Coasts: Systems and processes - Geomorphological processes Flashcards
Weathering, mass movement, erosion, transportation, deposition.
1
Q
What are the 2 sets of geomorphological processes that affect coastlines?
A
Marine processes
Sub-aerial processes
2
Q
What are marine processes?
A
Processes operating upon the coastlines that are connected with the sea
3
Q
What are sub-aerial processes?
A
Land based processes which shape the coastline.
4
Q
What are the 3 sub-aerial processes affecting the coastline?
A
Weathering
Mass movement
Runoff
5
Q
What are the 5 ways cliffs can be eroded?
A
Hydraulic action Wave quarrying Abrasion Attrition Solution
6
Q
What is abrasion also known as?
A
Corrasion
7
Q
What is solution also known as?
A
Corrosion
8
Q
How much energy can waves generate as they break against the foot of a cliff?
A
25-30 tonnes m^-2
9
Q
Describe hydraulic action.
A
A breaking wave traps air as it hits the cliff face. The force of the water compresses this air into any gap in the rock face, 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 over time is to weaken the cliff face. Storms may then remove large chunks of it.
10
Q
What is wave quarrying?
A
The impact on rocks of the sheer force of the water without debris, exerting enormous pressure upon a rock surface, weakening it and dislodging pieces
11
Q
Describe abrasion.
A
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, chipping away at the rock.
12
Q
As well as on cliffs, where else does abrasion occur?
A
Inter-tidal rock platforms where sediment is drawn back and forth, grinding away at the platform
13
Q
Describe attrition.
A
The action of waves and currents causes rock fragments in the sea to roll over each other. Friction smooths out angular rock fragments which reduce in size forming pebbles, shingle and sand.
14
Q
Is solution a form of weathering or erosion?
A
Weathering, however it contributes to coastal erosion.
15
Q
Describe solution as a process of marine erosion.
A
Some calcium-based rock such as chalk and limestone is readily soluble and dissolved minerals can then be removed in solution.
16
Q
Why can’t solution occur in pure seawater?
A
Seawater is slightly alkaline with a pH between 7.5 and 8.5.
17
Q
How can solution occur at the coast if seawater is not the agent for it?
A
Carbon-based rocks at the coast may be broken down in localised areas where freshwater meets seawater, by water flowing from the land, or by rainwater which may be slightly acidic.
18
Q
What 7 factors affect the rate of coastal erosion?
A
Waves (steepness and breaking point) Fetch Sea depth Shape of the coastline Beach presence Human activity Geology
19
Q
What are the 3 marine processes affecting the coastline?
A
Erosion
Transportation
Deposition
20
Q
How does wave steepness affect rates of erosion?
A
Steeper waves have more energy and therefore greater erosive power than, gentle, low energy waves
21
Q
How does wave breaking point affect rates of erosion?
A
Waves that break at the foot of a cliff release more energy so have greater erosive power than those that break some distance from the shore
22
Q
How does fetch affect rates of erosion?
A
Waves that have travelled further have generated more energy, so waves with larger fetches have greater erosive power
23
Q
How does sea depth affect rates of erosion?
A
A steeply-shelving seabed will create higher and steeper waves, increasing erosive power
24
Q
How does beach presence affect rates of erosion?
A
Beaches absorb wave energy so provide some protection against marine erosion.
25
What kind of beaches are good at dissipating the energy from flatter waves?
Steep narrow beaches
26
What kind of beaches are good at dissipating high and rapid energy inputs? Why?
Flatter, wide beaches as they can spread out the incoming wave energy. Shingle beaches can protect from steep waves as energy is rapidly dissipated through friction and percolation.
27
How does human activity affect rates of erosion?
People may remove protective material like sand and shingle from beaches, leading to more erosion.
On the other hand people may reduce erosion by the construction of sea defences, although these may lead to increased rates of erosion elsewhere on the same coastline.
28
What aspects of geology will affect rates of erosion?
Lithology
Structure
Variation along the coastline
29
What is differential erosion?
Variations in the rates at which rocks wear away
30
Give an example of how differences in resistance of rocks has affected rates of erosion.
In the past century, the granite at Land's End has been eroded by just 10cm, whilst the glacial till of the Holderness Coast has been eroded by 120m
31
Give examples of types of rock that is resistant to erosion and examples of types that's vulnerable to erosion.
Resistant - granite, chalk
| Vulnerable - clay, sands, gravels
32
What is lithology?
The physical strength and chemistry of rocks
33
How does lithology affect rates of erosion?
Physically stronger rocks will be less resistant to erosion
34
What are strata?
Layers of rock
35
What are bedding planes?
Horizontal, natural breaks in the strata caused by gaps in time during periods of rock formation
36
What are joints?
Vertical fractures caused either by contraction as sediments dry out or by earth movements during uplift
37
What are folds?
Permanent bends in strata formed by pressure during tectonic activity, which makes rocks buckle and crumple.
38
What are faults?
Fractures formed when the stress or pressure to which a rock is subjected exceeds its internal strength. The faults then slip or move along fault planes.
39
What is dip?
The angle at which rock strata lie
40
What kind of cliff profile will horizontal strata produce?
Steep cliffs
41
What kind of cliff profile will rocks that dip gently inland produce?
Steep, stable cliffs
42
What kind of cliff profile will rocks that dip steeply towards the sea produce? Why?
Gently sloping cliffs as rock slabs slide down bedding planes
43
What kind of cliff profile will rocks that dip gently inland but have well-developed joints perpendicular to bedding planes produce? Why?
Gently sloping cliffs as the joints act as slide planes
44
What kind of cliff profile will rocks that dip gently towards the sea produce?
Gently sloping cliffs
45
What is a concordant coastline?
Where rock types run parallel to the coastline, with a resistant rock protecting the coastline from erosion, only allowing the sea to break through in a few places.
46
What is a discordant coastline?
Where rock types run perpendicular to the coastline, causing differential erosion
47
What makes limestone vulnerable to erosion?
It is well-jointed, so the sea can penetrate along lines of weakness
48
What landforms can concordant coastlines produce?
Coves
49
What landforms do discordant coastlines produce?
Headlands and bays
50
Why do headlands and bays form along discordant coastlines?
Differential erosion occurs allowing the sea to penetrate weaker rocks and produce large bays whilst not eroding harder rocks, forming headlands
51
What are the 4 methods of marine transportation?
Traction
Saltation
Suspension
Solution
52
Describe traction.
Large stones and boulders are rolled and slid along the seabed and beach by moving seawater.
53
Which processes of marine transportation occur in high energy environments?
Traction and saltation
54
What is saltation (as a method of marine transportation)?
When small stones bounce or leapfrog along the seabed and beach
55
How does saltation occur (as a method of marine transportation)?
Small particles may be thrust up from the seabed and fall back to the bottom again, dislodging other particles when they land and causing more bouncing movements.
56
Describe suspension
Very small particles of sand and silt are carried along by moving water and picked up through the turbulence that exists in the water.
57
Describe solution as a process of marine transportation.
Dissolved materials are transported within the mass of moving water
58
What process moves material along the coast?
Longshore drift
59
Describe how longshore drift moves material along the coast.
When prevailing wind direction is oblique to the shore, swash travels up the beach in the same direction as the wind, carries material up the beach at an angel. The backwash drags material down the steepest gradient due to gravity, which is generally perpendicular to the shore. The net effect is a zigzag movement of sediment up and down the beach.
60
How does the material carried by longshore drift change over time
If carried some distance it will become smaller, more rounded and better sorted.
61
Why is longshore drift important in a sediment cell?
It is responsible for transferring vast amounts of sediment along the coastline and eventually out to sea
62
What can interfere with longshore drift and what impacts does this have?
Obstacles such as groynes and piers interfere, accumulating sediment on the windward side leading to entrapment of beach material. This can lead to distortions of natural patterns.
63
Where does the deposition of material carried by longshore drift take place? What can form here?
In sheltered locations such as the head of a bay where the coastline abruptly changes direction - here spits tend to develop.
64
What 2 methods use marine transportation processes to move sediment within and out of a coastal system?
Longshore drift
| Offshore currents
65
Describe how offshore currents move sediment.
Offshore currents move material out to sea perpendicular to the shore. The material is usually deposited some distance from the shore to form sand banks.
66
What are the 2 types of deposition?
Marine deposition
| Aeolian deposition
67
What triggers deposition to take place?
The decline of the energy flow moving the material
68
When does deposition occur?
When the velocity of the water or wind falls below a critical value for a particular size of particle which can no longer be transported.
69
What could cause marine deposition to occur?
- Currents may weaken
- Turbulence may occur where opposing currents meet, resulting in deposition below the surface
- Friction as waves move over the seabed or shore land features results in the deposition of heavier particles
- Rivers or landslips adding additional sediment to the sea and there being insufficient energy to transport the additional load
70
What is aeolian deposition?
The deposition of sediment by wind
71
Why does the wind on the coastal fringe tend to be from the sea?
Air moves in response to the small pressure differentials set up by the warmer land and colder sea
72
How does tidal range impact aeolian processes?
When there is a large tidal range, large amounts of sand may be exposed at low tide providing a supply of sediment to be entrained by the wind
73
Which sized sediment is the most significant in terms of depositional features at the coast?
Sand-sized sediment
74
What 2 factors affect the method of how sand is transported by the wind?
Wind speed
| How dry or moist the source of sand is
75
What are the 2 ways sand is transported by the wind?
Surface creep
| Saltation
76
What is surface creep (as an aeolian process)?
Where wind rolls or slides sand grains along the surface
77
What is saltation (as an aeolian process)?
Where the wind is strong enough to temporarily lift the grains into the airflow to heights of up to 1m for distances of up to 20-30m
78
What is sub-aerial weathering?
The disintegration of rock in situ, at or close to the ground
79
Why are weathering processes common at the coast?
Due to the presence of air and water, and cycles of wetting and drying, and exposed rock surfaces
80
What are the 3 main categories of weathering?
Mechanical
Biological
Chemical
81
What are the 4 types of mechanical weathering?
Wetting and drying
Freeze-thaw
Crystallisation
Exfoliation
82
Explain how wetting and drying causes weathering.
Some rocks expand when they get wet and contract again as they dry. This repeated expansion and contraction causes cracking.
83
What sort of rocks experience wetting and drying?
Any rocks containing clay
84
In what kind of areas does wetting and drying occur?
Anywhere rocks go through cycles of wetting and drying e.g in areas with large tidal ranges
85
Explain how freeze-thaw causes weathering.
Water seeps into cracks in rocks. When the water freezes it expands about 9% in volume, exerting pressure on the surrounding rock. With repeated freezing and thawing, cracks widen and fragments of rock break away and collect at the base of the cliff as scree.
86
What does rock experience when overlying material is removed (by weathering or mass movement)?
Pressure release
87
How can pressure release make rock more susceptible to other processes of erosion and weathering?
As overlying mass is unloaded, mechanisms within the rock cause it to develop weaknesses, or cracks and joints as it is allowed to expand.
88
Explain how crystallisation causes weathering.
When salt water evaporates it leaves salt crystals behind. These can grow over time and exert stresses in the rock, causing it to break up.
89
Explain how exfoliation causes weathering.
Rocks expand when they get hot and contract as they cool. This repeated expansion and contraction causes cracking.`
90
What sort of climates does exfoliation occur in?
Hotter climates
91
What sort of rocks experience freeze-thaw?
Porous and permeable rock e.g chalk
92
What sort of climates does freeze-thaw occur in?
Latitudes where temperatures fluctuate above and below freezing and there is a ready supply of water
93
What is biological weathering?
The breakdown of rocks by organic activity
94
What are 4 types of biological weathering?
Roots
Burrows
Decaying organic matter
Organism adaptations and activity
95
Explain how roots cause weathering.
Seeds fall into cracks in rocks on cliff tops. Rain causes the seedlings to grow. Growing roots within the rock can create and expand tiny fissures. These cracks widen as roots grow, which can break up the rock.
96
Give examples of animals that dig burrows into cliffs.
Cliff nesting birds - puffins, martins
| Animals - rabbits
97
Give an example of organism adaptations and activity causing weathering.
1. Sub-surface seaweed attaches itself to rocks and can weaken and detach them as it sways in the currents of stormy conditions.
2. Algae secrete chemicals that aid solution
3. A shellfish called the paddock has specially adapted shells that enable them to drill into solid rock, and are particularly active in areas of chalk
98
Explain how decaying organic matter causes weathering.
Decaying matter is acidic and can corrode rocks
99
What are the 4 types of chemical weathering?
Oxidation
Carbonation
Hydrolysis
Solution
100
Describe solution as a process of sub-aerial weathering.
Rock minerals such as halite are dissolved
101
Explain how oxidation causes weathering.
Oxygen dissolved in water reacts with some rock minerals, forming oxides and hydroxides and causing the rock to disintegrate.
102
What type of rocks are affected by oxidation?
Ferrous, iron-rich rocks
103
Explain how carbonation causes weathering.
Rainwater absorbs carbon dioxide from the air to form a weak carbonic acid. This reacts with the calcium carbonate in rocks to create calcium bicarbonate which is easily dissolved in water.
104
What type of rocks are affected by carbonation?
Rocks containing calcium carbonate such as limestone and chalk
105
What sort of climate is carbonation most effective in? Why?
Cooler climates as this increases the amount of carbon dioxide that is dissolved in water
106
Explain how hydrolysis causes weathering.
Mildly acidic water reacts or combines with minerals in rocks to create clays and dissolvable salts. This degrades the rock which makes it more susceptible to further degradation.
107
What other gases apart from CO2 can form acid rain?
Sulphur dioxide
| Nitric oxides
108
How has the burning of fossil fuels increased weathering?
There are increasing levels of other gases that react with rainwater to make it mildly acidic. This acid rain then reacts with various minerals in different rocks, weakening or even dissolving them.
109
What is mass movement?
The downhill movement of material under the influence of gravity.
110
Why is chemical weathering common on coasts?
It occurs where rocks are exposed to air and moisture so chemical processes can breakdown the rocks
111
Mass movement is common on coastlines with what kind of relief?
Steep relief
112
What 4 factors affect the nature of mass movement on a particular coastline?
Level of cohesion within the sediment
Slope - height and angle
Grain size within the sediment
Temperature
113
What are the 5 types of mass movement?
```
Landslides
Rockfall
Rotational slip (or slumping)
Soil creep
Mudflow
```
114
Explain how rockfalls occur.
Mechanical weathering or earthquakes trigger individual rock fragments to suddenly break away from a cliff face as weaknesses become unsupportable.
115
At what speed do rockfalls occur?
Fast
116
What are the 3 different natures of a mass movement process?
Fall
Slide
Flow
117
What is the nature of a rockfall?
Fall
118
What sort of cliffs and rocks are rockfalls associated with?
Steep or vertical cliffs in well-jointed, resistant rock
119
What forms at the base of a cliff after a rockfall?
Scree
120
Explain how landslides occur.
Heavy rainfall lubricates the slip surface. Due to reduced friction and sometimes a trigger like an earthquake, a block of rock moves downhill fast under gravity but remains in one piece.
121
At what speed do landslides occur?
Fast
122
What is the nature of a landslide?
Slide
123
What sort of rocks are landslides associated with?
Softer rocks
124
What sort of climate do landslides occur in?
Wet climates
125
Explain how mudflows occur.
Heavy rainfall increases pore water pressure. Rock particles are forced apart and fine particles of mud flow down the slope. As the soils become saturated surface layers become very fluid and flow downhill.
126
At what speed do mudflows occur?
Fast
127
What is the nature of a mudflow?
Flow
128
What sort of rocks are mudflows associated with?
Weak bedrock e.g clay
129
What sort of climate do mudflows occur in?
Wet climates
130
What 3 factors influence mudflows?
Level of saturation
Type of sediment
Slope angle
131
Explain how rotational slips occur.
Permeable rock overlying impermeable rock causes a build up of pore water pressure. Excessive lubrication allows for whole sections of the cliff face to move downwards along a concave slide plane, producing a rotational movement.
132
What is a rotational slip?
A slump of saturated soil and weak rock along a curved surface
133
At what speed do rotational slips occur?
Fast
134
What is the nature of a rotational slip?
Slide
135
What sort of rocks are rotational slips associated with?
Weak and unconsolidated clays and sands.
| Glacial deposits
136
What sort of climates do rotational slips occur in?
Wet climates
137
Explain how soil creep occurs.
Particles rise towards the ground surface due to wetting or freezing. As the soil dries out or thaws, particles return vertically to the surface in response to gravity.
138
What is soil creep?
The gradual movement of individual soil particles downslope
139
What does soil creep result in?
Terracettes on slopes
140
At what speed does soil creep occur
Slow
141
What is the nature of soil creep?
Flow
142
How does runoff affect the coastline?
Where overland flow occurs down a slope or cliff face, small particles may be moved downslope and onto the beach or into the sea.
