Using near-continuous LiDAR monitoring to quantify erosionprocesses at a rock glacier front

Erosion at rock glacier fronts can supply sediment to adjacent torrents, which can be mobilized as damaging debris flows. Understanding the mechanisms which govern this erosion process is therefore critical for hazard management in affected areas. Previous research shows that rock glacier advance and liquid water input are the two main drivers of erosion at rock glacier fronts. However, earlier studies that calculated erosion volumes at rock glacier fronts were limited to temporal resolutions ranging from months to years. Therefore, these studies exhibit a high uncertainty due to the opposing influences of rock glacier front advance and retrogressive erosion. This prevented an in-depth understanding of the underlying drivers of these processes and their magnitudes on a short timescale. To overcome this limitation, we adapt the setup by Aaron et al. (2023) and use a permanently installed LiDAR sensor to monitor surface changes at a rock glacier front. By calculating Digital Elevation Models of Difference (DoDs) with respect to the local surface normal, we are able to compute erosion volumes at an hourly temporal resolution. This enables the quantification of short-term and small-scale geomorphic changes at the rock glacier front, which could not be detected by previous studies.

Our study site is the fast-moving Ritigraben rock glacier (front velocity > 1cm/day) in the Mattertal (Valais). Its front is directly connected to a torrential channel, which regularly produced debris flows in the past and has been monitored for more than 30 years. Preliminary results show a link between erosion events and short-term precipitation with camera images showing signs of surface runoff in the affected areas. However, erosive events are triggered by comparatively common rainfall events. Small-scale reworking of material at the rock glacier front also occurs completely independently of precipitation events in some cases. Further investigation is needed to determine if the release of material is due to failure disposition from prior events and the rock glacier creep, or the influence of meltwater from the rock glacier body.

 

References

Aaron, Jordan, Raffaele Spielmann, Brian W. McArdell, and Christoph Graf (2023). “High-Frequency 3D LiDAR Measurements of a Debris Flow: A Novel Method to Investigate the Dynamics of Full-Scale Events in the Field”. In: Geophysical Research Letters 50.5. doi: 10.1029/2022GL102373.