COASTAL SYSTEMS AND LANDSCAPES CGP - The Coastal System Flashcards
What type of system are coasts?
Open systems - inputs and outputs of matter and energy.
Coast inputs
Sediment brought into system. Energy inputs come form wind, waves, tides and currents.
Coast outputs
Sediment can be washed out to sea, or deposited further along the coast.
Coast flows/transfers
Processes such as erosion, weathering, transportation and deposition can move sediment within system (e.g. from beach to dunes).
Coast stores/components
Landforms such as beaches, dunes and spits are stores of sediment.
What are coasts generally in?
Dynamic equilibrium - inputs and outputs are balanced.
Change in input or output often cause what that restores the balance of the system?
Negative feedbacks
Negative feedback in coastal systems and example
When a change in system causes other changes that have the opposite effect so effects of action are nullified. Restore balance of freedom. E.g. beach eroded, cliffs behind exposed to wave attack. Sediment eroded from cliffs deposited on beach, causing it to grow in size again.
Positive feedback in coastal system and example
When a change in the system causes other changes that have a similar effect so effect of change is amplified. Create new equilibrium. E.g. as beach stats to form it slows waves down, causes more sediment to be deposited, increasing beach size. New equilibrium reached when long-term growth of beach stops.
How is energy in coastal system transferred?
Air (as wind) and water (as waves, tides and currents).
How are winds created?
By air moving from areas of high pressure to areas of low pressure.
Why in events such as storms can winds be very strong?
The pressure gradient (difference between high and low pressure) is high.
What can strong winds generate?
Powerful waves
What is prevailing wind and what does this cause?
When wind consistently blows from the same direction. Causes higher-energy waves than winds that change direction frequently.
How are waves created? What gives it circular motion?
By wind blowing over surface of sea. friction between wind and surface of sea gives water circular motion.
What does the effect of a wave on the shore depend on?
Its height.
What is wave height affected by?
Wind speed and fetch of wave.
What is fetch?
Maximum distance of sea the wind has blown over in creating waves.
What creates higher and more powerful waves?
A heigh wind speed and a longer fetch.
What happens to waves as they approach the shore?
They break
How do waves break?
Friction with sea bed slows bottom of waves and makes motion more elliptical (squashed and oval shaped). Crest of wave is moving faster than bottom so rises up and collapses.
What is water washing up on the beach called?
Swash
WHat is water washing back to sea called?
Backwash
What are the two types of waves called?
Constructive waves and destructive waves.
Constructive waves
Low frequency (6-8 waves a min)
Low and long (gives more elliptical cross profile)
Weak backwash, powerful swash
Powerful swash carries material up beach and deposits it
Destructive waves
High and steep with more circular cross profile
Higher frequency (10-14 waves a min)
Weak swash
Strong backwash removes material from beach
Wave frequency
How many waves pass a point in a particular time
What are tides? Cause?
The periodic rise and fall of the oceans surface. Caused by gravitational pull of moon and sun.
What do tides affect?
The position at which waves break on the beach (at high tide break higher up shore).
The area of land between maximum high tide and minimum low tide is…
…where most landforms are created and destroyed.
What is a current?
The general flow of water in one direction.
What can currents be caused by?
Wind or by variations in water temperature and salinity.
What do currents do?
Move material along the coast.
Two types of coastlines
Higher energy and low energy.
In what form do high-energy coastlines receive high inputs of energy? Caused by?
From large, powerful waves. Caused by strong winds, long fetches and steeply shelving offshore zones.
What do high-energy coastlines tend to be like?
Have sandy coves and rocky landforms e.g. cliffs, caves, stacks and arches.
High energy coastline erosion and deposition
Rate of erosion higher than rate of deposition.
In what form do low-energy coastlines receive high inputs of energy? Caused by?
From small, genital waves. Caused by gentle winds (e.g. if location is sheltered), short fetches and gently sloping offshore zones. Some coastlines low energy because reef or island offshore protects coast from full power of waves.
What do low energy coastlines tend to be like?
Often have salt marshes and tidal mudflats.
Low-energy coastline deposition and erosion
Rate of deposition often higher than rate of erosion.
Inputs of sediment into coastal system
From: rivers, estuaries, cliff, shells, offshore deposits
How are rivers input of sediment?
Carry eroded sediment into coastal system from inland.
How are estuaries input of editing to coastal system?
Sea level rise can flood river values, forming estuaries. Sediment in estuary becomes part of coastal system.
Cliffs as sediment input?
Sediment eroded from cliffs by waves, weathering ad landslides.
Shells as input of sediment?
Sediment can be formed from the crushed shells of marine organisms.
Offshore deposits as input of sediment?
Waves, tides and currents transport sediment into coastal zone from offshore deposits e.g. sandbanks.
Sediment budget
The difference between the amount of sediment that enters the system and the amount of sediment that leaves the system.
What happens is more sediment enters than leaves a system?
Positive sediment budget and overall coastline builds outwards.
WHat happens if more sediment leaves system than enters?
Negative sediment budget and overall coastline retreats.
What is coast divided into?
Sediment cells (littoral cells).
What are sediment cells?
Lengths of coastline (often between two headlands) that are pretty much entirely self contained for the movement of sediment (i.e. sediment doesn’t move between cells).
What type of system is sediment cell and why?
Closed coastal system because processes going on in one cell don’t affect the movement of sediment in another cell.
