Impacts of fracturing patterns on the rockfall susceptibility and erosion rate of stratified limestone

- Rockfall susceptibility assessment based on the distribution of failure mechanisms
- The calculated rockfall susceptibility correlates well with the volume of blocks.
- Erosion rates are often underestimated because of the lack of large events.
- Erosion rate is corrected according to the distribution of blocks and instabilities.
- The characteristics of the fracturing network control the evolution of the relief.

The erosion of steep rock slopes is largely controlled by rockfalls, which are a relevant hazard in mountainous regions. The deposition of blocks allows us to quantify rockfall activities and analyze the fracturing pattern that is the key to understand the processes that result in rockfalls. At Monte Generoso (in southern Switzerland), we compared the calculated rockfall susceptibility with the measured rockfall activity for a thinly stratified limestone cliff area. Thus, we were able to determine the erosion rate for the past 40 years and verify the reliability of the method used to perform the rockfall susceptibility analysis. The geomorphology of the area and the fracturing pattern have been accurately analyzed and quantified in the field and using airborne laser scanning techniques. These results have been used to perform a rockfall susceptibility assessment based on the frequency of joints and the distribution of failure mechanisms. Five joint sets have been detected, and the large influence of wedge sliding is demonstrated. The emptying works carried out on a series of protective barriers and nets resulted in detailed data regarding the magnitude distribution of the blocks that fell over a period of 40 years. This information, coupled with the inventory of the present day rock slope instabilities, results in a method that can be used to correct the erosion rate. Power laws have been fit with the blocks and instability data. Then, several calibration options have been tested to consider the additional amounts of erosion due to larger and less frequent potential rockfall events. The rockfall susceptibility, calculated with the distribution of the failure mechanisms, is correlated well with the measured rockfall activity. This approach allows us to characterize the erosion processes in a steep geomorphological context to obtain new insights regarding the evolution of rock slopes.