Large scale structural control on regional coastline orientations: example from South-eastern France

Abstract

International audienceThe morphology of rocky coastlines is the expression of the interaction between external forcings and the intrinsic rock mass properties, leading to a specific erosional response. Among these rock mass properties the contribution of structural discontinuities is still poorly understood. Nevertheless, recent studies suggest that geological structures may have a first order influence in controlling the coast morphology. Understanding how the structural pattern interacts with erosion processes is fundamental to assess the evolution of these environments. We propose a regional comparison between the orientation of rocky shorelines and faults segments in six different litho-structural units in the Provence and Cote d'Azur area (southern France). Our analysis reveals that in many of these sectors the dominant fault trend (E-W) is also present in the distribution of coastlines orientations. In some particular areas, a complex geological inheritance (Maures) blurs this apparent relationship between faults and coastal morphology. We conclude that, in our study area, the level of complexity of the structural setting seems to significantly control the nature and shape of the coastline

Conceptual model of fracture‐limited sea cliff erosion: Erosion of the seaward tilted flyschs of Socoa, Basque Country, France

“…These are typical in this type of approach, and mirror the use of noise‐based detection thresholds in monitoring actively failing cliff faces (Dewez et al, 2013; Giuliano, 2015; Williams et al, 2018). A bias evident as the long‐wavelength doming effect has been described in the literature and previously explained by inaccurate camera parameters inverted by SfM methods (Giuliano et al, 2013; James & Robson, 2014; Wackrow & Chandler, 2008). While our ground‐based survey design explicitly included oblique shots to counteract this defect, a residual error remained.…”

“…The spatio‐temporal pattern of cliff failure is known to be controlled by discontinuities (e.g. Genter et al, 2004; Hoek & Brown, 1997), whereby major discontinuities such as faults can control regional coastline planform geometry (10 4 –10 5 m) (Giuliano et al, 2013). At the cliff scale (10 2 m), bulk rock resistance is considered a function of the discontinuities (characteristic spacing of 10 −3 –10 2 m) in the rock mass (Hoek & Brown, 1997; Selby, 1980).…”

Une analyse interdisciplinaire des vulnérabilités socioenvironnementales : le cas de falaises côtières urbanisées en Méditerranée

“…En revanche, au cours de la période historique (entre 290 ans et 6 800 ans avant le présent), des tempêtes extrêmes auraient engendré une érosion de grande ampleur sur la côte Paca à l'origine d'une forte abrasion marine des falaises. Quant à l'échelle plus ancienne du Quaternaire (centaine de milliers d'années), la côte régionale se serait formée sous l'action d'une très longue érosion produite lors de plusieurs variations du niveau marin associées aux grands épisodes de changements climatiques (Giuliano et al, 2013b ;Giuliano, 2015). Les falaises subissent actuellement une phase de dégradation préparant de futures instabilités gravitaires bien plus conséquentes que ce que nous connaissons de nos jours (action combinée des prochaines tempêtes d'intensité pluriséculaire, voire millénaire avec la hausse du niveau marin).…”