Linking rock weathering, rockwall instability and rockfall supply on talus slopes in glaciated hanging valleys (Swiss Alps)

In high-alpine valleys undergoing glacier retreat, the spatial distribution of talus slopes and their sediments have been frequently used as a proxy for rockfall activity. However, within this 'sediment-dominated' research focus, the deglaciated source rockwalls are often portrayed in an oversimplified way. Here, we investigate 12 rockwall-talus systems in three glaciated hanging valleys in the Swiss Alps and explore the role of source rockwalls on the spatial pattern of talus slopes and their paraglacial rockfall activity. Data from field-based talus slope surveys, rockwall geotechnical studies, rock temperature monitoring, frost cracking modeling and GIS-based topoclimatic analyses are evaluated by ergodic reasoning in a principal component analysis to identify patterns of rockwall-talus systems with respect to their topoclimatic, rock mechanical and paraglacial controls. The results show that four main factors (frost cracking, permafrost probability, rockwall morphometry and mechanical preconditioning by rock mass strength and Joint orientation) combine to dictate the paraglacial and spatial variability of sediment production, rockfall activity and block size. Our study demonstrates that more emphasis must be given to source rockwalls as their instability and weathering are directly linked to landform and material characteristics of talus deposits.