The Mont-Saint-Michel Bay: An Exceptional Megatidal Environment Influenced by Natural Evolution and Man-Made Modifications

Due to its exceptional tidal range and the immensity of its tidal flat, the Mont-Saint-Michel bay is a favored model for research on coastal hydro-sedimentary processes, reconstruction of the depositional wedge during the Holocene, and landscape evolution. The western tidal flat consists of a large muddy to sandy embayment, whereas the eastern intertidal domain consists of estuarine deposits characterized by finely laminated muddy sand, enriched in biogenic carbonate. The present-day morphology and sedimentary dynamics are the result of a complex balance between tide-dominated sediment supply and erosive processes under wave action and tidal channels migration. The bay has been filled for thousands of years to the rhythm of sea level oscillations, leading to the gradual progradation of the shoreline. In addition to this natural evolution, human activities have developed in the bay, both on the western tidal flat (fixed fisheries and shellfish farming) and on the eastern estuarine side (polder formation, dikes, and dam construction), and have progressively changed the landscapes. In 1884, Victor Hugo issued an appeal for the protection of the Mont-Saint-Michel in these terms: “The Mont-Saint-Michel is to France what the Great Pyramid is to Egypt. It must be protected from any damage. The Mont-Saint-Michel must remain an island. This combined work of nature and art must be conserved at all costs.” Since that time, salt marshes have progressed, the land reclamation and man-made developments to facilitate the access to the mount also continued, so the maritime character of Mont is still endangered.