Statistical and empirical analyses of the triggers of coastal chalk cliff failure

Abstract

International audienceThe triggering factors of rock falls remain unknown due to a lack of exhaustive, regular and accurate surveys. Based on an inventory of 331 rock falls collected weekly between 2002 and 2009 from Veules-les-Roses to Le Treport (Upper Normandy), the relationships between coastal chalk cliff rock falls (dates and geomorphological features) and external factors commonly agreed as triggering (rainfall, temperature variations, tide and wind) are studied. The combination of multivariate statistical and empirical analyses indicates that (1) “cold and dry weather” and “high rainfall and high wind” are the conditions most likely to trigger rock falls, (2) the main triggering factors of rock falls are effective rainfall (for rock falls mostly between 200 and 1,400 m3 or larger than 10,000 m3 and coming from the whole cliff face), freeze/thaw cycles (especially for rock falls smaller than 200 m3 and coming from the foot and top of the cliff face) and marine roughness (rock falls mainly smaller than 200 m3 and coming from the cliff foot). However, the contribution of each factor to triggering is difficult to determine because of combinations of factors (85 % of 331 cases), relays of processes and hysteresis phenomena. In view of these first results, it is still presumptuous to predict the location and time of triggering of rock falls. However, the statistical and naturalistic approaches adopted and the observations made in this study are from an original database, and constitute a real starting point for the prediction and prevention of the hazard of coastal chalk cliff rock falls in Upper Normandy

Optimal transport for data fusion in remote sensing

“…3, where the two 3D point clouds are represented in the top panel, and the magnitude of changes are depicted in the bottom panel. The lower right part of the area has strongly been affected by rockfalls, which is consistent with on site observations and with the study in [20]. However here, the important precision in quantifying altered areas using optimal transport makes this approach a very good alternative for future studies in LiDAR change detection.…”

“…However at the moment, changes are extracted using differences of Digital Elevation Models computed from the 3D point clouds LiDAR point cloud [20]. This is obviously not optimal, since it requires an interpolation step that could disturb areas especially those affected by local rockfalls, where the higher resolution of the LiDAR scan would be the most beneficial.…”

The temporal and spatial scales of rocky coast geomorphology: a commentary

“…New statistical techniques and utilisation of catalogues of observed cliff failure now provide great promise in reconciling these different timescales. In this Special Issue Letortu et al (2015) developed an inventory of 331 individual landslides between 2002 and 2009 on the Upper Normandy coast of France. A thorough statistical analysis of the boundary conditions for each of these events allowed 'a starting point for the prediction and prevention of the hazard of coastal chalk cliff rock falls' (p. 1371).…”

From physical geography to environmental geography: Bridges and gaps (a French perspective)

“…Concerning fluvial corridors, many scientific advances have direct applications to environmental and territorial management, including ecological river restoration and regulation (Dufour and Piégay ; Carbonneau and Piégay ; Arnaud‐Fassetta et al ; Corenblit et al ; Lespez et al ). Based on similar methods, research programmes have been recently carried out on coastal dynamics in order to understand and quantify the operating processes, map risks of marine erosion and submersion, and provide tools to managers in charge of coastal management (e.g., Hénaff and Manuelle ; Letortu et al ). Mountain and volcanic geomorphologies also provide good examples of the capacity of process geomorphologists to develop a rewarding continuum between a basic physical geography focusing on the understanding of ongoing processes, and an applied environmental geography responding to societal needs of sustainable management and development (e.g., De Bélizal et al ; Ravanel and Deline ).…”