3.2- Sources of energy at the coast- systems and processes

Question 1

The energy to drive the coastal system is provided by

Answer 1

Waves, wind, tides and currents

Question 2

Describe wind

Answer 2

Wind is the movement of air from one place to another. Air moves from areas of high atmospheric pressure to areas of low atmospheric pressure- this movement is known as wind. The greater the pressure gradient between 2 places, the stronger the wind

Question 3

Variations in atmospheric pressure primarily reflect differences in surface heating by the

Answer 3

Sun

Question 4

Wind is a vital input into the coastal system as it is a primary source of energy for other processes, but is also an important agent of

Answer 4

Erosion and transportation

Question 5

What are the features of wind as an input into the coastal system

Answer 5

• fetch
• wind is an agent of erosion
• wind is an important agent of moving sediment

Question 6

Explain how spatial variations in energy result from variations in the strength and duration of the wind

Answer 6

Where wind speeds are persistently high and uninterrupted, wave energy is likely to be higher. Although local weather patterns may influence short-term changes in wind speed and direction, most coastlines will have a prevailing wind direction. That is, 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 and also the direction of the transport of material in the coastal zone.

Question 7

Explain fetch

Answer 7

Refers to the distance of open water over which a wind blows interrupted by major land obstacles. The length of the fetch helps to determine the magnitude and energy of the waves reaching the coast. The longer the fetch, the more powerful the waves

Question 8

In the U.K. The prevailing (most usual) direction is from the ____-____. Before reaching our coast, the winds have blown over the broad expanse of the Atlantic Ocean- this means that the wind has blown over 3000 miles of open water

Answer 8

South-West

Question 9

Explain how wind plays a vital role in wave formation

Answer 9

Waves are created by the transfer of energy from the wind blowing over the sea surface, referred to as the frictional drag of the wind.

Question 10

The energy acquired by waves depends upon the strength of

Answer 10

The wind, the length of time it is blowing and the fetch

Question 11

Wind is also an agent of erosion as

Answer 11

It can pick up and remove sediment e.g. sand from the coast and then use it to erode features- the most common type of wind erosion is abrasion

Question 12

Wind is an important agent of moving sediment along the coast or further inland and beyond the shoreline as

Answer 12

It can pick up and transport material

Question 13

How are waves formed?

Answer 13

As air moves across the water, frictional drag disturbs the surface and forms ripples or waves. In the open sea there is little horizontal movement of water. Instead, there is an orbital motion of the water particles

Question 14

What are key wave characteristics?

Answer 14

• wave height
• wavelength or amplitude
• wave frequency or wave period

Question 15

What is wave height?

Answer 15

Height difference between a wave crest and the neighbouring trough

Question 16

What is wavelength?

Answer 16

Difference between successive crests

Question 17

What is wave frequency?

Answer 17

The time between one crest and the following crest passing a fixed point

Question 18

Why do waves break?

Answer 18

• as waves approach shallow water, the circular orbit of the water particles changes to an elliptical shape
• the wavelength and the velocity both decrease and the wave height increases due to friction with the seabed also increasing causing water to break up from behind and rise to a point where it starts to topple over (break)
• the water rushes up the beach as swash and flows back as backwash

Question 19

Once waves have been created by the wind they are the main agent that shapes the

Answer 19

Coastline. Waves breaking at the coast can build up or remove materials depending on their characteristics

Question 20

What are constructive waves?

Answer 20

Waves with a low wave height, but with a long wavelength and low frequency of around 6-8/min. Their swash tends to be more powerful than their backwash and as a consequence, beach material is built up

Question 21

What are destructive waves?

Answer 21

Waves with a high wave height with a steep form and high frequency (10-14/min). Their swash is gradually stronger than their backwash, so more sediment is removed than is added.

Question 22

Explain the characteristics of constructive waves

Answer 22

• tend to have low wave height but with a long wavelength often up to 100m
• low frequency around 6-8/min
• add to beach deposition as their swash pushes more materials from offshore up the beach than backwash removes.
• material is slowly, but constantly moved up the beach leading to the formation of ridges (berms)
• as the backwash is reduced, the following swash is less impeded in its movement up the beach

Question 23

Explain the characteristics of destructive waves

Answer 23

• have high wave height with a steep form and high frequency around 10-14/min
• powerful backwash as when they approach the beach they rapidly steepen and when breaking they plunge down- also inhibits the swash from the next wave
• very little material is moved up the beach, leaving the backwash to pull material back down the beach
• net effect is removal of beach material along the shoreline
• commonly associated with steeper beach profile
• the force of each wave may project some shingle well towards the rear of the beach where it forms a large ridge known as the storm beach

Question 24

Give an example of negative feedback regarding beaches and waves

Answer 24

Where constructive waves operate to build up a beach, eventually the beach profile steepens which encourages destructive waves (plunging rather than surging) which then removes material from the beach and deposit it offshore. This in turn can result in the beach profile becoming less steep again, encouraging constructive rather than destructive waves to form. All things being equal, this will continue until a state of dynamic equilibrium is reached

Question 25

Describe wave refraction

Answer 25

When waves approach a coastline that it indented they are refracted and become increasingly parallel to the coastline.

Question 26

Describe effect of wave refraction on a headland

Answer 26

• Waves tend to ‘bend’ and have a higher frequency, wave height and steepness, which gives them greater energy to erode. This is because the waves approaching the headland meet shallower water first, while the part of the wave approaching the bay is still in deeper water. Friction with the sea floor slows the headland-approaching waves and causes their frequency to increase. In bays, the reverse occurs and the waves spread out and become less frequent which leads to a reduction in wave energy and produces a more constructive impact
• the overall effect of wave refraction is the wave energy becomes concentrated on the headland. It accounts for the presence of erosive features at headlands (cliffs and stacks) and deposition features in the bays (beaches). In theory, continued erosion of the headland and deposition in the bays would result in a state of equilibrium where the shape of the coastline would remain static due to balance between the potential erodibility of the rocks and the effect of wave refraction. (In reality, conditions rarely remain stable enough for long enough for this to happen)

Question 27

The term currents refers to

Answer 27

The permanent or seasonal movement of surface water in the seas and oceans.

Question 28

What are the 3 types of currents?

Answer 28

Longshore currents, rip currents and upwelling

Question 29

Describe longshore currents

Answer 29

Occur as most waves do not hit the coastline ‘head on’ but approach at an angle to the shoreline. This generates a flow of water (current) running parallel to the shoreline which transports sediment parallel to the shoreline

Question 30

Describe rip currents

Answer 30

Rip currents are strong localised underwater currents that occur on some beaches and move water away from the shoreline. They develop when a series of plunging waves cause a temporary build-up of water at the top of the beach, met with resistance from the breaking waves. The fast-flowing offshore surge of water can be hazardous to swimmers.

Question 31

Describe upwelling

Answer 31

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

Question 32

What are tides?

Answer 32

Periodic rise and fall in the level of the sea- they are caused by the gravitational pull of the sun and the moon,although the moon has the greatest influence as it it nearer.

Question 33

How does the moon affect tides?

Answer 33

The moon pulls water towards it, creating a high tide, and there is a compensatory bulge on the opposite side of the Earth. In areas of the world between the two bulges, the tide is at its lowest

Question 34

When are spring tides formed?

Answer 34

As the moon orbits the high tides follow it. Twice in a lunar month,when the moon sun and Earth are in a straight line the tide-raising force is the strongest. This produces the highest monthly tidal range or spring tide

Question 35

When are neap tides formed?

Answer 35

Twice a month,the moon and the sun are perpendicular to each other in relation to the Earth. This alignment gives the lowest monthly tidal range or neap tides; at this time, the high and low tides are between 10 to 30% lower than average

Question 36

The UK coastline experiences two high and low tides how often?

Answer 36

Each day

Question 37

What is the tidal range?

Answer 37

The relative difference in height between high and low tides

Question 38

Tidal range can be a significant factor in the development of a coastline as

Answer 38

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

Question 39

A tidal range generates relatively powerful tidal currents (important sources of energy), as tides rise and fall, which can be particularly strong in estuaries and narrow channels. Why are these currents important?

Answer 39

These currents are important in the transfer of sediment within the coastal system or beyond (as an output)

Question 40

When do tidal/ storm surges occur?

Answer 40

When strong winds combine with high tides to produce much higher water levels than normal.

Question 41

The processes outlined combine to create low energy and high energy coasts. Define a low energy coast

Answer 41

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

Question 42

Define a high energy coast

Answer 42

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

Question 43

Give features of low energy coasts

Answer 43

• coastlines where wave energy is low
• the rate of deposition often exceeds the rate of erosion of sediment
• typical landforms include beaches and spits
• examples include: many estuaries, inlets and sheltered bays. The Baltic Sea is one of the best examples due to its sheltered waters and low tidal range

Question 44

Give features of high energy coasts

Answer 44

• coastlines where strong, steady prevailing winds create high energy waves
• the rate of erosion is greater than the rate of deposition
• typical landforms include headlands, cliffs, and wave-cut platforms
• examples include: exposed Atlantic coasts of Northern Europe and North America, including the North Cornish coasts in south-west England

Question 45

Alongside energy, sediment is an important input in coastal systems. Globally, most sediment comes from rivers, streams and coastal erosion, although there are local variations. What are the 5 main sources of sediment?

Answer 45

• rivers= sediment is transported in rivers and deposited in river mouth and estuaries where it is then reworked by waves, tides and currents. Most coastal sediment originates from rivers
• cliff erosion= particularly important along stretches of coastline where rocks are soft e.g. along Holderness coast, Yorkshire where glacial till forms unstable cliffs of boulder clay
• longshore drift= sediment is transported from one stretch of coastline (as an output) to another stretch of coastline (as an input)
• wind= in glacial or arid regions, wind-blown sand can be deposited in coastal regions. Sand dunes can act as both a sink and source of sediment (sand)
• offshore = sediment from offshore can be transferred into the coastal (littoral) zone by waves, tides and currents. In the UK, sea levels rose at the end of the last glacial period, resulting in a considerable amount of coarse sediment being bulldozed onto the south coast of England to form landforms such as Chesil Beach, Dorset. Storm surges can also result in inputs of sediment into the coastal system

Question 46

What is a sediment cell?

Answer 46

A distinct area of coastline separated from other areas by well-defined boundaries, such as headlands and stretches of deep water- there are 11 along the coastline of England and Wales e.g. Cell 2 on the east coast of England which stretches from Flamborough Head to the Walsh

Question 47

Research suggests that sediment movement occurs in

Answer 47

Distinct cells, within which inputs and outputs are balanced

Question 48

In theory sediment cells are seen as closed systems from which nothing is gained or lost. However, in reality

Answer 48

It is easy for sediment to find its way around headlands and into adjacent cells (open system)

Question 49

Cells vary in size and larger ones can be divided into smaller sub-cells for example

Answer 49

Cell 2 on the east coast of England which stretches from Flamborough Head to The Wash has a sub-cell within it that stretches from Flamborough Head to the mouth of the Humber Estuary

Question 50

• each cell has:

Answer 50

• inputs ( sources) such as sediment from rivers, coastal erosion and offshore sources
• transfers (flows) such as LSD and onshore and offshore processes including rip currents
• stores (sinks) including beaches, sand dunes and offshore deposits such as bars

Question 51

What is a coastal sediment budget?

Answer 51

The balance between sediment being added to and removed from a sediment cell coastal system

Question 52

Contrast positive budget and negative budget

Answer 52

• if more material is added to the cell than is removed then there is a net accretion of material= positive budget or a surplus of sediment and, over time, the shoreline builds towards the sea
• if more material is removed from the cell than is added a negative budget or a deficit in sediment supply will result. This will cause the shoreline to retreat landwards.

Question 53

In principle,what does the sediment budget seek?

Answer 53

Seeks to achieve a state of dynamic equilibrium where erosion and deposition are balanced. This balance however, can be upset by events, such as an increase in river sediment as a result of a flood; this in turn leads to exposition in the river estuary. A severe storm might also upset the balance by eroding a beach and transferring sediment outside the system

Question 54

Calculating the sediment budget for a cell requires

Answer 54

The identification of all the sediment sources and sinks, and an estimation of the amount of sediment added and removed each year. Calculating budgets is extremely difficult and relies on the use of complex models and estimations

Question 55

Coastlines are affected by two sets of geomorphological processes:

Answer 55

• marine processes = are those that operate upon a coastline that are connected with the sea, such as waves, tides and LSD
• sub-aerial processes= operate on land but affect the shape of the coastline- such as weathering, mass movement and run-off

All processes interact to create a wide range of uniquely coastal landscapes

Question 56

Marine erosion processes:

Answer 56

• hydraulic action
• wave pounding or quarrying
• abrasion
• solution
• attrition

Erosion:
Waves can break on the coastline with a large amount of energy- they may generate energy of 25-30 tonnes m (-2) as they break against the foot of a cliff
- in 2014, a particularly powerful storm hit Dawlish and destroyed part of the sea wall and a section of rail track cutting the rail connection between Devon and Cornwall for months. The storm of February 2014 altered the Devon coastline- large amounts of sediment were swept away from beaches and sand dunes at Dawlish Warren were seriously eroded

Question 57

Describe hydraulic action

Answer 57

When waves break against a rock face with joints facing the wave, air inside the joints is highly compressed, creating enormous pressure within the fissure. As the water pulls back, there is an explosive effect of the air under pressure being released. The overall effect of this over time is to weaken the cliff face. Storms then may remove large chunks of it

Question 58

Desribe wave pounding/quarrying

Answer 58

The impact on rocks of the sheer force of water itself (without debris). This can exert enormous pressure upon a rock surface, weakening and dislodging pieces

Question 59

Describe abrasion

Answer 59

The material that the sea picks up also wears away rock faces. As waves advance, they pick up sand and pebbles from the seabed. When they break at the foot of the cliff, the transported material is hurled at the base of the cliff-chilling away at the rock

Question 60

Describe solution

Answer 60

Some calcium-based rock such as chalk and limestone is really soluble and dissolved minerals can then be removed in the solution. This process is very similar to a type of weathering called carbonation

Question 61

Describe attrition

Answer 61

Whilst attrition does not directly alter the shape of the coastline it does result in a wearing away of rock particles. Angular rock fragments are smoothed and reducing in size, form pebbles, shingle and sand. This occurs due to friction as particles are rolled over each other by the action of waves and currents

Question 62

The rate of coastal erosion along any stretch of coastline is affected by a number of factors:

Answer 62

• waves: steeper high-energy waves have a greater erosive power than low energy waves. The point at which the wave breaks is important too- waves that break at the foot of a cliff release more energy than those that break off-shore
• fetch: a wave that has built up over a greater distance will have generated more energy
• sea depth: a steeply-shelving sea bed will create higher and steeper waves
• shape or the coastline: headlands attract wave energy through refraction
• beach presence: beaches absorb wave energy and provide some protection against erosion. Steep, narrow beaches are effective at dissipating energy from flatter waves. Flatter, wide beaches spread out incoming waves and are better at dissipating high wave- shingle beaches are absorb the impact of steep waves well, as energy is dissipated through friction
• human interaction: beach material (sand and shingle) is removed from some coastlines leading to an increase in erosion. In other areas, coastal protection, such as sea walls or groynes may reduce the rate of erosion
• geology

Question 63

Why is geology perhaps the most important factor in determining the nature of erosional processes?

Answer 63

Geology includes the lithology (the physical strength and chemistry of rocks) and structure (the variation and arrangement of rocks along a coastline)

• lithology: some rocks like granite are very resistant to erosion, whilst others such as clay are very vulnerable to erosion- the glacial till (boulder clay) of the Holderness coast has been eroded by 120cm (12 cm a year!). Some rocks like limestone are porous and cracked which means the sea can penetrate along the lines of weakness, making the, more vulnerable to erosion
• structure: along some stretches of coastline, rocks lie parallel to the coast (concordant) whereas in other areas, rocks lie perpendicular to the coastline (discordant)
• dip: where cliffs have bedding planes they may dip or slope. When rocks dip inland, steeper cliffs may form. Where rocks dip towards the coasts, cliffs tend to produce more gently sloping features

Question 64

Concordant and discordant coastline in more detail

Answer 64

Along a concordant coastline (e.g. Dorset) a resistant rock like limestone can protect the coastline from erosion, only allowing the sea to break through in a few places. Where the sea does break through it can more rapidly excavate the clay behind to form a cove e.g. Lulworth cove

Along a discordant coastline differential erosion occurs where there are band of hard and softer rock. This can result in a headlands and bays coastline

Question 65

What are the 4 processes of marine transportation?

Answer 65

• traction
• saltation
• suspension
• solution

Question 66

Wave or tidal energy not used for erosion or not lost through friction with the seabed can be used to

Answer 66

transport material at the coast

Question 67

The transportation of sediment by the sea is not only an important agent of change in terms of processes of erosion and deposition, but represents

Answer 67

A significant flow/transfer of material

Question 68

Describe traction

Answer 68

Large stones and boulders are rolled and slid along the seabed and beach by moving seawater- this happens in high energy environments

Question 69

Describe saltation

Answer 69

Small stones bounce or leapfrog along the seabed or beach- this process is associated with relatively high energy conditions and as the particles land they may dislodge others

Question 70

Describe suspension

Answer 70

Minute particles of sand and silt are carried along by the moving water, within the flow- suspension most likely where flow is turbulent. Large amounts of suspended load, especially near estuaries can cause a murky appearance of the sea

Question 71

Describe solution

Answer 71

Dissolved materials are transported within the mass of the moving water- this form of transportation plays an important role in the carbon cycle, transferring and depositing carbon in the oceans

Question 72

The direction of coastal transportation is important in terms of sediment movement along a coastline. While waves move material up and down beaches, waves rarely approach the the coastline head-on so

Answer 72

The processes of transport described above combine to move material along the coast

Question 73

Longshore drift occurs when

Answer 73

Waves approach the shore at the same direction as the prevailing wind at an angle and material is ‘pushed’ up the beach by the swash in the same direction as the wave approached. As the water runs back down the beach the backwash drags material down the steepest gradient, which is usually perpendicular back down the beach (due to the force of gravity), where it is then picked up by the following incoming wave- the net effect of this zig-zag movement is known as longshore (littoral) drift

Question 74

Longshore drift is responsible for

Answer 74

Transferring vast amounts of sediment along the coastline and eventually back to sea- it is very important in a sediment cell and if interrupted by coastal management strategies, such as groynes, natural patterns and processes can be distorted

Question 75

Note: offshore currents, including rip currents move material out to sea at right angles to the shore- the material they deposit is usually deposited

Answer 75

Some distance from the shore to form sand banks

Question 76

Deposition takes place when

Answer 76

The velocity of the water or the wind falls below a critical value for a particular size of particle and can no longer be transported and so occurs once the energy flow that is moving the material declines

Question 77

Regarding deposition, what are some factors which reduce the energy flow that moves the material?

Answer 77

• currents may weaken e.g. neap ride or prevailing winds may lighten in strength altering the energy source
• where opposing currents meet, turbulence may occur resulting in deposition below the surface- this can often happen at the end of a spit
• as waves move over the seabed or shore land features, friction occurs which results in deposition of larger particles
• where rivers add additional sediment to the sea, deposition may occur as energy is insufficient to transport the additional load

Question 78

Sediment deposition is an important part of a sediment cell- areas of deposition including

Answer 78

Beaches, spits, mudflats, sand dunes and offshore bars are all sediment sinks/stores; they can be both outputs and inputs

Question 79

What is aeolian deposition?

Answer 79

Aeolian processes relate to wind and wind plays an important role in shaping the coastline. During the day, wind tends to on-shore as the the sea is colder than the land. When there is a large tidal range, large amounts of sand may be exposed at low tide; this provides a supply of sediment that can be picked up and transported by the wind. Sand is most likely to be carried by the wind and is usually transported close to the ground and over relatively short distances

• -sand is transported by wind in 2 ways (which are dependent on wind speed and how dry or moist the source of sand is)
  1) surface creep: a process similar to traction, where wind rolls or slides sand grains along the surface
  2) saltation: where the wind is strong enough to temporarily lift the grains into the airflow to heights of up to one metre for distances up to 20-30cm
• wind action can shape and form a range of landforms along the coast, including beaches and sand dunes

Question 80

As well as marine processes there are also sub-aerial (land-based) processes which shape the coastline; these come under the general headings of

Answer 80

Weathering and mass movement

Question 81

Sub-aerial weathering includes processes that slowly (usually)

Answer 81

Break down the coastline, weaken the underlying rocks and allow sudden movements of erosion to occur more easily- material is broken down in situ, remaining near or near its original position

Question 82

Why are weathering processes common at the coast?

Answer 82

Due to the presence of air and water and cycles of wetting and drying and can be categorised as:

• mechanical/ physical weathering
• biological weathering
• chemical weathering

Question 83

Mechanical weathering processes that occur at the coast depend on the nature of

Answer 83

The climate- in latitudes where temperatures fluctuate above and below freezing, freeze-thaw action is common, especially as there is a ready supply of water

Question 84

What is mechanical weathering?

Answer 84

Involves the break-up of rocks without any chemical changes taking place

Question 85

Describe freeze-thaw

Answer 85

Water enters that enters cracks in rocks (often highly porous rocks) freezes as temperatures remain below 0 degrees; as it freezes, the water expands by 10% meaning the ice occupies more space and so exerts pressure on the surrounding rock. As the processes repeats, the crack widens and eventually pieces of rock break away and collect at the base of a cliff as scree. These fragments are then used by the sea to aid erosional processes such as abrasion

Question 86

Describe wetting and drying cycles (mechanical erosion)

Answer 86

Wetting and drying cycles are common on the coast and can affect rocks that are rich in clay- the clay expands when wet and contracts and cracks when dry; over time, this can cause the rocks to break up. Also, the cracks can allow water to seep into the cliff and make them more susceptible to other processes including mass movement

Question 87

What does biological weathering involve?

Answer 87

Involves the break down of rocks by organic activity, including vegetation and coastal organisms

Question 88

Describe some biological weathering processes

Answer 88

• the roots of surface plants on cliff tops can create and expand tiny fissures; these cracks widen as roots grow, which can break up the rock
• sub-surface seaweed, which attaches itself to rock, can weaken and detach them as it sways in the currents of stormy conditions

Question 89

Why is chemical weathering common on coasts?

Answer 89

It occurs where rocks are exposed to air and moisture so chemical processes can break down the rock- as mineral compounds undergo chemical reaction, they can alter the rock structure- solution is the most common chemical process

Question 90

What are the 4 main chemical weathering processes we need to know on top of solution?

Answer 90

• oxidation
• hydration
• hydrolysis
• carbonation

Question 91

Describe the process of oxidation

Answer 91

Oxidation causes rocks to disintegrate when the oxygen dissolved in water reacts with some rock minerals, forming oxides and hydroxides- it especially affects ferrous, iron-rich rocks evident by a brownish staining of the rock surface

Question 92

Describe the process of hydration

Answer 92

Makes rocks more susceptible to further chemical weathering, although it involves the physical addition of water to minerals in the rock, causing the rock to expand creating stress which can itself cause the rock to disintegrate. Overall, the process weakens the rock and creates cracks allowing further chemical weathering to occur

Question 93

Describe the process of hydrolysis

Answer 93

Where mildly acidic water reacts or combines with minerals in the rock to create clays and dissolvable salts; this itself degrades the rock, which makes it more prone to further degradation

Question 94

Describe the process of carbonation

Answer 94

Occurs where carbon dioxide dissolved in rainwater makes a weak carbonic acid; this reacts with calcium carbonate in rocks like limestone and chalk to create calcium bicarbonate which then dissolves easily in water- carbonation more effective in locations with cooler temperatures as this increases the the amount of carbon dioxide that is dissolved in water

Question 95

As well as naturally occurring carbon dioxide there are increasing levels of other gases associated with industry and the combustion of fossil fuels in the atmosphere that also react with rainwater making it

Answer 95

Mildly acidic- this acid rain then reacts with various minerals in different rocks weakening or even dissolving them

Question 96

What is mass movement?

Answer 96

The downhill movement of material under the influence of gravity, that can be rapid or slow- mass movement processes are a common feature of coastlines with higher relief. Mass movement processes are important in transferring both energy (in response of gravity) and sediment- the sediment provides an important input to shoreline processes, forming the ‘tools’ for erosion and providing material to be transported and deposited elsewhere along the coastline

Question 97

The nature of mass movement is experienced on a particular coastline is dependent on a number of factors:

Answer 97

• the level of cohesion within the sediment
• the height of the slope and the slope angle
• grain size within sediment
• temperature and level of saturation

Question 98

What are the types of mass movement we need to know?

Answer 98

• landslides
• rock falls
• mudflows
• rotational slip or slumping
• soil creep

Question 99

Describe landslides

Answer 99

Occur on cliffs made from softer rock or deposited rock, which slips as a result of failure within it when lubricated, usually following heavy rainfall

Question 100

Describe rockfall

Answer 100

Arch roofs, stacks and cliff faces collapse as a weakness becomes unsupportable- rockfalls are usually sudden and are often associated with steep or vertical cliffs in well-jointed and often quite resistant rock and mechanical weathering can trigger rock falls. As a result, scree forms at the base of the cliff until material is removed by waves

Question 101

Describe mudflows

Answer 101

Heavy rain can cause large quantities of fine material to flow downhill. Here the soil becomes saturated and if excess water cannot percolate deeper into the ground, surface layers become very fluid and flow downhill. The nature of the flow is dependent on the level of saturation, type of sediment and slope angle; on relatively gentle slopes, the flows are often referred to as ‘solifluction’

Question 102

Describe rotational slip/slumping

Answer 102

Where softer material overlies much more resistant materials, cliffs are subject to slumping. With excessive lubrication, whole sections of the cliff face may move downwards with a side plane that is concave, producing a rotation movement

Question 103

Slumps are a common feature of

Answer 103

The British coast, particularly where glacial deposits form the coastal areas

Question 104

Describe soil creep

Answer 104

The gradual movement downhill of individual soil particles; so the presence of soil increases the likelihood of soil creep- there is some uncertainty about about the exact causes of creep, but most geographers agree that the presence of soil moisture is important, together with a range of weathering processes

Question 105

Note: run-off is another important process that operates on coastlines. It may take the form of

Answer 105

A stream emerging in a bay, taking with it large quantities of of load during flood. It can also simply be water that flows over the surface to reach the coastline, the presence of which will assist many of the mass movement processes