Geography Paper 1- Coasts

Waves Characteristics

created when wind blows over the sea

size and energy depends on the fetch (how far te wave has travelled), the strength of the wind, how long the wind has been blowing for

Destructive vs Constructive Waves

Destructive- weak swash, strong backwash which removes sediment from the beach, waves are steep and close together

Constructive- strong swash, weak backwash, strong swash brings sediment that build the beach, waves are low and further apart

What are the types of erosion?

Hydraulic action- force of water hitting cliffs

Abrasion- material in water scapes against the cliff

Attrition- rocks in water knock against each other

Solution- Minerals in rocks dissolved by seawater

What are the types of weathering?

Physical- changes in temp eg freeze thaw

Biological- caused by plants and animals

Chemical- Dissolving of minerals in rocks over time rainwater

What are the types of mass movement?

Rockfall- Bits of rock fall off the cliff face, usually due to freez-thaw weathering

Mudlow- Saturated soil flows down a slope

Landslide- Large blocks of rock slide downhill

Rotational Slip- Saturated soil slips down a curved surface

What are the types of transport?

Traction- Large boulders

Saltation- Small particles bounced along seabed

Suspension- Small particle carried within water

Solution- Dissolved particles carried in water

Explain how longshore drift transports material along a coastline?

1) Waves approach coast at angle due to prevailing winds

2)Swash carried material to beach at an angle

3)Backwash carries material straight back down due to gravity

This moves material across the beach

Factors leading to deposition

waves slow down and loses and energy

shallow water

sheltered area e.g bays

little or no wind

Erosional Landforms-How are headlands and bays formed?

Headlands and Bays form where there are alternating bands of hard ans soft rock along the coastline.

The soft rock erodes faster to form a bay with a gentle slope.

Because the hard rock erodes more slowly, it juts out forming headlands with steep sides

(swanage bay & durlston head in Dorset)

How are cliffs formed?

Through erosion and weathering

Soft rocks form gentle sloping cliffs and hard rocks form high, steep cliffs

Erosional- How are caves, arches stacks and stumps formed?

1) Waves attack weaknesses in the base of the cliff through hydraulic action and abrasion

2) Over time, cracks are eroded and form a cave

3)The back of the cave is eroded over time until it goes all the way through creating an arch

4) Top of arch is eroded through weathering e.g chemical

5) This leaves a stack and the base is eroded through hydraulic action and the top is weakened through weathering

6)Eventually it collapses to leave a stump

(Old harry in dorset)

Erosional- How are wave-cut platforms formed?

1) The sea attacks the base of the cliff between the high and low water mark.

2) A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action - this is a dent in the cliff usually at the level of high tide.

3) As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.

4) The backwash carries away the eroded material, leaving a wave-cut platform.

Depositional-How are beaches formed?

Formed in areas where waves have less energy and deposit material

Usually a bay as water is shallower and there is wave refraction

Sandy beaches formed in bays and pebble beaches near a cliff

size of material is larger at back of beach b/c of storm waves carrying large sediment

The smallest material is found nearest the water as the waves break here and break down the rock through attrition

Depositional- How are spits formed?

Spit- extended stretch of sand or shingle jutting out into the sea from the land.

1)Sediment is carried by longshore drift

2)When there is a change in the shape of the coastline, deposition occurs. A long thin ridge of material is deposited. This is the spit.

3) A hook can form if thre is a change in the direction of wind

4)Waves cannot get past a spit, therefore the water behind a spit is very sheltered. Silts are deposited here to form salt marshes or mud flats.

(hurst castle spit Dorset)

Depositional- How is a bar formed?

Sometimes a spit can grow across a bay, and joins two headlands together. This landform is known as a bar. They can trap shallow lakes behind the bar, these are known as lagoons. Lagoons do not last forever and may be filled up with sediment.

Depositional- How are sand dunes formed?

These form on a wide beach where there is a plentiful supply of sand

Wind blows the sand inland where an obstacle such as a dead bird or litter will trap the sand and cause it to start to build up forming a ridge

The ridge itself can then be a barrier causing a further build up of sand

This creates an embryo dune that migrates inland

Marram grass grows on the dune (can survive in salty beach conditions). The roots hold the sand in place and the grass traps more sand being blown in from the beach. This makes the dune bigger. This creates a foredune

Over time, the death and decay of marram grass adds nutrients to the sand turning it into a soil creating what is called a yellow dune

The dunes can now support a wider range of vegetation such as heather and bracken.

The oldest dunes are found at the furthest point from the beach, have a much more fertile soil and can sometimes support entire woodlands or even golf courses. These are called grey dunes.

The areas between dunes called a dune slack can sometime be flooding when the water table rises.

As you move further inland the dunes become larger, taller, have a greater range in biodiversity, are more stable and have a more fertile soil.

(Studland Bay, Dorset)

Hard Engineering Methods

Sea wall-curved to reflect waves back to sea

ad-effective, people can walk along dis-expensive,waves can still erode sea wall

Rock Armour- large boulders at foot of cliff

ad- cheaper than sea wall+easier to maintain, can be used for fishing dis- look off, expensive to transport

Gabions- Rocks placed in rock cages

ad- cheap, absorbs wave energy dis- not very strong, look unnatural

Groynes-wooken or rock structures built out at right angles to sea

ad- builds beach-tourism, trap sedmient carried by longshore dirft

dis- starves beach further down, look unattractive

Soft Engineering Methods

Beach Nourishment- sand pumped onto beach to build it

ad- blends in with existing beach, larger beach= more tourism dis- needs constant replacement, sand brought in from somewhere else

Dune nourishment- marram grass planted on dunes to stabilise and trap sand in dune to build it up

ad-relatively cheap,keep natural looking coastline dis-can be damages by storm waves, area have to boarded off

Manages Retreat

controlled flooding of low lying coastal area. Can be used for low value land that is at high risk from erosion

ad- cheap comparied to other defences, creates salt marsh that provide habitat and natural defence against erosion or flooding

dis- land is lost, landowners need to be compensated