Waves are the most significant architects of our coasts. They shape the cliffs and the sand on beaches. The energy which drives them towards the land is powered by the wind far out on the open sea. Whipped up for longer by severe storms they can tower up to heights of 30 metres. On leaving the wind area they lose power and become more gentle. Most waves are no higher than 3 metres.
On steep coasts like here in Portugal, one after another they crash at full force onto the cliffs which reach a height of 50 metres. When the winter storms rage on the open Atlantic the rolling masses of water can get as high as 10 metres.
It´s not just the height of the waves that counts but their length as well. Waves of 3 metres in height and 30 metres in lenght exert 8 tons of pressure per square metre of rock. Waves with a height of 4 metres and 60 metres long produce 12 tons of pressure and in stormy seas up to 30 tons per square metre can be reached. This constant bombardment forces salt water into all the crevices, pressing its way into the finest cracks. Above all it is the rock at the base of the steep cliffs which cracks, gets leached and flushed out till it collapses. A cavity is created and in time the cliff above collapses. Bit by bit the steep coast gets carried away.