Abstract
Abstract. Cirque erosion contributes significantly to mountain denudation and is a key element of glaciated mountain topography. Despite long-standing efforts, rates of rockwall retreat and the proportional contributions of low-, mid- and high-magnitude rockfalls have remained poorly constrained. Here, a unique, terrestrial-lidar-derived rockfall inventory (2011–2017) of two glaciated cirques in the Hohe Tauern range, Central Alps, Austria, is analysed. The mean cirque wall retreat rate of 1.9 mm a−1 ranks in the top range of reported values and is mainly driven by enhanced rockfall from the lowermost, freshly deglaciated rockwall sections. Retreat rates are significantly elevated over decades subsequent to glacier downwasting. Elongated cirque morphology and recorded cirque wall retreat rates indicate headward erosion is clearly outpacing lateral erosion, most likely due to the cataclinal backwalls, which are prone to large dip-slope failures. The rockfall magnitude–frequency distribution – the first such distribution derived for deglaciating cirques – follows a distinct negative power law over 4 orders of magnitude. Magnitude–frequency distributions in glacier-proximal and glacier-distal rockwall sections differ significantly due to an increased occurrence of large rockfalls in recently deglaciated areas. In this paper, the second of two companion pieces, we show how recent climate warming shapes glacial landforms, controls spatiotemporal rockfall variation in glacial environments and indicates a transient signal with decadal-scale exhaustion of rockfall activity immediately following deglaciation crucial for future hazard assessments.
Highlights
Cirque erosion contributes significantly to the morphological appearance of glaciated mountain ranges
Cirque wall retreat is governed by rock slope failure, which can be statistically characterized by their magnitude– frequency distribution (Dussauge et al, 2003; Bennett et al, 2012)
The inventory was derived from detailed terrestrial lidar data and represents the most extensive high-resolution compilation of rockfall in cirque walls
Summary
Cirque erosion contributes significantly to the morphological appearance of glaciated mountain ranges. It controls rockwall retreat and creates emblematic high-alpine landform features such as horn-type peaks and sharp-edged ridges. The disposal of sediment from cirque walls represents a prominent entry point to the high-alpine sediment cascade and is key to understanding of high-alpine sediment flux (Hales and Roering, 2005; Krautblatter et al, 2012; Bennett et al 2014). Cirque wall retreat is governed by rock slope failure, which can be statistically characterized by their magnitude– frequency distribution (Dussauge et al, 2003; Bennett et al, 2012). Magnitude–frequency distributions are widely used to derive probabilistic recurrence rates of an event of a given size (Dussauge-Peisser et al, 2002) and are key Published by Copernicus Publications on behalf of the European Geosciences Union
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
