Coasts Flashcards
1
Q
What is fetch?
A
- The length of water over which a given wind has blown
2
Q
What are the characteristics of a destructive wave?
A
- They are created from big, strong waves when the wind is powerful and has been blowing for a long time.
- They occur when wave energy is high and the wave has travelled over a long fetch.
- They tend to erode the coast.
- They have a stronger backwash than swash.
- They have a short wave length and are high and steep.
3
Q
What are the characteristics of a constructive wave?
A
- They are created in calm weather and are less powerful than destructive waves.
- They break on the shore and deposit material, building up beaches.
- They have a swash that is stronger than the backwash.
- They have a long wavelength, and are low in height.
4
Q
What is hydraulic action?
A
- The force of waves hitting the cliffs and forcing pockets of air into cracks and crevices.
5
Q
What is abrasion?
A
- Caused by waves picking up stones and hurling them at cliffs and so wearing them away
6
Q
What is corosion?
A
- Dissolving of rocks by the acid in sea water
7
Q
What is attrition?
A
- A process whereby the material carried by the waves carried by the waves becomes rounded and smaller over time as it collides with other material.
8
Q
What is longshore drift?
A
- Longshore drift is caused by the oblique wave angles that create a near shore current.
- The zigzag pattern is because when a wave breaks, the swash carries material up the beach at the same angle as that which the wave approached the shore.
- As the swash dies away, the backwash and any material carried by it returns straight down the beach, at right angles to the waterline, as a result of gravity.
- Constructive waves
9
Q
What is weathering?
A
- The breakdown of rocks which is caused by freeze-thaw and the growth of salt crystals, by acid rain and by the growth of vegetation roots
10
Q
What is erosion?
A
- The wearing away of rocks by wind and rain
11
Q
What is mass movement?
A
- The removal of cliff-face material under the influence of gravity in the form of rock falls, slumping an landslides.
12
Q
When is deposition likely to occur?
A
- When waves enter an area of shallow water.
- When waves enter a sheltered area, eg a cove or bay.
- When there is little wind.
- When there is a good supply of material.
13
Q
What is a concordant coastline?
A
- Occurs where the bands of differing rock types run parallel to the coast.
- The outer hard rock (e.g. granite) provides a protective barrier to erosion of the softer rocks (e.g. clays) further inland.
14
Q
What is a discordant coastline?
A
- Occurs where bands of differing rock type run perpendicular to the coast.
- E.g. Dorset coastline running north from the Portland limestone of Durlston Head
15
Q
How does a cave form?
A
- 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.
16
Q
How does an arch form?
A
- If the cave is enlarged and extends back through to the other side of the headland.
17
Q
How does a stack form?
A
- The arch 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 on the other.
18
Q
How are wave-cut notches formed?
A
- When destructive waves repeatdely break at cliffs that rise steeply from the sea and this leads to the cliffs being undercut at the base.
19
Q
How are wave-cut platforms formed?
A
- Undercutting weakens the rock above the notch and it eventually collapses.
- Thus the cliff face retreats but its cliff face is maintained.
20
Q
What is a spit?
A
- An extended stretch of beach material that projects out to sea and is joined to the mainland at one end.
21
Q
How is a spit formed?
A
- Longshore drift moves material along the coastline.
- A spit forms when the material is deposited.
- Over time, the spit grows and develops a hook if wind direction changes further out.
- Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form.
22
Q
What is a tombolo?
A
- A spit connecting an island to the mainland.
- An example of a tombolo is Chesil Beach, which connects the Isle of Portland to the mainland of the Dorset coast.
23
Q
What is a bar?
A
- A ridge of sand that blocks off a bay or river mouth.
24
Q
How does Marram Grass help stop erosional processes?
A
- Absorbs the waves energy and by the time it reaches the coastline, the erosional impact has reduced by a factor of five.
- This form of defence is very common on the Lincolnshire Coastline where Marram Grass has been planted to deter coastal erosion.
25
Q
How are mangroves helpful?
A
- Mangroves provide a barrier of interlocking roots and trunks which greatly reduce the power of the waves as the roots will absorb that power and greatly reduce its eroding ability, thus providing a useful barrier to protect the land.
26
Q
How can mangroves have a negative knock on effect?
A
- This occurred in Nigeria where mangroves were imported from Singapore.
- The Nipa Palm - the imported, exotic mangrove became an invasive species and took over the nutrients of the natural, native organisms.
- This resulted in the total takeover and replacement of the native species of trees in the Nigerian mangrove swamp.
27
Q
What are emergent coastlines?
A
- Emergent coastlines form as a result of a fall in sea level.
- This may be as a result of greater ice storage, but they also form as a result of isostatic recovery.
- Raised beaches and wave cut platforms
28
Q
What are submergent coastlines?
A
- Submergent coastlines form as a result of sea level rise.
- The current period of sea level rise, caused by melting ice sheets and thermal expansion of the ocean is called eustatic change.
29
Q
What landforms are found in submergent coastlines?
A
- Fjords - found in Norwary, Iceland and Greenalnd
- Fjards - found in Sweden and Denmark
30
Q
- What are the potential impacts caused by construction on the coastline?
A
- Damage to the natural life on the coast including marine habitats
- Increased stress on the rock of the coastline
- Changed wave patterns and a range of secondary factors such as faster erosions rates
- A potential decline in tourism
- Increased pollution
- Loss of further sea life.
31
Q
How have increased pollution levels affected the coast?
A
- According to the IPCC, the increase in carbon dioxide concentration has lowered global ocean surface pH by 0.1 units since 1750.
- Global mean sea surface temperatures have risen about 0.6°C since 1950 with associated atmospheric warming in coastal areas.
- These oceanic changes can have knock on affects on the coastal ecosystem.
32
Q
How has Brazil’s ecoystem been damaged in recent years?
A
- Guanabara Bay, in Brazil, where there is heavy ship traffic involved in trade and tourism in the area.
- Its attractive scenery attract even more tourists to Rio and its diverse ecosystem has been damaged in recent time by urbanisation, deforestation and 3 oil spills.
33
Q
What are the advantages and disadvantages of a sea wall?
A
Advantages
- Effective defence against erosion and
flooding. - Have a long lifespan of 75 years.
- Socially reassuring to tourists.
Disadvantages
- Reflected energy picks up sediment, which
then is used in ‘scouring’ and can
undermine the sea wall. - Very expensive
£2000+ per metre. - Other areas left
exposed.
34
Q
What are the advantages and disadvantages to groynes?
A
Advantages
- Limit longshore drift
- Build up beaches.
- Very efficient in trapping sediment.
Disadvantages
- Sediment input lower down coastline is
reduced - Limiting protection offered to
cliffs lower down coast. - Rapid cliff erosion
can occur.- For example, Barton on Sea.
Lifespan of 25 years
- For example, Barton on Sea.
35
Q
At what rate does the Holderness coastline retreat?
A
- Rate of one to two metres every year.
36
Q
Why does the Holderness coastline erode so quickly?
A
- Strong prevailing winds creating longshore drift that moves material south along the coastline.
- The cliffs are made of a soft boulder clay. It will therefore erode quickly, especially when saturated.
- Glacial deposits
37
Q
What techniques have been used to defend Mappleton?
A
- A coastal management scheme costing £2 million was introduced involving two types of hard engineering - placing rock armour along the base of the cliff and building two rock groynes.
- The rock groynes have stopped beach material being moved south from Mappleton along the coast.
- However, this has increased erosion south of Mappleton. Benefits in one area might have a negative effect on another.
