Coastal Systems Flashcards
Is a coastal system open or closed?
Open system
What is dynamic equilibrium?
When the inputs and outputs of a system are in balance
Give an example of negative feedback
When a beach is eroded, the cliff behind it are exposed to wave attack. Sediment eroded from the cliffs is eroded and then deposited on the beach, causing it to grow in size again to protect the cliffs
Give an example of positive feedback in coasts
As a beach starts to form, it slows down the waves which can cause more sediment to be deposited, increasing the size of the beach
Give some inputs into the coastal system
Energy from - waves, wind, tides, sea currents
Sediment
Give some stores of the coastal system
Erosional and depositional landforms
Give some outputs of the coastal system
Dissipation of wave energy
Accumulation of sediment above the tidal limit
Sediment removed beyond local sediment cells
What is a sediment cell?
Separate divisions of the coastline. They can be seen as systems in themselves with clear inputs, transfers of sediment, stores and outputs
How many sediment cells is the coastline of England and Wales made up of?
11
Is a sediment cell an open or closed system?
Closed system
Within each cell, sediment is largely recycled, maintaining a state of relative balance
What is positive and negative sediment budget?
Positive sediment budget - if inputs of sediment exceed outputs (beach extends in height, length and width)
Negative sediment budget - if outputs of sediment exceed inputs (beach becomes smaller over time)
What must be occurring if a beach within a large sediment cell is experiencing positive sediment budget?
Another beach in the sediment cell must be experiencing negative sediment busget
Sediment cells are generally seen as closed systems but there may be —————
Loss of sediment to outputs beyond the system
When does loss of sediment to outputs beyond the sediment cell system occur?
When wave energy is very high or currents are very strong, sediment may be lost to other cells, ‘lost’ to deep sea areas offshore or transferred beyond the active coastal zone (upper beaches, coastal dunes)
What are the 4 zones of a single beach?
Backshore
Foreshore
Nearshore
Offshore
What is the backshore?
Areas between the high-water mark (HWM) and the limit of marine activity
Changes only take place here during storm events
What is the foreshore?
The area between the high water mark (HWM) and the low water mark (LWM)
Most important zone for marine processes
What is the nearshore?
Area between the low water mark (LWM) and the point where waves no longer have an effect on the land beneath them
What is the offshore?
The area beyond the point where waves cease to impact upon the seabed
Activity is limited to the deposition of sediments
What is erosion?
The wearing away of the Earth’s surface by the action of ice, wind and water
What is weathering?
The breakdown or decay of rock at or near the Earth’s surface in situ (its original position)
Rock fragment will remain until removed by erosion processes
Give the three types of weathering with an example
Mechanical (freeze-thaw)
Biological (tree roots, burrowing animals)
Chemical (calcium carbonate in chalk can be dissolved by sea water)
What is mass movement?
The movement of material downhill by gravity and often assisted by rainfall
What are the 4 sources of energy in coastal environments?
Wind
Waves
Tides
Currents
In what direction does the wind move?
From an area of high atmospheric pressure to low atmospheric pressure
Winds will be stronger when the pressure gradient is greater
What is the prevailing wind direction in the UK?
South-west
What factors impact wave energy?
Fetch (distance travelled over the open sea)
Duration
Strength
How is wind an agent of erosion?
It can pick up and remove sediment from the coast and then use it to erode other features
Most common type of wind erosion is abrasion
How are waves formed?
As the wind blows over the surface of the sea frictional drag leads to the transfer of energy and formation of waves
Why are waves so significant in shaping the coastline?
They can remove and deposit material (lead to the formation of beaches)
Why do waves break?
Waves initially form at sea and have a circular orbit
As waves approach the shore, friction slows down the base of the wave
This causes the orbit to become elliptical until the top of the wave breaks over
Water smashes up the beach
Describe the characteristics of constructive waves
Stronger swash than backwash
Long wavelength
Low wave height
Small frequency
Describe the characteristics of destructive waves
Steep in height
Short in frequency
Short wavelength
Syringe backwash than swash
What kind of beach profile do constructive and destructive waves form?
Constructive - gentle beach profile although over time they will build up the beach and make it steeper
Destructive - steep beach profile with the removal of sediment
How do constructive waves lead to the formation of a berm?
The swash is very strong so sand it carried up the beach and deposited. Over time a berm is formed
Give an example of negative feedback to do with beaches and waves
Where constructive waves build up a beach, eventually the beach profile will become steep which can encourage destructive waves . These waves remove material from the beach and deposit it offshore
This in turn can result in the beach profile becoming less steep, encouraging constructive waves
Over time, dynamic equilibrium is reached
What is wave refraction and how does it occur?
When waves approach a coastline that is indented, they are refracted to become increasingly parallel to the coastline
E.g around a headland the waves meet shallower water first so friction with the seabed slows the headland-approaching waves and causes their frequency to increase
Around bays the opposite happens due to the deeper water and their frequency decreases
What is the overall effect of wave refraction?
The wave energy becomes concentrated onto the headland
This will result in deposition in the bay and erosion of the headland
What are currents?
The permanent or seasonal movement of surface water in the seas and oceans
What are the three main types of current?
Longshore currents (sometimes known as littoral drift)
Rip currents
Upwelling
What are longshore currents?
Occur when waves approach the coastline at an angle. This results in a flow of water (current) running parallel to the shoreline
What are rip currents?
Strong localised underwater currents that occur on some beaches and move water away from the shoreline
They develop when a series of plunging waves cause a temporary build up of water at the top of the beach
Met with resistance from breaking waves, water returning down the beach is forced just below the surface causing an offshore surge of water
What is an upwelling?
The movement of cold water from deep in the ocean to towards the surface
The dense cold water replaces warmer surface water and creates nutrient rich cold ocean currents
Which currents are part of the pattern of the global atmospheric circulation model?
Upwellings
What are tides?
Changes in the water level seas or oceans due to the gravitational pull of the moon and the sun
Where the moon pulls water towards it due to gravity, there is a bulge in the water level and so a high tide
How many high and low tides does the UK coast experience per day?
2 high and 2 low
What is the tidal range?
Relative height difference between the high and low tide
How does the tidal range determine the extent of erosion and deposition?
The tidal range shows the limits of the sea water level so erosion and deposition can only occur in this area
This also determines the amount of time the littoral zone is exposed to weathering
What is a spring tide?
Maximum tidal range
When the Earth, moon and sun are parallel to each other in a line
What is a neap tide?
Minimum tidal range
When the moon is perpendicular to the Earth
What are the coastal sources of sediment?
Rivers (biggest one)
Cliff erosion
Glaciers
Longshore drift
Wind
Offshore sources
What is the coastal sediment budget?
Balance between the sediment being added to and removed from a sediment cell coastal system
What changes to the coastal sediment budget would:
1) Build up the beach
2) Beach retreat
1) Surplus of sediment
2) Sediment deficit
Name all of the erosion processes
Hydraulic action
Wave pounding or quarrying
Corrosion
Abrasion
Solution
Attrition
What is hydraulic action?
When waves break against a rock face, compressing air into the joins in the rock and so weakening the cliff face
What is wave pounding or quarrying?
The impact on rocks of the sheer force of the water from waves exerting pressure upon the rock surface, weakening it and dislodging pieces of
What is corrasion?
The material that the sea picks up (sand and pebbles from the seabed) so when the waves break at the foot of the cliff the transported material is hurled at it and chips away at the rock
What is abrasion?
As waves wash over rocky surfaces the sediment it carries is dragged to and fro so over time it erodes the rock with a ‘sand-papering effect’
What is solution?
Weak acids in the seawater can dissolve alkaline rock (calcium carbonate containing such as limestone). The dissolved minerals can then be removed in solution
What is attrition?
Angular rock fragments are smoothed and reduce in size forming small pebbles, shingle and sand. This occurs due to friction of rocks rolling over each other due to the action of waves and currents
What factors impact the rate of erosion?
Waves (energy, point at which they break)
Fetch
Sea depth
Shape of the coastline
Beach presence
Human activity
Geology (lithology, structure, dip)
What is a concordant coastline?
Where bands of rock lie parallel to the coast
What is a discordant coastline?
Where bands of rock lie perpendicular to the coastline
What is the dip?
Where cliffs have horizontal strata they may dip or slope
This may be a seaward or landward dip
Where rocks have an inland dip, steeper cliffs may form while where rocks have a seaward dip more gently sloping features form
Give an example of a concordant coastline
Lulworth Cove in Dorset
Name the different coastal methods of transportation
Traction
Saltation
Suspension
Solution
What is traction?
Large stones and boulders are rolled along the seabed by seawater. They are too heavy to be picked up and carried so will only move if the is high energy
What is saltation?
Small stones and pebbles bounce along the seabed and beach. As the particles land they may dislodge others on the seabed
What is suspension?
Very small particles of sand and silt are carried along by the moving water within the flow. This is most likely in high energy environments.
Large amounts of suspended load, especially near estuaries, make the water appear murky
What is solution?
Dissolves materials are transported within the mass of moving water
Very important in the carbon cycle
What is longshore drift?
Where smash transports material up the beach from the sea at an angle in the direction of the prevailing wind
The backwash then removes it perpendicular to the shore due to the force of gravity
This results in the movement of sediment in a zig zag pattern along the beach
What is deposition?
When material is dropped by the sea when the velocity of the water or wind falls below a critical value. The larger particles can no longer be transported and so are dropped first
What could be the reasons for deposition?
Opposing currents meeting resulting in turbulence so deposition occurs leg at the end of a spit
Currents weakening / prevailing wind lightening in strength
Friction as waves move over the seabed or with shore land features
Where rivers / land slips add additional sediment to the sea so there is no longer efficient energy to transport the load
What are aeolian processes?
To do with the wind
What are sub-aerial processes?
Land-based processes which occur at the coast such as weathering and mass movement
In freeze-thaw weathering, how much does the water in the rock joints expand by when it freezes?
10% expansion
What are the rock fragments called that collect at the bottom of the cliff?
Scree
Describe weathering by setting and drying
Impacts rocks that are rich in clay
When they become wet the clay expands and when wet it contracts which forms cracks
Over time this causes the rocks to break up, especially if water enters these cracks (makes them more vulnerable to mass movement)
What is a rockfall?
Type of mass movement
Occurs when arch roofs, stacks and cliff faces collapse when the weight becomes unsupportable
Often associated with steep or vertical cliffs (often resistant rock)
Can be initiated by mechanical weathering
Scree forms at the base of the cliff
What is a landslide?
Type of mass movement
Occur on cliffs made up of softer rock which slip due to slope failure
Can be triggered by heavy rainfall which can lubricate less consolidated maters a, e.g boulder clay
What is a mudflow?
Where fine particles of mud flow down the face of cliffs
Often heavily saturated with rainfall which makes it behave more like a liquid
Often sudden and fast flowing
What is a rotational slump?
Type of mass movement
Where softer material overlies much more resistant material
With lubrication due to heavy rainfall whole sections of the cliff face may move downwards along a concave side plane, producing a rotational movement
What is soil creep?
Type of mass movement
Where soil particles on a Hillslope get wet after rainfall so becomes heavier
Less friction due to lubrication from the rain
Soil particles slowly creep downslope, causing trees to bend until the soil dries and stops moving
Slowest form of mass movement
Evidenced by terracettes in the land
Called solifluction in cold environments
