Coasts - Waves

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How does a wave form?

1. Wind on the surface of the water causes FRICTIONAL DRAG which produces MOTION in the UPPER SURFACE of the water

2. The GREATER the wind the GREATER the wave SIZE

3. Only when the wave BREAKS is water moved on land

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Factors affecting the size of a wave

FETCH - this is the distance the wave travels.
THE GREATER THE FETCH THE LARGER THE WAVE

TIME - this is the length of time the wind has blown
THE LONGER THE TIME THE BIGGER THE WAVE AS MORE ENERGY HAS BUILT UP INSIDE IT

WIND - THE STRONGER THE WIND THE LARGER THE WAVE

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Swash and Backwash

SWASH = the movement of a wave up the beach. The angle is determined by the DIRECTION of the wind

BACKWASH = the movement of a wave down the beach. It is always perpendicular to the beach due to gravity

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Constructive Waves

CONSTRUCTIVE WAVES:

➖ strong swash
➖ weak backwash
➖ short fetch
➖ deposition greater than erosion
➖ shallow beach formed
➖ long wavelength
➖ long time period
➖ shallow wave height
➖ occur on low energy coastlines

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Destructive Waves

DESTRUCTIVE WAVES:

➖ weak swash
➖ strong backwash
➖ long fetch
➖ erosion greater than deposition
➖ steep beach formed
➖ short wavelength
➖ short time period
➖ steep wave height
➖ occur on high energy coastlines

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Sediment cells

-thought to be closed systems
-sediment within moves in an anti-clockwise motion
-a section of the coastline that sediment moves freely, but only within
-they are bounded by changes in the coastline such as headlands bays and estuarys
-sediment DOES NOT move from one cell to another
-though to be 11 in the UK

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Tides

What are tides?

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the MOON, SUN AND ROTATION OF THE EARTH

Some shorelines experience 2 equal high and low tides each day - this is called a semi-diurnal tide

The MOON has the greatest influence on a tide as it pulls the water to the side of the Earth that is nearest to the moon. This creates a BULGE or HIGH TIDE. This is compensated for where the water is REPELLING and areas experience a LOW TIDE

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Spring Tides

  • The moon and sun are in ORBITAL ALIGNMENT
  • The tidal range is at its MAXIMUM
  • High tides are higher than average and low tides are lower than average (due to more water being drained for high tide)
  • Stronger tidal currents - compared to normal

(SEE NOTES FOR HELPFUL DIAGRAMS)

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Neap Tides

  • The moon, Earth and sun are perpendicular to each other = tidal range at its MINIMUM
  • The gravitational pull is not as strong
  • Lowest high tides and highest low tides (because not as much water is being drained for his tide so low tide has more water)
  • Less extreme conditions here

(SEE NOTES FOR HELPFUL DIAGRAMS)

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High energy coastlines

1. Wave power is strong for a significant proportion of the year

2. Low pressure systems e.g. Depressions and tropical revolving storms such as hurricanes

3. High average wind speeds are associated with the frontal depressions which form at sunction between warm and cold air masses

4. Long fetch e.g. Chile and UK

5. Northern hemisphere located on west coasts

6. Strong winds are more frequent in areas with a cooler temp - western maritime culture

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Low energy coastlines

1. High pressure systems ( clear, calm, sun in summer) for large proportion of the year

2. Southern hemisphere located on East coasts

3. Sheltered enclosed seas such as Mediterranean and Baltic

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