Coasts 1 - The Coastal system Flashcards
What elements make the coast a system? (4)
- Inputs
- Outputs
- Flows
- Stores of sediment and energy
What are the inputs (Sediment and energy)?
Sediment can be bought into the system in various ways. Energy comes from wind, waves, tides and currents
What are the outputs?
Sediment can be washed out to sea or deposited further along the coast
What are flows and transfers?
Processes like erosion, weathering, transpiration and deposition
What are the stores / components?
Landforms like beaches, sand dunes and spits
What is dynamic equilibrium?
Inputs and outputs are balanced. A change in 1 input or output causes negative feedback that restores balance in the system
What is negative feedback?
A change in a system causes other changes that have the opposite effect
Give an example of negative feedback
As a beach erodes, the cliffs behind it are exposed to wave attack. Sediment eroded from the cliffs are deposited on the beach, causing it to grow in size again
What is positive feedback?
Change the balance of the system creating a new equilibrium
Give an example of positive feedback
Beach begins to form as waves slow down, causes more sediment to be deposited, increasing the size of the beach. The new equilibrium is reached when long term growth of the beach stops
How is energy transferred in the coastal system?
Air and water
How is energy transferred by air?
Wind
How is energy transferred by water?
Waves, tides and currents
How are winds created?
Air moving from areas of high to low pressure
What happens in events like storms?
The pressure gradient is high and winds are strong
What happens when there’s strong winds?
They generate powerful waves, in some areas wind constantly blows from the same direction (PREVAILING WIND) causing higher energy waves than winds that change direction frequently
What’s prevailing wind?
Wind consistently blowing from the same direction
How are waves created?
By the wind blowing over the surface of the sea. The friction between the win and surface of sea gives water the circular motion
What does the effect of the wave on the shore depend on?”
It’s height
What is wave height affected by?
Wind speed and fetch
What is the fetch
The maximum distance of sea the wind gas blown over creating waves
What does a high wind speed and long fetch create?
Higher and more powerful waves
What happens as waves approach the shore?
They break
What does friction with the seabed cause?
Slows the bottom of the waves and makes the motion elliptical. The crest of the wave rises and collapses
What is swash?
Water washing up the beach
What is backwash?
Water washing back towards the sea
What are the 2 types of waves?
Constructive and destructive
What are the characteristics of constructive waves? (4)
- Have a low frequency (6- 8 waves per min)
- Low and long
- Elliptical cross profile
- Powerful swash carries material up the beach and deposits it
What are the characteristics of destructive waves? (4)
- High and steep
- Circular cross profile
- High frequency (10 - 14 waves a min)
- Strong backwash removes material from the beach
What are tides?
Periodic rise and fall of the ocean surface, caused by gravitational pull of the moon and sun
What do tides affect
The position that waves break on the beach. The area of land between maximum high and minimum low is where most landforms are created and destroyed
What is a current
The general flow of water in 1 direction, its caused by wind or variations in water temp and salinity
What do currents do
move material along the coast
What do high energy coasts receive?
High inputs of energy as large powerful waves
What are large powerful waves caused by (3)
- Strong winds
- Long fetches
- Steeply shelving offshore zones
What dob high energy coastlines have and what’s the rate of erosion like
They have sandy coves and rocky landforms. The rate of erosion is higher than that of deposition
What do low - energy coasts receive?
Low inputs of energy in the form of small gentle waves
What are these waves caused by? (3)
- Gentle winds
- Short fetches
- Gently sloping offshore zones
Why are some coastlines low energy?
There’s a reef or island offshore which protects the coast from the full power of the waves
What do low energy coastlines have and what is the rate of erosion like
They have saltmarshes and tidal mudflats.
The rate of deposition is higher than that of erosion
Give 5 inputs of sediment into the coastal system
1) Rivers carry eroded sediment into the coastal system from inland
2) Sea level rise floods river valleys forming estuaries. Sediment in the estuary becomes part of the coastal system
3) Sediment is eroded from cliffs by waves, weathering and landslides
4) Sediment can be formed from the crushed shells of marine organisms
5) Waves, tides and currents transport sediment in the coastal zone from offshore deposits like sand banks
What is sediment budget?
Difference between the amount of sediment that enters and leaves the system
What is a positive sediment budget
When the sediment enters and the coastline builds outwards
What is a negative sediment budget?
When sediment leaves and overall the coastline retreats
How is the coast divided?
Into sediment cells (also called littoral cells)
What are sediment cells
Lengths of coastline (often between b2 headlands) self - contained for the movement of sediment. It means the process going on in 1 cell doesn’t affect movement in other places - each cell is closed.
