DSGSDs diagnostic landforms: a morphometric LiDAR based approach.

DSGSDs affect many Alpine slopes, depending on the stage of evolution and typology this phenomena can be masked by weathering and superficial erosion processes and the typical bulging at the hillslope foot can be not always present. This research aims to a more objective identification of DSGSDs focusing on the morphostructures (double ridges, scarps, counterscarps, trenches), considered by many authors the most “diagnostic” DSGSDs landforms, classified in between tectonic and landslides. We propose a methodology based on the visual interpretation and statistics analysis of morphometric indices: slope, curvatures, openness, ruggedness, etc., derived from a LiDAR-DEM with a multiscalar approach. Counterscarps results the most abundant on all the 4 DSGSDs study areas, controlled by different litologies/structural setting. These forms are generally considered and mapped like linear features, from a DEM based perspective, an areal definition is needed and conducted through a value threshold on profile curvature and slope. About 430 counterscarps were mapped and statistically analyzed, resulting long from 16 to 700 m, wide 10 to 150 m, with an average direction perpendicular to the maximum slope. Despite the dimensions their morphological relevance is low (<1-2 m), SRTM and GDEM are not able to catch it. Counterscarps results scale independent and characterized by well define changing in curvature (-\+) and mean values (>|0.4|), with an half concave part that changes to convex through an intermediate low gradient area (< 10°), the only “flat“ zones in the DSGSDs. The quantitative topographic analysis allow to identify a general “morphometric signature” of the counterscarps; different DSGSDs typology are more related to their spatial distribution/frequency instead of other shape factors; width is the only that shows some correlation with the foliation typology. A detailed field survey was conducted to validate the derived indices and the interpretation.