Coasts Flashcards
(20 cards)
coastal system
- coasts - where land meets the sea
- coastal systems are in dynamic equilibrium - inputs and outputs are balanced
positive feedback:
- beach starts to form - slows down waves - causes sediment to be deposited - size of the beach increases
negative feedback:
- high rates of erosion - cliff collapses - collapsed material at the base of the cliff dissipates wave energy - erosion rates reduce
inputs:
- sediment brought into coastal system via energy inputs e.g. energy inputs come from waves, wind, tides and currents
stores:
- landforms such as beaches, dunes and spits
outputs:
- sediment washed out to sea
flows:
- erosion, deposition, transportation, weathering, mass movement
sources of energy in coastal systems
wind:
- strong winds can generate powerful waves
waves:
1. waves are created by the wind blowing over the surface of the sea - friction between the wind and the surface of the sea creates small waves which gives the water a circular motion
2. when waves approach the shore they break - friction with the sea bed slows the bottom of the waves - the crest of the wave (top of wave) carries on moving - rises up and collapses
wave energy affected by:
- wind strength
- fetch of the wave (the maximum distance of sea the wind has blown over)
2 types of waves and characteristics:
constructive:
- low frequency - 6-8 per minute
- low and long
- strong swash, weak backwash
destructive:
- high frequency - 10-14 per minute
- high and steep
- strong backwash, weak swash
tides:
- tides - the periodic rise and fall of the level of the sea, caused by the gravitational pull of the moon and the sun
- spring tide - when the moon, earth and sun are in a line, the combined gravitational pull creates the highest high tides and the lowest low tides - greatest tidal range
- neap tide - when the sun and moon are perpendicular to each other, their gravitational pulls interfere with one another, giving the lowest high tides and the highest low tides - smallest tidal range
currents:
- currents - general flow of water in one direction
3 types of currents:
longshore currents (littoral drift)
- flow of water parallel to the coastline - move material along the coast
rip currents
- strong currents moving away from the beach
- waves cause a build up of water at the top of the beach - eventually the waves finds a route back out to sea - creates a strong current
upwelling
- winds drive water across the ocean surface, allowing cold, nutrient-rich water from the deep ocean to rise to the surface
high and low energy coastlines
high and low energy coastlines:
high energy coastlines:
- erosion > deposition
- powerful waves
- e.g. caves, stacks and arches
low energy coastlines:
- deposition > erosion
- gentle waves
- e.g. beaches and spits
sediment cell/budget
sources of sediment in coastal systems:
- rivers carry eroded sediment into the coastal system
- sediment is eroded from cliffs by waves
- waves, wind, tides and currents can transport sediment into the coastal zone
sediment budget:
- sediment budget - difference between the amount of sediment that enters and leaves the system
- more sediment leaves than enters - negative sediment budget
- more sediment enters than leaves - positive sediment budget
sediment cells:
- the coast is divided into sediment cells (also called littoral cells)
- these are lengths of coastline (often between two headlands) that are pretty much entirely self-contained for the movement of sediment - means that each cell is a closed coastal system
wave refraction
- occurs when waves approach a coastline that is not a regular shape (headland and bay)
- wave energy becomes concentrated on the headland, causing greater erosion
- in a bay, the waves lose power, causing deposition
coastal processes
- sub-aerial processes (operate on land)
- marine processes (operate in the sea)
- aeolian processes (driven by the wind)
erosion
erosional processes:
- abrasion - bits of rock/sediment carried by the sea are picked up by strong waves and thrown against rocks and cliffs, breaking bits off and smoothing surfaces
- wave quarrying - energy of wave is enough to detach bits of rock
- solution - soluble rocks get dissolved by the seawater e.g. limestone
- attrition - bits of rock in the water smash against each other and break into smaller bits
- hydraulic action - force of water crashing into rocks, compressing air in cracks, and breaking the rock apart
factors affecting erosion:
wave strength (strong waves = more erosion)
- controlled by fetch and wind strength/duration e.g. long fetches and stronger/longer winds create bigger and powerful waves - more erosion
weathering:
- weathering creates weaknesses in rocks which can be further exploited by the processes of erosion
- weathering rates are high - rates of erosion will be faster
rock type:
- sedimentary rocks e.g. limestone have lots of faults, making them weak and vulnerable to erosion whereas igneous and metamorphic rocks are made up of interlocking crystals, making them more resistant to erosion
transportation
transportation (eroded material being moved):
- solution - substances that can dissolve are carried along in the water e.g. limestone is dissolved into water that’s slightly acidic
- suspension - very fine material e.g. silt are carried along in the water (most eroded material is transported this way)
- saltation - larger particles e.g. pebbles are too heavy to be carried in suspension so particles bounce along the sea bed
- traction - very large particles e.g. boulders are dragged along the sea bed
longshore drift:
1. swash carries sediment up the beach in the direction of prevailing wind
2. backwash carries sediment back down the beach at right angles
3. overtime, sediment is moved along the beach
deposition
deposition (process of dropping eroded material):
- marine deposition - when sediment carried by seawater is deposited
- aeolian deposition - when sediment carried by wind is deposited
- both marine and aeolian deposition happen when the sediment load exceeds the ability of the water or wind to carry it - happens because sediment increases or wind/water slows down
wind and water slow down for similar reasons:
- friction increases - if waves enter shallow water or wind reaches land, friction increases, which slows down the water or wind
- flow becomes turbulent - if water or wind encounters an obstacle, flow becomes rougher and overall speed decreases
weathering
- weathering is a sub-aerial process (operates on land)
- weathering - weakens rocks and makes them more vulnerable to erosion
types of weathering:
- physical/mechanical - when rocks break up with no chemical changes
- chemical - rock breakdown due to a chemical reaction
- biological - rock breakdown due to organic activity
physical/mechanical:
salt weathering
1. salt water enters cracks in rocks at high tide
2. as the tide goes out the rocks dry and the water evaporates - salt crystals are left behind in the cracks
3. as the salt crystals form they expand, exerting pressure on the rock - this causes pieces to fall off
wetting/drying:
1. some rocks contain clay
2. when clay gets wet, it expands, exerting pressure on the rock - this causes pieces to fall off
freeze thaw weathering:
1. water enters cracks in rocks
2. when temperatures drop below 0°C, the water freezes and expands which causes the crack to widen
3. ice melts and more water fills into the cracks
4. the process repeats itself until the rock breaks
biological weathering:
1. plant roots growing in cracks of rock - widens cracks - cause rocks to breakdown
chemical weathering:
1. carbon dioxide in the atmosphere dissolves in rainwater, forming a weak carbonic acid - this acid reacts with rock that contains calcium carbonate e.g. limestone and the rocks are gradually dissolved
mass movement
- mass movement is a sub-aerial process (operates on land)
- mass movement - shifting of material downhill due to gravity
types of mass movement:
- slides - material shifts in a straight line (consolidated rock)
- rockfalls - material breaks up and falls (consolidated rock)
- mudflows - material flows downslope (unconsolidated rock)
- slumps - material shifts with a rotation (unconsolidated rock)
erosional landforms
caves, arches, stacks and stumps:
1. headlands have cracks - abrasion and hydraulic action widen the cracks
2. repeated erosion of cracks causes cave to form
3. continued erosion deepens the cave until it breaks through the headland to form an arch
4. arch is eroded until the roof collapses leaving a stack
5. a wave cut notch forms at the base of the stack, eventually causing it to topple over and collapse - leaving behind a stump
example: jurassic coast in dorset - old harry and old harry’s wife (stack and stump)
headlands and bays:
1. headlands and bays form at discordant coastlines - alternating bands of hard and soft rock at right angles to the coast
2. soft rock is eroded quickly, forming a bay
3. hard rock is eroded more slowly and forms a headland which sticks out
example: jurassic coast in dorset - swanage bay
wave cut platform:
1. sea attacks base of cliff forming a wave cut notch
2. repeated erosion causes rock above notch to become unstable and it eventually collapses
3. collapsed material is washed away and a new wave cut notch starts to form
4. the process repeats and the cliff continues to retreat, leaving behind a wave cut platform
example: jurassic coast in dorset - kimmeridge bay
blowhole:
1. waves approach the bottom of the headland where there’s a crack
2. water is forced and compressed into the cracks - hydraulic action
3. eventually water spurts out the top, forming a blowhole
example: the world’s largest blowhole is found in nakalele blowhole in hawaii
coves:
1. form at concordant coastlines
2. resistant outer band rock is eventually breached
3. erosion speeds up when waves reach the less resistant bands of rock - erosion spreads out laterally
4. once harder rock is reached again, erosion slows down
Example: jurassic coast in dorset - lulworth cove
depositional landforms
spits:
- spit - a finger of beach material extending out to sea
1. longshore drift moves material along the coastline
2. when the coastline changes direction e.g. at a headland, longshore drift doesn’t change direction
3. sediment builds out to sea - this creates a spit
4. a change in wind direction will cause the spit to curve at the end - recurved end
5. over time, several recurved ends form - compound spit
6. the area behind the spit is sheltered from the waves and often develops into mudflats and saltmarshes
- example: spurn head - holderness coast
bars:
1. a bar forms when a spit joins 2 headlands together
2. a lagoon forms behind the bar
- example: slapton sands in devon
tombolos:
- if a spit joins up to an island, it creates a tombolo
- example: angel road in japan
offshore bars:
- destructive waves remove sediment from the beach and form offshore bars
- often submerged
barrier islands:
- barrier islands are long, narrow islands of sand that run parallel to the shore and are detached from it
- it’s not clear exactly how barrier islands form - scientists think that they probably formed after the last ice age ended - ice melt - sea level rise - rising waters flooded land and transported sediment offshore, where it was deposited
- example: horn island
sand dunes:
- vegetation succession - plant community that changes over time - from pioneer species e.g. marram grass to climax community e.g. deciduous woodland
1. sand is deposited around an obstacle e.g. seaweed and driftwood
2. an embryo dune develops which may become vegetated by pioneer species such as marram grass
3. roots bind the sand together - sediment is deposited
4. several embryo dunes will join together to create foredunes and yellow dunes - tallest of the dune succession (yellow dunes)
5. grey dunes form - as plants die, nutrients are added to the sand dune, so more complex plants can grow
6. areas between dunes (slacks) may be damp or even contain water
example - sand dunes found at the holderness coast near spurn head
mudflats and salt marshes:
1. mudflats and saltmarshes form in sheltered, low-energy environments e.g. behind spits - protected from strong waves, allowing sediments to accumulate
2. as silt and mud are deposited by the river, mudflats develop - mudflats are then colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide (known as halophytes e.g. cordgrass) - these plants trap more mud and silt
3. as the mudflats rise and remain exposed for longer periods, they transition into a saltmarsh - plants such as sea lavender grow, which continue to stabilise and build the marsh
4. eventually, these species die - organic matter improves soil fertility - allows taller plants to grow - climax community forms
example: saltmarsh behind spit at the holderness coast
eustatic and isostatic sea level change
eustatic:
- eustatic sea level change is caused by a change in the volume of water in the sea (global)
causes of eustatic sea level change:
- an increase in temperature causes melting of ice sheets, which increases sea level
- as water becomes warmer, it also causes water to expand, which increases sea level further - thermal expansion
isostatic:
- isostatic sea level change is caused by movements of the land relative to the sea (local)
- any downward movement of the land causes sea level to rise, while uplift of land causes sea level to fall
causes of isostatic sea level change:
- a coastal region experiencing seismic activity (earthquakes) may experience land being shifted upwards or downwards as a result of pressures being released by an earthquake
- ice sheet adds lots of weight onto crust and pushes it down into the mantle below - results in sea level rise// ice sheet melts - crust rebounds and rises - sea level falls
sea level change:
- there’s been a sharp rise in average temperature (around 1°C between 1900 and 2000)
- increases in temperature are likely to cause increases in sea level, through melting of ice sheets and thermal expansion
- global sea level is currently rising at almost 2mm each year
impacts of sea level rise on coastal areas:
- coastal flooding
- submergence of low-lying islands - e.g. if the sea level rises by just 0.5m from its current level then most of the maldives will be submerged
- increase erosion
- salinisation
hard engineering
coastal management:
- coastal management put in place to prevent social, economic and environmental impacts
- all coastal settlements want to be defended, but the amount of money available is limited so not everywhere can be defended - CBA decides which places are defended
hard engineering:
- hard engineering - man made structures
sea walls:
- reflects waves back out to sea
- acts as a barrier to prevent flooding
- sea walls acts as promenades so people can walk across them - promotes tourism ✅
- expensive ❌
- waves can erode the sea wall ❌
revetments:
- sloping structures that absorb wave energy - reduce erosion
- beach access steps can be built into the revetment - promotes tourism ✅
- cheap compared to other hard engineering ✅
- visually unappealing ❌
groynes:
- fences built at right angles to the coast - they trap material transported by LSD - this creates wider beaches - absorbs wave energy - less erosion
- builds a wider beach - encourages tourism ✅
- can create erosion further down coast ❌
rock amour:
- large boulders placed in front of a cliff or sea wall - absorb wave energy and reduce erosion
- visually unappealing - they look different to the local geology as the rock has been imported from other areas ❌
- rocks are expensive to transport ❌
- can shift in storms ❌
gabions:
- wire cages filled with rocks - absorb wave energy and reduce erosion
- cheap compared to other hard engineering ✅
- wire cages can rust - unattractive - less tourism ❌
- if the wire cages break then they are very dangerous - people may trip on rocks or cut themselves with the broken wire// birds could injure themselves with the broken wires ❌
breakwaters:
- concrete blocks deposited off the coast - reduce wave energy before they reach the coast
- can be damaged in storms ❌
- expensive ❌
soft engineering
soft engineering:
- soft engineering - natural approach to manage coastal erosion and flooding
beach nourishment:
- beach nourishment is where sand and shingle are added to beaches from elsewhere - creates wide beaches, which reduces erosion
- bigger beaches good for tourism ✅
- very disruptive - e.g. material delivered by trucks will cause congestion in the road and beaches might need to be closed to allow this to happen ❌
- expensive - has to be repeated ❌
- taking material from places like seabed can kill organisms like sponges and corals ❌
dune regeneration:
- creating new sand dunes or restoring existing ones by planting vegetation to stabilise the sand - dunes act as a barrier and absorb wave energy - waves have less energy - less erosion
- dune regeneration increases biodiversity ✅
- dunes can be easily damaged by storms ❌
- areas have to be zoned off from the public while plants grows - less tourism ❌
creating marshland:
- managed retreat - land is allowed to flood - vegetation will colonise the land - becomes a salt marsh - vegetation helps to absorb wave energy - reduces erosive power and also flooding
- increases biodiversity - marshlands create habitats for wildlife ✅
- required to compensate for people who lose buildings and farmland ❌
sustainable coastal management strategies
- hard engineering is often expensive, and disrupts natural processes
- soft engineering tends to be cheaper and works with the natural environment
- so soft engineering is a more sustainable management strategy than hard engineering because it has a lower environmental impact and economic cost
shoreline management plans:
- the coastline is split into sediment cells
- for each cell, a plan is created for how to manage different areas
- for each area within a cell, authorities can decide to hold, advance or retreat the line, or to do nothing
- hold the line - maintain the existing coastal defences
- advance the line - build new coastal defences further out to sea than the existing line of defence
- do nothing - build no coastal defences at all
- managed realignment - where areas are intentionally allowed to flood to protect more important places
ICZM:
- ICZM considers all elements of the coastal system when coming up with a management strategy - holistic approach
- it is a dynamic strategy - decisions are re-evaluated regularly
- aim to protect the coastal environment - manage flood and erosion risk
- SMP in the UK are a form of ICZM
Holderness Coast Case Study
- The Holderness coastline is 61km long - it stretches from Flamborough Head to Spurn Head
- One of the fastest eroding coastlines in Europe - eroding at a rate of 1.8m per year
- Most of the cliffs are made of boulder clay
- The coast is exposed to powerful destructive waves from the North Sea during storms
- Prevailing winds from the North East transport material southwards
Landforms:
- Spurn Head has formed via the transportation of eroded material via longshore drift
- Sand dunes - around Spurn Head, material transported by the wind is deposited, forming sand dunes
- Headland - chalk is prevalent in the north of the area. The chalk is harder and less easily eroded - headland is formed (Flamborough Head) - Flamborough Head has features such as stacks, caves and arches
- Beaches - the area to the south of Flamborough Head is sheltered - deposition occurs and beaches form e.g. Bridlington
- Slumping - boulder clay is prone to slumping when it’s wet
Coastal management:
- A total of 11.4km of the 61km coastline is currently protected by hard engineering (only 11.4 km of the 61km coastline is protected, leaving large sections exposed to rapid erosion)
- Mappleton - two rock groynes and a revetment were installed in 1991 at a cost of £2 million - successfully reduced erosion locally - however, this intervention disrupted natural processes and has starved areas further south of sediment (terminal groyne syndrome) - as a result, erosion rates increased in areas such as Great Cowden, demonstrating that human action can unintentionally accelerate erosion elsewhere (the rate of erosion has been around 10m/year)- ‘holding the line’
- Bridlington - 4.7km long sea wall - protects population of over 40,000 (expensive and require maintenance)// (short term solutions – these structures provide temporary protection but do not stop erosion in the long term) - ‘holding the line’
- Skipsea - people in Skipsea feel that nothing has been done to protect their village with a population of 700 whilst money has been spent on coastal defences in neighbouring towns and villages - decisions were made as a result of CBA - ‘doing nothing’
- Easington gas terminal is only 25m from the cliff edge - it’s protected by a revetment and the SMP recommends that these defences are maintained for as long as the gas terminal is operating - ‘holding the line’ (however, the defences only span about 1km in front of the gas terminal, meaning that the village of Easington isn’t protected)
Why does the Holderness Coast need to be managed:
- Loss of settlements and livelihoods e.g. the village of Skipsea is at risk - 80000 m^2 of farmland is lost each year - huge effect on farmers’ livelihoods
- Loss of Sites of Special Scientific Interest (SSSIs) - e.g. the Lagoons near Easington provide habitats for birds
- Loss of infrastructure - easington gas terminal is only 25m from the cliff edge
Sundarbans case study
Subdarbans Case Study:
- The Sundarbans region is in southwest Bangladesh and east India
- It is the largest mangrove forest in the world
- The land is very flat and low-lying
- The Sundarbans region is home to more than 4 million people
Opportunities:
- The flat, fertile land is ideal for growing crops e.g. rice - social, economic local
- The rich ecosystem of the mangrove forest provides the local population with fish, crabs and honey etc - social, economic local
- The mangrove forests provide timber for construction and furniture - social, economic local
- The mangrove forest provides a natural defence against flooding and coastal erosion - happens on a larger scale - environmental
- There are opportunities for tourism - visitors are attracted by the mangroves - generates $53 million annually - economic local (however, if not properly managed, tourism can cause environmental damage)
Challenges:
Human:
- Deforestation – increasing flood and erosion risks
- Limited electricity and communication – only 20% of households have access mains electricity, making flood warnings difficult to receive
- Poor infrastructure – few, low-quality roads makes it much harder for people to evacuate during floods and access medical care after disasters
Physical:
- Flooding and salinisation – flooding can make the soil too salty for crops to grow
- Dangerous wildlife - tigers, sharks, and crocodiles pose a threat to humans
- Rising sea levels – low-lying land is at risk due to global warming - rising by around 4mm annually
Attempts to overcome these risks:
Resilience - being able to cope challenges
Examples:
- Better roads and bridges are being built in the region. However, this can lead to deforestation and other environmental damage
- Mains electricity is being extended to more areas - will make it easier for flood warnings to reach communities
Mitigation - reducing the impacts of hazards
Examples:
- 3500km of embankments were built to prevent flooding. However, the embankments are gradually being eroded - around 800km are vulnerable to being breached during storms and tsunamis
- Coastal management projects aim to protect existing mangrove forests and replant areas that have been removed, to protect against flooding and erosion. However, it is difficult to prevent illegal forest clearance throughout the whole region and growth of newly planted mangroves is slow
- The government and NGOs have provided funding for cyclone shelters and early warning systems, which should help people shelter or evacuate. However, many people may not have transport available to enable them to evacuate quickly
Adaptation - adjusting behaviour to fit the environment
Examples:
- In some areas, salt-resistant varieties of rice are being grown - this could help residents cope with flooding and sea level rise. However, relying on a smaller range of crops can reduce biodiversity and may increase vulnerability to pests and diseases
- People can adapt to sea level rise or flooding e.g. by building houses on stilts. However, infrastructure such as roads cannot be protected as easily
coastlines or emergence and submergence
coastlines of emergence:
- occurs when sea level falls
raised beaches:
- raised beaches are formed when sea level falls
- over time, beach sediment becomes vegetated and develops into soil
- the cliffs above raised beaches are no longer eroded by the sea, and slowly get covered by vegetation - relict cliffs - can see wave-cut notches, caves, arches and stacks within relict cliffs
- example: isle or arran, scotland - raised beach
coastlines of submergence:
- occurs when sea level rises
rias:
- rias are formed where river valleys are partially submerged
- V shaped valley - gentler sides and shallower water
- example: milford haven in south wales
fjords:
- fjords are formed where glacial valleys are partially submerged
- U shaped valley - steep sides and deep water
- example: longest and deepest fjord is found in norway
dalmatian coastlines - islands parallel to the coastline:
- where valleys lie parallel to the coast, an increase in sea level can form a dalmatian coastline
- example: dalmatian coast in croatia
