Coasts

Coasts









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Waves

How waves form?



Waves are usually formed by the wind blowing across the sea. This causes ripples on the top of the

surface and these develop into waves. The stretch of open water over which the wind blows is called

the fetch. The longer the fetch the more powerful the wave.



Video showing wave formation - http://www.bbc.co.uk/learningzone/clips/understanding-wave-

formation/4018.html









The above diagram shows you what happens when a wave moves closer towards the coast and

crashes onto a beach.



Crest - this is the top part of the wave and eventually topples onto the beach.

Swash - this is the water that rushes up the beach

Backwash - this is the water that flows back towards the sea



Types of waves



There are two types of waves; constructive and destructive waves.

Constructive waves:









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 Constructive waves are waves that surge up the beach

and have a powerful swash

 They carry large amounts of sediment and 'construct'

the beach making it more extensive





Main characteristics: They have a strong swash and a weak backwash and are smaller in height

compared to destructive waves. They are waves which contain a small amount of energy.



Destructive waves



 Destructive waves are named because they 'destroy'

the beach.

 When the waves hit the beach they rear up and smash

down onto the beach.

 There is very little swash when the wave breaks but

has a powerful backwash.

 The backwash removes the sediment which leads to

the 'destruction' of the beach





Main characteristics: They have a strong backwash, lots of energy and are waves which are high in

height









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Processes influencing our coastlines

Coastal processes can be split into two different categories:





 Land processes influencing our coastlines

 Marine coastline influencing our coastlines





Video showing the processes of erosion - http://www.bbc.co.uk/learningzone/clips/weathering-

erosion-and-coastal-features/4022.html



Excellent animation showing coastal processes and defences -

http://www.as.uky.edu/academics/departments_programs/EarthEnvironmentalSciences/EarthEnviron

mentalSciences/Educational%20Materials/Documents/elearning/module14swf.swf



Weathering



The processes of weathering affects rocks exposed at the coast. Freeze-thaw weathering in

particularly effective if the rock is porous (contains holes) and permeable (allows water to pass

through it). This can lead to dramatic rockfalls as shown below.





Full explanation as to how freeze-thaw weathering works can be found at the following link:



http://onlinegeography.wikispaces.com/Ice+as+a+shaping+agent



Mass movement

Mass movement is the downhill movement of material under the influence of gravity. In 1993 60m of

cliff slid onto the beach near Scarborough in North Yorkshire, taking with it part of Holbeck Hall Hotel.









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Marine Processes

Coastal erosion



Erosion – use the acronym CASH

Corrasion – (abrasion) is caused by large waves hurling beach material against the cliff

Attrition – is when waves cause rocks and boulders on the beach to bump into each other and

to break up into small particles

Solution – (corrosion) is when salts and other acids in seawater slowly dissolve a cliff

Hydraulic pressure (power/action) – is the force of waves compressing air in cracks in a cliff

One final process of erosion is:



Abrasion: this is the 'sandpapering' effect of pebbles grinding over a rocky platform, often causing it to

become smooth.



Coastal transportation



Processes of Transportation





 Traction – rolling stones along the sea floor (needs the

most energy)

 Saltation – sand-sized particles bounce along the sea

floor in a ‘leap frog’ movement

 Suspension – silt and clay-sized particles are carried

within the water flow·

 Solution – some minerals dissolve in the water (this needs

the least energy)





Longshore Drift

Video showing how Longshore Drift works - http://www.bbc.co.uk/learningzone/clips/landforms-

created-by-longshore-drift-and-coastal-deposition/9965.html



 Waves approach the beach in the same direction as

the wind

 When the wave breaks, swash carries material up the

beach at the same angle as the wind

 The backwash carries the material straight back down

the beach under gravity·

 This process slowly moves material along the coastline









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Remember when drawing:





 To draw in a beach

 An arrow showing the prevailing wind

 An arrow showing the direction of longshore drift

 To draw in the movement of the pebbles

 To use the terms ‘swash’, ‘backwash’ and ‘gravity’ when

describing the movement of the pebbles





Coastal deposition



Deposition occurs in areas where the flow of water slows down. The sediment can no longer be

carried or rolled along an has to be deposited. Coastal deposition most commonly occurs in bays,

where the energy if the waves is reduced on entering the bay. This explains the presence of beaches

in bays and accounts for the lack of beaches at headlands, where the energy of the waves is uch

greater.









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Landforms of erosion

Very useful BBC videos:

Formation of landforms - http://www.bbc.co.uk/learningzone/clips/coastal-erosion-and-

landforms/9966.html

Wave-cut platforms and headlands/bays - http://www.bbc.co.uk/learningzone/clips/wave-cut-

platforms-and-headland-erosion/4021.html

Weathering and erosion - http://www.bbc.co.uk/learningzone/clips/weathering-erosion-and-coastal-

features/4022.html

An example of stump formation - http://www.bbc.co.uk/learningzone/clips/old-harry-rocks-

dorset/3244.html

An example of stump formation - http://www.bbc.co.uk/learningzone/clips/old-harry-rocks-coastal-

processes-and-landforms/3245.html

More landforms - http://www.bbc.co.uk/learningzone/clips/coastal-landforms-west-wales/3084.html

Cliff slumping - http://www.bbc.co.uk/learningzone/clips/coastal-landforms-blowholes-and-cliff-

slumping/3085.html





Headlands and bays



Cliffs rarely erode at an even pace. Sections of cliff that are particularly resistant to erosion stick out to

form headlands. Weaker sections of coastline that are more easily eroded form bays.









 Form where there are alternating outcrops of resistant

outcrops of resistant (harder) and less resistant

(softer). ·

 Destructive waves erode the soft rock move quickly to

form bays·







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 The harder rock is more resistant and are left

protruding into the sea·

 The headlands protect the adjacent (next by) bays

from destructive waves

As the headlands protect the bays sand is deposited to

form a beach. At the headlands there often wave-cut

platforms and notches.



Cliff and wave-cut platforms









 Wave erosion is greatest when large waves break against

the foot of the cliff ·

 The waves undercut the foot of the cliff to form a wave-cut

notch ·

 Over time the notch enlarges the until the cliff above it is

unsupported and collapses ·

 The gentle sloping expanse of rock marking the foot of the

retreating cliff is called a wave-cut platform ·

 Wave-cut platforms are exposed at low tide but hidden at

high tide









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Caves, arches and stacks









When drawing a diagram label:





 What and where the different processes of erosion are

occurring ·

 Where wave-cut notches may be formed ·

 Check you have the correct sequence·

 Explain what hydraulic power, corrosion and abrasion









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Landforms of deposition

Video showing all of the coastal landforms of deposition -

http://www.bbc.co.uk/learningzone/clips/depositional-coastlines/4023.html

Beaches







 They are usually found in sheltered bays between two

headlands

 The headlands protect the area from erosion

 Low constructive waves deposit material on the shore

 Gradually a beach is built up

 Material on a beach is well sorted – the biggest pebbles are

nearest the land with the smallest nearest the sea

 The larger the material the steeper the beach – pebble is

steeper than sand







Spits

http://www.geographyalltheway.com/ks3_geography/coasts/imagesetc/deposition.swf - an amazing

animation which explains the formation of a spit!!

Video showing the formation of a spit - http://www.bbc.co.uk/learningzone/clips/the-formation-of-

spits/3246.html









A spit is an area of sand or shingle that has been transported by longshore drift and then deposited

as the coastline has changed direction. It is attached to the land at one end. It is a depositional

landform. Hurst Castle Spit in Hampshire is a very famous example.



Where the coastline changes direction, sediment is deposited in the same direction as the original

coastline (i.e. in line with the prevailing wind direction). Where there is a break in the coastline and a

slight drop in energy, longshore drift will deposit material at a faster rate than it can be removed and

gradually a ridge is built up. The material is deposited in the deeper water offshore until the ridge is

built above the level of the sea. Drift continues along the seaward side of the spit extending it further



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down the coast while salt marsh develops in the slow-moving water on the landward side.



Spits can become a permanent feature. This happens when the prevailing wind picks up sand from

the beach and blows it inland across the spit to form sand dunes. These dunes will then be colonised

by vegetation, which stabilises them. It is common for a salt marsh to develop in the sheltered area

of water behind the spit. Water is trapped behind the spit, creating a low energy zone. As the water

begins to stagnate, mud and marsh begin to develop behind the spit.



A spit may grow out across a river estuary. Where the spit is crossing a river mouth, the river will be

diverted so that it follows the coastline for some miles before reaching the sea.



Bars









Bars can form in several ways:

(a) a spit grows the whole way across a bay

(b) a sandbank develops offshore, parallel to the shore, and is moved towards the coastline by the

waves and wind until it joins the mainland





Slapton Sands is an example of a bar. The lagoon of water than has formed on the landward side of

the bar is called Slapton Ley.





A tombolo is formed where a spit joins an island to the mainland. An example is the Isle of Portland

which is joined to the mainland by a shingle ridge known as Chesil Beach.









Useful weblinks:



BBC Class Clips video - Blakeney Point

BBC Class Clips video - Kaitorete Spit, New Zealand

BBC Scotland video about spits, bars and tombolos

BBC Bitesize - Spits

BBC Bitesize - Tombolos









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Sea-level rise

Videos on Youtube channels

The causes of sea-level rise:



One of the effects of global warming is sea-level rise. Over the last 15 years, global average sea

levels have risen by 3mm a year. The latest estimate from the Intergovernmental Panel on Climate

Change (IPCC) suggests a rise in global sea levels of between 28 and 43 cm by the end of the

century.



The main cause of sea-level rise is thermal expansion of seawater as it absorbs more heat from the

atmosphere. Also the melting of ice on land e.g. from Greenland and will increase the level of the

oceans.



The actual amount of sea-level rise will vary from place to place due to variations in the level of the

land and the amount of deposition of sediment occurring at the coast.



The effects of sea-level rises:



In the UK, East Anglia is likely to be hardest hit and this threatens coastal defences and natural

ecosystems. Elsewhere in the world, vast areas of low-lying coastal plains such as Bangladesh and

whole chains of islands such as the Maldives and Tuvalu could disappear. More than 70% of the

world's population live on coastal plains so the effects of sea-level rises are going to be devastating.









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Cliff Collapse

BBC videos on cliff collapse:

Buildings threatened by erosion - http://www.bbc.co.uk/learningzone/clips/a-dairy-farm-is-threatened-

by-coastal-erosion-at-holderness-east-yorkshire/3190.html

Buildings threatened by erosion - http://www.bbc.co.uk/learningzone/clips/a-farm-is-threatened-by-

coastal-erosion-at-holderness-east-yorkshire/3189.html

Buildings threatened by erosion - http://www.bbc.co.uk/learningzone/clips/a-house-threatened-by-

coastal-erosion/3188.html

Erosion at Hallsands - http://www.bbc.co.uk/learningzone/clips/coastal-erosion-at-hallsands-causes-

and-effects/9967.html

Erosion at Holderness - http://www.bbc.co.uk/learningzone/clips/coastal-erosion-at-holderness-east-

yorkshire/3187.html

Erosion at Hallsands - http://www.bbc.co.uk/learningzone/clips/hallsands-destruction-of-

coastland/3242.html

Case study on Happisburgh - http://www.bbc.co.uk/learningzone/clips/living-with-coastal-erosion-in-

happisburgh-east-anglia-pt-1-2/7361.html

Case study on Happisburgh - http://www.bbc.co.uk/learningzone/clips/living-with-coastal-erosion-in-

happisburgh-east-anglia-pt-2-2/7364.html

Various factors can contribute to cliff collapse. These include:





 weathering processes - such as heavy rainfall that can

saturate the land and make it unstable

 mass movement such as sliding and slumping - which

is more likely if the land is made of soft weak rock

types

 the power of the waves - crashing against the cliffs and

undercutting them from below





Barton-on-Sea, Hampshire



Barton-on-Sea is a small village in Christchurch Bay and has long been affected by coastal erosion

and cliff collapse.



Over the years a number of buildings and most recently a cafe have been lost to the sea.



Sea defences have been built to prevent coastal erosion but in 2008 there was a fresh landslip. The

older houses in the settlement are now only 20m from the sea. It is expected that the houses will be

lost to the sea in the next 10 to 20 years.



Why are the cliffs at Barton-on-Sea so prone to collapse?





 the rocks are weak sands and clays. They are easily

eroded by the sea and have little strength to resist

collapse.

 the arrangement of the rocks causes water to 'pond-up'

within the cliffs. This increases the weight of the cliffs.

The increase in water pressure within the cliffs which

encourages collapse.

 the coastline is exposed to the direct force of the

prevailing south-westerly winds. This means a very

long fetch and as a result the waves are very powerful

leading to rates of erosion as much as 2m a year in

places.







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 small streams increase the amount of water entering

the cliffs which increases the weight of the cliff and

then leading to collapse

 buildings on the cliff top have increased the weight on

the cliffs, making them more vulnerable to collapse









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Sea Defences – See Website for excellent videos and

animations

http://onlinegeography.wikispaces.com/C+-+Sea+defences

Salt Marshes

Salt marshes are areas of periodically flooded low-lying coastal wetlands. They are often rich in

plants, birds and animals.



A salt marsh begins life as an accumulation of mud and silt in a sheltered part of the coastline for

example in lee of a spit or bar. As more deposition takes place, the mud begins to break the surface

to form mudflats. Salt-tolerant plants such as cordgrass soon start to colonise the mudflats. These

early colonisers are called pioneer plants. Cordgrass is tolerant of the saltwater and its long roots

prevent it from being swept away by the waves and the tides. Its tangle of roots also helps to trap

sediment and stabilise the mud.



As the level of the mud rises, it is less frequently covered by water. The conditions become less harsh

as rainwater begins to wash out some of the salt and decomposing plant matter improves the fertility

of the newly forming soil. New plant species such as sea asters start to colonise the area and

gradually, over hundreds f years, a succession of plants develops. This is known as a vegetation

succession.



Salt Marsh Vegetation Succession









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Case study: Keyhaven Marshes

Make sure you can describe the threats to the ecosystem and management options there.









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Glossary

Fetch: the distance of open water over which the wind can blow



Beach: a deposit of sand or shingle at the coast, often found at the head of a bay



Crest: the top of a wave



Swash: the forward movement of a wave up a beach



Backwash: the backward movement of water down a beach when a wave has broken



Constructive wave: a powerful wave with a strong swash that surges up a beach



Destructive wave: a wave formed by a local storm that crashes down onto a beach and has a

powerful backwash



Rockfall: the collapse of a cliff face or the fall of individual rocks from a cliff



Hydraulic power: the sheer power of the waves



Corrasion: the effect of rocks being flung at the cliff by powerful waves



Solution: the dissolving of rocks, such as limestone and chalk



Attrition: the knocking together of pebbles, making them gradually smaller and smoother



Traction: heavy particles rolled along the seabed



Solution: the transport of dissolved chemicals



Saltation: a hopping movement of pebbles along the seabed



Suspension: lighter particles carried (suspended) within the water



Longshore drift: the transport of sediment along a stretch of coastline caused by waves approaching

the beach at an angle



Headland: a promontory of land jutting out into the sea



Bay: a board coastal inlet often with a beach



Wave-cut platform: a wide, gently sloping rocky surface at the foot of a cliff



Cave: a hollowed-out feature at the base of an eroding cliff



Arch: a headland that has been partly broken through by the sea to form a thin-roofed arch



Stack: an isolated pinnacle of rock sticking out of the sea



Spit: a finger of new land made of sand or shingle jutting out into the sea from the coast



Salt marsh: low-lying coastal wetland mostly extending between high and low tide



Bar: a spit that has grown across a bay



Shoreline Management Plan: an integrated coastal management plan for a stretch of coastline in

England and Wales



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Hard engineering: building artificial structures such as sea walls aimed at controlling natural

processes



Soft engineering: a sustainable approach to managing the coast without using artificial structures



Managed retreat: allowing controlled flooding of low-lying coastal areas or cliff collapse in areas

where the value of the land is low



Pioneer plant: the first plant species to colonise an area that is well adapted to living in a harsh

environment



Vegetation succession: a sequence of vegetation species colonising an environment









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