Coasts EQ2 - Coastal landforms Flashcards
What are the characteristics of constructive waves?
- low wave height (less than 1m)
- long wave length (up to 100m)
- strong swash, weak backwash
- low frequency (8-10 waves per min)
What are the characteristics of destructive waves?
- wave height of over 1m
- wavelength of around 20m
- strong backwash and weaker swash
- high frequency (10-14 per min)
What is beach morphology?
The shape of a beach, including its width and slope (beach profile) and features such as berms, ridges and runnels. Also includes type of sediment
What is fetch?
The uninterrupted distance across water over which a wind blows, and therefore the distance the waves have to grow in size
What factors does wave size depend on?
- strength of wind
- duration wind blows for
- water depth
- wave fetch
What are human changes that can cause beach profiles to change?
- construction of dams blocking sediment supply
- global warming creating more storms
- coastal management intefering with sediment supply
What is hydraulic action and the influence of lithology on it?
Air trapped in cracks and fissures is compressed by the force of the waves crashing against the cliff face, causing blocks of rock to become dislodged.
Heavily jointed/fissured sedimentary rocks are therefore vulnerable
What is abrasion and the influence of lithology on it?
Sediment picked up by breaking waves is thrown at the cliff face, which acts like a tool on the cliff, gradually wearing it down.
Loose sediment must be available for abrasion to be effective. Softer sedimentary rocks more vulnerable than hard igneous ones
What is attrition and the influence of lithology on it?
Sediment is moved around by waves, causing collisions between particles to chip fragments off, causing sediment to become smaller and more rounded.
Softer rocks very rapidly reduced in size by attrition
What is corrosion/solution and the influence of lithology on it?
Carbonate rocks (limestones) are vulnerable to solution by rainwater, spray from the sea and seawater (the rock gets dissolved).
Mainly affects limestones, vulnerable to solution by weak acids
How does a blow hole form?
When a coastal cave turns upwards and breaks through the flat cliff top. Usually this is because of erosion of especially weak strata or the presence of a fault line.
How is a wave cut platform formed?
- Wave cut notch is eroded between high and low tide water marks, through erosion processes at a cliff face.
- The notch deepens by further erosion until the overlying material collapses by mass movement due to gravity, forming a cliff.
- The process repeats, and the position of the cliff retreats (coastal recession)
- The rock just below low tide level is always submerged, it’s uneroded as it’s never exposed to wave impact.
- As the overlying material is eroded, uneroded rock at low tide level is left as flat rock surface, the wave cut platform.
Explain the cave-arch-stack-stump formation process
- Weaknesses in rocks at a cliff face (joints, faults etc) are exploited by marine erosion from waves causing a sea cave to form
- This is accentuated by wave refraction, as energy is directed at lateral erosion of the headland
- Where a line of weakness extends right through the headland caves form on both sides. Marine erosion deepens the caves until they connect up, forming an arch.
- Undercutting of sides of arch leads to collapse of overlying material, eroding arch wider
- Weathering and sub aerial processes cause arch roof to collapse and this creates a stack
- Marine erosion at the base of the stack will form a notch on all sides until the stack collapses by blockfall - forming a stump
How is a cliff formed?
- Marine erosion of land between the high tide and low tide mark by hydraulic action and abrasion forms a wave cut notch
- The notch deepens until the overlying rock collapses by mass movement due to the force of gravity.
- The exposed face forms a cliff.
What factors affect sediment transportation?
- angle of wave attack
- process of longshore drift
- tides
- currents
What are the 4 processes of sediment transport, and the type of sediment they transport?
- traction - pebbles, boulders
- saltation - sand sized particles
- suspension - silt and clay particles
- solution - chemical compounds in solution
What is a swash aligned coast?
Where wave crests approach parallel to the coast, so there is limited longshore movement of sediment
What is a drift aligned coast?
Where wave crests break at an angle to the coast, so there is consistent longshore drift and generation of elongated depositional features
What is gravity settling?
When sediment is deposited because the energy of transporting water becomes too low to move sediment