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.