WHAT CAUSES WAVES?

You should be able to explain the causes of waves, explain how wind and fetch affect the size of waves, and compare the key features of destructive and constructive waves.

Have a look at the picture. What do you think caused this?



KEY TERM: WAVES - Ripples in the sea caused by the transfer of energy from the wind blowing over the surface of the sea. The largest waves are formed when winds are very strong, blow for lengthy periods and cross large expanses of water. 

(all of the key terms that are used in this site are exactly as defined by the exam board)



This diagram shows how long the fetch is from different directions. The fetch is the distance over which the wind has blown. A bigger fetch means bigger waves. This means that waves hitting the South West have a much larger fetch than waves hitting the South East. This means that the South West gets much larger waves.

So, how do waves form?

1. Wind blows across surface of sea.
2. Friction is created producing a swell.
3. Wind energy causes particles to rotate inside the swell.
4. This moves the wave forwards.

Task: Produce a story board that shows how a wave is created. Use annotations to explain the process.

Look at THIS CLIP to get a better idea of how the process works.

So why do they break?

The bottom of the wave touches the bed which causes it to slow down. The top of the wave continues at the faster speed so the wave starts to lean forward. Eventually the top of the wave topples over due to gravity.

Try working through THIS TASK to show what you have learnt so far.

The height of waves depends on 3 factors:

1. the stronger the wind the bigger the wave
2. the longer the wind blows the bigger the wave
3. the greater the distance the wave travels over open water (fetch) the bigger the wave

So what happens to the wave energy as it reached the coast?

Swash is the movement of a wave up the beach after the wave has broken.

Backwash is the return flow of water after a breaking wave. Gravity means this is always at right-angles to the beach.

Some waves build up the beach. These are known as CONSTRUCTIVE WAVES.

Some waves take material away from beach. These are known as DESTRUCTIVE WAVES.

Check your learning using THIS sorting task

Okay, that's the introduction to waves done. Check the list of stuff you should know (at the top of the page) and make sure you know it! Test yourself with the following question:


With the aid of annotated diagrams compare constructive and destructive waves. [6 marks]

(Annotated means labels that contain explanation. You should allow yourself about one mark per minute for exam questions.)