Coastal Environments

Key information and concepts for Coastal Environments.

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Wave Period

The time taken for a wave to travel between one wavelength

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Wave Frequency

The number of waves per minute

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Wave Energy

α LH2

E= Energy of the wave

L= Wavelength

H= Wave Height

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Wave Steepness

The ratio of waveheight to wavelength

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What is a coast?

The narrow zone where the land and the sea overlap.

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What wave energy is determined by

  • Wind Velocity
  • Duration
  • Fetch
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The movement of water up a beach

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The movement of water back down a beach under gravity

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What causes constructive waves?

  • Low wave height
  • Low wavelength
  • Low wave frequency
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How do constructive waves create a sloping beach?

  • Breaking waves have enough time to percolate into the beach
  • The waves deposit material as they break
  • The backswash of the beach does not have enough energy to take significant amounts of sediment with it.
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What is wave refraction?

As waves approach the coast, they are more greatly affected by friction, as the relative height of the sea floor is rising. this causes the waves to slow down, increasing wave height and decreasing wave length.

Where the coastline is irregular, as is the case where a headland is present, some waves are slowed down before other waves, as the relative height of the sea floor rises before the headland. This causes a concentration of wave energy on the headland and a dissapation of energy in the bays.

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What is a sediment cell?

A length of coastline that is relatively self contained in terms of sand and shingle movement. The interuption of the movement of sediment in one cell shouldn't significantly affect adjacent cells.

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What is a tide?

The regular rising and falling moment of the surface of the sea.


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What causes the tides?

They are caused the the gravitational pull of the moon and the sun on the oceans.

The moon has the greatest influence as it is closer than the sun.

This pull creates an outwards bulge in the oceans closest to the moon and another on the other side of the earth.

Low tides are created when the bulging of the oceans causes water to move from coasts further out.

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What is the tide cycle?

The time taken between the peak of one high tide to the next.

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What creates spring tide?

When the moon is between the earth and the sun, the gravitational pull is greatest, creating the highest tides and lowest tides.

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What is the tidal range?

the difference between the highest point of a high tide and the lowest point of a low tide.

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What are neap tides?

When the earth, moon and sun create a right angle, the gravitational pull of the moon and sun interfere with eachother creating:

  • The lowest high tides
  • The highest low tides

The means that the tidal range is at it's lowest.

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Where are the effects of the tides greatest?

The pattern of tides are significantly modified by the nature of the ocean bed, the proximity of land masses and the effect of the Coriolis force.

Places where there is a narrow neck of water usually experience the greatest local tidal range.

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What factors do tidal ranges determine?

  • The vertical range of erosion and deposition
  • The length of time the littoral zone (The coast) is exposed to sub aerial weathering
  • The speed of the incoming and outgoing tides can affect scouring
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What can tidal ranges be classified as?

  • Macrotidal = More than 4 meters
  • Mesotidal = between 2 and 4 meters
  • Microtidal = less than 2 meters
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What is freeze thaw?

The process by which water repeatedly freezes and melts within joints/cracks in rocks where the dirunal range hovers around 0 C. As water expands by about 9%, it exerts pressure on the surrounding rock, which is released when the ice melts. These repeated fluctuations in pressure may cause it to break off.

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What is pressure release?

When jointed rocks (such as granite) have pressure of any overburden removed, the rock expands, which may cause joints/cracks to open up and be exposed to weathering.

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What is biological weathering?

Refers to weathering resulting from organic agents, such as tree roots growing into and widening joints or burrowing animals.

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Where does Chemical weathering tend to occur?

Tends to occur where there is alternate wetting and drying and/or towards the bottom of slopes where material and moisture often accumulate.

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What is oxidation?

Where rocks are exposed to oxygen in the air or in water a chemical reaction can take place which changes the properties of the rock.

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What is hydration in terms of weathering?

Rocks that are high in salt content absorb water, causing them to swell. This makes them more susceptible to decomposition. The effect is greatest where there are alternating phases of wet and dry,

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What is Hydrolysis in terms of chemical weathering

H+ and OH- ions combine with ions within the mineral resulting in decomposition.

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In what way does carbonation cause chemical weathe

CO2 dissolved in water produces carbonic acid (H2CO3. This attacks the calcium carbonate found in limestones and many other rocks. The soluble producst is often washed away.

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What is solution in terms of chemical weathering?

Water can cause some rocks to dissolve within in, which are then washed away.

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What is organic weathering?

Humic acids derived from plant decay contain element such as calcium, magnesium and iron. These may bond with rocks and cause decomposition.

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What is acid rain?

Human activities have resulted in large amount of carbon dioxide, sulphur dioxide and nitrous oxide being released into the atmosphere, which may form acids in solution in rainwater. Limestones are susceptible to decomposition from these acids.

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What is soil creep?

The slowest form of mass movement

  • Raindrop impact in intense storms may cause a splash of soil particles.
  • Wet periods add additional moisture, which causes soil particles to swell and slide down slope.
  • Freeze thaw lifts soil up when frozen and sets it back down slightly more downhill when it thaws.
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What is Solifluction?

Occurs mainly in tundra areas where there isn't vegetation to hold soil in place. When the frozen water melts, it can't percolate downwards because it's still frozen underneath, this  results in an active layer of soil that flows about.

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What other factors can affect coastline weathering

  • Marine erosion
  • Waves and beaches
  • Geology
  • Human activity
    • Sea walls and coastal defences
    • Land reclamation
    • Development on cliff tops
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