New insight of geomorphology and landslide prone area detection using digital elevation model(s)

Landslide hazard assessment can be improved by using new digital documents such as digital elevation models (DEM). Geographic Information System (GIS) and geo-referenced documents being more and more available, the geomorphologic theories and methods that were developed before the computer age are now being updated and improved. They yield new insights for landslide hazard assessment. Slope processes and associated morphology were extensively studied during the last two centuries (Gilbert 1880, De La Noe & De Margerie 1888). Terrain slope is the first way to qualify the topography (Strahler 1950) and the basic information used for slope modeling (Young 1972). Terrain slope depends on many factors such as weathering and rock types (Young 1961). In rock slopes, joints play an important role on the slope shaping (Terzhaghi 1962, Scheidegger 1980, Selby 1982). Slope stability is dependent on rock mechanical properties. On one hand, landslides in loose materials (for example in sand piles) are often located within a defined terrain slope angle range (Rautela & Thakur 1999). On the other hand, rock slope stability is strongly controlled by discontinuities that decrease rock strength. Thus, the analysis of the topography reflects the mechanical and structural features of the slope (Locat et al., 2000). Digital elevation models (DEM) makes it possible to perform more detailed and systematic morphological analysis. Using the orientation of each single cell, a DEM can be represented by 3D shaded relief that displays one color for each dip and direction of dip. This kind of representation permits a very simple slope analysis providing quick information for slope hazard assessment. Different cases in the western Swiss Alps are presented.