Coastal Landscapes and Changes EQ2 Flashcards
1
Q
What is a wave?
A
A wave is the transfer of energy from one water molecule to its neighbour with the individual water particles moving in a circular orbit.
2
Q
How are waves formed?
A
A wave is created through friction between the wind and water surface, transferring energy from the wind into the water. This generates ripples, which grow into waves when the wind is sustained, the water itself is only moving up and down not horizontally.
3
Q
What does the wave size depend on?
A
- the strength of the wind
- the duration for which the wind blows
- water depth
- wave fetch
4
Q
What is a fetch?
A
The uninterrupted distance across water over which a wind blows, and therefor the distance waves have to grow in size.
5
Q
How do waves break?
A
- As the wave approaches the shore and reach wave depth 1/2 their wave length the internal orbital motion of water within the wave touches the sea bed
- The friction between the sea bed begins to distort the wave particles orbit from circular to elliptical and slows down the bottom of the wave
- As the wave continues to approach the shore wave length decreases and wave height increases and waves ‘bunch’ together.
- The wave crest is then moving significantly faster than the wave trough and the wave eventually toppled forward as a break.
6
Q
What is the swash?
A
The flow of water up a beach as a wave breaks. Runs up the beach in the direction of the prevailing winds.
7
Q
What is backwash?
A
When water runs back down the beach to meet the next incoming wave. Driven by gravity, meaning it run back at a right angle to the beach.
8
Q
What is a constructive wave?
A
A constructive wave is a low energy wave which is normally found at low energy coastlines. It contains a strong swash and weak backwash resulting in sediment being deposited as a berm.
9
Q
What are the characteristics of a constructive wave?
A
- low energy
- low, flat wave heigh (<1m)
- long wavelength (100 m)
- low wave frequency (meaning swash is unimpeded by previous backwash)
- strong swash
- weak backwash
10
Q
How do constructive waves influence beach morphology?
A
- Constructive waves alter beach morphology by causing the net movement of sediment up the beach, creating a gentle slope
- As the swash reached the high tide kind a berm is created through deposition of sediment.
- As swash is strong it can carry heavy sediment but the weaker backwash can only carry light sediment creating a sorting of material with heavy pebbles at the back of the beach and sand closer to the sea.
11
Q
What is a destructive wave?
A
A destructive wave are wave that are very high energy, which are normally found at higher energy coastlines subjected to strong winds and storms. They have a weak swash and strong backwash greeting a net movement of particles away from the beach (erosion).
12
Q
What are the main characteristics of a destructive wave?
A
- high energy waves
- large wave height (>1m)
- short wavelength (20m)
- high wave frequency
- strong backwash
- weak swash
13
Q
How do destructive waves influence beach morphology?
A
- weak swash and strong backwash produces a net transport of sediment down the beach reduces beach gradient
- the eroded sediment is deposited offshore in an offshore ridge or berm
- large sediment is dragged down the beach by backwash
14
Q
How does beach morphology vary decadally?
A
- climate change is expected to produce more extreme weather (storms) meaning more destructive waves and their beach profiles
- winter profiles may be present for a longer time over the course of the year
- more frequent and more powerful destructive waves may reduce beach size allowing high tides to reach further inland increasing rates if coastal erosion.
- damn building may reduce the availability of sediment
15
Q
How do beach morphology vary seasonally in the UK?
A
- in the winter destructive high energy waves dominate. Lowering the angle of the beach, redistributing shingles and forming offshore berms
- in the summer constructive low energy waves dominate steepening beach angles and sorting particles by size.
16
Q
How does beach morphology vary over a month?
A
- tide height varies over the course of lunar months
- lower high tides may produce a sire of berms at lower points in the beach
- and whne high tide return these berms are destroyed as material pushed up the beach.
17
Q
How does beach morphology vary daily?
A
- storm events in the summer may produce destructive waves reshaping the beach profile in a few hours
- calm conditions in winder can produce constructive waves and being re building the beach
- wind intensity can change wave type
18
Q
What are the differnt erosional processes?
A
- hydraulic action
- corrosion
- abrasion
- attrition
19
Q
What is hydraulic action?
A
Hydraulic actions happens whne air trapped in cracks and fissures is compressed by the force of the waves. The increased pressure forces the crack open, meaning more air is trapped and greater force experienced in the next cycle of compression. This dislodges blocks from the rock of the cliff face.
20
Q
Where does hydraulic action take place?
A
- in hard resistant igneous rock where it can attack the cooling joints. (May be the only effective mode of erosion)
- where there is high energy, high height waves
- in heavily jointed sedimentary rocks
21
Q
What is abrasion?
A
Abrasion is whne seidment picked up by waves is thrown against the cliff face. This acts like a tool of the cliff slowly chiselling away at the surface gradually wearing it away.
22
Q
Where does abrasion normally take place?
A
- areas with high energy destructive waves and large wave height
- areas with high sediment supply (loose sediment shingles or pebbles)
- softer sedimentary rock more vulnerable
23
Q
What is attrition?
A
Attrition is whne material transported by the waves is eroded through constant collisions with other load items. This breaks the rock into smaller particles are slowly rounds them.
24
Q
Where does attrition normally occur?
A
- occurs normally in the foreshore and nearshore where sediment is moved by swash and backwash
- areas with a high abundance of soft rock
25
What is corrosion?
This is where the wave water, sea spray and rain dissolves rock minerals which are immediately carried away.
26
Where does corrosion normally take place?
- areas with high amounts of limestone (carbonate rocks)
E.g. chalk
- sedimentary rocks with calcite cement
27
How are erosional processes influenced by wave type, size and lithology?
- most effective during high storm events with large destructive waves
- When wind is blowing directly onshore
- faster when tide is high (bringing deeper water closer to the cliff so less energy is lost to friction before impact
- heavy rainfall
C > under normal conditions even on soft rocked areas very little erosion takes place
28
What is an example of high rates of erosion?
- Boulder clay of the Holderness coast has retreated by 120m in the last 100 years
29
What are the main erosional landfroms?
- wave cut notches
- wave cut platforms
- cliffs
- cave, arch, stack, stump
- blow hole
30
What is a wave cut notch, and formation?
Wave cut notches are curved indentations that extend along the base of the cliff. It forms between the high tide and low tide marsh were destructive wave hit the cliff. Eroded by hydraulic actions and abrasion.
31
What is a wave cute platform and formation?
A wave cut platform is a flat rock surface exposed at low tide, they extend from the base of a cliff.
1. Marine erosion between high tide water mark and low tide water mark forms wave cut notches
2. The notch is deeper by erosion until the overlying material can no longer be supported as falls as a mass movement
3. The processes repeats and the cliff retreats
Often slope at 4 degrees and only exten pt a few hundred metre and wave energy sill being to disperse or break further from the cliff.
32
What are cliffs and formation?
Cliffs are steep slopes that are usually unvegatated
1. Marine erosion between high tide water mark and low tide water mark forms wave cut notches
2. The notch is deeper by erosion until the overlying material can no longer be supported as falls as a mass movement (Driven by gravity)
3. This exposed face forms a cliff
33
How does a cave - arch - stack -stump sequence form?
1. Rocks have joints, faults or vertically dipping strata in their geological structure
2. These weaknesses are exploited by erosional proccess (hydraulic action, abrasion) from the refracting waves around a headland. Deepening and widening the cracks forming a cave
3. Marine erosion deepens the caves until they break through the headland forming an arch
4. Lateral erosion from refracted waves attack biht side of the arch, indercutting to form notches. When the overlying rock can no longer be support its collapses in a mass movement.
5. This leaves one end of the arch detached as a tall vertical volume - a stack
6. Marine erosion at the base of the stack will continue until it collapses leaving a stump
34
What is a blow hole and formation?
Forms whne a coastal cave turns upwards and breaks through the flat cliff top. Usually this is because of erosion of weak strata around a fault line.
35
What are the four main processes of sediment transportation?
- traction
- saltation
- suspension
- solution
36
What is traction?
Were large sediment is rolled along/pushed along the seabed.
37
What is saltation?
Lighter sediment bounced along the seabed (waves) or beach (wind). Sand particles are usually transportered this way.
38
What is suspension?
This is where very light sediment is carried along within a body of water or air. (Silt or clay particles)
39
What is solution?
Where sediment is carried along dissolved in the water.
40
How does angle of the wave influence sediment transport?
Angle of the wave is the main determinant of the direction of sediment transport in the foreshore zone. The direction of the wind in,fun enough the wave angle and the angle sediment is pushed up a beach. If the wind is bellowing directly onshore the sediment will be moved up and down the beach with no net lateral movement.
41
What is longshore drift?
Longshore drift is the net lateral transport of material along the beach when the waves approach the coast at an angle.
42
What is the proccess of longshore drift?
1. Incoming swash transports sediment up the beach at an angle driven by the prevailing wind.
2. Gravitational backwash then transports seidment back down the beach at a 90 degree angle to the coast
3. This creates a zigzag pattern of sediment up and down the beach creating a net lateral movement of sediment.
43
How do tides and current influence sediment transportation?
Currents can transport sediment through the global thermohaline circulation and rip currents in the beach transporting sediment a few metres out to sea
The incoming and ebbing tides can create tidal currents in the nearshore that transport sediment
44
Where does deposition happen?
Deposition occurs when the waves no longer have sufficient energy to continue to transport material this may be due to
- wind intensity dropping
- residence by obstruction (groyne)
- dissipation of energy through refraction
45
What are the two ways deposition happens?
- gravity settling
- flocculation
46
What is gravity settling?
This occurs whne the energy of transporting water become to low to move sediment. Larger sediment will be desposited first.
47
What is flocculation?
This is when particles suspended in the water clump together due it chemical attraction and become large/heavy enough to sink p. Imports to for small particles such as clay.
48
What are swash-aligned coasts?
Wave crests approach parallel to the coast, so there is limited longshore movement of sediment.
49
What are drift-aligned coastlines?
Wave crests break at an angle to the coast, meaning there is a constant net lanteral movement of seidment and the generation of depositional landforms.
50
What is a spit?
A spit is a linear ridge of sand or shingle that stretch into the sea beyond a turn in the coastline. They are connected to the land at one side. Form on diff aligned coasts.
E.g. spurn head on Holderness coast, East rinding Yorkshire
51
What’s the process of spit formation?
1. Incoming swash transports sediment up the beach at an angle driven by the prevailing wind.
2. Gravitational backwash then transports seidment back down the beach at a 90 degree angle to the coast
3. This creates a zigzag pattern of sediment up and down the beach creating a net lateral movement of sediment.
4. As the coastline changes shape, the waves are sheltered and energy is dispersed.
5. This results in deposition through gravity settling
6. Over time the seidment builds up and the sediment breaks the surface extending the beach into the sea as a spit
52
What is a recurved/hooked spit?
A spit whose end is curved landwards towards a bay or inlet. Fromed at the end of a spit.
E.g. Hurst Caslte spit, Hampshire
53
Why do recurved spits form?
- wave refracts around the end of the spit depositing sediment for a short distance in the landward direction
- a secondary wind or current directions generating short periods of longshore drift in the landward direction
54
What are double spits?
Where two spits extend out in opposite directions from both sides of the bay, towards the middle.
55
How do double spits form?
- when longshore drift is occurring in different directions on opposite sides of the bay
- rising sea level drive ridges of material onshore form the offshore zone
56
What are offshore bars?
Ridges of sand of shingle running parallel to the coast in an offshore zone.
57
How do offshore bars form?
They are formed from the deposition of sediment eroded if the beach by destructive waves carried by backwash.
58
What is a bar/barrier beach?
Bars are linear ridges of sand/shingle that extend across a bay and are connected to land on both sides.
59
How do bars form?
- on drift aligned coastlines when longshore drift extends a spit across the entire width of the bay
60
What is a tombolo?
Tombolos are linear ridges of sand and shingles connecting an offshore island to the coastline of the mainland.
E.g. St Ninism tombolo, Shetland
61
How do tombolos form?
- on drift aligned coastlines when longshore drift builds a spit out form lands until in makes contact with an offshore island
- on swash aligned coasts when there is wave refraction around both sides of the island (collision of waves cancelling each other out creating deposition
62
What is a cuspate foreland?
Low lying triangular shoes headlands extending out from a shoreline formed from deposited sediment
E.g. Dungeness
63
How are cuspate forelands formed?
Whne longshore drift currents from opposing direction converge at the boundary of two sediment cells.
64
Why are depositional landforms unstable?
- made up of unconsolidated material
- they are dynamic as they loose material transported by waves, tides and wind
65
How does vegetation stabilise depositional landforms?
1. Plant roots bind together unconsolidated material together
2. Encourage deposition by creating friction between waves and water
3. Reduce erosion by slowing water and wind flow
4. Built land up through additions of organic matter
66
What is a sediment cell?
A sediment cell is a linked system of sources, transfers and sinks of sediment along a section of coastline. They operate in a closed systems wiht no external inputs and outputs. The coastline of England and Wales is divided into 11 primary cells.
E.g. Flanborough head (source region)
Holderness coast (transfer zone)
Spurn head (sink region)
67
What are sources in the sediment cell?
Sources are places where sediment is generated, such as cliffs or eroding sand dunes. They create the sediment inputs.
68
What is a transfer in the sediment cell?
Places where sediment is moving along shore through longshore drift and offshore currents (drift aligned coasts). Beaches, parts of dunes and salt marshes perform this function.
Transfers include longshore drift, swash, backwash, currents and winds
69
What are sinks in sediment cells?
Sinks are locations where the dominant process is deposition, creating depositional landforms such as sand dunes, bars and spits
70
Why are sediment cells described as dynamic?
Sediment cells are dynamic because sediment is constant movement of sediment through source, transfer and sink. Dynamic equilibrium is reached when inputs of seidment form the source region are balanced by the amount being deposited in the sink. If the equilibrium is interrupted it will change to return the balance. (Negative feedback)
71
What is negative feedback?
When the change produced created effects that operate to reduce or work against the original changes.
72
What is an example of negative feedback in a sediment cell?
- erosion leading to a mass movement. And the collapsed debris acts as a barrier protecting the base of the cliff, slowing or preventing erosion for a period of time.
- major erosion of sand dunes could lead to excessive deposition of sediment offshore, creating an offshore bar reduces energy of waves allowing dunes to recover.
73
What is positive feedback?
When the changes produces an effect that operates to increase the original change.
74
What is an example of positive feedback?
- when wind erosion of a dune section during high velocity storms may remove stabilising vegetation, resulting in further wind erosion.
75
What is the main sub aerial processes?
- weathering (biological, mechanical and chemical)
- mass movements
76
What is the definition of weathering?
The insitu breakdown of rocks by chemical, mechanical or biological agents. It does not involve any movement and crates rock fragments that from sediment.
77
What is weathering influenced by?
- climatic conditions (temperature and type and amount of precipitation)
- lithology of the rocks
78
How does weathering influence the rates of recession?
- weakens rocks, making them more vulnerable to erosion and mass movement processes
- have a contribution to wave cut notches affecting the overall stability of the cliffs
79
What is mechanical weathering?
Mechanical weathering is the break down of rocks due to the extertion of a physical force. Examples include freeze thaw weathering and salt crystallisation.
80
What is freeze thaw weathering?
This is a type of mechanical weathering where water seep into fissure in the rocks, before freezing and expanding 9%. This experts a tensions, force widening and breaching the rock. Repeated cycles force cracks to open further.
81
What rocks are vulnerable to freeze thaw weathering?
- any rocks with cracks and fissures
- areas experiencing cold temperatures (below 0)
82
What is the proccess of salt crystallisation?
This is a type of mechanical weathering and its is the growth of salt crystals in cracks and pore spaces exterting a breaking force.
83
What rocks are vulnerable to salt crystallisation?
- porous and fractured rocks (s sandstone)
- effect it greater in hotter drier climates where evaporation levels are high
84
What is chemical weathering?
This is weathering that involves a chemical reaction and the generation of new chemical compounds. Three examples are carbonation, hydrolysis and oxidation
85
What is carbonation and what rocks are vulnerable to it?
A weak carbonic acid is formed through the combination of precipitation and carbon dioxide. This weak acid reacts with the calcium carbonate in the rocks to form soluble calcium bicarbonate solution. This is soluble and is immediately carried away by water.
Limestone and other carbonate rocks are vulnerable.
86
What is hydrolysis and what rocks are vulnerable?
The addition of water that causes the breakdown of minerals to form new clay minerals, plus material in solution.
Vulnerable rocks include igneous and metamorphic rocks containing feldspar and silicate minerals.
87
What is oxidation and what rocks are vulnerable?
Oxidation is the gaining of oxygen to minerals, producing metal oxides increasing volume and contributing to mechanical weathering.
Vulnerable rocks include rocks containing iron compounds such as sandstones and shales
88
What is biological weathering?
biological weathering is the break down of rock in situ by living or once living organisms such as plants, bacteria and animals . It often speeds up mechanical and chemical weathering.
Examples include plant roots and rock boring.
89
How does plant roots perform biological weathering and what rocks are vulnerable?
If plant seeds land in crack in the rocks, they can germinated and grow. As it grows it’s root systems expands exerting force to widen the rock.
Vulnerable areas are areas that are highly vegetated and contain fissures.
90
What is rock boring, and what rocks are vulnerable?
Rock boring is a type if biological weathering where species of clams and mollusc bore into rocks breaking them apart. Additionally they may secret chemicals that dissolve rock.
Sedimentary rocks (especially carbonate rocks) located near intertidal zone are vulnerable.
91
What is mass movement?
The downslope movement of rock and soil under the force of gravity. It’s an umbrella term for a range of specific movements which it determined upon litholgy.
Unconsolidated material (slumping)
Consolidated rock (sliding)
92
What are the types of mass movement?
- rockfall
- rotational slumping
- landslides
- flows
93
What is rockfall?
These are a rapid form of mass movement were blocks of rock are dislodged by mechanical weathering or hydraulic action. Undercutting of cliffs can led to huge rock falls.
94
What type of cliffs are prone to rock falls?
- a geological structure with many joints, faults or bedding planes
- steep, near vertical strata dip
- earthquake prone areas
95
What is rotational slumping?
A mass movement that occurs on a curved rock plane. Huge masses of material can slowly rotate downslope over longer term periods. It is facilitated by the presence of water (reducing friction and adding weight p)
96
Where does rotation slumping occur?
- weak rocks (clay and shales)
- unconsolidated material
- in rocks with complex geology
E.g. Christchurch Bay, Hampshire were unconsolidated mater (sand) overly clay.
97
What are landslides?
A landslide is the downslope movement of rock down a flat/,inerrancy slip plane, maintaining contact with the cliff surface throughout. The discrete blocks are released by meachnicka weathering, with gravity pulling the loose blocks down.
98
Where do landslides take place?
- consolidated rocks wiht joints or a bedding plane sloping seaward
- high precipitation levels as it reduces friction making it more likely to happen.
99
What are flows?
Flows occurs when unconsolidated fine grained sediment (clay) mix with large volumes of water. They become saturated losing any cohesion and flow downslope.
100
What’s are the distinct landforms created through mass movement?
- rotational scars
- talus scree slopes
- terraced cliff profiles
101
What’s are rotational scars?
A fresh, curved, unweathered and unvegatated rock surface on the cliff face. It’s is exposed after a rotational slumping mass movement.
102
What are talus scree slopes?
Talus scree slopes are a fan shaped mound of material. They are are created after rockfalls when the deprivation accumulates at the cliff foots.
103
What are terraced cliff profiles?
This is when rockfalls and rotational slumps create a stepped cliff profile. This is created through the detachment of slopes due to weathering detaches often with vegetation intact falls (driven by gravity) leaving small ‘steps’
