Inshore Analysis of the Morphostructural Evolution of the Coastal Cliffs of Bessin, Basse Normandie, France

The limestone–marl cliffs along France’s northern coast, particularly from Arromanches-les-Bains to Longues-sur-Mer, are experiencing significant erosion. This study investigates cliff retreat mechanisms and classifies instability types through image analysis, LiDAR measurements, and field observations. Key instabilities comprise various types of rock instabilities within limestone formations, principally promoted by erosion and creeping of the underlying marls. Direct limestone panel sinkings, wave-cut notches and rockslides are also observed. All of these are controlled by environmental exposure, weathering, and pebble beaches. A review of images from 1947 to 2012 showed that cliff recession occurs in discrete events, averaging 0.06–0.30 m per year. Notably, a May 2013 rockslide near Cape Manvieux displaced around 30,000 cubic m of material, triggered by interactions between creeping marls and destabilized limestone. This research emphasises the significance of comprehending these processes.