Year 9 Geography Christmas Exam

Coasts

Coastal processes – Erosion, transport and deposition

Three key processes take place in the coastal zone:

Erosion - waves can erode the coastline in a similar way to the water in rivers. This usually occurs when the sea takes lots of energy from the power of destructive waves.
Transportation - the movement of eroded material up and down, and along the coast.
Deposition - when the sea loses energy, it drops the sand, rock particles and pebbles that it has been carrying, depositing them.

4 types of erosion – abrasion, attrition, solution and hydraulic action

The sea shapes the coastal landscape. Coastal erosion is the wearing away and breaking up of rock along the coast. Destructive waves erode the coastline in a number of ways:

Hydraulic action: Air may become trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
Abrasion: Bits of rock and sand in waves grind down cliff surfaces like sandpaper.
Attrition: Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.
Solution: Acids contained in sea water will dissolve some types of rock such as chalk or limestone.

Longshore drift

Deposition occurs when the sea has less energy, eg in sheltered bays. Material that has been eroded from the coast is transported by the sea and later put down.

Longshore drift is a process of transportation that shifts eroded material along the coastline.

Waves approach the coast at an angle.
Swash carries sediment up the beach at an angle.
Backwash carries sediment down the beach with gravity – at right angles to the beach.
This creates a zig-zag movement of sediment along the beach.

Coastal landforms- caves, arches, stacks and stumps

Erosion can create caves, arches, stacks and stumps along a headland.

Cracks in the rock erode through abrasion.
Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action and abrasion are the predominant erosion processes.
If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
The arch will continue to be eroded (attrition) and will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.

Stumps

Stump formation: Step 1

Waves cause weaknesses to form cracks at the base of the headland

Stump formation: Step 2

Over time the cracks become larger to form a cave

Stump formation: Step 3

The cave gets bigger and cracks appear above the cave to the top of the headland

Stump formation: Step 4

The arch grows larger and eventually collapses leaving a stack separated from the mainland

Stump formation: Step 5

The stack erodes and becomes a stump

Coastal protection techniques

There are different options available for managing coastlines:

hard engineering, where man-made structures such as groynes are built to stop longshore drift
soft engineering, where more natural processes are used, such as regenerating sand dunes

Using hard engineering

Hard engineering strategies involve building man-made structures to defend the coast. Here are some examples:

Sea walls

Sea walls are concrete barriers built along the seafront that deflect waves back to sea. They also protect the land behind them from flooding.

Advantages - Very hardwearing, protect against erosion and flooding.

Disadvantages - Usually the most expensive option, they can sometimes be eroded themselves and so need maintenance.

Rock armour

Large rocks or boulders can be placed in front of a cliff to absorb the energy of the waves and slow the rate of erosion.

Advantages - A fairly cheap defence, the rocks look more natural than a concrete wall.

Disadvantages - Strong waves can cause the boulders to move meaning they need to be replaced.

Groynes

Wooden or rock barriers built at right angles to the beach. These trap sediment to build up a larger beach, which absorbs wave energy and reduces erosion. This has been successful in protecting the town of Mappleton on the Holderness Coast. However, the groynes have prevented sediment from moving southwards along the coastline, which has led to an increase in erosion elsewhere.

Advantages - Builds up a large beach which, as well as providing protection from erosion, can attract tourists.

Disadvantages - As groynes stop the movement of sediment they can cause sediment starvation further down the coast, leading to further erosion there.

Gabions

Gabions are cages of rocks. These provide a barrier between the sea and the land, reducing erosion and providing stability to the shoreline.

Advantages - Cheap and easy to build.

Disadvantages - Some people find gabions ugly as they don’t look as natural as other defences, especially as the wire cage starts to rust.

Using soft engineering

Soft engineering options use natural processes to protect the coast. Here are some examples;

Beach nourishment

Sand or shingle is placed on a beach to create a higher and wider beach. This will absorb more wave energy and protect the land behind.

Advantages - The beach looks natural and it can help to attract more tourists.

Disadvantages - The new sand and shingle wash away and so the process needs to be repeated over time.

Dune regeneration

Sand dunes provide natural protection against storms and flooding. By planting marram grass in the area, sand is trapped and large dunes form, providing a barrier between the sea and the land.

Advantages - Sand dunes provide natural protection from the sea. It is relatively cheap to carry out planting projects.

Disadvantages - There is no guarantee that the sand dunes will stay in place. They may be damaged by storms or by people walking over them.

Managed retreat

Some areas of low-value land are allowed to flood creating a salt marsh. This area of land acts as a buffer.

Advantages - Salt marshes provide natural protection from the sea and they are an important habitat for wildlife.

Disadvantages - Land is sometimes lost to the sea and so compensation has to be paid to the landowners.

Coastal erosion along the east coast of England (Norfolk)

There are two contrasting approaches to coastal management.

Hold the line – this is when coastal defences are built or maintained to protect a coastline against the impacts of sea level rise and coastal erosion/flooding. Often a mixture of hard and soft engineering strategies is used. This is often expensive but popular with local residents.
Retreating the line (managed realignment) – this is when people move out of the dangerous, most vulnerable areas and there is no defence against the elements. The coastline is often eroded inland creating salt marshes. This is less expensive but not always popular with local residents.

At Happisburgh in Norfolk, eastern England, the decision was to hold the line.

Reasons for management

The coastline is eroding at an average of 2 metres a year. There are several reasons why the coast at Happisburgh is eroding so rapidly:

Rock type – the cliffs are made from less resistant boulder clay (made from sands and clays) which slumps when wet.
Naturally narrow beaches – these beaches give less protection to the coast as they don't reduce the power of the waves.
Man-made structures – groynes have been installed to stop longshore drift and build up the beaches in certain places. This narrows unprotected beaches elsewhere even further, as new sand does not come down to replace sand eroded by waves.
Powerful waves – waves at Happisburgh travel long distances over the North Sea (so have a long fetch) which means they will increase in energy.

Happisburgh is protected by a wooden groynes, wooden revetments (now badly damaged) and rock armour.
Coastal management at Happisburgh has tried to make the beach wider by using groynes, and also uses a sea wall to protect the coast.

Cost benefit analysis

There are many social and economic reasons why some coastlines such as Norfolk have been heavily protected, while others have not. Cost benefit analysis involves working out all the benefits of something and comparing with the costs (problems) that the new idea may create. In areas with many people at risk the benefits of protecting an area often outweigh the costs of doing nothing.

Social reasons – many people who live along eroding coastlines believe their safety and security must be maintained. Some people disagree with where the sea defences have been located, especially if it means the land in their community is not protected.
Economic reasons – some sea defences negatively impact tourism and reduce the amount of money coming in to the area. Sea defences are very expensive, so if the number of people living there is low (low land value) then governments and councils may choose not to protect.
Environmental reasons – managing coastlines are important to help preserve and protect wildlife and natural habitats from destruction.

Population

Factors causing population change

Population pyramids

When looking at population, structure as well as total numbers is important. This means looking at the number of people in each age group and how those numbers are changing. These are known as population pyramids. Countries at different stages of the DTM have different shaped population pyramids.

The interpretation of a population pyramid can help a geographer understand the structure of a country, for example:

a wide base to the pyramid indicates a young population
wider bars at the top of the pyramid indicate an ageing population

There may be anomalies in the pyramid, for example:

a longer than expected bar may indicate a large amount of immigration at that age range
a shorter than expected bar may be due to war or famine

Population pyramid for Kenya

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