62 terms

Coasts

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Depositional Landforms
Formed through LSD and include spits, bars and salt marshes
Formation of salt marshes
Salt marshes form behind the spit as the water behind the spit is a low energy environment
The mud brought in when the tide rises accumulates in the sheltered water
Plants grow encouraging deposition, by slowing the water further
As the mud level rises the area becomes known as a salt marsh
Spits
Shape
Long and narrow with one end attached to land and the other extending into open water
Due to LSD

Formation
Sand and shingle is moved along the coast by LSD and deposited where the coast changes direction

Distinct features
They have hooked ends when onshore wind blow waves from a different angle to that of the prevailing wind. If the spit grows back in the original direction, it will have a hooked end

Changes
Over time a spit would be likely to gain a hooked end or become a bar
Formation of bars
A bar forms when a spit extends all the way from one bank to the other because enough material has been deposited to do so. The area of water enclosed by a bar is called a lagoon. This water begins as salt water but will be replaced with fresh water if a river enters it. If rivers repeatedly deposit their load the lagoon becomes a marsh
Beaches
Comprised of sand and shingle. The more coarse, shingle forms a steep slope at the highest parts, while the finer sand forms a gentler slope at the lower parts. All the material has been eroded further along the coast and then carried and deposited by LSD normally relatively calm waters
Sand dunes
Embryo dunes→ Dunes move→ Semi-fixed grey dunes→ Fixed dunes→ Slacks→ Young dunes
Embryo dunes
These are the dunes closest to the coastline. They are formed when an obstacle obstructs the onshore wind, slowing it, causing it to deposit the sand it is carrying
Dunes move
The dunes grow and form a fore dune. They move inland as the wind picks up the sand from the seaward face of the dune and carries it to the leeward side
Semi-fixed grey dunes
Plants grow and then eventually die. The dune becomes a semi-fixed grey dune because humus from the plant decay helps to form a soil giving the dune a grey colour
Fixed dunes
These dunes are the oldest and the further inland they are the older they are. Over time the depth of soil increases as does the humus content. This leads to more plant species growing. The vegetation becomes denser and taller
Slacks
These are long marshy depressions, some with water that lie between the dune ridges. Water loving plants grow in these, but fewer grow in slacks further inland, as those slacks are saltier and have more sediment in them
Young dunes
These are very fragile as no plants can tolerate the trampling. The wind easily moves the exposed sand, leaving a valley shape like shape cut through the dune called a 'blowout'. When this happens fences are put up to give the vegetation recovery time
Formation of Mangrove Swamps
Initially formed in the same way as salt marshes, then Mangrove grows with either roots above or below ground encouraging further deposition of mud, building up a thick swap
Features of Mangrove Swamps
Can grow 15m tall
-Protect from, flooding, strong winds and hurricanes
E.g. A tsunami in the Indian Ocean. A village without Mangrove Swamps suffered 6000 deaths whereas one with Mangrove Swamps suffered only 2
Formation and features of Coral Reefs
Corals are tiny marine animals called polyps that form reefs when millions live together in colonies
The skeletons are calcareous cups which are joined together with others to form a hard, stony mass
As one generation dies, the next grows on top of it so the reef grows upwards and outwards
Reefs run parallel to the coast and they often have breaks at river mouths
Fringing reef
A coral reef 'hugging' a land mass
Barrier reef
A coral reef surrounding a land mass
Atoll reef
A coral reef surrounding a lagoon, with no land mass
Coral reef conditions for growth
Cannot live in sea temperatures of less than 18 degrees
Grow best when the mean temp is 22-25 degrees and are thus found within 30 degrees of the equator
Cannot survive out of water for long so most are found at low tide level
Need clear, clean, sunlit water and cannot live where rivers deposit their load
Grow best in conditions of high salinity
Rarely found deeper than 30m because the cannot live without single-celled algae and plankton (their food), both of which require sunlight which decreases with depth
There has to be a solid surface for the reef to start growing on
Soft engineering
A method of costal management which works with natural processes found along the coast, usually unobtrusive. It does not require major construction work
Beach nourishment
Engineering- Soft
Description- The addition of sand or shingle to an existing beach to make it higher or broader. The sediment is usually obtained locally so that it blends in
Cost- £3,000/m
Advantages- Cheap and easy to maintain, blends in, increases tourist potential
Disadvantages- Needs constant maintenance
Dune regeneration
Engineering- Soft
Description- Marram grass is planted to stabilise the dunes and help them to develop, areas can be additionally fenced off
Cost- £2,000/100m
Advantages- Maintains natural costal environment, cheap
Disadvantages-Time consuming, people dislike being prohibited from certain areas, can be damaged by storms
Marsh creation
Engineering- Soft
Description- This involves allowing low lying costal areas to be flooded by the sea to become salt marshes. These marshes are then a barrier to the sea
Cost- £5,000-£10,000/hectare
Advantages- Cheap, creates a much needed space for wildlife
Disadvantages- Land is lost, farmers/land owners would need compensation
Hard engineering
A method of costal management which requires major construction work
Sea wall
Engineering- Hard
Description- Concrete or rock is placed at the base of a cliff, it also has a curved face to reflect waves back into the sea
Cost- £6,000,000/km
Advantages- Effective at stopping the sea, often has a walkway/promenade
Disadvantages- Looks unnatural and is very expensive to build and maintain
Groynes
Engineering- Hard
Description- Timber or rock structures are built out to the sea from the coast. They trap sediment and hence slow LSD and thus enlarges the beach. The longer beach acts as a barrier to waves and protects the cliffs
Cost- £10,000 each at 200m intervals
Advantages- Bigger beach and so more tourists, useful structures for fishers
Disadvantages- Interrupts LSD and so starves another area of sand hence moving the erosional problem there, unnatural and look ugly
Rock armour
Engineering- Hard
Description- Piles of boulders are dumped at the foot of a cliff. The rocks force the waves to break and thus absorb their energy, protecting the cliff
Cost- £1,000-£4,000/metre
Advantages- Cheap and useful for fishers
Disadvantages- Can be expensive to transport, do not fit in with the local geology, can be very obtrusive
Spring tide
A tide due to the combined gravitational pull of the sun and moon
Neap tide
A tide due to the gravitational pull of the moon being perpendicular to that of the sun
Coast and coastline
The coast is the zone where the land meets the sea and the coastline follows the high water mark on the coast
Tides
The sea rises and falls twice a day
Wave speed factors
Wind speed, the length of time the wind blows in one direction for and the fetch (the length of sea over which the wind can act.)
How waves work
Water particles within a wave move in a circular orbit
Each particle moves up and down
The shape of the wave and its energy are the only things which are transferred horizontally towards the coast
As water rises it forms a wave crest as it falls it forms the wave trough, the distance between these is the wave height
The wave length is the distance between two wave crests
When a wave reaches shallower water the velocity at its base reduces, due to friction with the sea bed
The circular orbit consequently changes to a more elliptical shape
The top of the wave unaffected by friction becomes higher and steeper until it breaks
The water rushes up the beach, this is the swash and finally drains back down, this is called the backwash
Destructive waves characteristics
Weak swash and strong backwash resulting in these waves removing material from the beach by dragging pebbles and sand off it

Steep, high, close together, crash down and have a high frequency of 10-15 per min
Constructive waves characteristics
Very strong swash and a weak backwash resulting in these waves building up the beach by dragging pebbles and sand up it

Low, far apart, spill up the beach and have a low frequency of 6-8 per min
Sub-aerial processes
Weathering and erosional processes acting on land at the earths surface as opposed to under water
Biological weathering
Erosional processes due to wildlife and plants
Hydraulic action
Water is forced into cracks in the rocks, compressing the air in the gaps and thus causing a blast resulting in bits of rock being chipped off
Corrasion
Loose rocks and sediment are thrown against the cliff and chip bits of the rock off
Corrosion
The seawater dissolves material from the rock, it happens when calcium carbonate is dissolved in limestone
Attrition
Loose sediment is swirled around by the waves and bashes into other sediment making the sediment smaller and rounder
Mass movement
The movement of downslope of rock fragments and soil under gravity
This material is not incorporated into ice or water and so moves of its own accord, however it can be triggered by increased water pressure or heavy rainfall
Rockfall
Fragments of rock break away from the cliff face, often due to freeze-thaw weathering
Landslide
Blocks of rock slide downhill
Mudflow
Saturated soil and weak rock flows down a slope
Rotational slip
Slump of saturated soil and weak rock along a curved surface
Suspension
Fine, light material is carried along
Solution
Minerals are dissolved in the water. This is a chemical change
Traction
Large boulders and rocks are rolled along the sea bed
Saltation
Small pebbles and stones are bounced along the sea bed
Long Shore Drift (LSD)
Pebbles and sediment are carried up the beach by the swash in a diagonal direction due to the position of the waves
The pebbles and sediment are then carried directly down the beach by the backwash due to gravity
This continues and material is slowly moved across the beach

This results in many problems, inc. Smaller beaches leading to fewer tourists

Groynes are used to protect against LSD and work by trapping the material
Erosional landforms
Headland → Bay → Cliff → Wave-cut platform → Cave → Arch → Stack → Stump
Headland
A promontory of land jutting out into the sea
Bay
A broad costal inlet often with a beach
Wave-cut platform
A wide gently sloping rocky surface at the foot of a cliff
Wave-cut notch
A small indentation cut into a cliff roughly at the level of high tide caused by concentrated marine erosion at this level
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
Stumps
A stack which has fallen over and is thus half height
Bay and headland coast
Form along a discordant coast
Destructive waves erode the softer rock to form bays
Headlands are left protruding
The headlands thus become the focus of erosion
The headlands are eventually eroded and thus the process restarts
Process of cliffs and wave-cut shore
Sea water erodes the cliff base and forms a wave cut notch through the processes of hydraulic action and abrasion
As the notch enlarges the cliff eventually collapses due to gravity
The cliff deteriorates and collapses meaning it moves backwards
As the cliff retreats due to hydraulic action and abrasion a wave cut platform is created above the low tide mark
The flat cliff profile is left and the process continues