Abstract
Abstract. In four study areas within different lithological settings and rockfall activity, lidar data were applied for a morphometric analysis of block sizes, block shapes and talus cone characteristics. This information was used to investigate the dependencies between block size, block shape and lithology on the one hand and runout distances on the other hand. In our study, we were able to show that lithology seems to have an influence on block size and shape and that gravitational sorting did not occur on all of the studied debris cones but that other parameters apparently control the runout length of boulders. Such a parameter seems to be the block shape, as it plays the role of a moderating parameter in two of the four study sites, while we could not confirm this for our other study sites. We also investigated the influence of terrain parameters such as slope inclination, profile curvature and roughness. The derived roughness values show a clear difference between the four study sites and seem to be a good proxy for block size distribution on the talus cones and thus could be used in further studies to analyse a larger sample of block size distribution on talus cones with different lithologies.
Highlights
Rockfall is an important geomorphic process on steep rock slopes and plays a significant role in geomorphic dynamics especially in high mountainous regions (e.g. Hungr and Evans, 1988; Krautblatter and Dikau, 2007; Bennett, et al, 2012; Frattini et al, 2012)
The data show a very homogeneous distribution and only small maximum values in Piton de la Fournaise (PF) and the ZBT, whereas in GA and DTS a very large dispersion and high maximum values (Table 4) are obvious. This indicates that a correlation between the lithological conditions and the block sizes involved in rockfall processes is very likely, as the largest blocks are mainly found in areas with banked limestones
The extremely small block sizes are striking in the ZBT area, which consists of metamorphic rocks
Summary
Rockfall is an important geomorphic process on steep rock slopes and plays a significant role in geomorphic dynamics especially in high mountainous regions (e.g. Hungr and Evans, 1988; Krautblatter and Dikau, 2007; Bennett, et al, 2012; Frattini et al, 2012). Rockfall is an important geomorphic process on steep rock slopes and plays a significant role in geomorphic dynamics especially in high mountainous regions Hungr and Evans, 1988; Krautblatter and Dikau, 2007; Bennett, et al, 2012; Frattini et al, 2012). The occurrence and magnitude of rockfalls depend on the preconditioning and the preparatory factors (e.g. Meißl, 1998; Dorren, 2003; Dietze et al, 2017a) as well as on triggering events. The preconditioning and preparatory factors are mainly lithology, topography of the slope (aspect, steepness, altitude), vegetation (e.g. Meißl, 1998; Jaboyedoff and Derron, 2005), rainfall and weathering, frequency of freeze– thaw cycles, sun exposure, and root growth Wegner et al.: Assessing the effect of lithological setting, block characteristics and slope topography
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