The Coastal Zone

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  • Created by: AlaiaM
  • Created on: 04-05-14 19:13
What is the coast?
The narrow contact zone between the land and sea
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What factors affect the coast?
Waves, currents, local geology, changes in sea level, human activity
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What is wavelength?
The distance between two successive waves or troughs
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What is wave frequency?
The number of waves per minute
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What is wave height/amplitude?
The distance between the trough and the crest
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What is the fetch?
The amount of open water over which a wave has passed or the amount the wind blows over the sea to create a wave
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What is velocity?
The speed of a travelling wave
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What influences velocity?
Wind, fetch, depth of water
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What is swash?
The movement of water up the beach
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What is backwash?
The movement of water down the beach
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How are waves formed?
Friction between wind and sea surface
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What is a wave?
A forward moving surge of energy
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Characteristics of constructive waves?
build the beach, usually on a sandy beach with a shallow gradient, has an elliptical orbit, long wavelength, low height, strong swash, weak backwash, formed by a faraway storm, long fetch, far apart, powerful, surging, good to surf on
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Characteristics of destructive waves?
destroy the beach, usually on a shingle beach with a steep gradient, have a circular orbit, short wavelength, high height, weak swash, strong backwash, caused by a near storm, a short fetch, close together, chaotic, crashing, not good for surfing
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What causes a wave to break?
The seabed interrupts the circular orbit of water and as there is less water the orbit becomes more elliptical causing the wave crest to rise until it breaks and falls down onto the beach
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Why are larger pebbles found further up on the beach?
Swash carries the sediment up the beach but due to being absorbed by sand and shingle there is less water and wave energy to carry the sediment back down the beach
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What are land processes that shape our coastline?
human activity, sub aerial processes, weathering, biotic factors
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What are the marine processes that shape our coastline?
abrasion, corrasion, hydraulic pressure, solution, currents, wave pounding, attriction
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What are biotic factors?
The burrowing and browsing of organisms
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What are sub aerial processes?
Surface runoff, rain wash, weathering, land slides
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What are currents generated by?
Waves and tides
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What is hydraulic action
When a wave hits a cliff face any air trapped in cracks in put under great pressure. When the wave retreats the build up of pressure is released with an explosive force that weakens the cliff face
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What is corrasion?
Fragments of rock are hurled at a cliff by the sea
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What is abrasion?
The 'sandpapering' effect of pebbles grinding over a rocky platform until it becomes smooth
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What is attrition?
Rock fragments carried by the sea knock against each other and make each other smaller and smoother
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What is solution? (The erosion process)
Rocks such as limestone and chalk contain calcium carbonate that dissolves in the slightly acidic sea water
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What is solution? (The transport process)
Soluble minerals are dissolved in sea water and carried in solution. The load is not visible.
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What is suspension?
Small particles carried in water, this can make the water look cloudy.
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What is saltation?
Load is bounced along sea bed
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What is traction?
Larger sediment is rolled along the sea bed by the force of water
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What is longshore drift?
The waves come up the beach at the angle of the prevailing wind and drain down at a right angle to the sea due to gravity. The beach moves in the direction of longshore drift and the material gets smaller as waves move sediment.
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What is weathering?
The breakdown of rocks in situ (without movement)
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What is mechanical weathering?
Freeze thaw - pourous or permeable rocks get saturated with water which freezes and expands which weakens and cracks the rock
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What is chemical weathering?
Carbonation and solution - alkali rocks contain calcium carbonate which reatcs with rain that is acidic due to having dissolved carbon dioxide in it which has formed a weak carbonate acid. The reaction forms calcium bicarbonate which is soluble.
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What is mass movement?
The downhill movement of material under the influence of gravity. Can include rockfalls, landslides, mudflows and rotational slips. Results in cliff collapse.
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Why are cliffs prone to collapse?
Made of weak rock (easily eroded). Permeable sands on top of impermeable clay means water 'ponds' in cliff. Buildings on cliff add weight. Streams around cliff make it heavier. Faces south-west winds, a long fetch with powerful waves for erosion.
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Cliff collapse in Barton-on-sea?
Due to five previous reasons, in 10-20 years a housing development 20 metres from edge of sea will be lost.
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What is rockfall?
Fragments of rock break away from cliff face
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What is landslide?
Blocks of rock slide downhill
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What is mudflow?
Saturated soil and weak rocks flow down a slope
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What is rotational slip?
A slump of saturated soil and weak rock along a curved surface
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How do bays and headlands form?
Softer, less resistance rock is eroded to form a bay but harder more resistant rock on either side is not eroded as easily so forms a headland
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How is a cove formed?
A strip of soft rock behind a strip of hard rock. There is a weakness in the hard rock which enables it to be eroded so that the waves can reach the soft rock and erode it to form a cove
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What is headland erosion?
Weaknesses on a headland form a crack and then a cave. Hydraulic action and abrasion continue until two back to back caves meet to form an arch. The arch gets bigger until the roof collapses, forming a stack. The stack is weathered to make a stump.
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What is a cave?
A hollow at the base of a cliff in a headland
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What is an arch?
A hollow in a headland that goes all the way through the base. The rock at the top is called a keystone.
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What is a stack?
A pillar of rock no longer connected to a headland
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What is a stump?
a short column of rock, a shorter version of a stack
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What is a cliff?
A bare face of rock by the sea
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What facts affect cliffs?
coastal erosion, strength of rock, presence of joints and bedding planes
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How do you form a wave cut platform?
Waves break against a cliff and form a wave cut notch. Erosion continues until the notch is so deep the overhanging cliff collapses. The material at the base is further eroded to form a wave cut platform.
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Properties of clay?
grey/brown colour, gets soft and heavier when wet, small pieces when dry, one smooth chunk when wet
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Properties of chalk?
white colour, quite strong but easily eroded as has lines of weakness, very alkaline so reacts strongly with acid rain
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Hard coastal engineering strategies?
rock armour, sea wall, groynes
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Soft coastal engineering strategies?
dune regeneration, marsh creation, managed retreat, beach nourishment/replenishment
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What is rock armour (rip-rap)?
Piles of large boulders dumped at cliff foot which force waves to break and absorb their energy, therefore protecting the coast.
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Advantages and disadvantages of rock armour?
cheap and easy to maintain, provides visual interest, rocks expensive to transport, do not always fit in with local geology, can be obtrusive
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What is a sea wall?
Concrete or rock barrier at foot of cliff or top of beach. Has a curved face to reflect waves back into sea. Usually 3-5 metres high.
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Advantages and disadvantages of a sea wall?
effective, can have walkway or promenade for tourists, can be obtrusive, very expensive and high maintenance costs
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What is a groyne?
Timber or rock structure built out at sea that traps sediment moved by longshore drift so creates a larger beach that acts as a buffer for incoming waves
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Advantages and disadvantages of groynes?
Bigger beach, useful fishing structure, not too expensive, problem shifted instead of solved, unattractive
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What is beach nourishment?
Addition of sand or shingle to beach to make it higher and broader
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Advantages and disadvantages of beach nourishment?
cheap and easy to maintain, blends in with existing beach, creates bigger beach, needs constant maintenance
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What is dune regeneration?
sand dunes are effective buffers to sea but are easily damaged so marram grass is planted to stabalise them and help the develop. They can also be fenced off.
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Advantages and disadvantages of dune regeneration?
Maintains a natural coastal environment, cheap, time consuming, people do not like being restricted from areas, can be damaged by storms
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What is marsh creation?
The sea is allowed to flow into low lying coastal areas to form a salt marsh as a buffer to the sea
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Advantages and disadvantages of marsh creation?
cheap, creates a habitat for wildlife, land lost, farmers need compensation
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What is managed retreat?
Coastline is retreated
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Advantages and disadvantages of managed retreat?
cheap, land lost, farmers need compensation
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What is a beach?
A gently sloping area of land between the high and low water marks, sand beaches slope gently to sea, shingle beaches have steep gradients with ridges
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What is a berm?
The ridges in shingle beaches, mark where the tide has come up to
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How are beaches formed?
Wave deposition and longshore drift carry material to and from beach
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Where are sandy beaches formed?
Sheltered bays where wave energy is reduced by wwave refraction
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Where are shingle beaches formed?
Where cliff erosion rate is high and there are higher energy waves to carry larger pebbles
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What is a spit?
A beach of sand or shingle linked at one end to land
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Where are spits found?
Indented coastlines or at river mouths
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How is a spit formed?
longshore drift moves beyond a steep curve in coastline and spit is formed where material is deposited. Hooks may occur is wind direction changed further out. Waves cannot get beyond spit so is a sheltered area with mud flats and salt marshes.
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What is a bar?
A ridge that blocks off a bay or river mouth
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How is a bar formed?
same as spit but deposition continues across an entrance until water is trapped. Occurs when river flow is not fast enough to push deposited material out of the way. Can move onshore due to sea level rise.
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What is a tombolo?
Where a feature links land to an island
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What is wave refraction?
When waves enter a bay and change their shape to mirror the shape of the coastline they are going to hit as water gets shallower when it enters the bay.
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How is a bay head beach formed?
Wave refraction spreads out and reduces wave energy so deposition occurs and a beach is formed
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What is the difference between a bar and a barrier beach?
A bar is newly formed by longshore drift but a barrier beach is made when an offshore bar is driven onshore due to sea level rise.
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Essex marshes uses?
wildlife habitats, marine life, bird feeding, marsh plant communities
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Threats to Essex marshes?
2500 hectares remain of 30,000 hectares in 1600, accelerated coastal erosion
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Essex marsh conservation strategies?
flooding areas, 300 metres of sea wall destroyed in 2006, RSPB spending £12 million on low lying sea walls to separate arable land
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Thames Estuary in London problems?
Vulnerable to flooding (bad storm in January 1953), not enough flood defences
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Impacts of London flooding?
1.5 million commuters work near Thames, property assets around £100 billion, 1.25 million people live in Thames flood zones, 69 tube station, 400 schools, 16 hospitals in zone, old buildings
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Solutions to Thames flooding?
Thames barrier constructed between 1974 and 1984 and coast £1.6 billion. Expected to cope until 2030-2050, in 2007 was raised more than 100 times. Will be replaced by 16km barrier. w
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Card 2

Front

What factors affect the coast?

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Waves, currents, local geology, changes in sea level, human activity

Card 3

Front

What is wavelength?

Back

Preview of the front of card 3

Card 4

Front

What is wave frequency?

Back

Preview of the front of card 4

Card 5

Front

What is wave height/amplitude?

Back

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