Creation of multi-temporal landslide inventories from the analysis of series of optical images : the case of the Ubaye Valley, South French Alps

Schlögel, R., Malet, J.-P., Doubre, C.

Institut de Physique du Globe de Strasbourg, CNRS UMR 7516, Université de Strasbourg, 5 rue Descartes, F-67084 Strasbourg Cedex

Creating landslide inventory maps is a fundamental aspect for proposing quantitative hazard assessment at regional scales. The inventory maps should assemble several categories of information, such as the landslide type, the evolution of the landslide boundaries and of important geomorphological features within the landslide body and the evolution of the soil surface state. This basic information can be used to estimate the temporal and spatial displacement pattern over long periods in the absence of instrument monitoring, and to define frequency-magnitude relationships. Creating landslide inventory maps is however hampered by some uncertainties (associated to the scale and characteristics of the source documents, the changing vegetation coverage, and the expertise of the scientist in charge of the analysis) which have to be assessed. A multi-temporal landslide inventory has been created for the Ubaye Valley (South French Alps) by combining information from a set of orthophotographs and optical satellite images (1956, 1972, 1984, 1995, 2000, 2004, 2008 and 2010), existing reports (RTM catalogues), geomorphological maps (1989, 2001) and field survey (2012). The inventory distinguishes five types of slope movements (e.g. translational slide, rotational slide, rock-block-slide, mudslide, complex) and different geomorphological measures have been estimated (length, area, volume, degree of activity, vegetation coverage) and accuracy indicators are proposed.