and permafrost processes jointly drive postglacial rockwall erosion in our research area. Field observations and modelling experiments demonstrate that all three processes are strongly conditioned by elevation. Our findings on catchment scale provide a potential multi-process explanation for the increase of rockwall erosion rates with elevation across the European Alps. As alpine basins warm during deglaciation, changing intensities and elevation-dependent interactions between periglacial and paraglacial processes result in elevational shifts in rockwall erosion patterns. Future climate warming will shift the intensity and elevation distribution of these processes, resulting in overall lower erosion rates across the Alps, but with more intensified erosion at the highest topography most sensitive to climate change.
Highlights
Mountainous topography reflects an interplay between tectonic uplift, crustal strength, and climate-conditioned erosion cycles
Our findings provide a potential explanation of rockwall erosion rate pattern that we compiled for the European Alps that is characterised by increasing erosion with increasing elevations
Smaller glaciers are sensitive to climatic changes[37], so future climate warming will drive disproportionate retreat of small glaciers
Summary
The results suggest that all three elevation-dependent processes (deglaciation history, permafrost, and frost cracking) correlate, and are potentially involved in explaining the modern rockfall activity at Hungerli Valley. It is probable that the rates from long-term measurements exceed those of the short-term measurements due to integrating an aggressive period of paraglacial adjustment (expected soon after glacier retreat), and more intense permafrost thaw and frost cracking during colder phases (e.g. LIA) of the Holocene. The short-term and long-term erosion rates in the Hungerli Valley both share the same positive relationship between elevation and erosion rates that was found for data compiled for the entire European Alps (Fig. 5a), especially at elevations above 2500 m (Fig. 5b). Our catchment scale study suggests that paraglacial processes will be responsible for a short-term increase (i.e. rapid adjustment) in rockwall erosion, especially at elevations above 2500 m. The areas of most intense periglacial and paraglacial processes and resulting erosion will shift to higher elevations, in locations where higher topography exists
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