Rock Slope Failure (RSF) in the Western Alps : a systematic inventory with perspectives on causes, geohazards and geoheritage

• Main Author: Blondeau, Sylvain
• Other Authors: Lyon, Gunnell, Yanni
• Format: Thesis
• Language: French
• Published: 2018
• Subjects: Tectonique de versant; Classification de ruptures rocheuses; Incidence spatiale; Lithologie; Holocène; Pergélisol; Processus paraglaciaires; Sismicité; Géopatrimoine; Slope tectonics; Landform classification; Spatial incidence; Lithology; Permafrost; Paraglacial processes; Seismicity; Geoheritage; geo; envir; permafrost; pergélisol
• Online Access: http://www.theses.fr/2018LYSE2084

The study of rockslope failure (RSF) is usually focused on the instrumental monitoring of hazardous sites, sometimes extended to a population of RSF in a valley or massif. Few studies survey and analyse RSF at the much broader scale of a mountain range. Here we produce a systematic inventory of RSF in the Western Alps based on satellite imagery provided by the open-access platform Google Earth Pro™, and using a series of ground-truth-tested visual detection methods. Based on a categorisation inspired by existing classifications but adapted to the range of RSF observed in the study area, five main RSF types were identified: rockfalls and rock avalanches, rockslides, earthflows, deep-seated gravitational slope deformations (DSGSD), and slope deformations. We analyse the spatial incidence of those five categories in relation to a range of likely cumulative causes. The analysis covers lithology and rock fabric, geological structure (faults, thrust fronts), seismicity, slope angle, local relief, the intensity of Würmian glaciation, modern rainfall patterns, and permafrost degradation. Results from a total population of 1400 RSF occurrences show that RSF incidence and mode are overwhelmingly susceptible to rock type, but that local relief enhanced by past glaciation generates the gravitational potential needed to move the rock masses. Other conditional factors receive lower rankings at the regional scale, but stronger connections appear in local settings. At places, RSF size or density are seen to correlate with faults, thrust fronts, and with permafrost degradation (restricted, however, to the rockfall category). Among all the likely causes of RSF, rainfall totals represent the weakest link. Among the 1400 sites we focus on a subset of flagship RSF occurrences that we consider relevant to either geoheritage or land-use planning concerns. The criteria were selected on the basis of morphological characteristics (uniqueness, educational and scientific value) or from the perspective of the hazards that some of the ...