A Microscopic Foundation
The brilliant white cliffs of Étretat are a link to a vastly different prehistoric world. They are composed almost entirely of chalk, a soft limestone that is the fossilized remains of countless single-celled marine algae called coccolithophores. For millions of years during the Late Cretaceous Period—specifically the Turonian and Coniacian stages, around 90 million years ago—these microscopic organisms thrived in the warm, shallow sea that covered this part of Europe. As they died, their minuscule calcium carbonate plates, called coccoliths, rained down on the seabed, accumulating in immense layers. Over geologic time, the sheer weight of these deposits compacted them into the thick chalk beds visible today, with some cliffs reaching heights of 90 meters (300 feet).
Embedded within the white chalk are distinct horizontal bands of dark flint. These nodules are not formed from different sediment layers but from a chemical process that occurred after the chalk was deposited. The silica required for flint formation came from the dissolved skeletons of other marine organisms, like sponges. This silica-rich water moved through permeable pathways in the soft chalk sediment, often along the burrows of ancient creatures, and precipitated into the hard, microcrystalline quartz that constitutes flint.
A Landscape Shaped by the Sea
The dramatic arches and sea stacks of Étretat's coastline show differential erosion. The relentless action of the English Channel's waves exploits weaknesses and faults in the chalk. Softer sections of the cliff face erode more quickly, carving out sea caves. When two caves on opposite sides of a headland erode and meet, a natural arch is formed.
The three famous arches are the Porte d'Amont, the Porte d'Aval, and the largest, the Manneporte, which is only visible from the sea or further down the coast. The famous 70-meter (230-foot) sea stack known as L'Aiguille, or "The Needle," is the remnant of a former arch whose top has collapsed, leaving the more resistant pillar standing alone. This entire process is ongoing. The cliffs are constantly changing, retreating at an average rate of 30 to 40 centimeters per year due to wave action, rain, and freeze-thaw cycles that weaken the rock. The pebble beach at the base of the cliffs is a defense; the flint pebbles, rounded by the sea, absorb a significant amount of wave energy, slowing the erosion of the cliff toe.
The unique chalk environment supports specialized flora adapted to the harsh coastal conditions, including sea cabbage (Crambe maritima) and sea thrift, which cling to the cliff faces. The cliffs also provide nesting grounds for seabirds such as herring gulls and Arctic fulmars.