coasts including management Flashcards
What can the coast be considered, and why?
An open system, as it receives inputs from outside the system and transfers outputs away from the coast and into other systems
What other systems can coast’s outputs be transferred to?
Terrestrial, atmospheric or oceanic
- Can include the rock, water and carbon cycles
What are sediment cells?
- These are the sections that coasts are split into
- They are typically considered a closed system in terms of sediment, there’s virtually no inputs or outputs from outside of the cell
- A linked system of inputs, transfers and outputs of sediment along a section of coastline
What are sources in sediment cells?
Where the sediment originates from (e.g cliffs, offshore bars)
What are through flows in sediment cells?
The movement of sediment along the shore through longshore drift
What are sinks in sediment cells?
Locations where deposition of sediment dominates (e.g spits, beaches)
How does the coastal system operate under normal conditions?
- It operates in a state of dynamic equilibrium
- Dynamic equilibrium in a sediment cell is where inputs and outputs of sediment are in a constant state of change, but remain in balance.
- Physical and human actions can change this equilibrium
Describe the negative feedback loop in coastal systems?
- Lessens any change which has occurred within the system
Give an example of a negative feedback loop?
A storm could erode a large amout of a beach, taking the beach out of dynamic equilibrium as there is a larger input of sediment into the system than output:
- Destructive waves from storm lose their energy and deposit excess sediment as an offshore bar
- The bar dissipates the waves energy, protecting the beach from further erosion
- Over time the bar gets eroded instead of the bach
- Once the bar has gone normal conditions ensue and the system goes back to dynamic equilibrium
Describe the positive feedback loop in coastal systems:
- This exaggerates the change, making the system more unstable and taking it away from dynamic equilibrium
Give an example of a positive feedback loop?
- People walking over sand dunes desroys vegetation growing there and causes erosion
- As the roots from the vegetation have been holding the sand dunes together, damaging the vegetation makes the sand dunes more susceptible to erosion. This increases the rate of erosion
- Eventually the sand dunes will be completely eroded leaving more of the beach open to erosion, taking the beach further away from dynamic equilibrium
What is the littoral zone and why is it constantly changing and varying?
- The area of the coast where land is subject to wave action.
It is constantly changing and varies due to:
- Short-term factors like tides and storm surges
- Long-term factors like changes in sea level and climate change
What are the subzones within the littoral zone?
Backshore- area above high tide level and only affected by exceptionally high tides
Foreshore- this is land where most wave processes occur
Offshore- the open sea
What does Valentine’s Classification describe?
The range of coastlines that can occur
Why might a coastline be advancing?
- Due to the land emerging or deposition being the prominent process
Why might a coastline be retreating?
- Due to the land submerging or erosion becoming the prominent process
What might be the cause of emergent or submergent coastlines?
Post-glacial adjustment (the land wobbles as the glacier above it melts, causing isostatic sea level change
What are the main processes of erosion?
Corrasion
Abrasion
Attrition
Hydraulic Action
Corrosion
Wave Quarrying
What is corrasion?
- Sand and pebbles are picked up by the sea from an offshore sediment sink or temporal store and hurled against the cliffs at high tide
- This causes the cliffs to be eroded
- The shape, size, weight and quantity of sediment picked up, as well as the wave speed, affects the erosive power of this process
What is abrasion?
- This is the process where sediment is moved along the shoreline, causing it to be worn down over time.
What is attrition?
- Wave action causes rocks and pebbles to hit against each other, wearing each other down and so becoming round and eventually smaller.
- Attrition is an erosive process within the coastal environment, but has little to no effect on erosion of the coastline itself
What is hydraulic action?
- As a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults within the rock.
- The high pressure causes the cracks to force apart and widen when the wave retreats and the air expands.
- Over time this causes the rock to fracture.
- Bubbles fond within the water may implode under the high pressure, creating tiny jets of water that over time erode the rock- this process is called cavitation
What is cavitation?
Bubbles found within water may implode under the high pressure, creating tiny jets of water that over time erode rock
What is corrosion?
- Also known as solution
- The mildy acidic seawater can cause alkaline rock to be eroded and is very similar to the process of carbonation weathering
What is wave quarrying?
- This is when breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m².
- It is very similar to hydraulic action but acts with significantly more pressure to directly pull away rocks from a cliff face or remove smaller weathered fragments.
- The force of the breaking wave hammers the rocks surface, shaking and weakening it and leaving it open to attack from hydraulic action and abrasion
When are erosion rates the highest?
- Waves are high and have a long fetch
- Waves approach the coast perpendicular to the cliff
- At high tide- waves travel higher up the cliff so a bigger area of cliff face is able to be eroded
- Heavy rainfall occurs- water percolates through permeable rock, weakening the cliff
- In winter- destructive waves are the largest and most destructive during winter
What is the resistance of a rock influenced by?
Whether rocks are clastic or crystalline
- sedimentary rocks like sandstone are clastic as they are made up of cemented sediment particles, therefore are vulnerable to erosion, whereas igneous and metamorphic rocks are made up of interlocking crystals, making them more resistant
The amount of cracks, fractures and fissures
- The more weaknesses there are in the rock the more open it is to erosional processes, especially hydraulic action
The lithology of the rock
- The type of rock and the conditions of the rock’s creation directly affects its vulnerability to erosion
What are examples of igneous rock?
Granite
Basaslt
What are examples of metamorphic rock?
Slate
Schist
Marble
What are examples of sedimentary rock?
Limestone
What is the rate of erosion of igneous rock?
Very slow
<0.1cm/year
What is the rate of erosion of metamorphic rock?
Slow
0.1-0.3cm/year
What is the rate of erosion of sedimentary rock?
Very fast
0.5-10cm/year
What is the structure of igneous rock?
Interlocking crystals which allow for high resistance
What is the structure of metamorphic rock?
Crystal all orientated in the same direction
What is the structure of sedimentary rock?
Lots of fractures and bedding planes making them weak
Where do caves, arches, stacks and stumps form?
Pinnacle headlands
Describe the formation of caves, arches, stacks and stumps:
- Marine erosion widens faults in the base of the headland, widening over time to create a cave
- The cave will widen due to both marine erosion and sub-aerial processes, eroding through to the other side of the headland to create an arch.
- The arch continues to widen until it is unable to support itself, falling under its own weight through mass movement,
- This leaves a stack as one side of the arch becomes detached from the mainland
- With marine erosion attacking the base of the stack, eventually it will collapse into a stump
Describe the formation of wave-cut notches and platforms:
- Marine erosion attacks the base of a cliff, creating a notch of eroded material between high tide height and low tide height
- As the notch becomes deeper (and sub-aerial weathering weakens the cliff from the top) the cliff becomes unstable and falls under its own weight through mass movement.
- This leaves behind a platform of the unaffected cliff base beneath the wave-cut notch
What are retreating cliffs?
Through the process of repeat wave-cut notches and platforms, new cliff faces are created, whilst the land retreats
What are blowholes?
- A combination of two features: a pot hole on top of a cliff, creating by chemical weathering, and a cave, formed by marine erosion
- As the cave erodes deeper into the cliff face and the pothole deepens, they may meet.
- In this case, a channel is created for incoming waves to travel into and up the cliff face (occasionally water splashes out of the top of the blowhole)
What is Longshore Drift?
- How sediment is predominantly transported along the coast
- It transports sediment along the beach and between sediment cells
Describe the process of longshore drift:
- Waves hit the beach at an angle determined by the direction of the prevailing wind
- The waves push sediment in this direction and up the beach in the swash
- Due to gravity, the wave then carries sediment back down the beach in the backwash
- This moves sediment along the beach over time
What are other transportation processes?
Traction
- large, heavy sediment rolls along the sea bed, being pushed by currents
Saltation
- Smaller sediment bounces along the sea bed, being pushed by currents
Suspension
- Small sediment is carried within the water column (a body of water)
Solution
- Dissolved material is carried within the water
What does the impact of transportation depend on?
The severity of the angle that waves travel onto land
What does swash-aligned mean?
Wave crests approach parallel to the coast so there is limited longshore drift
Sediment doesn’t travel far up the beach
What does drift-aligned mean?
Waves approach at a significant angle, so longshore drift causes the sediment to travel far up the beach
What is gravity settling?
A type of deposition
- Occurs when the wave’s energy becomes very low, so heavy rocks and boulders are deposited followed by the next heaviest sediment
What is flocculation?
A type of deposition
- Clay particles clump together due to chemical attraction and then sink due to their high density
What are some examples of depositional landforms?
Spits
Bars
Tombolo
Cuspate forelands
Offshore bars
Sand dunes
Beaches
Why might waves lose energy?
- The wind dropping, meaning an energy source has been removed
- Resistance by obstruction, such as a groyne or headland
- Dissipation of energy through refraction
- Friction from extended transport across shallow angled nearshore and foreshore zone
What are beaches?
- Accumulations of sand and/or shingle found in the foreshore and backshore zones
How are beaches produced?
- By material being deposited by constructive waves
- The swash has the strength to carry material up the beach, but the backwash only has enough energy to transport some of the material back down, leaving the remainder deposited
What are spits?
- A long narrow strip of land formed due to deposition.
How are spits formed?
- Longshore drift occurs along the coast line but as the waves lose enrgy (normally due to going into a sheltered area such as behind a headland) they deposit their sediment.
- Over time, this creates a spit.
What is a hooked / recurved spit and how is it formed?
- A spit whose end is curved landward, into a bay or inlet
- This occurs when prevailing wind periodically changes direction.
What can happen around a spit?
Over time, the sheltered area behind can turn into a salt marsh
What is the length of a spit influenced by?
- Influenced by surround currents or rivers
What is a double spit?
- Where two spits extend out in opposite directions from both sides of the bay, towards the middle
What is a bar?
- A spit which, over time, crosses a bay and links up two sections of coast (the water within the bay is called a lagoon)
What is a tombolo?
- A bar or a beach that connects the mainland to an offshore island
How is a tombolo formed?
- It is formed due to wave refraction off the coastal island reducing wave velocity, leading to deposition of sediment
What is a cuspate foreland?
- Low-lying triangular shaped headlands, extending out from a shoreline and formed from deposited sediment
- Longshore drift alongside each side of the headland creates beaches, and where they meet, they form a cuspate headland
What are offshore bars and how do they form?
- A region offshore where sand is deposited, as the waves don’t have enough energy to carry the sediment to shore.
- Ridges of sand or shingle running parallel to the coast in an offshore zone
- They can be formed as the wave breaks early, scouring the seabed and instantly depositing its sediment as a loose-sediment offshore bar
What are offshore bars used for?
- To construct wind farms, such as Scroby Sands in Norfolk
- As a source of sand for beach nourishment
- For shingle dredging for construction material
When do sand dunes occur?
- They occur when prevailing winds blow sediment to the back of the beach.
- The formation of dunes requires large quantities of sand and a large tidal range, which allows the sand to dry so that its light enough to be picked up and carried by the wind to the back of the beach
- Frequent and strong onshore winds are also necessary
How do dunes develop
- As a process of vegetation succession
What are the stages dunes go through in plant succession?
Embryo dunes
Yellow dunes
Grey dunes
Dune slack
Heath and woodland / Climax
Explain embryo dunes:
- Upper beach area where sand starts to accumulate around a small obstacle, such as driftwood or a ridge of shingle
- Pioneer species colonise the bare sand, such as prickly saltwort which has high salt tolerance and leaves that retain moisture.
- The roots of these plants bind the sand together
Explain yellow dunes:
- The pioneer species die and decompose, helping to form a thin soil.
- Other species move in, such as marram grass.
- The soil is still alkaline but will begin to tolerate a wide range of plants
Explain grey dunes:
- The soil deepens and becomes less alkaline as more organic matter forms. This is called humus.
- Small plants, such as hawkweed, and larger plants, such as gorse and heather move in.
What are dune slacks?
- Dune slacks are very large depressions that are often deep enough to expose the water table.
- As fresh water is exposed at the surface, new types of vegetation such as reeds grow
Explain heath and woodland:
- Sandy soils develop as there is a greater nutrient content, allowing for less brackish plants to thrive.
- Trees will also grow (willow, birch, oak trees) with the coastal woodland becoming a natural windbreak to the mainland behind)
- These gradually become the dominant climax species
Describe the stability of depositional landforms:
- They consist of unconsolidated sediment and are therefore vulnerable to change
- Depositional landforms depend on a continuous supply of sediment to balance erosion, which may see some landforms changed as their dynamic equilibrium shifts
What is weathering?
The breakdown of rocks (mechanical, biological or chemical) over time, leading to the transfer of material into the littoral zone, where it becomes an input to sediment cells
What is mechanical weathering?
- The breakdown of rocks due to exertion of physical forces without any chemical changes taking place
Give examples of mechanical weathering:
Freeze-thaw
Salt Crystallisation
Wetting and drying
What is freeze-thaw?
- Water enters cracks in rocks and then the water freezes overnight during the winter
- As it freezes, water expands by around 10% in volume which increases the pressure acting on a rock, causing cracks to develop
- Over time, these cracks grow, weakening the cliff making it more vulnerable to other processes of erosion
What is salt crystallisation?
- As seawater evaporates, salt is left behind.
- Salt crystals will grow over time, exerting pressure on rocks, forcing cracks in them to widen.
- Salt can also corrode ferrous (materials that contain iron) rock due to chemical reactions
What is wetting and drying?
- Rocks such as clay expand when wet and the contract again when they are drying.
- The frequent cycles of wetting and drying at the coast can cause these rocks and cliffs to break up
What is chemical weathering?
The breakdown of rocks through chemical reactions
What are the different types of chemical weathering?
Carbonation
Oxidation
Solution
What is carbonation?
- Rainwater absorbs CO2 from the air to create a weak carbonic acid
- This carbon acid then reacts with calcium carbonate in rocks to form calcium bicarbonate which can then be easily dissolved
- Acid rain reacts with limestone to form calcium bicarbonate, which is then easily dissolved allowing erosion
What is oxidation?
- When minerals become exposed to the air through cracks and fissures, the mineral will become oxidised which will increase its volume, causing the rock to crumble
What is the most common oxidation within rocks?
- Iron minerals becoming iron oxide, turning the rock rusty orange after being exposed to the air
What is solution?
When rock minerals such as rock salt are dissolved
What is biological weathering?
The breakdown of rocks due to the actions of plants, bacteria and animals
What are the different types of biological weathering?
Plant roots
Birds
Rock boring
Seaweed acids
Decaying vegetation
How do plant roots cause weathering?
- Roots of plants grow into the cracks of rocks, which exerts pressure and eventually splits them
How do birds cause weathering?
- Some birds such as puffins dig burrows into cliffs, weakening them and making erosion more likely
What is rock boring?
- Many species of clams secrete chemicals that dissolve rocks
- Piddocks may burrow into the rock face
How do seaweed acids cause weathering?
- Some seaweeds (such as kelp) contain pockets of sulphuric acid, which if hit against a rock or cliff face will dissolve some of the rock’s minerals
How does decaying vegetation cause weathering?
- Water that flows through decaying vegetation and then over coastal areas will be acidic and thus cause chemical weathering
What does the type of mass movement that occurs depend on?
- The angle of the slope / cliff
- The rock’s lithology and geology
- The vegetation cover on the cliff face
- The saturation of the ground / previous weather patterns
What are the two different categories of mass movement?
A slide
- Sediment keeps its same place within the whole material and simply moves downhill
A flow
- All the material flows down and mixes
What are the different types of flows?
Soil creep
Solifluction
Mudflows
What is soil creep?
- The slowest but continuous form of mass movement involving the movement of soil particles downhill
What is solifluction?
- Occurs mainly in tundra areas where the land is frozen. As the top layer thaws during summer (but the lower layers remain frozen due to permafrost) the surface layers flow over the frozen layers
What are mudflows?
- An increase in the water content of soil can reduce friction, leading to earth and mud flowing over underlying bedrock
What are the different types of slides?
Rock falls
Rock slides
Slumps
What are rock falls?
- Occur on sloped cliffs (over 40°) when exposed to mechanical weathering breaks large chunks of the cliifs away
- Material that breaks off is called scree and bounces down the cliff to the bottom
What are rock slides?
- Water between joints and bedding planes (which are parallel to the cliff face) can reduce friction and lead to more sliding
- Slabs of rock slide over the underlying rock, which is called a slip or a plane
What are slumps?
- Occur when the soil is saturated with water, causing a rotation movement of soft materials (such as clay and sand)
- These occur on moderate to steep slopes
- Slumping causes rotational scars, and if it repeats, it will form a terraced cliff
What types of weathering are more common in different climates?
- In colder climates, mechanical weathering is more common
- In warmer climates, chemical weathering is more common
What are the two main characteristics that influence cliff profiles?
- The resistance of the rock to erosion
- The dip in rock strata in relation to the sea
What are many cliffed coastlines, and what does this mean?
- Many cliffed coastlines are composite, meaning they have different rock layers
- This makes explaining cliff profiles very complex
What are concordant coastlines?
- Where the rock strata run parallel to the coast
- The rock type varies, but normally consists of bands of more resistant and less resistant rock
What can concordant coastlines lead to the formation of?
- The formation of Dalmatian coastlines
How are Dalmatian coastlines formed?
- A rise in sea levels leads to the wide river valleys between headlands being flooded
- The headlands become islands, running perpendicular to the mainland
What other types of coast are dependent on a concordant coastline?
Haff coasts
What are Haff coasts?
- Large bays are crossed by spits, creating extensive lagoons
What are discordant coastlines?
- Where the rock strata run perpendicular to the sea which can create successions of headlands and bays
- Less resistant rocks are eroded faster than the more resistant rocks, which leads to the formation of bays
What do headlands and bays cause?
- They have an effect on incoming waves and cause wave refraction
What is wave refraction?
- The process by which waves turn and lose energy around a headland on uneven coastlines.
- The wave energy is focussed on the headlands, creating erosive features in these areas
- The energy is dissipated in bays, leading to the formation of features associated with lower energy environments such as beaches
What is vegetation essential in?
Stabilising any landforms from change
How does vegetation help to stabilise coastal sediment?
- Roots of plants bind soil together which helps to reduce erosion
- When completely submerged, plants provide a protective layer for the ground and so the ground is less easily eroded
- Plants reduce the wind speed at the surface and so less wind erosio ocurs
What are plants either?
Xerophytes
Halophytes (or brackish)
What are xerophytes?
Plants that are tolerant of dry conditions
What are halophytes?
Plants that are tolerant of salty conditions
What is plant succession?
A long-term change in a plant-community in an area
Describe the process of plant succession:
- On coasts when there is a supply of sediment and deposition occurs, pioneer plants begin to grow in bare mud and sand
- Due to the salty conditions, only certain plants can grow there
- As more deposition occurs and the vegetation dies and releases nutrients into the sand, the saltiness of the soil si reduced which means different plants can start growing there
- These processes continue over time allowing new species of plants to colonise
What is a good example of a pioneer plant?
Marram grass
Why is marram grass a good pionner plant?
- It is tough and felxible, so can cope when being blasted with sand
- It has adapted to reduce water loss through transpiration
- Their roots grow up to 3 metres deep and can tolerate temperatures of up to 60°c
What are the stages in salt marsh succession?
Algal stage
Pioneer stage
Establishment stage
Stabilisation
Climax vegetation
What is the algal stage?
- Gut weed and Blue green algae establis as they can grow on bare mud, which their roots help to bind together
Describe the pioneer stage:
- Cord grass and Glasswort grow
- Their roots begin to stabilise the mud allowing the estuarine to grow
Describe the establishment stage:
- Salt marsh grass and Sea asters grow, creating a carpet of vegetation
- The height of the salt marsh therefore increases
Describe the stabilisation stage:
- Sea thrift, Scurvy grass and Sea lavendar grow, and so salt rarely ever gets submerged beneath the marsh
Describe the climax vegetation stage:
- Rush, Sedge and Red fescue grass grow since the salt marsh is only submerged once or twice a year
What are high energy coastlines associated with?
- More powerful waves
- They therefore occur in areas where there is a large fetch
- They typically have rocky headlands and landforms and fairly frequent destructive waves
- As a result these coastlines are often eroding as the rate of erosion exceeds the rate of deposition
Describe low-energy coastlines:
- Less powerful waves
- Occur in sheltered areas where constructive waves prevail and as a result these are often fairly sandy areas
- There are landforms of deposition as the rates of deposition exceed the rates of erosion
What does the size of a wave depend on?
The strength of the wind
How long the wind has been blowing for
Water depth
Distance of fetch
Describe constructive waves:
Strong swash, weak backwash
Low wave height, long wavelength
Low frequency
Depositional
Describe destructive waves:
Strong backwash, weak swash
High wave height, short wavelength
High frequency
Erosional
What are the reasons for short-term sea level change?
High tide and low tide
- A daily phenomena due to the gravitational pull of the moon
Wind strength and direction
- These can change causing a change in sea level for a couple of minutes or longer
Atmospheric pressure
- The lower the pressure, the higher the sea levels
What is isostatic change?
Localised sea level change
Why might isostatic sea level change occur?
Due to post-glacial adjustment
- Glaciers weigh down the land beneath, and so the land subsides until it melts
Give an example of where post-glacial adjustment has occurred:
- Post-glacial adjustment for the UK after the Ice Age has caused Southern England to subside around 1mm per year
- It has also resulted in Scotland rebounding and increasing by around 1.55mm each year
What may also cause isostatic sea level change?
Tectonic activity
- It may cause land subsidence, therefore causing isostatic sea level increase
What is Eustatic rise?
Global sea level change
Why does eustatic rise occur?
Thermal expansion
- Water expands when it gets warmer and so the volume of water increases as a result, rising sea levels
- This is due to global warming
What is coastalisation and why does it occur?
- The movement of people towards the coast
- Many people move despite the high flood risk due to tourism, high-yield agricultural lands or housing pressure
What can coastalisation result in?
- It can increase the environmental vulnerability of locals to flooding due to storm surges
When does a storm surge occur and why?
- When there is a short-term change in sea level, which may be due to low pressure during a depression or tropical cyclone
What can cause a storm surge to be exacerbated?
Subsidence of the land
- Through tectonic activity or post-glacial adjustment
Removing natural vegetation
Global warming
- As the surface of oceans gets warmer, its estimated that the frequency and intensity of storms will increase, so the severity of storm surges and flooding is also expected to increase
Describe the importance of mangrove forests:
- They are the most productive and complex ecosystem in the world
- They also provide protection against extreme weather events like cyclones which are very common in places such as the Bay of Bengal
- However, due to pressure for land space, many mangrove forests are destroyed for tourism, local industry or housing plains.
What are joints?
These divide rock strata up in blocks with a regular shape
What are fissures?
Smaller cracks in rocks. Often they are only a few cm long
What are faults?
A major line of weakness within the rock. This causes large fractures.
What is dip on cliff profiles?
Dip is the angle of rock strata (layers of sedimentary rock) in relation to the horizontal. Dip is a tectonic feature.
Describe horizontal dip:
- Produces a near vertical profile
- With notches reflecting weathering / small scale mass movement of strata that are easily eroded
Describe seaward dip, high angle:
- High angle of seaward dip produces a sloping, low angled profile with one rock layer facing the sea
- Vulnerable to rock slides down the dip slope when uppermost strata are attacked by sub-aerial processes
Describe seaward dip, low angle:
- Low angle of seaward dip produces a steep profile that may even exceed 90 degrees
- This creates areas of overhanging rock
- Vulnerable to rock falls
- Frequent small-scale mass movement of material weathered from ciff face
- Major cliff collapse when undercutting by marine erosion makes overhang unsustainable
Describe landward dip:
- Landward dipping strata produce steep profiles on 70-80 degrees as downslope gravitational force pulls loosened blocks into place
- Very stabile profile with few rock falls
- The water doesn’t get to the strata, making the cliff more stable
What can the angle of the cliff dip profile affect?
Erosion occurring at different rates along the coastline
What is lithology?
The general physical characteristics of a rock or the rocks in a particular area
What can tectonic pressures do to rocks?
Tectonic forces (sometimes ancient) can deform rock layers through compressional (pushed together) and tensional (pulled apart) forces.
Under high pressure and heat, rocks may bend or break apart.
What are synclines?
A downward, U-shaped fold in the layers of rock in the Earth’s surface
What are anticlines?
An upward, curved fold in the layers of rock in the Earth’s surface
What are tides?
The periodic rise and fall of sea levels
What causes tides?
- They are caused by the gravitational pull of the Sun and the Moon.
- The moon pulls the water towards it, creating high tides.
- On the other side of the Earth, a compensatory bulge is created causing high tides there as well.
- The area between the two bulges are where the tides are at their lowest.
What are spring tides?
Twice in a lunar month when the sun, moon and earth are all in a straight line, the tide force is at its strongest and highest
What are neap tides?
Twice a month the Sun and Moon are positioned at 90° to each other in relation to the Earth
What are emergent coastlines?
Formed as a result of a (relative) fall in sea level.
What are the features of an emergent coastline?
Raised beaches
Relict cliffs
Describe raised beaches:
Areas of former wave-cut platforms and their beaches are left at a higher level than present sea level due to sea level change.
They are found at a distance inland from the present coastline
Describe relict cliffs:
Caves, arches and stacks formed when they were at sea level are now left high up on the cliff face today.
What causes a storm surge?
- The main cause is high winds pushing the sea water towards the coast, causing it to pile up there.
- There’s also a smaller contribution from the low pressure at the centre of the storm that ‘pulls’ the water level up
What are submergent coastlines?
Formed as a result of sea level rise
What are the features of a submergent coastline?
Rias
Fjards
Fjords
Describe Rias:
- Rias are submerged river valleys
- The lowest part of the river’s course and the floodplains alongside the river may be completely drowned, but the higher land forming the tops of the valley sides and the middle and upper part of the river’s course remain exposed
Describe fjards:
- Fjards are drowned glacial lowlands
- They are typically covered with scattered small islands
Describe fjords:
- Submerged glacial valleys
- Due to the effects of the glacial erosion which shaped the original landscapes, these features have very steep sides and the water is very deep
What is the Tees-Exe line?
An imaginary northeast-southwest line that can be drawn on a map of Great Britain which roughly divides the country into lowland and upland regions
Where are resistant rock coastlines found?
Western and Northern Britain
Describe resistant rock coastlines:
- Rocky coastline of igneous granite / basalt can withstand frequent storms with little erosion
- It also has compacted older sedimentary rocks (such as old sandstone) and metamorphic rocks (slates and schists)
What is schist?
A medium grade metamorphic rock, formed by the metamorphosis of mudstone / shale, or some types of igneous rock, to a higher degree than slate
Where are coastal plain landscapes found?
Eastern and Southern Britain
Describe coastal plain landscapes:
- Consists of younger, weaker sedimentary rocks (chalks, clay, sand and sandstone)
What do coasts classifications depend on?
Their geology
- which can relate to rocky, sand and estuarine coasts as well as concordant and discordant
The level of energy
- creating high or low energy coasts
The balance between erosion and deposition
- Creating either erosional or depostional coasts and features
Changes in sea level
- Creating emergent or submergent coats
What do the lithology physical characteristics of a rock include?
The strata
- Layers of rock
Bedding planes
- Natural breaks (horizontal) in the strata caused by gaps in time during periods of rock formation
Joints
- Vertical fractures either caused by contraction as sediments dry out or by earth movements during uplift
Folds
- Formed by pressure during tectonic activity which makes rocks buckle and crumple
Faults
- Formed when the stress or pressure to which a rock is subjected exceeds its internal strength.
Dips
- Refers to the angle at which rock strata lie
Qualities of igneous rocks:
Crystalline
Resistant
Impermeable
Qualities of sedimentary rocks:
- Formed in strata (layers)
- Jointed rocks are permeable
- Others have airspace making them porous
- Shale is fine and compacted making it impermeable
Qualities of metamorphic rocks:
Very hard
Resistant
Impermeable
Qualities of unconsolidated materials:
Loose
Easily eroded
If compacted, the particles can stick together and form an impermeable layer within a cliff strata
What are waves?
- A medium through which energy is transferred
- They are created by the wind blowing across the surface of the sea
- Frictional drag increases as the wind speed increases, making the wave bigger
What is the wave orbit?
- The shape of the wave: varying between circular and elliptical
Why does a wave break?
- When out in open water, there is little horizontal movement of ocean water, the bulk of the motion is vertical
- This changes when waves approach the coastline
- As the water approaches the coastline, it encounters increasing contact with the shelving sea bed, which exerts a frictional force on the base of the wave.
- This changes the normal circular orbit of the wave into an elliptical orbit
- as the waves get closer to the coast the impact of friction grows, with the top of the wave moving faster than the base of the wave.
- Eventually, a critical point is reached where the wave’s crest curves over and creates a breaking wave.
Describe how dip occurs in cliffs:
- Rocks tend to form in layers of different rock types known as beds.
- These beds are subjected to tectonic forces that tilt and deform them so they dip at an angle
- The angle the beds dip at affects how they are eroded and the profile of the resulting cliffs
What variation can rock structure cause between cliff profiles?
- Vertical dipping beds produce steep cliffs
- Beds that dip seaward produce getler cliffs but are less stable because loose material can slide down the bedding planes by mass movements
- Landward dipping beds produce stable and steeper cliffs
How is cliff morphology influenced by the permeability of rock?
- Cliffs which have impermeable rocks overlying permeable rock limit perlocation (movement of fluid) and are therefore more stable, preventing mass movement
- Cliffs in which permeable rocks overlie impermeable rock, water may oak into the cliff and make slope failure more likely as water builds up between the junction of the two rocks.
What are sediment cell inputs?
Eroding cliff
Onshore transport
Erosion of beach materials
Supply from dune stores
Sub-aerial erosion (weathering)
River discharge
Beach nourishment
Littoral drift into the cell
River transportation
What are sediment cell throughputs?
Longshore transport
Onshore transport
Offshore transport
What are sediment cell outputs?
Offshore banks, spits, bars, shoals
Beach accumulation
Dune encroachment and deflation
Particle attrition and offshore transport of fine sediment
Dredging
Littoral drift out of cell
Why are sediment cells dynamic?
- Because the sediment is constantly generated in the same source region, transported through the transfer region and deposited in the sink region
What are the four different approaches to managing coastal areas?
Hold the line
- Defences are built to try and keep the shore where it is
Managed realignment
- Coastline moves inland naturally but managed
Advance the line
- Defences are built to try and move the shore seawards
Do nothing
- No defences are put in place and the coast is allowed to erode
What factors are looked at when deciding which coastal management policy to use?
Economic value of assets that could be looked at
The technical feasibility of engineering solutions
The ecological and cultural value of land
What is eustatic change?
- When the sea level itself rises or falls.
- These changes occur more globally
What are isostatic changes?
- These changes are more local in scale
- When the weight of an ice sheet on land causes it to sink (isostatic subsidence) this gives the appearance that the sea has risen
- When the ice melts the reduced weight causes the land to readjust and rise (isostatic recovery) which can give the appearance that the sea level is falling
What does not have a direct effect on sea level?
- Sea-based ice melting
- This is because it is already part of the ocean system
Describe thermal expansion:
- Heating of water imparts heat energy to the water molecules which then begin to move.
- This free movement of the molecules causes the expansion of the liquid.
When does eustatic sea level change occur?
When there is a global change in the amount of water stored in the oceans, or a change in the geometry of the ocean basins which alters the volume of water they can hold
What is glacial eustasy?
When the sea level changes in response to the amount of water stored in ice caps
What are the four possible causes of sea-level change?
- Warming of ocean’s water and thermal expansion
- Storage of water as ice in glaciers
- Changes in rate of sea-floor spreading
- Continent-continent collision (reduction of area of continental crust)
What are the characteristics of a Ria?
Plan View:
- Show a winding profile, reflecting the original route of the river and it’s valley
Cross Section:
- Relatively shallow water- becomes increasingly deep towards the centre. Exposed valley sides- gently sloping
Long profile:
- Have a quite even and smooth profile with water of a fairly uniform depth- although deepest water is at the mouth
What are the characteristics of a fjord?
Plan view:
- Straighter profile than a ria, as the glacier has truncated any interlocking spurs
Cross section:
- Steep, almost cliff-like valley sides- water is uniformly deep
- The cross-section is u-shaped, which reflects the original shape of the glacial valley
Long profile:
- Fjords are not deepest at their mouth- they have a shallower section at the seaward end known as a threshold
What are the impacts of rising-sea levels on property and agriculture?
- Expensive relocation
- Major roads and railways near coasts threatened
- Major cities such as Tokyo, Shanghai, London and Calcutta threatened
- Coastal nuclear reactors at risk
- Significant economic loss if agricultural areas are flooded
What are the impacts of rising sea levels on tourism?
- Affects scenic value of coastlines, affecting tourist revenue
- as the tide becomes higher, beaches are smaller
- More hard defences necessary to reduce flooding are unattractive
- Economic losses
What are the impacts of rising sea levels on wildlife?
- Coastal ecosystems such as sand dunes and salt marshes at risk
- Coastal areas are home to some of the most important wildlife
What is marine transgression?
When there is a rise in the relative sea level and the sea flows over the land to cover areas which would have formerly been exposed
- During this time the coastline is said to retreat
What is marine regression?
- When sea level falls and land is revealed
- Coastlines advance.
What are glacio-eustatic changes?
- Changes in sea level owing to accumulating and melting of ice that covers continental land masses
What are steric changes?
Related to changes in how atoms in a molecule are arranged.
As oceans cool they reduce in size and when they warm they expand
Changes in temperature are only believed to be able to make a difference of around 10 metres to global sea levels
What are Epeirogenic movements?
Large-scale vertical tectonic motions of the crust involving depression or uplift of ocean floors and continents
Describe the impact of Epeirogenic movements on sea level:
- if the shape of ocean basins is altered, their water -holding capacity will change- such changes are termed tectono-eustatic
- Epeirogenic movements can also change the level of the land when continents rise periodically.
How can sediment accumulation impact sea level?
- Global changes in sea level can occur if there is a large accumulation of sediments carried from land to offshore locations
- This can reduce the ocean basin’s holding capacity, leaving to a rise in sea level
- This is a slow and small increase
- The sediment mass could also depress the ocean floor, which would increase the ocean’s volume leading to a fall in sea level
How can sediment accumulation affect the land?
- Land can also subside under the weight of sediment, in coastal regions, leading to a rise in relative sea level.
How can volcanic activity impact sea levels?
- The creation of volcanic ocean islands could displace water and increase sea levels.
- The weight of volcanic islands such as those in the Pacific Ocean may also act to depress the crust supporting them, thus leading to epeirogenic changes involving a lowering of sea level
How can volcanic activity impact the land?
- it may result in relative sea level change as magma chambers below the Earth’s surface fill and empty resulting in uplift and subsidence of the land, and therefore relative falls and rises in sea levels
- This is known as bradyseismic change
How can human actions impact sea level?
- Through greenhouse gas emissions which enhance the greenhouse effect, leading to global warming and associated sea level rises
How can human actions impact land level?
- By removing oil, natural gas or water from within the ground, land can subsidise, and therefore there’ll be a rise in relative sea level.
Why do some cliffs erode faster than others?
Long wave fetch- creates destructive ocean waves
Soft geology, especially unconsolidated sediments such as boulder clay
Cliffs with structural weaknesses such as seaward rock dip and faults
Cliffs vulnerable to mass movement and weathering as well as marine erosion
Strong longshore dirt, eroded debris is quickly exposed to further erosion
Describe ICZM:
- Sections of the coastline are being managed as a whole, rather than by individual villages/towns
- This is because human actions in one place will affect other places further along the coast because sediment moves along the coast in sediment and littoral cells
What is hard engineering?
Hard engineering options tend to be expensive and involve building structures to protect the coast.
They may also have a high impact on the landscape or environment and be unsustainable
What is soft engineering?
Soft engineering options are often less expensive than hard options.
They are usually more short-term with less impact on the environment
Name some hard-engineering structures:
Groynes
Sea walls
Rip Rap
Revetments
Offshore Breakwater
What are groynes?
Timber of rock structures built at right angles to the coast.
They trap sediment being moved along the coast by longshore drift- building up the beach
What are the advantages of groynes?
- The built up beach increases tourist potential and protects the land behind it
- Groynes work with natural processes to build up the beach
- Not too expensive
What are the disadvantages of groynes?
- They starve beaches further along the coast of fresh sediment, because they interrupt longshore dirft. This often leads to increased erosion elsewhere
- Groynes are unnatural and rock groynes can be very unnatractive
What are the costs of groynes?
£10,000 to £100,000 each, with five needed per km.
What are sea walls?
Made of stone or concrete at the foot of a cliff, or at the top of a beach.
They usually have a curved face to reflect waves back into the sea.
What are the advantages of sea walls?
- Effective prevention of erosion
- They often have a promenade for people to walk along
What are the disadvantages of sea walls?
- They reflect wave energy, rather than absorbing it
- They can be intrusive and unnatural-looking
- They are very expensive to build and maintain
What are the costs of sea walls?
Up to £5000 per metre
What is rip rap?
Large rocks placed at the foot of a cliff, or at the top of a beach
It forms a permeable barrier to the sea- breaking up the waves, but allowing some water to pass through
What are the advantages of rip rap?
- It is relatively cheap and easy to construct and maintain
- It’s often used for fishing from, or for sunbathing by tourists
What are the disadvantages of rip rap?
- The rocks are usually from somewhere else (e.g granite) so they don’t fit in with the local geology and can look out of place
- It can be very intrusive
- The rocks can be dangerous for people clambering over them
What is the cost of rip rap?
Up to £6000 per metre
What are revetments?
Sloping wooden, concrete or rock structures- placed at the foot of a cliff or at the top of a beach.
They break up a wave’s energy
What are the advantages of revetments?
They are relatively inexpensive to build
What are the disadvantages of revetments?
They are intrusive and very unnatural-looking
They can need high levels of maintenance
What is the cost of revetments?
Up to £3000 per metre
What is an offshore breakwater?
A partly submerged rock barrier, designed to break up the waves before they reach the coast
What are the advantages of offshore breakwaters?
They’re an effective permeable barrier
What are the disadvantages of offshore breakwaters?
It is visually unappealing
It’s a potential navigation hazard
What is the cost of offshore breakwaters?
£3000 per metre
Name some forms of soft engineering:
Beach nourishment
Cliff regrading and drainage
Dune stabilisation
Marsh creation
What is beach nourishment?
The addition of sand or pebbles to an existing beach to make it higher or wider.
The sediment is usually dredged from the nearby seabed
What are the advantages of beach nourishment?
- Relatively cheap and easy to maintain
- It looks natural and blends in with the existing beach
- It increases tourist potential by creating a bigger beach
What are the disadvantages of beach nourishment?
- It needs constant maintenance, because of the natural processes of erosion and longshore drift
What is the cost of beach nourishment?
£300,000 for 100 metres
What is cliff regrading and drainage?
Cliff regrading reduces the angle of the cliff, to help stabilise it.
Drainage removes water to prevent landslides and slumping
What are the advantages of cliff regrading and drainage?
- Regrading can work on clay or loose rock, where other methods won’t work
- Drainage is cost effective
What are the disadvantages of cliff regrading and drainage?
- Regrading effectively causes the cliff to retreat
- Drained cliffs can dry out and lead to collapse (rock falls)
What is dune stabilisation?
Marram grass can be planted to stabilise dunes.
Areas can be fenced in to help keep people off newly planted dunes
What are the advantages of dune stabilisation?
- It maintains a natural coastal environment
- It provides important wildlife habitats
- It is relatively cheap and sustainable
What are the disadvantages of dune stabilisation?
- It is time-consuming to plant marram grass
- People may respond negatively to being kept off certain areas
What is the cost of dune stabilisation?
£200 to £2000 for 100 metres
What is marsh stabilisation?
A form of managed retreat, by allowing low-lying coastal areas to be flooded by the sea. The land then becomes a salt marsh.
What are the advantages of marsh stabilisation?
- It is relatively cheap because it often involves land reverting to its original state before it was managed for agriculture.
- It creates a natural defence- providing a buffer to powerful waves
-It creates an important wildlife habitat
What are the disadvantages of marsh stabilisation?
- Agricultural land is lost
- Farmers or landowners need to be compensated
What is the cost of marsh stabilisation?
The cost is variable- depending on the size of the area left to the sea
What is the aim of ICZM?
- To bring together all of those involved in the development, management and use of the coast.
- The aim is to establish sustainable levels of economic and social activity, resolve environmental challenges and conflicts, and protect the coastal environment
What are difficulties when looking at coastal management?
Engineering feasibility
Political, social and economic reasons
Impacts on Coastal Processes
Land use and value
Environmental sustainability
Describe engineering feasibility:
This considers the following:
- Is it the right method? (i.e what would work best)
- Is it achievable?
- Is it within budget?
- What are the risks?
Describe political, social and economic reasons surrounding coastal management:
- Agriculture is a key employer in the area- many jobs depend on it
- Tourism is another key industry along the coast, and is a major contributor to the local economy
- Most coastal villages will not be at risk of erosion over the lifetime of management plans
- Politically, costs have to be acceptable to the government of the day- and often something has to be seen to be ‘done’. ‘Do nothing’ may be a reasonable option, but its rarely accepted by those affected
