Retreat analysis of a sandstone marl interbedded cliff based on a three-year remote sensing survey: A case study at La Cornalle, Switzerland

Rockwall retreat by rockfalls in high alpine mountains has received increasing attention due to the increased rock failure activities and the corresponding damage under global warming in the past 20 years. However, the face retreat by rockfalls of subalpine rock cliffs is not sufficiently monitored and analyzed. In the present work, the nearly vertical sandstone-marls Molasse cliff formed by the La Cornalle-Les Luges landslide was monitored by a three-year monthly drone-based SfM photogrammetry and TLS scanning to establish the rockfalls inventories. The cumulative monthly detachment volumes from the sandstone and marls layers were analyzed using the frequency-magnitude relationships fitted by a negative power law, respectively, which help to calculate the retreat rate and reveal the spatiotemporal evolution of rockfalls between these two layers. Meanwhile, the cliff retreat volume in different months was correlated to the environmental factors (e.g., air temperature, precipitation, and rock surface temperature) using linear regression. A weather station and thermal couples in the rock collected the data of these factors. As a result, this work will contribute to a better understanding of the retreat pattern and rate of freshwater Molasse walls under global warming and provide a rock detachment model on a cliff with interbedded hard and soft rock layers in the subalpine regions.