✅COASTS 3.1.3.2 - Systems and Processes Flashcards
What are some of the sources of energy in the coastal system?
Wind- blows sediment, makes waves
Waves, Currents, Tides
Rivers
Cliff erosion- especially in areas w/ unconsolidated rock
Calving glaciers
How does the wind provide energy?
Strong winds move across the water surface, creating frictional drag. This creates orbital motion of water particles in waves.
As seabed gets shallower,orbit becomes more elliptical, higher waves, lower length and velocity, causing wave to break
Longer the fetch (distance wind blows) more powerful waves are. So waves are most powerful in storms
Winds with large fetches can transfer more energy
How longshore drift transports sediment?
sediment moves along beach due to prevailing winds,
backwash pushes it back into waves which continue to carry it in direction of prevailing wind, and so on
Can make spits and bars when coastline changes direction
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
More material on and off coastline regularly, great force
What are rip currents?
Powerful underwater currents close to shore when plunging waves cause a build up of water at the top of the beach. Backwash forced under surface due to resistance of the breaking waves. Makes current. Gap in sandbar can make them faster.
In Holderness coast, rip currents hasten erosion
What are upwelling currents
Movement of cold water from deep in ocean towards the surface due to convection currents. The dense cold water replaces the warmer surface water creating currents. Vital part of global circulation pattern.
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
What are tides?
Periodic rise and fall of the sea level due to gravitational pull from sun & moon. Goes from high to low twice a day.
What is spring tide?
Biggest tidal range. When sun and earth are in alignment.
What is neap tide?
Smallest tidal range. When sun and moon are at 90 degrees.
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
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 height with long wavelength
Strong swash
Common on gently sloped beaches
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
Common on steep beaches
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, (erosional land forms)
What are low energy coastlines like?
Sandy, estuarine and where waves are less powerful as the coast is sheltered (deposition)
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 land forms tend to be on low energy coasts?
Beaches, spits and coastal plains
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 factors determine mass movement?
Slope, saturation, sediment size, unconsolidated or not
Examples of mass movement
Landslides- rain lubricates, causes sliding
Rockfalls- from undercut cliffs
runoff
Rational slipping/ slumping- soft permeable rock slips off impermeable rock
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
Examples of biological weathering
algae secreting chemicals promoting solution
animals burrowing into cliffs
What is chemical weathering?
Involves chemical reactions dissolving the rocks such as through acid rain, oxidation and solution
Examples of chemical weathering
solution, oxidation, carbonation, hydration (water in rock causes rock to expand, weaken)
What is mechanical/physical weathering?
The breakup of rocks without ant chemical changes taking place, such as via freeze thaw or salt crystallisation
Examples of mechanical/physical weathering
freeze thaw- water enters rock, freezes, expands by about 10%, cracks rock
pressure release- when overlying material is removed, rock beneath experiences a pressure relief, weakness occurs, cracking rock
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
Positive feedback: spits
spit extends across estuary > slows river velocity > deposition > further flowing of the river
Positive feedback: sea level rise
SLR > more water in contact w/ice > more melting > SLR
Negative feedback: mass movement
cliff erosion/ undercutting > mass movement > sediment deposition at base of cliff > sediment takes time to be eroded, rate of erosion temporarily slowed
Negative feedback: LSD
cliff erosion from LSD > groynes installed > prevents LSD > prevents output of sediment > forms wider beach > beach absorbs more wave energy > reduces cliff erosion
Negative feedback: mangroves
Coastal erosion/ flooding > plant mangroves > reduced wave energy > waves deposit sediment due to larger beach > waves slow > less erosion
