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g: coasts > 3.2 - Hodder > Flashcards

3.2 - Hodder Flashcards

1
Q

Define erosion.

A

The wearing away of the Earth’s surface by the mechanical action of processes of glaciers, wind, rivers, marine waves and wind.

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2
Q

Define fetch.

A

‘Fetch’ refers to the distance of open water over which a wind blows uninterrupted by major land obstacles.

The length of the fetch helps to determine the magnitude (size) and energy of the waves reaching the coast.

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3
Q

Define mass movement.

A

The movement of material downhill, under the influence of gravity, but may also be assisted by rainfall.

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4
Q

Define weathering.

A

The breakdown and / or decay of rock at or near the Earth’s surface, creating regolith that remains in situ until it’s moved later by erosional processes.

Weathering can be mechanical, chemical or biological.

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5
Q

What is the energy to drive the coastal system provided by?

A
  • waves
  • winds
  • tides
  • currents
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6
Q

Variations in the strength and duration of the wind are due to…

A

Spatial variations in energy.

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7
Q

Why is the prevailing wind important?

A

Prevailing wind means the wind will generally reach the coast from one direction.

This is important as it is one factor that controls the direction that waves approach the coastline, as well as the direction of the transport of material in the coastal zone.

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8
Q

In what way does wind play a vital role in wave formation?

A

Waves are created by the transfer of energy from the wind blowing over the sea surface (the fractional drag). And the energy acquired by the waves depends upon the strength of the wind, the length of time it is blowing and the fetch.

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9
Q

Wind acts as an agent of _______.

A

Erosion.

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10
Q

How can wind act as an agent of erosion?

A

Because it can pick up and remove sediment from the coast (eg sand from a beach) and use it to erode other features.

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11
Q

The most common type of wind erosion is…?

A

Abrasion. This is where the wind uses. The material it carries to wear away landscape features.

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12
Q

________ are the primary agent of shaping the coast.

A

Waves.

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13
Q

Define wave height.

A

The height difference between a wave crest and the neighbouring trough (up and down).

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14
Q

Define wave length (aka amplitude).

A

The distance between successive crests.

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15
Q

Define wave frequency (aka wave period).

A

This is the time for one wave to travel the distance of one wavelength.

Or the time between one crest and the following crest passing a fixed point.

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16
Q

What happens when waves approach shallow water?

A

When waves approach shallow water, friction with the seabed increases and the base of the wave begins to slow down. This has the effect of increasing the height and steepness of the wave until the upper part plunges forward and the wave breaks onto shore.

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17
Q

Define backwash.

A

The action of water receding back down the beach towards the sea.

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18
Q

Define swash.

A

The rush of water up the beach after the waves break.

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19
Q

Define constructive wave.

A

Waves with a low wave height, but with a long wavelength and low frequency of around 6/min.

Their swash tends to be more powerful than their backwash - so as a consequence, beach material is built up.

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20
Q

Define destructive waves.

A

Waves with a high wave height, with a steep form and high frequency 12/min.

Their backwash is generally more powerful than their swash, so more sediment is removed than is added.

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21
Q

Constructive waves have a long wave length of around _____m.

A

100m.

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22
Q

Why do constructive waves have a weak backwash?

A

Because as constructive waves approach the beach, they gently spill onto the beach surface. Consequently, swash rapidly loses volume and energy as water percolates through the beach material.

This gives a weak backwash which has insufficient force to pull sediment off the beach.

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23
Q

Constructive waves result in the formation of ______.

A

Ridges (berms).

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24
Q

Why do destructive waves have a strong backwash?

A

As they approach the beach, they rapidly steepen, and when breaking, plunge down, creating a powerful backwash as there is little forward movement of water. It also inhibits the swash from the next wave.

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25
Q

Destructive waves often form ________.

A

A large ridge aka a storm beach.

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26
Q

Why do destructive waves form storm beaches?

A

Because the force of each destructive wave may project some shingle well towards the rear of the beach where it forms a large ride (aka storm beach).

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27
Q

In what way are constructive and destructive waves part of a negative feedback system that maintains dynamic equilibrium?

A

Constructive waves build up the beach, resulting in a steeper beach profile. This encourages waves to be more destructive (as destructive waves are associated with steeper beach profiles).

But, with time, destructive waves move material back towards the sea, reducing the beach angle and encouraging more constructive waves.

So the pattern repeats itself.

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28
Q

Why dopes wave refraction occur?

A

When waves approach a coastline that’s not a regular shape.

29
Q

Why do high energy waves reach a headland, and low energy waves reach the bays?

A

Due to wave refraction.

As each wave approaches the coast, it tends to drag in the shallow water (which meets the headland). This increases the wave height, wave steepness and shortens the wavelength.

The part of the wave in deeper water moves forward faster, causing the wave to bend. The overall effect is that the wave energy becomes concentrated on the headland, causing greater erosion. And the low energy waves spill into the bay, resulting in beach deposition.

30
Q

Define current. And what are the three types?

A

Current - the permanent or seasonal movement of surface water in the seas and oceans. There are three types: longshore current, rip current, upwelling.

31
Q

Longshore currents are a type of current. Outline what they are.

A

Most waves don’t hit the coastline ‘head on’ but approach at an angle to the shoreline. This generates a current (flow of water) running parallel to the coastline.
This not only moves water along the surf zone, but also transports sediment parallel to the shoreline.

32
Q

Rip currents are a type of current. Outline what they are.

A

Rip currents are currents moving away from the shoreline. They develop when sea water is piled up along the coastline by incoming waves.

Initially the current may run parallel to the coast before flowing out through the breaker zone (possible at a headland / where coastline changes direction). These can be hazardous to swimmers.

33
Q

Upwelling are a type of current. Outline what they are.

A

Upwelling is the movement of cold water from deep in the ocean towards the surface.
The more dense, cold water replaces the warmer surface water and creates nutrient rich cold ocean currents.

These currents form part of the pattern of global ocean circulation current.

34
Q

Define longshore drift (aka littoral drift).

A

Where waves approach the shore at an angle and swash and backwash then transport material along the coast in the direction of the prevailing winds.

35
Q

Define wave refraction.

A

When waves approach a coastline that is not a regular shape, they are refracted and become increasingly parallel to the coastline.

The overall effect is that the wave energy becomes concentrated on the headland, causing greater erosion.
The low energy waves spill into the bay, resulting in beach deposition.

36
Q

Define tides.

A

Tides are the periodic rise and fall in the level of the sea.

37
Q

What are tides caused by?

A

The gravitational pull of the sun and moon. Although, the moon has the greatest influence because it’s nearest.

38
Q

How are tides formed?

A

The moon pulls water towards it, creating high tide. And there is a compensatory bulge on the opposite side of the Earth.

39
Q

What is spring tide?

A

Twice in a lunar month, when the moon, sun and Earth are in a straight line, the tide raising force is strongest. This produces spring tide.

40
Q

What is neap tide?

A

Twice a lunar month, the moon and sun are positioned perpendicular (90*) to each other in relation to the Earth.

This alignment gives the lowest monthly tidal range (neap tides).

41
Q

Neap tides are ____% lower than average.

A

20

42
Q

What is a tidal range?

A

The difference in the height of the seawater at high and low tide.

43
Q

In what way can tidal range be a significant factor in the development of a coastline?

A

Tidal ranges determine the upper and lower limits of erosion and deposition, and the amount of time in a day that the littoral zone is exposed and open to sub-aerial weathering.

44
Q

What are tidal (or storm) surges?

A

Occasions when meteorological conditions give rise to strong winds which can produce much higher winds which can produce much higher water levels than those at high tide.

45
Q

Define coastal sediment budget.

A

The balance between sediment being added to and removed from the coastal system
(that system being defined within each individual sediment cell).

46
Q

Define high energy coast.

A

A coastline where strong, steady prevailing winds create high energy waves and the rate of erosion is greater than the rate of deposition.

47
Q

Define low energy coast.

A

A coastline where wave energy is low and the rate of deposition often exceeds the rate of erosion.

48
Q

Define sediment cell.

A

A distinct area of coastline separated from other areas by well defined boundaries, e.g. headlands and stretches of deep water.

There are 11 across the UK.

49
Q

Outline features in low energy costs.

A
  • coastlines where wave energy is low
  • rate of deposition often exceeds rate of erosion
  • typical landforms: beach, spit
    Example: the Baltic Sea
50
Q

Outline features in high energy coasts.

A
  • coastlines where strong, steady prevailing winds create high energy waves.
  • rate of erosion exceeds rate of deposition.
  • typical landforms: headlands, cliffs, wave cut platforms.
    Example: North Cornish coast.
51
Q

Coastal sediment is an important input in systems. But where does it come from?

A
  • streams / rivers flowing into the sea
  • estuaries
  • cliff erosion
  • offshore sand banks
  • material from a biological origin; including shells, skeletons, coral fragments
52
Q

Give an example of a positive sediment budget.

A

More material is added to the cell than is removed - a net accretion of material.
Surplus of sediment.
Shoreline builds towards the sea.

53
Q

Give an example of a negative sediment budget.

A

More material is removed from the cell than is added.
Deficit in sediment supply.
Shoreline retreats landwards.

54
Q

What do the processes of coastal erosion control?

A

The level of deficit, as they removed material from the shoreline. And if more sediment is removed than added, then the coastline will recede.

55
Q

What can the sediment budget be used to identify?

A

The sources that deliver sediment to the cell and to the sites where sediment is stored, or sediment sinks.

56
Q

Define marine processes.

A

Marine processes operate upon a coastline and are connected with the sea, eg waves tides and longshore drift.

57
Q

Define sub-aerial processes.

A

Includes processes that (usually) break down the coastline, weaken the underlying rocks and allow sudden movements of erosion to happen more easily.

Material is broken down in situ. These may affect the shape of the coastline, and include weathering, mass movement and runoff.

58
Q

Coastlines are affected by two sets of geomorphological processes:

A

Marine processes and sub aerial processes.

59
Q

In what way are marine and sub-aerial processes different?

A

Marine processes operate upon a coastline that is connected with the sea. Whereas sub aerial processes operate on the land, but affect the shape of the coastline.

60
Q

Outline 5 coastal processes.

A 
Mass movement
Weathering
Erosion
Transport
Deposition
61
Q

What are the 3 types of weathering?

A

Chemical
Biological
Mechanical

62
Q

What are the 5 types of weathering?

A 
Land slide
Mudflow
Rock fall
Rotational slumping
Soil creep
63
Q

What are the 5 ways that coastlines can be eroded?

A 
Abrasion
Attrition
Hydraulic action
Solution 
Wave quarrying
64
Q

Abrasion erodes a coastline. How?

A

The rocks in the sea which carry out abrasion are slowly worn down into smaller and more rounded pieces.

65
Q

Abrasion (corrosion) can erode the coastline. How?

A

The material that the sea has picked up wears away rock faces. Sand, shingle and boulders hurled against a cliff does a lot of damage.

This is apparent on inter tidal rock platforms where sediment is drawn back and forth, grinding away the platform.

66
Q

Hydraulic action erodes the coastline. How?

A

Hydraulic action refers to the impact on rocks if the sheer force of the water (w/o debris). This can exert enormous pressure on a rock surface, thus weakening it.

67
Q

Solution can erode a coastline. How?

A

Calcium based rocks (eg limestone) dissolve, making the sea water slightly acidic. ????????????????

68
Q

Wave quarrying erodes a coastline. How?

A

A breaking wave traps air in it as it hits a cliff face. The force of water compresses this air into any gap in the rock face, creating enormous pressure within the joint.

As the water pulls back, there is an explosive effect of the air under pressure being released. This overall effect is to weaken the cliff face.

g: coasts (12 decks)

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