The Coastal System Flashcards
What is the coast?
The coastal zone is an area where interaction of marine, terrestrial and atmospheric processes occurs.
6 reasons why coasts are important?
- Settlements (coastal erosion)
- Employment
- Resources
- Transport
- Tourism
- Flooding
4 reasons why coasts change over time
- Waves/energy
- Tides
- Coastal management
- Sea level rise
What is temporal variation
Change over time e.g. Winter storms
What are 4 components that all open systems are made up of?
- Inputs
- Outputs
- Processes
- Stores
Name 4 processes of an open coastal system
- Erosion
- Transport
- Weathering
- Deposition
Name 4 stores of an open coastal system
- Beach
- Bar
- Sand dunes
- Spits
Name 5 outputs of an open coastal system
- Sediment via submarine canyons
- Wavecut platform (erosional)
- Energy loss
- Cliffs (erosional)
- Stacks (erosional)
Name 5 inputs of an open coastal system
- Currents (energy)
- Winds (energy)
- Waves (energy)
- Tides (energy)
- Sediment from cliffs rivers and offshore
Define backshore
The furthest inland that the sea ever gets to e.g. Cliffs
Define foreshore
Between high tide line and low tide line
Define nearshore/inshore
Between the low tide line and the point where waves do not affect the sea bed
Define offshore
Beyond where waves have an effect on the sea bed
What is a wave?
A disturbance that travels through the sea from one location to another
How are waves formed?
Wind blows over the water surface. The upper layer of air sinks and friction pushes down on the surface of the water creating waves.
Why do waves break?
As the beach gets more shallow, friction slows down the bottom of the wave.
The top overtakes the bottom.
This caused the wave to rise up and eventually topple over in the surf zone.
What are the 4 factors that influence wave size?
- Wind speed
- Distance of open water that wind blows over (fetch)
- Time/duration the wind has blown over a given area
- Water depth
How does wind speed increase wave size?
The faster the wind speed, the larger the waves because more pressure is pushing down on the water surface.
How does fetch influence wave size?
The waves have a longer distance to form so they can be bigger.
How does time exposed to wind influence wave size?
The waves have a longer time to form and therefore can be bigger.
How does water depth influence wave size?
A larger depth means larger waves as there’s more water to make waves from.
Swell waves
(from distant storms)
They travel long distances, are less steep, have a longer wavelength, and longer wave period.
Usually constructive
Sea waves
(from local winds)
Don’t travel very far, steep, they have a short wavelength and short wave period.
Usually destructive
Define wavelength
The distance between two successive crests or troughs
Define wave period
The time in seconds between two successive crests or troughs
Define wave frequency
The number of waves per minute
Define wave height
The distance between the trough and the crest
Define fetch
The amount of open water over which a wave has passed
Define velocity
The speed a wave travels at and is influenced by wind, fetch, and depth of water
Define swash
The movement of water up the beach
Define backwash
The movement of water down the beach
Characteristics of a destructive wave (winter)
Destroys beach as backwash is stronger than swash.
Net erosional waves Called surging,storm,plunging waves Short wavelength, high frequency (10-12/min) Circular orbit, high height Low period (one every 5-6/ sec) Beach has a steep gradient
Characteristics of a constructive wave (summer)
Builds up the beach as swash is greater than backwash
Net depositional waves Called spilling,swell waves Long wavelength, low frequency (6-8/ min) Low height, elliptical orbit High Period (one every 8-10/sec) Beach has a low gradient
How does water move in waves?
Water particles do not actually move far.
They move in circles as the wave passes through. It is the energy that moves.
Below the wave base, there is no sensation of the waves moving.
What is wave refraction and how is it caused?
Where orthogonals (wave fronts) are modified/ they bend.
Cause: changing depth in water. The wave base interacts with the sea bed.
How is an erosional environment created from wave refraction?
An erosional environment is created due to the wave energy converging/ focusing.
Sediment is eroded from the headland and is moved to quiet beaches.
How can a depositional environment be caused by wave refraction?
A depositional environment is created when the energy on the waves is dissipating/diverging, because the waves have the same amount of energy, but it is spread over a longer stretch of beach.
Sediment from headlands collects on quiet beaches.
Positive feedback
Positive feedback pushes a coastal system away from equilibrium by modifying its morphology until a threshold is reached, whereby a different type of response occurs.
Negative feedback
Negative feedback is a stabilising mechanism acting to oppose changes to coastal morphology and establish equilibrium. A coastal environment in equilibrium is able to dissipate or reflect incoming energy without the occurrence of sediment input or output and change to morphology.
Define sediment cell
A section of coastline where movements of sediment are largely self contained.
Give two examples of sediment cell boundaries
Large estuaries
Prominent headlands
Explain longshore drift
Swash moves sediment up the beach at the angle of the prevailing wind direction.
Backwash carries sediment straight back down the beach due to gravity.
This keeps going until the sediment is stopped by natural breakwater or a groyne.
Define tidal range
The difference in vertical height between high and low tide
What are tides caused by?
Tides are caused by the combined effects of the gravitational forces exerted by the sun and moon
How many rides to places around the world experience?
Most places in ocean usually experience two high tides and two low tides each day (semidiurnal tide).
Some locations experience only one high tide each day (diurnal ride).
What are the times and amplitudes of the tides influences by?
They are influenced by the alignment of the sun and moon, by the pattern of the tides in the deep ocean and by the shape of the coastline.
What are spring tides and when do they occur?
Spring tides happen just after every full and new moon, when the sun, moon and earth are in line. That’s when lunar and solar tides line up and reinforce each other.
What are neap tides and when do they occur?
Neap tides occur when the moon is in the first or third quarter (when the sun, earth and moon form a right angle). The lunar high tide coincides with the solar low tide and they partly cancel out giving a small total tide.
What is an amphidromic point?
A place with no tide
What is a tidal bore?
If the tide comes into an estuary/river it gets funnelled and can produce a wave called a tidal bore. E.g., river Severn
Why are tides symmetrical?
Because you need to have equilibrium on both sides of earth
Why does the moon have a stronger affect on the tide?
It has a stronger gravitational pull as it is closer to earth
Why are there different tide times around Britain?
The shape of the coastline and the bathymetry (water depth) result in different tide times.
