Abstract
Abstract. When connected to torrential channels, periglacial moving landforms (including rock glaciers, push moraines and high-altitude landsliding masses) may constitute important active sediment sources for gravitational and torrential transfer processes such as debris flows. However, still very little is known about the location and the number of such types of sedimentary connection in given regions, as well as about the typical sediment transfer rates that can be expected. Therefore, this contribution aims at (i) describing a new methodology developed to identify and characterize moving landforms connected to the torrential network system at a regional scale and (ii) presenting the results yielded from the application of this method in a 2000 km2 region in the southwestern Swiss Alps. The developed approach is based on the analysis of simple data such as a high-resolution digital elevation model (DEM), time series of aerial images and a slope movement inventory. The approach allowed both the fast identification of moving landforms connected to torrential channels and the estimation of annual sediment transfer rates for these inventoried landforms. In the study region, results showed that such types of sedimentary connection appeared to be rather rare. Results also showed that most connected moving landforms were characterized by relatively low sediment transfer rates (<500 m3 yr−1) but several sites were identified as transferring large amounts of sediment into the torrents (>1000 m3 yr−1). As sediment transfer rates depend on the kinematical behavior of the landforms, values calculated may change in regard to the evolution of the surface velocities, which are currently generally increasing in the European Alps. When connected to torrents, periglacial moving landforms may thus represent substantial active sources of sediments for the development of debris flows and should be considered in the management of torrential catchments.
Highlights
Periglacial moving landforms, which are defined here as landforms resulting from ground motion and located in mountain permafrost environment, can occur in the headwaters of high mountain torrential catchments
The spatial extent of some DInSAR polygons was too large, giving the misleading impression that the moving landforms were directly adjacent to the torrential channel while the real moving parts were located at a sufficient distance to be disconnected for instance by the presence of flat areas between them and the channel (Fig. 8)
The goal of producing a relatively simple approach asked for several simplifications in both the connectivity assessment, which is basically carried out through visual observation of aerial images, and the estimation of sediment transfer rates
Summary
Periglacial moving landforms, which are defined here as landforms resulting from ground motion and located in mountain permafrost environment (e.g., rock glaciers, deepseated rockslides, push moraines), can occur in the headwaters of high mountain torrential catchments. Depending on their location within the basin, they may represent substantial sources of coarse debris for the development of torrential sediment transport processes such as debris flows. The sedimentary connection or connectivity, i.e., the potential transfer of sediments from one morphological unit to the other (Bracken et al, 2015), occurs when the moving landform and the torrential channel are directly adjacent or separated by uninterrupted steep slopes where sediments can be eroded and guided downwards (Fryirs, 2013). The present contribution is mainly concerned with characterizing the level of connectivity between periglacial moving landforms and torrential channels at the scale of a few decades
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