Significance of rockfall magnitude and carbonate dissolution for rock slope erosion and geomorphic work on Alpine limestone cliffs (Reintal, German Alps)

摘要

The proportional contribution of low-, mid- and high magnitude rock slope failure orchestrates rock slope erosion and rockfall hazard in Alpine and Arctic environments. In this study, we compare sediment yield, geomorphic work and rock wall retreat of carbonate dissolution and five different magnitudes of rock slope failure in the steep Alpine Reintal trough valley. We combine a four-year rockfall collector measurement of 140 Mg of fragmental rockfall, a 20th century scientific record of mid-magnitude rockfall as well as carbon-dating and a historical record of 15th to 19th century rock avalanche activity. The total rockfall sediment yield of 8.6 (± 3.4) * 10~3 m~3year~(-1) is dominated by high-magnitude rock avalanches (>10~6 m~3: 62%) and low-magnitude debris falls (<10 m3:18%), while mid-magnitude boulder, block and cliff falls are less important. The magnitude signal contradicts studies on siliceous rocks where mid-magnitude rockfall dominates rock slope erosion. The geomorphic work released in the 17.3 km~2 large catchment by rockfalls (123 (±47) W km~(-2), i.e. 0.38 (± 0.15) mm year~(-1)) and solute transport (34 (± 18) W km~(-2), i.e. 0.05 (± 0.03) mm year~(-1)) exceeds previously published Alpine values by one to multiple orders of magnitude. We hypothesise that the magnitude signal of enhanced small and high magnitude rockfall is characteristic for carbonate cliffs. The elevated porosity-related susceptibility to fragmentation and persistent carbonate dissolution along potential sliding planes are likely to favour both low- and high-magnitude rock slope failures. Here we show how the magnitude signal of rock slope failure influences rock wall retreat, geomorphic work, rockfall deposition and sediment connectivity.