Coastal erosion processes

You need to be able to define the four main processes of coastal erosion.

Corrasion (abrasion) - this is where the bits of rock and sand carried in the waves grind down cliffs.

Attrition - this is where the waves cause rocks and pebbles that they are carrying to smash into each other and break down. They become smaller and rounder.

Solution - this is where acids contained in sea water slowly dissolve certain types of rock.

Hydraulic Action - this is the constant force of waves crashing on the shore. When waves crash against the cliffs they force air into cracks in the rock. The air is trapped, and pressure builds up. As the waves move back, pressure is released and the trapped air expands. Small explosions take place and weaken the rock.

You might find it useful to remember the 4 processes using the phrase CASH.

The BBC Bitesize website has a useful animation showing these four processes. Click here to visit this page.

Remember the Coastal Kung Fu from our lessons? This activity was designed by Portchy from SLN. Thanks! Click on the image to re-live the experience.

Click to play

Constructive and Destructive Waves

Constructive waves are low energy waves with a stronger swash than backwash. Where there are less than 8 waves breking each minute they tend to be constructive waves.

Constructive waves tend to deposit material and build up a beach.


By contrast, destructive waves have much higher energy. They are much larger in height. They have a weak swash but a strong backwash, and they therefore erode the beach by pulling sand and shingle (beach materials) down the beach as water returns to the sea.


The Wycombe High School website has some excellent animations of both constructive and destructive waves. You can see them here. Alternatively, you could look at the Curriculum Bits website animations.

Waves

Waves get their energy from the wind. As the wind blows over the surface of the sea, it creates friction. This frictional drag causes water particles to rotate and their energy is transferred forward in the form of a wave. Whilst the water moves forward, the water particles return to their original position.

As a wave reaches shallow water, friction between the sea bed and the bottom of the wave causes it to slow down. Its shape becomes more eliptical (rather than circular). The top of the wave is not affected by the friction, and it becomes steeper until it eventually breaks.

When the wave breaks, water rushes up the beach. This is called the swash.

The movement of water back down the beach is called the backwash.

There are three main factors that affect the strength of a wave:

1. The strength and speed of the wind.
2. The duration of the wind - this is the length of time for which the wind has blown.
3. The fetch - this is the distance over which the wind has blown.

The Wave Machine Simulator helps you to see the impact of these three variables.

A model of the coast

As we work through this unit, try to keep this model of the coastal system at the front of your mind. Remember that the processes of erosion, transportation and deposition are closely linked. The lesson about coastal processes in Harlech should remind you of this!

Water, landforms and people: coasts

The exam board has set the following key questions for this section of the course:

* What is meant by processes of erosion,transport and deposition at the coast?
* How do these processes contribute to the development of distinctive coastal landforms?
* What coastal landforms are produced?
* In what ways do these natural processes and the coastal landforms they produce affect human activity?
* In what ways does human activity affect the natural processes and coastal landforms?
* What conflicts arise from the management of coastal processes and landforms?
* How and why do these conflicts arise?
* How can conflicting interests be managed to minimise negative effects and maximise the positive effects of human activity on coastal processes and landforms?

Here is the topic overview sheet which you were given in the lesson.

Coasts outline - Upload a doc

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