1. What are the processes by which water helps to shape the coastal landscape?

What is the coast?

It is a narrow zone between the land and the sea that is constantly changing due the effects of the land, sea and air acting upon it.

You may recall the processes that create river landscape are
  • Erosion
  • Weathering
  • Transportation
  • Deposition
  • Mass movement
Well you will meet them again here but there are a few changes (if you can't remember them go here)
These can also be called sub-aerial processes because it takes place ‘under the air’ or at the surface of the land. it includes physical and chemical weathering, mass movement, erosion and deposition but not biological weather - for reasons that I am not entirely sure about - but take it from the Edexcel man, its true.

Types of Coastal Erosion

Erosion is the process that wears away material by something else – an agent – and the most usual agent on coasts is water in the form of waves, so not only do you have the usual water-type erosion processes but you have another couple that refer to waves alone. Erosion is also a process of wearing away prior to removal ( unlike weathering – see below).So there are 6 main types of erosion processes in action at the coast
1. Abrasion (corrasion) - this is where breaking waves hurl rock fragments against the cliffs gradually wearing away the cliff material.
2.1A_Erosion.png2. Hydraulic Pressure - this is where erosion occurs due to the pressures exerted by breaking waves as air trapped in cracks in the cliff is compressed by the water. This compression and sudden release gradually forces the cracks apart.
3. Solution (corrosion) - this is where salt water can act to dissolve some chemicals in the rocks, for example in limestone, calcium carbonate is dissolved, weakening the rock.
4. Attrition - as rock fragments are swirled around by waves they are gradually broken down as they hit against each other.
5. Wave scouring - waves breaking at the base of the cliffs swirl around the base and result in the removal of loose rock.
6. Wave Pounding - breaking down of the cliff face due to the sheer force of the wave which can exert upwards of 30 tonnes / m2 when crashing on the cliffs.
As well as the action of the sea causing the erosion of the cliffs, weathering processes and human activity can also be responsible for affecting the wearing away of the rock.

As well as the action of the sea causing the erosion of the cliffs, weathering processes and human activity can also be responsible for affecting the wearing away of the rock.

Weathering Processes:

With weathering, unlike erosion, it has to do with the breaking off taking place in situ which is where it tends to stay put.
Freeze-thaw processes (as water freezes and thaws in cracks in cliffs, the expansion and contraction forces the rock open, making them more susceptible to the action of waves).
Chemical weathering - water running down the face of cliffs, either from surface runoff from above or from rainfall can result in solution so that rock cracks are enlarged, leaving the remaining rock loosened
Biological weathering - burrowing organisms and roots of vegetation forces open cracks, making them more susceptible to wave erosion) [NOT sub-aerial]

Human Activity

Can also cause cliff to collapse
Pressure on cliffs (construction work)
Sea Defences (although designed to reduce erosion - in some instances (e.g. the use of groynes) can increase erosion by starving down stream areas of sediment)

Coastal Transport

Weathering and erosion at the coast produces large amounts of material which is moved along the coast line and out to sea by the action of waves.
Up and down the beach: Material is moved up the beach in the swash and back down the beach in the backwash. Constructive waves move large amounts of material up the beach as they have a strong swash, whereas destructive waves move large amounts of material down the beach due to their strong backwash.
The movement of material by waves: The movement of material within the waves themselves depends on (i) the size of the material and (ii) the energy available for transporting the material. There are four possible types of transport within the water:

Solution - material carried dissolved in the water
Suspension - fine material carried suspended within the water itself
Saltation - material which is too heavy to be continuously held in suspension is bounced along the sea bed.
Traction - the heaviest material is simply rolled along the sea bed.
Longshore drift Movement of material along the coastline. But before this process is explained, you need to know a bit more about waves!
2.1BLongshore_drift.png1. Waves break on the beach at an angle controlled by the prevailing wind direction. Material is moved up the beach in the swash.
2. Material then moves straight back down the beach in the backwash under the influence of gravity.
3. As the processes continues material moves along the coast in a zig-zag movement.

How is energy transferred to create waves?
1. Wind creates friction on the waters surface; 2.1C_Wave.png
2. Frictional drag between the wind and the waters surface causes water particles to rotate and energy is transferred forward;
3. When the wave reaches shallow water, it slows down due to friction between the base of the wave and the sea bed. The shape of the wave becomes increasingly elliptical;
4. The top of the wave continues to move forward as it is unaffected by the friction with the sea bed. It becomes steeper and steeper and eventually breaks;
5. Water moves up the beach as the swash;
6. Water then returns back down the beach as the backwash.

There are two main types of waves: 2.1D_Constructive.png
A constructive wave is
  • small in height
  • has a gentle angle: there is a shallow gradient between the waves because there is a long gap between them and each wave is not very high
  • has less energy
  • has a stronger swash than backwash (material is moved up the beach by the strong swash).
So it is constructive because it is building the beach up – it is constructing it

2.1E_Destructive.pngA destructive waves is
  • large in height
  • has a steep angle: the is a steeper gradient between the waves because there is a shorter gap between the waves and each wave is high
  • has lots of energy
  • has a weaker swash than backwash (beach is scoured and degraded as the strong backwash pulls sand and shingle back down the beach)
So it is destructive because it is removing material from the beach – it is destroying it

What determines how much energy waves have?
  1. Wind speed
  2. Wind duration (length of time for which wind blows)
  3. The Fetch of the wave (distance of open sea over which the wind has blown)

Try this game to see if you know your destructive wave from your constructive one.

Click here for full screen version

What you need to know

  • What the coast is
  • Define all the words in BOLD
  • Know in detail about the actions of the 5 types of sub-aerial process
  • Draw the diagram to illustrate how the rocks on the coast are broken down
  • Explain longshore drift with the use of a diagram
  • Know the difference between swash and backwash
  • Be able to explain the difference between constructive and destructive waves
  • Know that destructive waves have more energy and know how they can acquire it

Need to add mass movement