The White Cliffs of Dover are made of soft white calcium carbonate chalk with a very fine grain. They also contain quartz and flint. The chalk is different from the chalk typically used on chalkboards, which is usually gypsum or calcium sulphate.Continue Reading
The chalk of the White Cliffs of Dover is a type of limestone. It is the composed of the calcium carbonate skeletons of single-celled planktonic algae and some other organisms. This limestone is over 1,000 feet thick in places. It first formed during the Cretaceous period, tens of millions of years ago. Geological uplift raised the surface of the sedimentary rock above the ocean's surface, and flooding during the ice age wore it away and exposed the cliffs at the same time as the Strait of Dover.
Due to their soft materials, the cliffs erode at a rate of about 0.4 inches per year. This is the reason they remain white. Where the erosion is stopped by artificial structures, the surface is quickly overgrown by plants. Occasionally, larger pieces of the cliffs fall off; there was a very large collapse in 2001 and another in 2012. The Cliffs of Dover are a popular tourist attraction, but visitors are advised to keep their distance because of the possibility of collapse.Learn more about Earth Science