Coasts 1 Flashcards
(122 cards)
1
Q
Waves
A
Ripples in the sea caused by the transfer of energy from the wind blowing over the surface of the sea.
2
Q
What do waves play a role in?
A
-Coastal erosion
-Transportation
-Deposition
3
Q
Step 1 in wave formation:
A
- Wind blowing over the ocean creates friction with the water surface causing ripples to form.
4
Q
Step 2 in wave formation:
A
- Faster moving ripples merge with slower ones, forming larger and more organised waves (in straight lines called sets).
5
Q
Step 3 in wave formation:
A
- The longer the waves travel for, the larger and more organised they become.
The distance over which the wind has blown is called the fetch.
6
Q
What are the two types of wave?
A
-constructive (surging) waves
-destructive (plunging) waves
7
Q
Characteristics of constructive waves
A
-Swash more powerful than backwash
-This means material is deposited, constructing a gentle beach
-Low frequency
-Gently sloping wave fronts
-Wave crests far apart
-Waves have a large fetch
8
Q
Fetch
A
The distance over which the wind has blown.
9
Q
Characteristics of destructive waves
A
-Backwash more powerful than swash
-So they erode away material from the beach
-High frequency
-Steep wave front
-Wave crests are close together
10
Q
A beach is…
A
…the best form of coastal protection.
We can change the beach profile so that waves deposit material.
11
Q
What are the five main coastal processes?
A
-erosion
-deposition
-transportation
-weathering
-mass movement
12
Q
What are the three processes of erosion (by which waves wear away the coast)?
A
-Hydraulic action (with cavitation)
-Corrasion (Abrasion)
-Attrition
13
Q
Hydraulic power
A
The sheer force of the water as it crashes against a cliff.
This compresses air into natural weaknesses in the rock, eventually causing it to break apart (known as cavitation).
14
Q
Corrasion (Abrasion)
A
Eroded particles are hurled against a cliff by the water, scraping and rubbing against the rock which removes small pieces of the cliff.
15
Q
Attrition
A
Eroded particles in the water collide, breaking into smaller pieces and becoming more rounded.
16
Q
Material that’s been eroded is…
A
…moved along the coast and deposited by waves.
17
Q
How is eroded material transported along the coast?
A
Longshore drift.
18
Q
What are the first two steps in longshore drift?
A
1.Waves follow the direction of the prevailing wind.
- They usually hit the coast at an oblique angle.
19
Q
What are the third and fourth steps to longshore drift?
A
3.The swash carries material up the beach, in the same direction as the waves.
- The backwash then carries material down the beach at right angles, (due to gravity) back towards the sea.
20
Q
What is the final step in longshore drift?
A
- Over time, material moves laterally along the coast (in a zig-zag motion).
21
Q
In your geography exam, wen explaining something, you can…
A
Use ANNOTATED diagrams.
22
Q
How material is transported depends on…
A
-How powerful the movement of water is (how much energy)
-The size of the particles
23
Q
Traction
A
Large particles like boulders are pushed along the sea bed by the force of the water.
24
Q
Saltation
A
Pebble-sized particles are bounced along the sea bed by the force of the water.
25
Suspension
Small particles like silt and clay are carried along in the water.
26
Solution
Soluble materials (e.g. limestone) dissolve in the water and are carried along.
27
Deposition
-The dropping of material.
-Occurs when water carrying sediment loses energy and slows down.
28
When do coasts build up?
When the amount of deposition is greater than the amount of erosion.
29
For constructive waves, is there more erosion or deposition?
More deposition because they drop more material than they remove.
30
What factors can increase the amount of material that is deposited on an area of coast?
-There's lots of erosion elsewhere on the coast (so more material is available)
-Lots of material is transported into the area
31
Types of weathering;
-Mechanical
-Chemical
-(Biological)
32
Chemical weathering
The breakdown of rock by changing its chemical composition.
33
Carbonation weathering
-A type of chemical weathering
-Happens in warm and wet conditions
34
How does carbonation weathering occur?
1. Rainwater has Carbon Dioxide dissolved in it, making it a weak carbonic acid.
2.Carbonic acid reacts with the calcium carbonate in rocks such as carboniferous limestone and chalk.
3. The rocks are dissolved and washed away in solution,
35
Biological weathering (not on spec)
Living things such as burrowing animals and plant roots make the rock's structure weaker, and eventually pieces of rock may fall away.
36
Mechanical weathering
The break down of rock by physical forces e.g. freeze-thaw weathering.
37
Freeze-thaw weathering steps 1 and 2.
1. It happens when the temperature is transgradial.
2.Water enters joints and bedding planes (natural weaknesses) in rocks due to rainfall.
38
Freeze-thaw weathering step 3.
3. When the water freezes (below 0°C) it expands.
Expanding ice is often stronger than the tensile strength of rock.
This puts pressure on the rock, pushing it's cracks wider.
39
Freeze-thaw weathering steps 4 and 5.
4. When the water thaws, it contracts releasing the pressure on the rock.
5. Repeated freeze-thaw cycles push the cracks even wider, causing the rock to break up.
40
What is mass movement?
The shifting of rocks or loose material down a slope due to the force of gravity.
(force of gravity acting on a slope is greater than the force supporting it).
It causes coasts to retreat rapidly.
41
What increases the likelihood of mass movement occurring?
When material is full of water. This is because water acts as a lubricant, and also makes the material heavier.
42
Types of mass movement:
-Sliding
-Slumping
-Rockfalls
-(mudflows)
43
Slides
Material shifts in a straight line along a slide plane (do a diagram).
44
Slumps
-Rainfall penetrates permeable rock types, causing these rocks to become saturated and heavy.
-Rain also acts as a lubricant.
-These rocks slump downward, causing a curved slip plane to be formed.
(diagram!)
45
Rockfalls
-Material breaks up, often along bedding planes, and falls down the cliff face.
-This leaves piles of rock (scree) at the boulder field at the base of a cliff.
(diagram!)
46
Mudflows (not named in spec)
-Saturated soil (soil filled with water) flows down a slope.
You get a large lobe of soil and debris at the bottom.
47
Rotational slip (not named in spec)
Saturated soil slumps down a concave plane.
This can occur after periods of heavy rainfall when water saturates overlying rock, making it heavy and liable to slide.
48
Why do periods of heavy rainfall increase the risk of mass movement?
Water saturates rock, making it heavy and liable to slide.
49
How does rock type influence coastal forms?
Less resistant rocks (e.g. clays and sands) are eroded at a faster rate than more resistant rocks (e.g. chalk, limestone).
This is known as differential erosion.
50
How do geological structures influence the erosional landforms that develop on a coastline?
The type of coastline affects how it is shaped and eroded over time.
The two types of coastline are discordant and concordant.
Headlands and bays are formed along discordant coastlines, whereas features like coves form on concordant coastlines.
51
Discordant coastline
Made up of alternating bands of more and less resistant rock outcropping at right angles to the coast.
52
Formation of headlands and bays:
1.Headlands and bays form on discordant coastlines, where there are alternating bands of more and less resistant rock.
2. The less resistant rock is eroded faster, forming a bay with a gentle slope.
3. The more resistant rock erodes more slowly, so it juts out, forming a headland with steep sides.
53
Weathering
The breaking down of rocks by mechanical, chemical, or biological processes in situ (where they are=no transportation).
54
Headland
A narrow piece of more resistant rock which projects outwards from the coast (surrounded by the sea on three sides).
55
Bay
A crescent shaped indentation in the coastline, found between and sheltered by two headlands.
It usually has a beach, which may be composed of sand or shingle.
56
Landform
A feature of the landscape that has been formed of sculpted by the processes of erosion, transportation, and deposition.
57
What are headlands eroded to form?
-caves
-arches
-stacks
-(stumps)
58
How are caves formed?
-The resistant rock that makes up headlands often has weaknesses like cracks
-Waves crash into the headlands and - by hydraulic power, cavitation, and abrasion - enlarge the cracks
-Repeated erosion and enlargement of cracks causes a cave to form.
59
How are arches formed?
-Lines of weakness likely run through a band of rock
-This means that continued erosion from each side of a headland will eventually deepen caves either side until they join together
-The headland is broken through, forming an arch, e.g. Durdle door.
60
How are stacks formed?
Either erosion wears away the rock supporting the arch, until it eventually collapses
or
Weathering occurs, eroding the top of the arch which eventually collapses forming a stack.
(Durdle door is carboniferous limestone = chemical weathering)
61
What are the two ways in which a stump can form?
-Erodes at base and collapses (fast)
-Erodes more slowly due to weathering (more ridged)
62
How are cliffs formed?
-Erosion
-Weathering
-Softer rock erodes easily to create gently sloping cliffs, whereas harder rock is more resistant so forms steep cliffs
63
Wave-cut platform
A wide, gently-sloping surface found at the foot of a cliff.
64
Erosional landforms include:
-headlands
-bays
-cliffs
-wave-cut platforms
-caves
-arches
-stacks
-(stumps)
65
How is a wave-cut platform formed? (steps 1 and 2)
1. Waves cause most erosion at the foot of a cliff, forming a wave-cut notch which is enlarged over time.
2. Repeated erosion causes the rock above the notch to become unstable and it eventually collapses
66
Example of a wave-cut platform
Southerndown, Wales.
67
How do you differentiate between a stack and a stump?
A stack can be seen 24 hours a day, whereas a stump is underwater at high tide.
68
What are the factors that affect the rate of erosion?
-Local geology (rock types)
-Type of wave (constructive/destructive)
-Type of coastline (discordant/concordant)
69
Why do waves curve?
The friction of the narrowing sea bed slows waves, so they curve.
70
Depositional landforms include:
-beaches
-sand dunes
-spits
-bars
71
Beach
A deposit of sand and shingle along the coastline.
72
Where are beaches found?
On coasts between the high and low water marks.
73
How are beaches formed?
Constructive waves depositing material.
74
Sand beach characteristics
-Created by low energy waves
-Flat, wide, and gently sloping
75
Why are sand beaches long and gently sloping?
Sand particles are small so the weak backwash can move them back down the beach, creating a long, gentle slope.
76
Shingle beach characteristics:
-Created by high energy waves
-Steep and narrow
77
Why are shingle beaches steeply sloping?
Sand particles are washed away but larger shingle is left behind.
The shingle particles build up to create a steep slope.
78
Formation of a spit (step 1)
1. Sediment is transported laterally along a beach (but in a zig zag motion) due to longshore drift.
79
How are salt marshes formed?
The area behind a spit is sheltered from waves, so when material (mud and silt) is deposited here, it accumulates, and plants are able to grow.
Over time, the sheltered area can become a salt marsh (or a mud flat).
80
Bar
A spit that joins two headlands together.
81
How are lagoons formed?
-A bar cuts off a bay between two headlands
-This allows a lagoon to form behind the bar
82
How can offshore bars form?
If the coast has a gentle slope, friction with the sea bed causes waves to slow down and deposit sediment offshore, creating a bar that is not connected to the coast.
83
Tombolo
A spit that joins up with an island.
84
Berm
A ridge in the beach which marks high tide.
85
Why does the beach profile change throughout the year?
The beach profile depends on the type of wave.
During summer, waves are often constructive, and deposit sand or onto a beach
Whilst winter storm waves (destructive) transport sand offshore.
86
Winter beach profile
-Berms (+sand dunes) are eroded by destructive waves
-Waves drag beach deposits offshore, creating an offshore bar, lowering the height of the beach
-So beaches are steeper and narrower
87
Summer beach profile:
-Offshore bar provides material
-Constructive waves transport and deposit this at high tide to form a berm
-So beaches are rebuilt.
88
Sand dune
A hill of loose sand formed by wind or water.
These can be stabilised by vegetation.
89
Sand dune systems are unique ecosystems found where?
The British Isles
90
Dune succession
The changing conditions from one end of a dune to the other.
91
Explain the formation of the sand dune system. (first 2 steps)
1. The formation of sand dunes depends on there being objects (e.g. driftwood) on the strand line.
2. Sand particles get blown over these obstacles to the lee side, where it is sheltered , so sand is deposited, forming embryo (mobile) dunes.
92
Explain the formation of the sand dune system. (3rd step)
3. Embryo dunes are colonised by plants e.g. Marram grass.
The roots of the vegetation stabilise the sand, encouraging more sand to accumulate there.
This forms foredunes and, eventually, mature dunes.
New embryo dunes form in front of stabilised dunes.
93
Explain the formation of the sand dune system. (4th and final step)
4. Dune slacks (small pools) can form in hollows between dunes.
94
Strand line
The line where the sea goes up to at high tide.
95
Dunes which can move (In order)
-embryo dunes
-fore dunes
-Yellow dunes
96
Dunes which cannot move (in order)
-Grey dunes
-Mature dunes
97
Why do grey dunes not move around as much as other dunes?
Grey dunes have more vegetation cover than embryo/fore/yellow dunes.
This means there is less exposed sand, which means that they do not change shape or move around as much.
98
Why do mature dunes never move?
Due to the large amount of vegetation holding them in place.
99
Why might dune slacks have water in the bottom?
They are closer to the water table.
100
Dune slacks are sheltered. This means that...
They have better conditions for growing.
101
What do you need for the formation of sand dunes?
-A high tidal range
-A large supply of sand
-Obstacles on the strand line
-A strong onshore breeze
-Mainly constructive waves
-Marram grass and other specialist plants
102
Why do you need a high tidal range for the formation of sand dunes?
This ensures the sand has time to dry out between tides so it can be blown about.
103
Why do you need a strong onshore breeze for the formation of sand dunes?
This ensures sand is predominantly blown up the beach.
104
Why do you need obstacles on the strand line for the formation of sand dunes?
These trap sand, and keep it still for long enough for plants like Marram grass to gain a foothold.
105
Why do you need mainly constructive waves for the formation of sand dunes?
This helps ensure the dunes are not eroded over time and can build up.
106
Why do you need marram grass and other specialist plants for the formation of sand dunes?
Their leaves trap sand and help build up the dunes.
107
Cove
A small type of (circular/oval) coastal inlet, usually with narrow, restricted entrances, and often situated within a larger bay.
108
How is a wave-cut platform formed? (steps 3 and 4)
3. The collapsed material is washed away and a new wave-cut notch starts to form.
4. After repeated collapses, the cliff retreats, leaving a wave-cut platform.
DIAGRAMMMM
109
Formation of a spit (step 2)
2.When the end of the land is reached, sediment continues to be transported laterally in the direction of the prevailing wind, so the beach extends into a spit.
110
Formation of a spit (step 3).
3.The spit will likely gain a recurved end as a secondary wind will sometimes prevail and transport sediment in a different direction.
111
How are sand dunes formed?
The deposition of sand.
112
What do sand dunes form?
A natural coastal defence.
113
Sand dunes need...and have...
very particular conditions to form
a life cycle which, if unsuccessful, the dune dies.
114
Fore dunes
-1st main ridge
-Several m high
115
Yellow dunes
-Constantly changing shape
-10 to 15m from the sea
-Marram grass dominant, but can find other plants, e.g. Orache here
116
Why are grey dunes grey?
Due to organic matter.
This means plants that are less specialised can grow here.
117
Mature dunes
-May be thousands of yrs old
-Have a deeper layer of organic matter
-Growing conditions are almost normal
-This enables a large variety of plants and trees to grow e.g. witch hazel.
118
What is our example of a section of coastline in the UK to identify its major landforms of erosion and deposition?
The Dorset coastline (part of the Jurassic coast)
119
Name the key locations at the Dorset coastline, Swanage area. (north to south)
-Poole harbour
-Studland bay
-Ballard point (with old Harry and his wife)
-Swanage bay
-Durlston head
120
Which way do the waves flow near the Dorset coastline, Swanage area?
East to west, towards the (discordant) coastline.
121
Durdle Door
A natural limestone arch on a small headland in Dorset, on the south coast of England.
122
Lulworth cove
A natural cove in Dorset, on the south coast of England.
It has its shape because the rate of erosion increases as less resistant rock behind a band of more resistant rock that has been eroded in a narrow area is hit by waves.
DIAGRAM PLEASE
