Why are there sandy beaches and others pebble?

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Why are there sandy beaches and others pebble

The composition of a beach (pebble, sand, etc.) depends on the geological history of the region. © equinoxefr, Flickr, cc by nc sa 3.0

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The composition of a beach depends above all on the geological formation of the region. Indeed, the beach is essentially the result of the erosion of the surrounding rocks (the biological activity of marine organisms also contributes to the formation of beaches but to a lesser extent).

Examples of different beaches: pebbles, sand…

For example, in Normandy, the rocks are essentially made up of chalk (like the cliffs of Étretat) within which are enclosed pebbles of flint. When the rain, the wind or the sea erodes these rocks, the chalk dissolves causing the release of the pebbles. Thanks to the sea currents, these are then deposited on the shore and form beaches.

On the other hand, in a region rich in sandstone (like the South-West of France), the result will be very different. In fact, sandstone comes from the sedimentation grains of sand that have undergone aggregation and cementation. When this rock undergoes erosion, grains of sand are separated, then the sea deposits them on the shore.

Finally, with granitic rocks (certain Breton coasts), we obtain a slightly less fine sand.

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