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14
Wearing cliffs away
Many waves lift sand and pebbles and throw them against the cliffs. The effect of this is to scrape the rock away like natural sandpaper.
Just the sheer weight of moving water can reduce a cliff to rubble, as we saw on pages 12 and 13. But most waves are not simply water – they also carry sand and pebbles that they have picked up from the sea bed (picture ).
As waves crash against the foot of a cliff, so the sand and pebbles caught up in the water batter the cliff and knock little pieces off. At the same time the sand and pebbles are broken up and made smaller and more rounded. This sandpaper-like action is called abrasion.
Cliff notch
You can see the force of abrasion in the smooth groove, or notch, near the foot of a cliff (picture 2). On the beach in front of it will lie the pebbles and sand that are picked up by the waves and thrown at the cliff during storms (picture 3).
When a wave-cut notch becomes too deep, the top of the cliff above will fall down. In this way, the whole cliff is eroded when the bottom of the cliff is worn away.
These large stones are called pebbles.
  All of these stones were once parts of rocky cliffs. Once plucked from the cliffs they were thrown back at the cliffs by storm waves. This helped to scour away the cliff and, at the same time, made the stones smaller and more rounded.
These smaller pieces are gravel. They are pebbles that have been broken up as they crashed against the waves.
These finer pieces are sand. They are the smallest grains on a beach. They too are the result of the crashing action of waves.