11:00 AM - 11:15 AM
[HGM04-07] Geomorphic process connectivity within a low-activity landslide: Oashi-sawa landslide, Southern Japanese Alps
Keywords:landslide, connectivity, UAV, SfM
Understanding the connectivity of all geomorphic processes within landslides is necessary to estimate landslide-internal erosion, sediment deposition, and sediment delivery to rivers. In this study, the connectivity of geomorphic processes within a landslide was analyzed based on five Digital Elevation Models (DEMs) obtained from UAV-SfM and on-site monitoring (rain gauge, interval camera) of the Oashi-sawa landslide in the upper basin of the Oi River between July 2023 and November 2024.
The observed geomorphological processes were rockfall and water erosion but no debris flow. Although in all periods the mean depth of rockfall was smaller than that of water erosion, in comparison to volume, rockfall exceeded water erosion. This shows that rockfall contributed more to the erosion of the landslide throughout the year. From winter to spring, rockfall accounted for more than 90 % of the erosion in the landslide. Freeze-thaw processes are known to be active in the Southern Alps in winter, and it is hypothesized that the Oashi-sawa is also affected by this process. The deepest mean erosion was 8.0 cm during the analysis period, indicating low activity.
The slope components were connected continuously by supplying sediment to the main channel during all periods, whereas the connectivity of the tributaries to the upper fan varied depending on rainfall and sediment distribution. However, there was no connectivity between the upper and lower fan or between the fan and river during the entire observation period, as sediment was not transported to the lower part of the landslide. This connectivity pattern might change over a longer time scale when infrequent, high-magnitude rainfall events (e.g., typhoons) impact the landslide and cause high connectivity throughout the landslide.
The observed geomorphological processes were rockfall and water erosion but no debris flow. Although in all periods the mean depth of rockfall was smaller than that of water erosion, in comparison to volume, rockfall exceeded water erosion. This shows that rockfall contributed more to the erosion of the landslide throughout the year. From winter to spring, rockfall accounted for more than 90 % of the erosion in the landslide. Freeze-thaw processes are known to be active in the Southern Alps in winter, and it is hypothesized that the Oashi-sawa is also affected by this process. The deepest mean erosion was 8.0 cm during the analysis period, indicating low activity.
The slope components were connected continuously by supplying sediment to the main channel during all periods, whereas the connectivity of the tributaries to the upper fan varied depending on rainfall and sediment distribution. However, there was no connectivity between the upper and lower fan or between the fan and river during the entire observation period, as sediment was not transported to the lower part of the landslide. This connectivity pattern might change over a longer time scale when infrequent, high-magnitude rainfall events (e.g., typhoons) impact the landslide and cause high connectivity throughout the landslide.