Coasts part 1
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what is a coast?
The area where the land meets the sea
What factors effect the shape of the coastline
- Destructive/constructive waves
- sea level change
- human activity (eg. dredging)
How are waves formed?
- Wind blows across the surface of the sea which causes friction
- Friction causes the water to ripple and the surface becomes rougher and easier for the wind to grip, intensifying the size of the waves
Movement of energy through water
What is the wave crest?
Highest point of wave
What is the wave trough?
Lowest point of wave
what is the wavelength?
Distance between 2 successive waves
What is the wave height?
Height of wave from trough to still water level
What three factors determine the energy of a wave?
- Wind speed
- Wind strength
- Length of fetch (big fetch = big waves)
What is the wave energy equation?
Energy = wave length x wave height2
What is the swash?
Body of foaming water which surges up the beach
What is the backwash?
Any water returning back to the sea
Do waves in deep water have an elliptical or orbital flow?
Do waves in shallow water have an elliptical or orbital flow? Why is this?
- Elliptical flow (rugby ball shaped)
- As a wave approaches shallow water, friction with the sea bed increases and the base of the wave begins to slow down. This has the effect of increasing the height of the wave until it breaks onto the beach
Describe the characteristics of a constructive wave (4)
- Low frequency, break 6-8 times a minute
- Under 1m tall
- Widely spaced (100m apart)
- Swash stronger than backwash
- Creates flatter beach profile
Describe the characteristics of a destructive wave (4)
- High frequency (10-14 times a min)
- Usually over 1m tall
- Closely spaced (20m apart)
- Backwash stronger than swash
- Creates steeper beach profile
Name three reasons why waves refract
- The coastline is irregular
- The surface of the sea is irregular
- Waves arrive oblique (at an angle) to the coastline
What happens to waves that refract around a headland? (4)
- Depth of waves decreases
- Waves get higher
- Velocity decreases
- Wavelength decreases
- Erosion to headland
- Wave energy directed to bays
How many littoral cells are there around England and Wales?
Define: littoral/sediment cell
A section of coastline that is involved in the complete cycle of sediment transportation and deposition
Define: sediment budget
The balance between the movement of smaller and larger particles into, within and out of a littoral cell
What causes the tides?
The gravitational pull of the moon
What is tidal range?
THe gap between the two high tide peaks
What are neap tides?
When the Moon and the Sun are at right angles to the Earth causing low high tides and high low tides (small tidal range) because there is less gravitational pull
What are spring tides?
When the Sun, Moon and Earth are in alignment causing high high tides and low low tides because there is a lot of gravitational pull from Moon
What are storm surges?
When meteorological conditions produce strong winds that generate waves that go over the high tide mark
How can sediment be lost from the sea? (2)
- Deposited inland
- Removed by humans
What are sediment sinks?
Where sediment transport paths meet, sediment is deposited and builds up
Oscillations in the sea surface caused by the gravitational pull of the moon and the sun
Do Spring tides or Neap tides have the largest tidal range?
Name 2 inputs into a sediment cell
- Cliff erosion
- Eroding depositional features (such as spits)
Name 2 transfers inside a sediment cell
Name 2 stores in a sediment cell
The breakdown of rocks in-situ on the Earth's surface
Define: sub-aerial weathering
Processes operating on the land but affect the shape of the coastline, such as biological weathering
What is freeze-thaw weathering?
Water percolating into weaknesses in rocks and freezing. Frozen water expands by 9% causing stress on the rocks resulting in cracks.
What is a scree?
Rocks from the cliff that have been eroded off and collected at the base of the cliff
What is salt weathering?
Salt crystals left behind by evaporated salt grow over time and cause rocks to break apart
What is biological weathering?
- A form of sub-aerial weathering
- Plant roots prising apart rocks
- Birds digging into cliffs (eg Puffins)
What is water layer weathering?
- Also known as wetting and drying
- The cycle of cliffs expanding when wet and contracting when dry causing clifs to crack and break up
What is carbonation?
Slow dissolving of calcium carbonate from rocks that turns into carbonic acid when it absorbs carbon dioxide in the air. Acid reacts with the rocks and dissolves them
More effective in colder waters
What is chemical weathering?
Decomposition of rocks due to chemical change. For example, oxidation or carbonation
What is hydration?
A form of weathering whereby rocks absorb water causing it to swell and become less stable
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