Publié par AFTER Beach dans Les News le 29/08/2016 à 00:00
Do you know what the composition of sand is and how it appeared on the coast? Explanations in detail.
What is the composition of sand?
Beach sand is moving sedimentary rock made up of debris, small particles from minerals such as granite, quartz, iron oxide and carbonate fragments. The grains are of different sizes. The beaches were formed by the erosion of ancient continental rocks. Common sand, made up of grains of quartz, is formed by the erosion of rocks under the effect of water and temperature and carried by rivers and wind. During the Ice Age 2 million years ago, sand accumulated over a great many years in dunes or fossil beaches, for example: Corréjou cliffs in Brittany. During storms, the sand moved again and washed up on the beaches.
The colours of sand
Of organic origin, composed of fragments of corals, shells and skeletons of organisms, white sand can be found on picture-postcard atolls (coral islands in tropical oceans). Black sands, on the other hand, come from volcanic rock, such as basalt. Other colours of sand can be found, such as pink, red, garnet and even green.
Leave the sand on the beach
More and more sand is being extracted from beaches. It is used in construction and dams. The fight against the erosion of banks and dunes as well as the melting of glaciers and rising sea levels are not helping.
The people who live among the dunes in Trégor will explain the struggle to you because their beaches are receding and gradually disappearing.
What happened in Aquitaine
In the Middle Ages, the build-up of water resulted in the appearance of the coastal lakes that are visible today on the coast of the Gironde and the Landes.
The rhythm of the beaches
In winter, between the tip of Brittany and the Pyrenees, the beaches get narrower and during strong storms, the sand is drawn towards the sea. It can be disturbed by up to 5 to 15 m and as far down as 40 meters. In summer, the beaches grow. Small waves bring the sand back to the beach but this phenomenon is very slow before the curve regains its natural shape.
Today, we enjoy the world's beaches to the full, but they are fragile and at risk of disappearing if we do not leave the sand behind.