Coastal Landscapes and Changes EQ2 Flashcards
What is a wave?
A wave is the transfer of energy from one water molecule to its neighbour with the individual water particles moving in a circular orbit.
How are waves formed?
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.
What does the wave size depend on?
- the strength of the wind
- the duration for which the wind blows
- water depth
- wave fetch
What is a fetch?
The uninterrupted distance across water over which a wind blows, and therefor the distance waves have to grow in size.
How do waves break?
- 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.
What is the swash?
The flow of water up a beach as a wave breaks. Runs up the beach in the direction of the prevailing winds.
What is backwash?
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.
What is a constructive wave?
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.
What are the characteristics of a constructive wave?
- 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
How do constructive waves influence beach morphology?
- 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.
What is a destructive wave?
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).
What are the main characteristics of a destructive wave?
- high energy waves
- large wave height (>1m)
- short wavelength (20m)
- high wave frequency
- strong backwash
- weak swash
How do destructive waves influence beach morphology?
- 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
How does beach morphology vary decadally?
- 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
How do beach morphology vary seasonally in the UK?
- 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.
How does beach morphology vary over a month?
- 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.
How does beach morphology vary daily?
- 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
What are the differnt erosional processes?
- hydraulic action
- corrosion
- abrasion
- attrition
What is hydraulic action?
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.
Where does hydraulic action take place?
- 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
What is abrasion?
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.
Where does abrasion normally take place?
- 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
What is attrition?
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.
Where does attrition normally occur?
- occurs normally in the foreshore and nearshore where sediment is moved by swash and backwash
- areas with a high abundance of soft rock
What is corrosion?
This is where the wave water, sea spray and rain dissolves rock minerals which are immediately carried away.
Where does corrosion normally take place?
- areas with high amounts of limestone (carbonate rocks)
E.g. chalk - sedimentary rocks with calcite cement
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
What is an example of high rates of erosion?
- Boulder clay of the Holderness coast has retreated by 120m in the last 100 years
What are the main erosional landfroms?
- wave cut notches
- wave cut platforms
- cliffs
- cave, arch, stack, stump
- blow hole
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.
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.
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
How does a cave - arch - stack -stump sequence form?
- Rocks have joints, faults or vertically dipping strata in their geological structure
- 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
- Marine erosion deepens the caves until they break through the headland forming an arch
- 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.
- This leaves one end of the arch detached as a tall vertical volume - a stack
- Marine erosion at the base of the stack will continue until it collapses leaving a stump
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.
What are the four main processes of sediment transportation?
- traction
- saltation
- suspension
- solution
What is traction?
Were large sediment is rolled along/pushed along the seabed.
What is saltation?
Lighter sediment bounced along the seabed (waves) or beach (wind). Sand particles are usually transportered this way.
What is suspension?
This is where very light sediment is carried along within a body of water or air. (Silt or clay particles)
What is solution?
Where sediment is carried along dissolved in the water.
How does angle of the wave influence sediment transport?
This is the main determinant of the direction of sediment transport (in the foreshore zone).
Where the wind is blowing directly onshore, the incoming swash transports the material direction up the beach at 90’ to the coastline.
Backwash then transports sediment perpendicularly back down to the beach to its original starting position.
Sediment is moved up and down the beach, but there is no net lateral movement.
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.