Coastal Enviroments Flashcards
What is the coast
The transition zone between land and the sea
What is the coastline
The frontier between land and sea
What marine processes
Processes carried out by the sea
Erosion
Deposition
Transportation
What are waves created by
Created by winds blowing over the sea , friction sets the waves into motion
What can waves do
Erode , transport or deposit sediment
What is the height of a wave determined by
Strength of wind
Length of time wind blows
Fetch ( distance over which wind blows )
What does an increase in wave height mean
Increase in wave energy
What is the main method of transport
Long shore drift
How does long shore drift occur
When waves approach the beach from an angle , prevailing winds determine wave direction .swash follows wave direction and moves material , backwash is perpendicular to coastline due to gravity and moves material backwards into sea. Long shore drift leads to gradual movement of material up the beach
What is deposition
When the wave loosss energy it drops the sand , rock particles and pebbles it has been carrying . This is called deposition and happens when swash is stronger than backwash ( constructive waves)
When is deposition likely to occur
when waves enter an area of shallow water
Waves enter a sheltered area e.g cave or bay
There is little wind
There is a good supply of material
What are constructive waves
Low frequency (6-8 per minute ) Beach gradually develops Low height (<1m) High power swash relative to backwash Long wavelength ( up to 100m) relative to hight
What are destructive waves
High frequency (10-12 per minute ) High height (>1m) High power backwash relative to swash Sediment forced out to sea Short wavelength (<20m) relative to height
What are the 4 processes of marine erosion
Hydraulic action
Solution
Abrasion
Attrition
Hydraulic action
Waves push against cliff and force air into the cracks and prises them apart creating lines of weaknesses
Attrition
Sea water hurls rocks towards each other . As the rocks collide sharp edges are knocked off over time rocks become smaller smoother and rounder this forms small pebbles and sand
Abrasion
Rocks scrape against each other wearing them away . Waves pick up stones and hurl them at cliffs wearing the cliff away
How does shape of coastline influence erosion
Shape of coastline
Headlands of a coastline are exposed to full force of destructive waves whereas bays are more sheltered from waves due to wave refraction. Headlands are therefore eroded quicker because they are hit by the waves with a larger force
Weathering influencing erosion
Weakens rocks and leaves them susceptible to erosions
Wave strength influencing coastline
More powerful waves erode more. Only destructive waves erode . If the wave hits the cliff at a high energy level it will have a higher erosive capability.
Width of beach affecting erosion
A wider beach will absorb more wave energy reducing erosion
Human activity affecting erosion
Structures built to defend vulnerable coastlines = weakened erosion e.g gabions, rock armour
Geology - rock structure affecting coastline
How rock strata are aligned in relation to incoming waves
Geology rock type influencing erosion
Hard rocks are more resistant to erosion e.g chalk and limestone these will be eroded slower and form steep cliffs
Soft rocks lik clays and standstone will be eroded faster and form bays
What are sub aerial processes
Coastlines are shaped by wind and rain ( sub aerial processes ) as well as by wave erosion ( marine processes ) . These natural atmospheric processes lead to weathering as well as mass movement
Weathering
The break down of rocks caused by freeze thaw and the growth of salt crystals by acid rain and the growth of vegetation roots
Mass movement
The removal of cliff gave material under the influence of gravity in the form of rock falls , slumping and landslides
How is weathering different To erosion
Weathering is the break down of rock in situ ( one place ) whereas erosion is the wearing away and carrying away of rock by a moving force
Physical weathering
Water gets into a crack In a rock and freezes
Water expand as it turns to ice
This is known as freeze thaw weathering and occurs when temperatures rise and fall above and below freezing
As water turns to ice it forces te cracks to widen
The process is most efficient when there is a large temperature difference between night and day
Water contracts as it thaws the ice melts and the rock splits
Biological weathering
Plants and animals break down rocks
Seed falls into crack in rock
Seed starts to grow and sends roots into rock
The roots force cracks to widen and the rocks split
Chemical weathering
Rain is a weak acid and falls into rocks burning of fossil fuels creates acid rain
The acid slowly eats into rock making it softer limestone is easily dissolved by acid
The rock crumbles at the surface
Landforms of erosion
Headlands and bays are the most common
Wave cut platforms
Canes arches stacks and stumps
Landforms of deposition
Beaches spits bars and tombolos
Where is the Dorset coast
Located on the south coast of England and stretches from Lyme Regis to Bournemouth . It is part of the Jurassic coast
What happens in mass movement
Weathered material is forced downslope by mass movement
Rapid mass movement example
Slumping - a large area of land moves down a slope and leaves behind a curved surface . Clay contracts and cracks when it rains water runs into cracks and is absorbed until the rock becomes saturated this weakens the tick and it slips down the slope on a slip plane . Slumping is also known as rotational slip
Slow mass movement example
Slow mass movements are barely detectable e.g soul creep . Gravity pulls water contained in the soil down a slope . The soil moves downward with water . This increases aftein heavy rainfall . Soil creep leaves overhanging soil and vegetation and ripped terracettes
What materials are more susceptible to mass movement
Steepness of the slope and the nature of material on the slope . A slope must be able to contain its own weight to remain stable . Sandstone and shales are more likely to collapse as they consist of loose fitting sediments
Granite and limestone are more likely to sustain their own weight
How are caves created
Formed on the side of headlands . Headlands attacked by hydraulic action and abrasion . Faults and joints in the cliff are attached leading to the opening of a cave
How is an arch created
The cave is eroded more and enlarged and extends back to the other side of the headland possibly meeting and other cave and forming an arch .
How is a stack created
Continued erosion by the sea widens the arch as the sea undercuts pillars of the arch the roof is weakened and eventually collapses leaving a stack separated from the headland . E.g old harry rocks
How is a stump created
Further erosion at the bar of the stack causes it to collapse and leave a small flat portion of the original stack as a stump . It may only be visible at low tide
What is a wave cut platform
An area at the base of a cliff formed by marine erosion
How is a wave cut platform formed
Wave cut notch created by hydraulic action at high tide and low tide
Overtime an overhang is created as the cliff has nothing to support it it will collapse and fall in the sea causing the cliff to retreat
The cliff will retreat until the wave cannot reach the base of it and a wave cut platform will be formed . The sea no longer reaches base of cliff
What is a tombolo
A beach which joins and island to a mainland e.g chesil beach which joins the isle of Portland to Dorset mainland . They are spots which have continued to grow seawards until they teach and join an island
Tombolo formation
There is a bar of sand and shingle
Prevailing winds cause waves to gradually roll the sand and shingle to the shore . Salt marshes may develop in the calm waters sheltered by the tombolo
What is a spit
A landform resulting from marine deposition and longshore drift . It is a long narrow accumulation of sand or shingle with only one end attached to Land , the other end projects out into the sea or across a river estuary e.g Spurn head
How is a spit formed
Direction of prevailing winds dicatate wave direction and longshore drift direction
Wave erosion destroys soft boulder clay of the holderness coastline
Longshore drift transports material across the Coastline
Where the coastline changes direction the material carried by LSD is deposited in a line out to sea across a river mouth
Waves are unable to reach the area behind the spit to quiet backwards form
The hooked end of the spit is the result of a Short term change in wind and wave direction
Mud and silt settle creating mud flats and salt marshes in the Humber estuary
On the holderness coastline the spit cannot progress any further due to strong current of river that prevents the spit from progressing further across the estuary
How are beaches formed
Accumulation of material deposited when swash is stronger than backwash it is a stretch of shad shingle and pebbles deposited between the high and low water marks along a coast . Created by constructive waves when sediment accumulates more quickly than us carried away . Sediment comes partly from cliff erosion. But mostly from Rivers
What is a bar (barrier beach )
E.g slapton sands . Long and narrow and extends across a bay , a lagoon will often form on the landward side of the beach . They are usually formed by the ‘rolling a shore ‘ of a sand or shingle bar by the wave
How is a bar formed
Prevailing winds determined wave direction
. A sand or shingle bar is rolled a shore
. A bar of sand is created across the entrance to a shallow bay
A lagoon develops behind the barrier beach in slapton sands it’s a freshwater lagoon fed by Rivers
What is a storm beach
When waves have more energy during storms and can carry large materials up a beach
Why is a coast a system
It is an open system as there are inputs e.g
Wind which causes long shore drift and deposition and outputs materials carried out to sea and sediment deposited above high tide mark
What would a cliff made of soft rock look like vs hard rock
Hard - high and steep, cliff face bare rocked rugged , foot of cliff has boulders and role
Soft - lower and less steep , cliff face - smoother evidence of slumping, cliff foot - few rocks some sand and mud
How is a beach formed
A beach is a stretch of sand shingle and pebbles deposited between high and low water marks along a coast .formed by constructive waves when wave energy drops they deposit the sand shingle and pebbles they have been carrying . Long shore drift extends the beach . The stronger swash than backwash of the wave means material is moved up the beach
Longshore drift wave type
Destructive
What happens when waves approach the coast
Friction slows the notion of the wave down creating a crest
What do destructive waves do
Plunge material down which then carried away by strong backwash
How are landforms of erosion formed on discordant coastline
Rock strata is at rights angles to sea . Soft rock (clays and sands ) are eroded faster by hydraulic action forming bays (circular inlets ) e.g studland bay , swanage bay Hard rocks ( chalk and limestone ) are not eroded as fast and form an outcrop of resistant rock e.g Ballard point durlstom head . Te headland are exposed to waves and erode over time then the whole process starts again
What do concordant coasts loook like
Rock strata is parallel to sea producing straighter coastlines
What caused sea level fall
During the ice age large amounts of water was stored as ice and snow causing sea level fall. This left the old coastline high above sea level . Since the ice age sea levels have risen but not to their precious levels.
What does sea level fall reveal
More coastline , beaches are no longer combed by waves An left stranded and exposed above the new lower sea level . These are raised beaches
What is an emergent coastline
A coastline asssociated with sea level fall
What is a raised beach
An area of sloping ground that sits above present tide line .it is where the sea level used to be . They are covered in shrubs and bushes showing physical inactivity
What are relict cliffs
Commonly have wave cut notches , caves arches and stacks . They are behind the raised Beach and were formed due to marine erosion when sea levels were higher. It is a cliff where the souls would previously have been attacking it but is now far from the sea and no longer experiences coastal erosion
What is A coastline with a rising sea level
Submergent coastline will have rias and fjords
What is aria and how is it formed
A coastal inlet formed by submergence of a lower portion of the river valley .they are drowned river valleys
What is a fjord and how’s it formed
Deep , narrow elongated sea or lake drain with steep land on 3 sides . Fjords are steeper and deeper variants of rias . They have a shallow mouth as this is where the glacier deposited its sediment . They are particularly found in icy sections of the world . They are drowned glacial valleys