The Coastal System and Coastal Processes Flashcards
What are coasts?
Coasts are systems - they have inputs, outputs, flows and stores of sediment and energy
Eg events such as storm surges give high energy inputs - this can increase sediment inputs or outputs
What are the inputs
Sediment can be brought into the system in various ways
Energy inputs come from wind, waves, tides and currents
What are the outputs
Eg sediment can be washed out to sea, or deposited further along the coast
What are the flows/transfers
Eg processes such as erosion, weathering, transportation, and deposition can move sediment WITHIN the system eg from beach to dune
What are the stores/components
Landforms such as beaches, dunes and spits are stores of sediment
Coastal systems are generally in…
Dynamic equilibrium - inputs and outputs are balanced.
A change in one input or output often causes negative feedback that restore the balance of the system
Coastal systems also experience positive feedback that change the balance of the system, creating a new equilibrium
What is a negative feedback
A negative feedback is when a change in the system causes other changes that have the opposite effect.
For example, as a beach is eroded, the cliffs behind it are exposed to wave attack. Sediment eroded from the cliffs is deposited on the beach, causing it to grow in size again.
What is positive feedback
Coastal systems also experience positive feedback that change the balance of the system, creating a new equilibrium
A positive feedback is when a change in the system causes other changes that have a similar effect.
For example, as a beach starts to form it slows down waves, which can cause more sediment to be deposited, increasing the size of the beach. The new equilibrium is reached when the long term growth of the beach stops.
In a coastal system - how is energy transferred
Energy is transferred by air (as wind) and by water (as waves, tides and currents)
How is wind a source of energy in a coastal system
Winds are created by air moving from areas of high pressure to areas of low pressure. During events such as storms, the pressure gradient (the difference between high and low pressure) is high and winds can be very strong.
Strong winds can generate powerful waves. In some areas, wind consistently blows from the same direction (this is called a prevailing wind) - this causes higher energy waves than winds that change direction frequently.
What is the prevailing wind
Wind that consistently blows from the same direction
Tell me about waves as a source of energy in a coastal system / how they form
Waves are created by the wind blowing over the surface of the sea. The friction between the wind and the surface of the sea gives the water a circular motion.
The effect of a wave on the shore depends on its height. Wave height is affected by the wind speed and the fetch of the wave.
A high wind speed and a long fetch create higher and more powerful waves.
As waves approach the shore they break. Friction with the sea bed slows the bottom of the waves and makes their motion more elliptical. The crest of the wave rises up and then collapses.
Waves in an area are usually mainly constructive or mainly destructive
What is the fetch
The maximum distance of sea the wind has blown over in creating waves
What is the swash
Water rushing up the beach is called the swash
What is the backwash
Water washing back towards the sea is called the backwash
What does the effect of a wave on the shore depend on
It’s height
Wave height is affected by wind speed and fetch - a high wind speed and a long fetch can create higher and more powerful waves
How many types of waves are there
2
Constructive and destructive
Tell me the characteristics of a constructive wave
Constructive waves have a low frequency (around 6-8 waves per minute)
They’re low and long, which gives them a more elliptical cross profile. The powerful swash carries material up the beach and deposits it.
Tell me the characteristics of destructive waves
Destructive waves are high and steep, with a more circular cross profile. They have a higher frequency (10-14 waves a minute) the strong backwash removes material from the beach.
What is wave frequency
How many waves pass a point in a particular time
What are tides (a source of energy) in coastal systems
Tides are the periodic rise and fall of the ocean surface, caused by the gravitational pull of the moon and the sun
Tides affect the position at which waves break on the beach (at high tide they break higher up the shore) the area of land between maximum high tide and minimum low tide is where most landforms are created and destroyed.
What are currents (a source of energy) in the coastal system
A current is the general flow of water in one direction - it can be caused by wind or by variations in water temperatures and salinity.
Currents move material along the coast
What energy can coasts be
Toxic energy 🤢 jk
They can be high energy or low energy
Tell me about high energy coasts
High energy coasts receive high inputs of energy in the form of large, powerful waves. These can be caused by strong winds, long fetches and steeply shelving offshore zones. High energy coastlines tend to have sandy coves and rocky landforms, eg cliffs, caves, stacks and arches. The rate of erosion is often higher than the rate of deposition
Tell me about low energy coasts
Low energy coasts receive low inputs of energy in the form of small, gentle waves. These can be caused by gentle winds (eg sheltered location), short fetches and gently sloping offshore zones. Some coastlines are low energy because there is a reef or island offshore, which protects the coast from the full power of waves. Low energy coastlines often have salt marshes and tidal mudflats. The rate of deposition is often higher than the rate of erosion.
Tell me about sediment sources (potential inputs) into the coastal system
Rivers carry eroded sediment into the coastal system from inland
Sea level rise can flood river valleys, forming estuaries. Sediment in the estuary becomes part of the coastal system
Sediment is eroded from cliffs by waves, weathering and landslides.
Sediment can be formed from the crushed shells of marine organisms
Waves, tides and currents can transport sediment into the coastal zone from offshore deposits eg sandbanks.
What’s the sediment budget
The difference between the amount of sediment that enters the system and the amount that leaves is the sediment budget. If more sediment enters than leaves, it’s a positive sediment budget and overall the coastline builds outwards. If more sediment leaves than enters, its a negative sediment budget and overall the coastline retreats.
What are sediment cells
The coast is divided into sediment cells (also called littoral cells)
These are lengths of coastline (often between two headlands) that are pretty much entirely self contained for the movement of sediment. (Eg sediment doesn’t move between cells). This means that processes going on in one cell don’t affect the movement of sediment in another cell - each cell is a closed coastal system
Where are closed coastal systems
Individual sediment cell is a closed coastal system.
What are the two types of processes that affect the coast
Marine processes and sub-aerial processes
Marine processes are caused by the sea (erosion, transport and deposition) sub-Ariel processes aren’t directly caused by the sea (weathering, run off and mass movement)
Name the six main ways waves erode the coastline
Corrosion (abrasion) Hydraulic action Cavitation Wave quarrying Solution (corrosion) Attrition
What is corrosion also known as
Abrasion
What is solution also known as
Corrosion - notice it’s spelt with o, unlike corrAsion which is also known as abrasion
What is corrasion/abrasion
Bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking buts off and smoothing the surfaces.
What is hydraulic action
Air in cracks in cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces.
What is cavitation
As waves recede, the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off.
What is wave quarrying
The energy of a wave as it breaks against a cliff is enough to detach bits of rock.
What is solution/ corrosion
Soluble rocks (E.g. limestone, chalk) get gradually dissolved by the seawater.
What is attrition
Bits of rock in the water smash against each other and break into smaller bits
What is transportation generally
The process of eroded material being moved.
The energy provided by waves, tides and currents transports eroded material. There are four main processes
List the four main transportation processes
Solution
Suspension
Saltation
Traction
These processes can transport sediment along the shore - this is called long shore drift
What is the transportation process of solution
Substances that can dissolve are carried along in the water. Eg. Limestone is dissolved into water that’s slightly acidic
What’s the transportation process of suspension
Very fine material, such as silt and clay particles, is whipped up by turbulence (erratic swirling of water) and carried along in the water. Most eroded material is transported this way.
What’s the transportation process of saltation
Larger particles, such as pebbles or gravel, are too heavy to be carried in suspension. Instead, the force of the water causes them to bounce along the sea bed.
What is the transportation process of traction
Very large particles, eg. Boulders, are pushed along the sea bed by the force of the water.
What is longshore drift also known as
Littoral drift
What is longshore drift
Swash carries sediment (eg shingle, pebbles) up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline.
When there’s an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash move the sediment along the shoreline.
What simply is deposition
Deposition is the process of dropping eroded material
When material is being transported, it’s dropped on the coast.
What is marine deposition
Marine deposition is when sediment carried by seawater is deposited.
What is aeolian deposition
Aeolian deposition is when the sediment carried by wind is deposited.
What causes deposition
Both marine and aeolian deposition happen when the sediment load exceeds the ability of the water or wind to carry it. This can be because sediment load increases (eg if there’s a landslide), or because wind or water flow slows down (so it has less energy).
Wind and water slow down for similar reasons:
-Friction increases - if waves enter shallow water or wind reaches land, friction between the water/wind and ground surface increases, which slows down the water or wind.
- flow becomes turbulent - if water or wind encounters an obstacle (eg. a current moving in the opposite direction, or an area of vegetation), flow becomes rougher and overall speed decreases .
If the wind drops, wave height, speed and energy will decrease as well.
What is sub-aerial weathering
It’s the gradual break down of rock by agents such as ice, salt, plant roots and acids. Weathering weakens cliffs and makes them more vulnerable to erosion.
What are the 4 types of sub-aerial weathering
Salt weathering Freeze-thaw weathering Wetting and drying Chemical weathering Biological weathering
What is salt weathering
Salt weathering is caused by saline (salty) water.
This saline water enters pores or cracks in rocks at high tide.
As the tide goes out the rocks dry and the water evaporates, forming salt crystals. As the salt crystals form they expand, exerting pressure on the rock - this causes pieces to fall off.
What is freeze thaw weathering
Freeze thaw weathering occurs in areas where temperatures fluctuate above and below freezing.
Water enters the joints and crevices in the rocks.
If the temperature drops below 0 degrees C, the water in the cracks freezes and expands.
Over time, repeated freeze-thaw action weakens the rocks and causes pieces to fall off.
What is wetting and drying
It’s a weathering process
Some rocks contain clay, when clay gets wet, it expands and the pressure caused by this breaks fragments off the rock.
What is chemical weathering
Chemical weathering is the breakdown of rock by changing its chemical composition.
For example, carbon dioxide in the atmosphere dissolves in rainwater, forming a weak carbonic acid. This acid reacts with rocks that contains calcium carbonate, eg. Carboniferous limestone, so the rocks are gradually dissolved.
What is biological weathering
Eg. Plant roots growing into cracks in the rock and widening them - can also cause rocks to breakdown.
What is mass movement
Mass movement simply, is when material moves down a slope.
Mass movement is the shifting of material downhill due to gravity. In coastal areas, it is most likely to occur when cliffs are undercut by wave action - this causes an unsupported overhang, which is likely to collapse.
What are the types of mass movement
Types of mass movement include landslides, slumping (a type of landslide), rockfalls and mudflows. Material can also move gradually downwards by soil creep.
What are slides
Material shifts in a straight line
What are slumps
Material shifts with rotation
What are rock falls
Materials breaks up and falls
What are mudflows
Material flows downslope
How do mass movements happen
Unconsolidated rocks (eg clay) are prone to collapse as there’s little friction between particles to hold them together.
Heavy rain can saturate unconsolidated rock, further reducing friction and making it more likely to collapse
Runoff (the flow of water over the land) can erode fine particles (eg sand and silt) and transport them downslope.
