Coastal environment and geology





 

During the Mesozoic,  from hundred and fifty to sixty-five million years ago ,under a  warm and damp  climate , not only did the dinosaurs but many other species become extinct among which ammonites and sea urchins constituting the marine plankton. It is the sedimentary accumulation of their calcareous remains that created the high cliffs that we can admire today.

 

The one hundred and thirty kilometres of chalk cliffs along the coast, called the alabaster coast , are a unique setting highly sensitive to erosion.

 

Under the effect of the swell, frost, water  seepage, and other factors linked to the constitution of the chalk itself, the cliffs are eroded of about twenty centimetres a year. The blocks that fall down on the strand  release chalk and flint.

The chalk is rapidly dissolved in the sea while the flint is rolled and crushed by the sea and eventually becomes a pebble.

The pebbles gather into an offshore bar which constitutes a natural  barrier which protects  the bottom of the cliffs against   direct attacks from the waves.

This phenomenon is common to all the cliffs along the Channel coasts , so this is what happens in Sussex with the Seven Sisters for example.

 

Man has made this natural environment change. Indeed, the economical development of ports induced the building of piers and sea walls in order to allow an easy access to bigger and bigger boats .

 The setting up of heavy equipment, such as the oil rig at Antifer or the two nuclear power stations around Dieppe, changed the coastal landscape and accelerated the erosion and the recession of the cliffs. ( from half a meter to a meter a year) . Huge sections fall down into the sea  causing the collapse of houses built on top of the cliffs .

 

Pebbles are also a valuable industrial resource. The traditional collecting of pebbles on the beaches of Dieppe and Le Treport was forbidden in 1985 in order to preserve the stock of pebbles and ensure the protection of the cliffs . This activity increased however in the area of the Somme mouth where the stock of pebbles is important. 

The pebble , made of ninety-nine per cent of silica , is exported to eighty countries over the world because it can be used in industry  in three different ways :

 

-         Round regular-shaped pebbles are used to crush fragile chemicals in cosmetology and pharmacology. Their purity do not alter the products.

-         In spite of their hardness, pebbles can be crushed into grains of different sizes which are then used as gas or water filters or come into the making of glass-paper

-         When the pebble is brought to a temperature of one thousand and six hundred degrees centigrade, it changes into a white powder which is used to make earthenware and ceramic, such as the famous English Wedgwood or the French Luneville. The burnt pebble also comes into the making of toothpastes, road-paints or architectural coatings.



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