Waves are the primary force causing erosion along coastlines. A wave is formed by the wind blowing across the surface of the water, creating ripples, which then grow into waves. As waves reach the coast the lower section slows due to friction. The upper section topples over and breaks forward.
The Fetch determines how powerful a wave may be. It is the distance that the wave has travelled. For instance, a wave hitting the coast of Cornwall may have travelled over 4000 miles to get there, all the way across the Atlantic. However a wave hitting Dover may have only travelled the width of the English Channel.
The Strength Of The Wind also influences the power of the waves, so even those with a relatively short fetch can have a great deal of energy, and there fore cause a lot of damage to the coastline.
The coastal system is an ever-changing physical environment, powered primarily by the waves. These come in two main forms: destructive (or erosive) waves, and constructive (or depositional) waves.
1. Destructive Waves have a number of important characteristics:
i) Their backwash is much stronger than their swash, thus allowing them to remove material from the beach.
ii) They are frequent in number, usually between 10 and 15 per minute.
iii) They are tall waves, meaning they have a greater distance to fall when they break. This causes them to scour out the beach material.
iv) Destructive waves create a steep narrow beach.
2. Constructive Waves have a number of important characteristics:
i) Their swash is much stronger than their backwash, causing the beach to be built up by the deposited material.
ii) They are less frequent, reaching shore between 6 and 9 times each minute.
iii) They are long waves and so roll onto the beach rather than crashing onto it.
iv) Constructive waves create a wide, gently sloping beach.