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Coastal Systems and Environments > Tides and Currents > Flashcards

Tides and Currents Flashcards

1
Q

What is the global ocean conveyor belt?

A

This is a constant circulation of water driven by temperature and salinity.

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2
Q

What type of water sinks to the bottom in the global ocean conveyor belt?

A

Cold, salty water.

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3
Q

What waster rises to the top in the global ocean conveyor belt?

A

Warm water.

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4
Q

What will cause the water to return to the surface?

A

The wind and also the mixing of the warm and cold water.

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5
Q

What drives ocean currents?

A

Wind drives ocean currents within 100m of the surface.

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6
Q

Where does the global ocean conveyor belt start?

A

It starts in the Norwegian Sea.

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7
Q

Which direction does the global ocean conveyor belt move?

A

It moves south.

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8
Q

What is upwelling?

A

This is a type of current that can move sediment. Cold water moves from deep in the ocean towards the surface. This cold water replaces the warmer surface water which creates nutrient rich, cold ocean currents which form part of the global ocean circulation currents.

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9
Q

What does upwelling allow?

A

It allows a high amount of biological activity. Therefore there are more fish which is good for fishing.

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10
Q

What is the reverse of upwelling?

A

Down welling.

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11
Q

What causes down welling?

A

This happens when wind causes the surface water to build up along a coastline. This build up of water sinks to the ocean bed.

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12
Q

What is a current?

A

This is a mass flow of water. They describe the motion of water.

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13
Q

What are currents influenced by?

A

Tidal currents
Wind
Thermohaline circulation.

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14
Q

What is a tidal current?

A

This is the rise and fall of the tide. It is the vertical motion of the tides near the shore.

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15
Q

What drives thermohaline circulation?

A

Density differences.

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16
Q

What is coriolis force?

A

This is the force from the gravitational rotation of the Earth.

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17
Q

How do tidal currents change?

A

They change in a very regular way and so can be predicted.

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18
Q

What drives tidal currents?

A

Winds drive currents at or near to the oceans surface at either a localised or global scale.

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19
Q

What is meant by a globalised scale?

A

This means the open ocean.

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20
Q

What is meant by a localised scale?

A

This is near coastal areas.

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21
Q

Where do currents that are driven by thermohaline circulation occur?

A

They occur at both deep and shallow ocean levels and move much slower than tidal or surface currents.

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22
Q

What are currents measured in?

A

They are typically measured in knots.

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23
Q

How do you work out the speed of a current?

A

This is distance/time.

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24
Q

How do you work out current velocity?

A

speed x direction

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25
Q

What are the four types of current?

A

Littoral drift/ longshore currents
Rip currents
Flood currents
Ebb currents

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26
Q

What is an ebb current?

A

This is essentially the outgoing tide.

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27
Q

What is a flood current?

A

This is the incoming tide along the coast into bays and estuaries.

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28
Q

What type of current drives longshore drift?

A

Littoral drift/ longshore currents.

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29
Q

What direction are long shore currents?

A

These run parallel to the shoreline and the waves approach the beach at an angle. Backwash then transports material.

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30
Q

Are rip currents dangerous?

A

They are dangerous for swimmers and small boats.

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31
Q

What causes rip currents?

A

Sea water is piled up against the coastline by incoming waves.

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32
Q

Which way do rip currents flow?

A

They run parallel to the coast before flowing out through the breaker zone, possibly the headland or where the coast changes direction.

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33
Q

When do the strongest ebb and flood currents occur?

A

The occur before or near the time of high and low tide.

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34
Q

When do the weakest ebb and flood currents occur?

A

They occur at slack tides.

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35
Q

What is high-tide?

A

This is when the crest of a wave reaches a particular location.

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36
Q

What is a low-tide?

A

This corresponds to the trough of a wave reaching a particular location.

37
Q

What is the tidal range?

A

This is the difference in height between high and low tide.

38
Q

What is the crest?

A

This is the highest part of a wave.

39
Q

What is thetrough?

A

This is the lowest part of a wave.

40
Q

What is a tide?

A

This is the periodic rise and fall of the level of the sea.

41
Q

What controls tides?

A

The forces from the moon and the sun.

42
Q

What do tide appear as when they reach the coastline?

A

They appear as the regular rise and fall of the sea surface.

43
Q

Why are tides studied?

A 
Safe navigation
Recreation
Coastal development
Fishing
Habitat restoration
Projects such as bridge constructions.
44
Q

What is the difference between tides and currents?

A

Tides are driven by coriolis force whereas currents describe the flow of water.
Tides flow up and down and follow a pattern but currents are influenced by numerous factors.

45
Q

What happens as the position of the moon changes

A

Two tidal bulges rotate around Earth.

46
Q

What do the tidal bulges represent?

A

They represent high tide.

47
Q

What causes the tides to cycle around the planet?

A

As the Earth spins, different areas of the planet face the moon and it is this rotation that causes the ides to cycle around the planet.

48
Q

When do high tides occur?

A

They occur every 12 hours and 25 minutes.

49
Q

What is the time span between high and low tide?

A

There is a span of 6 hours and 12.5 minutes between high and low tides.

50
Q

Where are the two tidal bulges?

A

One is in front of the moon and the other is on the directly opposite side of the Earth.

51
Q

What causes the tidal bulge?

A

A greater and lesser gravity than the centre of the Earth.

52
Q

What is the spring tide?

A

This produces the highest monthly tidal range.

53
Q

What causes the spring tide?

A

This happens when the sun, moon and Earth are all in line, making the tide raising force the strongest/

54
Q

What is the neap tide?

A

This gives the lowest monthly tidal range.

55
Q

What causes a neap tide?

A

This happens when the moon and sun are perpendicular to each other in relation to the Earth.

56
Q

How often do spring tides occur?

A

Twice a lunar month.

57
Q

How often do neap tides occur?

A

Twice a lunar month.

58
Q

What are storm surges?

A

These are times when meteorological conditions give rise to strong winds which can cause much higher water levels than at high tide.

59
Q

What is another crucial factor in determining the effects of wave action?

A

The topography of the coastline.

60
Q

What happens when waves approach a coastline that is not a regular shape?

A

The waves are refracted and become increasingly parallel to the coastline.

61
Q

What happens as each wave approaches the coast?

A

It tends to drag in the shallow water which meets the headland.

62
Q

What effect does this drag have on the wave?

A

The wave height and steepness increases whilst the wavelength shortens.

63
Q

What part of the wave moves faster?

A

The part of the wave in the deeper water moves faster.

64
Q

What part of the water moves faster?

A

The part of the wave that is in the deeper water, causing the wave to bend.

65
Q

What is the overall effect of the bent wave?

A

Wave energy becomes concentrated on the headland.

66
Q

What happens as a result of the increased wave concentration on the headland?

A

There is more erosion at the headland.

67
Q

What type of wave spills in the bay?

A

Low energy waves spill in the bay.

68
Q

What happens when the low-energy waves reach the bay?

A

They deposit material.

69
Q

What happens as the waves pile against the headland?

A

There is a slight local rise in sea level that results in a longshore current from the headland, moving some eroded material to the bays.

70
Q

What type of frequency do low energy waves have?

A

They have a low frequency.

71
Q

What type of wavelength do constructive waves have?

A

They have a long wavelength.

72
Q

What type of wave height do constructive waves have?

A

They have a low wave height.

73
Q

What is the frequency of constructive waves?

A

6-8/min

74
Q

What tends to be stronger in a constructive wave: the awash or the backwash?

A

The swash.

75
Q

What type of wave builds up the beach?

A

Constructive

76
Q

What type of wave erodes the beach?

A

Destructive

77
Q

What kind of wave height do destructive waves have?

A

They have a high wave height with a steep form.

78
Q

What type of frequency do destructive waves have?

A

10-14/min

79
Q

What is swash?

A

This is the rush of water up the beach after a wave breaks.

80
Q

What is backwash?

A

This is the action of water receding back down the beach towards the sea.

81
Q

What happens to the wave front steepness as constructive waves approach the beach?

A

It steepens slowly, causing the waves to spill gently on onto the beach.

82
Q

What type of wave makes berms?

A

Constructive waves make berms when their swash pushes material up the beach and because their backwash isn’t strong enough to move it back down.

83
Q

What happens to the steepness of destructive waves as they approach the beach?

A

They rapidly steepen and plunge down when they break this creates a powerful back wash because there is a very small forward movement of water, it also inhibits swash from the next wave.

84
Q

What type of beach profile is associated with destructive waves?

A

A steeper beach profile.

85
Q

What type of wave is associated with a storm beach?

A

The force of each destructive wave may project some shingle well towards the rear of the beach where it forms a large ridge known as the storm beach.

86
Q

True or false: a beach can only experience either destructive or constructive waves?

A

This is false, beaches are subject to an alternating cycle of destructive and constructive waves.

87
Q

What happens as the beach profile becomes steeper because of constructive waves?

A

This encourages waves to become more destructive.

88
Q

What is an example of negative feedback?

A

The alternating cycle of constructive and destructive waves.

Coastal Systems and Environments (24 decks)

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