🏖️3.1.3.2 - Systems and Processes Flashcards
What are some of the sources of energy in the coastal system?
Wind
Waves
Currents
Tides
How does the wind provide energy?
Strong winds move the water surface and create waves
Winds with large fetches can transfer more energy
How do waves provide energy?
Waves have powerful errosive energy, can destroy features
Moves sediment around, creates as well as destroys
How do currents provide energy?
Can move sediment on the sea floor
How do tides provide energy?
Moves sediment up the beach and down again, carries material
Dictates where waves can get to, location of the energy
How does the sun provide energy?
It causes differences in air pressure due to different rates of heating, when then creates wind
How is wind energy formed?
By air moving between areas of different pressure
How are powerful winds created?
The greater the difference in air pressure gradient, the faster the wind speed and the more powerful
What are the factors impacting the size of waves?
Strength of the wind
The fetch
Duration of the wind
How does wind strength impact waves?
The stronger the wind, the more power and energy the waves have and so the more powerful and potentially destructive they are.
What are some terrestrial features affecting the coastal system?
Tectonics
Sediment supply
Sub aerial processes
Fluvial processes
What are some marine features affecting the coastal system?
Wave shape/size Fetch Wave direction Tides Sea level change
What are some human features affecting the coastal system?
Development Sea defences Tourism and recreation Pollution Global Warming Conservation
What are some atmospheric features affecting the coastal system?
Winds Temperature Precipitation Solar energy Glaciation
How are waves formed?
By energy passing through the water, causing it to move in a circular motion
What do waves transmit?
Energy, not water
What are wind driven waves caused by?
Frictional drag between the wind and the surface water
How do waves change as they approach the shore?
Disturbance to the circular motion beneath the surface leads to a more horizontal movement and the wave breaks
What are the features of constructive waves?
Add material to coastline
Low wave with long wavelength
Strong swash
What are the features of destructive waves?
Tall in relation to length Remove material from coastline Common in winter Strong backwash Never reach the backshore Causes cliff face erosion
What are orthogonals?
Lines of wave energy
What are high energy coastlines like?
Rocky, ocean facing coasts where waves are powerful
What types of landforms tend to be on high energy coasts?
Wave cut platforms and headlands
What are low energy coastlines like?
Sandy, estuarine and where waves are less powerful as the coast is sheltered
How do rates of deposition and erosion compare at high energy stretches of coast?
Rate of erosion exceeds rate of deposition
How do rates of deposition and erosion compare at low energy stretches of coast?
Rate of deposition exceeds rate of erosion
What types of landforms tend to be on low energy coasts?
Beaches, spits and coastal plains
What is a sediment cell?
A stretch of coastline within which sediment movement is more or less contained
What are sediment cells usually bordered by?
2 large headlands
What can sediment cells be further subdivided into?
Sediment subcells
What are some example sources of sediment?
Rivers
Cliff erosion
Offshore sediment
Wind
How do rivers act as a source of sediment?
Fluvial sediment often accounts for the vast majority of coastal sediment as it is deposited in the river mouths and estuaries, where it is reworked by waves, tides and currents
How does cliff erosion act as a source of sediment?
Can be extremely important locally in areas with soft rock where sand and clay are easily eroded
How does offshore sediment act as a source of sediment?
Can be transferred into the coastal zone by waves, tides and currents. When sea levels rose at end of last ice age, large amounts of coarse sediment was moved to South coast and formed landforms
How does wind act as a source of sediment?
In glacial or hot environments, wind blown sand can be deposited in coastal regions. Sand dunes are semi dynamic features at the coast that represent both accumulation of sand and potential sources
What might dictate the amount of sediment input into a sediment cell at any given time?
The amount of rainfall, and therefore fluvial sediment
Destructive/constructive waves
Season
Amount of weathering
How does water depth affect wave refraction?
As water depth decreases, there is a reduction in wave velocity and the waves are bent towards that part of the shoreline where they are moving most slowly
How do headlands affect wave refraction?
The higher relief and therefore shallower water off the headlands slows the approaching wave.
Wave crests converge onto headlands, increasing the energy released by the breaking wave in the bay
What happens to the energy where orthogonals diverge?
The energy per unit wave crest decreases
What are processes which shape the coast?
Chemical/Physical weathering Deposition Erosion Mass movement events Transfer processes
What are some marine processes?
Transportation, erosion and deposition
What are some sub-ariel processes?
Weathering, mass movement
What is traction?
Large particles like boulders are pushed along the sea bed by the force of water
What is suspension?
Small particles like silt and clay are carried along in the water
What is saltation?
Pebble sized particles are bounced along the sea bed by the force of the water
What is solution?
Soluble materials dissolve in the water and are carried along
How does a high energy coast affect transportation?
Small particles easily transported whilst larger and heavier material is deposited. Shingle beaches formed
How does a low energy coast affect transportation?
Even the smallest material is deposited forming mudflats and salt marshes
What is hydraulic action?
Refers to the impact on rocks of the sheer force of the water. This can exert enormous pressure upon the rock
What is wave quarrying?
A braking wave traps air as it hits a cliff face. The air is compressed into any gaps causing huge pressures. As the water retreats there is an explosive effect of the air pressure being released
What is abrasion/corrosion?
Eroded material being thrown against the rock by the waves. Also conducts erosion of wave cut platforms due to movement of material back and forth
What is attrition?
Rocks which are carrying out abrasion are slowly worn down into smaller and rounder particles
What is a concordant coastline?
Rocks on these coastlines run parallel to the sea
What is a discordant coastline?
Rocks on these coastlines run perpendicular to the sea
What is a cliff profile?
The gradient of the cliff face, responsible for whether the cliff has a steep gradient
What are factors influencing the rate of cliff retreat?
Rock type, geographical location and climate/season
What is biological weathering?
The breakdown of rocks by organic activity, such as by plant roots and water running through decaying vegetation
What is chemical weathering?
Involves chemical reactions dissolving the rocks such as through acid rain, oxidation and solution
What is mechanical/physical weathering?
The breakup of rocks without ant chemical changes taking place, such as via freeze thaw or salt crystallisation
What features do cliffs with horizontal bedding planes have?
A stable profile with a steep cliff face
What features do cliffs with downward tilted bedding planes have?
Very stable with slow rates of erosion as the cliff is supported by deeper running strata
What features do cliffs with upward tilted bedding planes have?
A cliff profile similar to the angle of the tilt and frequent mass movements when the base of the cliff is eroded
What features do cliffs with weathering joints have?
Very vulnerable to erosion as gravitational pull is created and cracks make them fragile
What are the 4 sources of energy in the coastal system?
Wind
Waves
Currents
Tides
Wind: When is wave energy likely to be higher?
When wind speeds are greater
Wind: How are waves created?
Wind transfers energy when it blows over the sea surface due to friction
Fetch
Distance of open water over which wind blows uninterrupted by major obstacles
Determines the magnitude and energy of waves
Waves: What happens as they reach the coast?
Approach shallower water
Sea bed friction increases so base of the wave slows down
Increases wave height and steepness
Until upper part of the wave plunges forward
Waves: Constructive wave characteristics
Low frequency (6-8 a min)
Low wave height and long length (up to 100m)
Swash > backwash, as there’s insufficient energy to pull sediment off the beach
Material slowly but constantly moved up the beach (ridges)
Waves: Destructive wave characteristics
High frequency (10-14 a min)
High wave height and short length
Backwash > swash, material pulled down beach, wave’s force can project shingle to back of beach (storm beach)
Little material moved up the beach
Strong backwash inhibits swash of next wave
Waves: Link between constructive and destructive waves
Constructive waves build up beaches
Steeper profiles
Encourages destructive waves to erode
Shallower profiles
Encourages constructive waves etc
Waves: Wave Refraction
Occurs when waves approach an irregularly shaped coastline
Near shore, slow down due to friction
Parts of the wave that haven’t reached shore bend- travel faster
Energy focused on headland- increasing erosion
Waves reaching the bay have less energy, so deposit material
Currents: Current
The permanent or seasonal movement of surface water in the seas and oceans
Currents: 3 types of current
Longshore Current
Rip Currents
Upwelling
Currents: Longshore Current
Occurs when waves have an angled approach to the coastline
Transports sediment
Currents: Rip Currents
Strong currents moving away from the shoreline
Develop when sea water is piled up along the coastline by incoming waves
Currents: Upwelling
. Movement of cold water from deep in oceans to the surface
. More dense, cooler water replaces warmer surface water, creating nutrient rich cold ocean currents
Tides: Tides
The periodic rise and fall in the level of the sea, caused by the pull of the sun and moon
Tides: Why does the moon have a greater influence on tides than the sun?
Because it’s closer to the Earth
Tides: Spring Tide
Highest monthly tidal range, as sun and moon are aligned so greater force
Tides: Neap Tide
Lowest monthly tidal range where sun is perpendicular to moon, with tides between 10-30% lower than average
Tides: What 2 factors do they determine?
Upper and lower limits of erosion and deposition
Amount of time each day the shoreline is exposed to sub aerial weathering
Tides: What causes tidal (storm) surges? What makes them worse?
They occur when meteorological conditions give rise to strong winds, producing much higher water levels than high tide, increasing erosion in the short term
They are worsened by spring tides
Low Energy Coast
A coastline where wave energy is low and the rate of deposition exceeds the rate of erosion
Contains depositional features
i.e. Baltic Sea
High Energy Coast
A coastline where strong, steady prevailing winds create high energy waves, so the rate of erosion exceeds the rate of deposition
Contains erosional features
i.e. North Cornish Coast
Sources of sediment
Offshore sand banks
Cliff erosion
Shells and coral fragments
Fluvial sources
Sediment Cell
A distinct area of coastline separated from another by a well-defined boundary like a headland or stretch of deep water
Coastal Sediment Budget
Balance between sediment being added and removed from the system
Sediment Surplus
A positive budget where more material is added than removed
Shoreline extends seaward
Sediment Deficit
A negative budget where more material is removed than added
Shoreline retreats landward
Marine Process
Operates upon the coastline and is connected with the sea
Waves, tides, LSD
Aeolian Process
Transport or deposition of sediment by wind
Transport or deposition of sediment by wind
Operates on land and affects the shape of the coastline
Abrasion
Sand, shingle in water grinding down the cliff face
Wave Quarrying
Air forced into cracks under high pressure when a wave impacts a cliff face
Widens them
Cracks grow over time, destabilising the cliff
Cavitation
Compression of air causes sea water to be compressed in crack
Air fizzes out of water due to reduced pressure when the wave recedes
Enlarges fissures with in the joints
Hydraulic Action
Impact of the waters’ sheer force on the rocks
Puts pressure on them so they weaken
Attrition
Rocks carrying out abrasion are warn down
Become smaller and rounder
Solution
Dissolving of calcium based rocks in acidic water
Acidity caused by dissolved CO2
Marine Processes of Erosion
Abrasion
Wave quarrying
Cavitation
Hydraulic action
Attrition
Solution
Marine Processes of Transportation
Traction
Saltation
Suspension
Solution
Why does Marine Deposition occur?
Abundant supply of material
Waves lose energy -decreased velocity -decreased volume of water
Aeolian Processes of Transportation
Surface Creep
Saltation
Surface Creep
Wind rolls grains along the surface
Saltation
Fine particles lifted into the air and drift horizontally
Sub Aerial Processes of Erosion
Mechanical weathering
Biological weathering
Chemical weathering
Example of Mechanical Weathering
Frost shattering
Example of Biological Weathering
Seaweed- roots bury into rocks, exploit cracks
Rabbits burrow- exploit cracks
Examples of Chemical Weathering
Oxidation (dissolved O2 reacts with minerals)
Carbonation (acid rain dissolving minerals)
Hydration
Discordant Coastline
Perpendicular to bands of rock
Concordant Coastline
Parallel to bands of rock
Examples of resistant rock
Granite
Chalk
Examples of less resistant rock
Limestone
Landslide key points
Cliffs (steep) made of softer rock
Failure lubricated- often after heavy rainfall
Mass moves downslope in straight line, fractures into smaller pieces at the foot
Rockfall key points
Near vertical slope
Caused by freeze thaw weathering or undercutting in the intertidal zone
Resistant rock breaks up and falls in small chunks
Mudflow key points
Soil saturated
Excess water can’t percolate deeper, layers become fluid and flow downhill
Caused by prolonged heavy rainfall
Soft rock i.e. boulder clay
Rotational Slump key points
Softer material overlies harder material
Marine processes erode and undermine base
Saturated clay slips along plane
Moves with rotation
Soil Creep key points
Continuous movement of individual soil particles downslope
1 cm a year, slope bigger than 5 degrees
Caused by: freeze thaw -repeated expansion and contraction
