Analysis of a landslide multi-date inventory in a complex mountain landscape: the Ubaye valley case study

We propose a methodology (1) to prepare a multi-date landslide inventory for a mountainous area affected by several landslide types with different degrees of activity, and (2) to estimate the temporal occurrence and the intensity of the landslides through the analysis of morphological indicators. The inventory, covering the period 1956-2010, is constructed for the middle section of the Ubaye valley (South French Alps) based on the analysis of multi-source documents (geomorphological maps, historical reports of landslide events, field surveys, series of orthophotographs and SAR satellite images). The uncertainties in the interpretation of the documents and the landslide morphological features are taken into account in relation to the scale of the source documents. Several morphological indicators are calculated to describe quantitatively the evolution of the landslides (length, area, relative elevation, runout distance). Frequency-area density functions are calculated to estimate the changes in the landslide distributions. A Poisson model is used to estimate the probability of reactivation of the observed landslides. The proposed multi-date inventory and the associated statistics give additional information to the event catalogue managed by local authorities.