Geography > Coasts > Flashcards
Coasts Flashcards
Soil creep
surface runoff slowly moving soil downhill
slumping
Area of saturated land slips downhill
Physical (freeze-thaw)
Rocks break due to changes in temperature
Biological
plants and animals break up the rocks
Chemical
acid in rainwater dissolves the rock
Corrosion (solution)
Material dissolved by the river
Abrasion (corrasion)
Load wears away river channel
Hydraulic action
force of current dislodges loose material
Attrition
Load collides
Traction
Rolling of large load
Saltation
Bouncing of smaller load
suspension
Fine material held within the water
solution
rocks dissolved within the water
Headlands and bays
Headlands and bays are usually found together on the same stretch of coastline.
Headlands and bays form on discordant coastlines, where bands of rock of alternating resistance run
perpendicular to the coast.
Bays form where weak (less resistant) rocks (such as sands and clays) are eroded, leaving bands of stronger
(more resistant) rocks (such as chalk, limestone, granite) forming a headland.
Cliffs, wave cut notch and wave cut platforms
In areas of more resistant cliff material erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff.
- Erosional processes such as hydraulic action and abrasion cut into the base of the cliff forming a wave-
cut notch. As the notch increases in size the weight of the cliff above become too much and the cliff collapses. - The material from the cliff is broken up through attrition and is smoothed out through abrasion, this
leaves a flat terrace at the base of the cliff known as a wave cut platform.
Caves, arches, stacks and stumps
Even hard rock, that forms headlands, contains weaknesses. Hydraulic action forms cracks in the rock
until an opening is formed.
* As the waves continue to attack the rock it is hollowed out to form a cave.
* Further erosion means that the cave is widened and deepened until it becomes an arch.
* Widening of the arch through undercutting means that material becomes unsupported and collapses
into the sea forming a stack.
* Further undercutting causes the stack to collapse leaving only a stump.
Longshore drift
Material is moved in a zigzag manner along the
coastline by a process called Longshore drift.
Waves are pushed towards the shore by prevailing
wind.
The swash carries material up the beach at an angle.
The backwash carries material back to sea at right
angles to the coastline.
If the waves are constructive more material is
deposited than is removed as the swash is stronger
than the backwash.
4 processes of transportation
Traction, saltation, suspension and solution
2 processes of movement
soil creep and slumping
3 processes of weathering
Physical, biological and Chemical
4 processes of erosion
Corrosion, abrasion, hydraulic action and attrition
How are beaches formed
Beaches are made up from eroded material that has been transported and then deposited by the sea.
* Deposition occurs when waves have limited energy, so beaches often form in sheltered areas like bays.
* Constructive waves build up beaches as they have a strong swash and a weak backwash.
* Sandy beaches are usually found in bays where the water is shallow, and the waves have less energy.
* Pebble beaches often form where cliffs are being eroded, and where there are higher energy waves.
* Beaches profile has lots of ridges called berms. They show the lines of high tides and storm tides.
* The size of the material is larger at the top of the beach, due to the high-energy storm waves carrying
large sediment.
* The smallest material is found nearest the water as the waves break here and break down the rock
through attrition.
* A sandy beach typically has a gentle sloping profile, whereas a shingle beach can be much steeper.
* On sandy beaches, the backwash of the waves removes material forming a gently sloping beach. On
shingle beaches the swash is dissipated because the large particle size allows percolation, so the
backwash is not very powerful, and the beach remains steep.
What is a spit?
A spit is a long beach made up of sand and
shingle that extends out to sea. It is found:
* In areas of shallow water.
* On a bend in the coastline.
* Eroded material is carried along the
coast by longshore drift. This action continues
until secondary winds and waves force the spit
to start to curve.
How are spits formed
Sediment is carried by longshore drift
When there is a change in the shape of the coastline deposition occurs. A long thin ridge of material is deposited, this is the spit
A hooked end can form if there is a change in wind direction
Waves cannot get behind the spit meaning that the land behind will erode less and is very sheltered.
Slits are deposited here to form salt marshes or mud flats
Soft engineering options
Soft engineering options
Soft engineering options are often less expensive than hard engineering options. They are usually also more
long-term and sustainable, with less impact on the environment.
Types of soft engineering:
Beach nourishment
* This replaces beach or cliff material that has been removed by erosion or longshore drift.
* The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beaches
also attract tourists.
* While it can be a relatively inexpensive option it requires constant maintenance to keep replacing the
beach material as it is washed away.
Beach Reprofiling
The beach is re-shaped by redistributing sediment from the lower part of the beach to the upper part of the
beach.
Advantages
* Cheap and simple.
* Reduces the energy of the waves.
Disadvantages
* Only works when wave energy is low.
* Needs to be repeated continuously.
Dune stabilisation
Marram grass planted on sand dunes stabilises the dunes and helps to trap sand to build them up.
Advantages
* Relatively cheap.
* Maintains a natural-looking coastline.
Disadvantages
* Can be damaged by storm waves.
* Areas have to be zoned off from the public, which is unpopular.
Managed retreat
* This is where areas of the coast are allowed to erode and flood naturally. Usually this will be areas
considered to be low value.
* The advantages are that it encourages the development of beaches (a natural defence) and salt marshes
(important for the environment) and cost is low.
* While this is a cheap option, it will not be free as people will need to be compensated for loss of buildings
and farmland.
Hard engineering options
Concrete sea wall
Solid facing to a coastal wall or cliff.
Benefits
Traditional, long used and with proven effectiveness. Absorbs and deflects wave energy back to sea. Recurved upper lip dampens down oncoming wave power
Issues
Requires regular repair Quarrying at base can undermine sea wall foundations. Expensive to construct Gives an artificial appearance to the coast
Revetment
Open slanted concrete or wooden facing/fence offering partial resistance but letting some seawater to pass through
Benefits
Cheaper to construct than a sea wall Along a beach they allow beach material to be deposited behind Reduce power of oncoming waves
Issues
Can restrict sea access from a beach Unattractive along a length of beach Can be damaged in high energy conditions Require regular maintenance & repair
Rip rap / rock armour
Massive blocks of natural rock placed in position and piled up at the base of a cliff
Benefits
Requires less maintenance than a sea wall Granite often used that is barely eroded even under highest energy conditions May look more natural than a concrete sea wall
Issues
Expensive to extract, transport and place in position Can impede access to a beach by visitors Can lead to injuries climbing over Rodents may inhabit spaces between rocks
Tetrapods
Moulded multi-angular concrete shapes formed on site and tipped onto beach to form interlocking components
Benefits
Cheaper than rock armour but doing the same role by being constructed on site from liquid concrete Effective along long stretches of coastline requiring protection
Issues
Less attractive than natural rock – look artificial May protrude into sea and endanger swimmers/small craft Almost impossible to climb over to get access to a beach
Gabions
Rock-filled wire cages placed along a vulnerable coast
Benefits
Cheaper than tetrapods but doing the same role May look more attractive than alternatives
Issues
Wire containers may rust and be broken under high energy conditions Require regular repair & replacement Rodents may inhabit spaces between rocks
Groynes
Wooden (or less often, boulder) ‘breakwaters’ at right angles to a beach extending into the sea designed to capture longshore drift sediments to build up beach width and height
Benefits
Effective at increasing a natural barrier of beach between sea and shore Tourism amenity as wider beaches attract more visitors Attractive Groynes can act as ‘wind breaks’ for visitors Calmer inshore water
Issues
Traditionally constructed of hardwood – which is increasingly environmentally unsustainable Require maintenance and repair Speed up downcoast erosion by robbing adjacent beaches of sand
Offshore reefs
Artificial sand/gravel offshore deposits designed to intercept destructive wave action
The most ‘natural’ of hard engineering techniques Create additional shore habitat Create calmer water conditions between them and shore – benefits tourist use
Issues
Vulnerable to storm conditions Less reliable than ‘concrete/rock’ strategies May be overwhelmed by rising sea levels
Formation of tropical storms
Tropical storms begin when thunderstorms move over tropical ocean water.
* Tropical oceans (at least 27°C) warm the air above it.
* This warm, moist air starts to rise.
* Because this air is evaporating, there is less air left near the surface. This causes an area of low air pressure.
* As the warmed, moist air rises and cools, the water in the air forms clouds.
* As the storm moves over the ocean, it picks up more warm moist air and grows. The speed of
its winds increases as more air is sucked in.
* Surrounding air rapidly moves into the low-pressure area to fill the space, causing wind speeds
to increase.
* The whole system of clouds and wind spins due to the trade winds and the earth’s rotation
(coriolis effect).
* It can take hours or days to fully form a tropical storm. The eye is an area of calm winds, which
is surrounded by the ferocious eyewall of high winds and heavy rain.
What are the coastal oppurtunities on the US gulf coast
Tourism: The gulf coast region contains some of the US’s best beaches e.g., beaches at Destin and Pensacola
in Florida. This creates a lot of opportunities for tourism which leads to jobs and economic growth for area of
the gulf coast.
Commercial fishing is a multi-million-dollar industry in the Gulf of Mexico: Shrimp, snapper, grouper, and
stone crab are some of the Gulf’s most important commercial species.
Oil industry: The Gulf Coast region is the technical and financial centre of the US oil and gas industry, with
many company headquarters concentrated along coast. This region is home to 1/5 of total crude oil
production in the U.S., 45% of U.S. petroleum refining capacity and 51% of U.S. natural gas processing plant
capacity.
Ports: The Gulf Coast is a major centre of economic activity. The Port of Louisiana and the Port of Houston are
two of the ten busiest ports in the world by cargo volume.
What are the threats of living near a costal area like the US gulf coast
Tropical storms
* Each year, an average of ten tropical storms develops over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Many of these remain over the ocean. Six of these storms become hurricanes each year.
* See also impacts of Hurricane Katrina, 2005.
Oil spills
* The BP oil spill was an industrial disaster that began on 20 April 2010, in the Gulf of Mexico. It was the
largest marine oil spill in the history of the petroleum industry and one of the largest environmental disasters in world history. This disaster brought serious economic consequences for the oil industry as well as the fishing and tourism industries. Furthermore, it brought consequences for human health.
Climate change
* Rising sea levels increase the risk from coastal flooding along the Gulf Coast. Climate change is also thought to increase the intensity of tropical storms.
fringing reef
the most common type, extend outward from a body of land with no water separating the reef from land.
barrier reef
- Barrier- Barrier reefs are platforms separated from the shoreline by a channel or a lagoon.
- Barrier reefs are created due to the sea level rising or the land sinking. The coral grows upwards so they can
continue to photosynthesize, and this leaves a gap between the land and the reef. - The longest barrier reefs are found along the coasts of Belize and Australia.
Atoll reef
- Atolls are coral islands that consist of a narrow, horseshoe shaped reef with a shallow, central lagoon.
- They often form around volcanic islands that have sunk due to the process of subduction.
- Over 300 atolls are found throughout the South Pacific.
Mangroves
- Mangroves are trees or shrubs which grow in tidal, tropical, coastal swamps.
- They have tangled roots that grow above ground and form dense thickets.
- It is thought that they originate from South-east Asia and then spread across the globe.
- Because they grow in the intertidal zone, they live in a constantly changing environment.
Where they are located
* In sheltered tropical and subtropical coastal areas.
* In general, this is an area between latitudes of 30 degrees north and 30 degrees south of the equator.
Conditions required
* Mangrove trees thrive in hot, muddy, salty conditions that would quickly kill most plants.
* Temperatures – Most mangroves grow in warm waters within 30 degrees latitude of the equator.
* They only grow in areas where the temperature remains above 20 degrees Celsius
* They grow in calm, shallow, sheltered areas with no strong waves or currents.
* They develop in areas where there is a large area between the high and low water mark.
Characteristics
* Mangrove swamps contain many different species of tree.
* Mangroves live in salty water as they are halophytes (salt tolerant plants).
* Mangroves are home to a diverse range of species including fish, birds, frogs, snakes, crocodiles, swamp rats,
monkeys and tigers.
* Mangroves create a barrier to the shoreline and protect it from storms.
Adaptations
* Salt filtering roots that keep out much of the salt.
* Prop roots that help to hold the mangrove upright in the shifting sediments where land and water meet.
* Aerial roots that allow them to take in oxygen.
Sand dunes
what are they?
Sand dunes are large heaps of sand that form on the dry backshore of a sandy beach.
For a sand dune to form, it needs:
*A large flat beach,
*A large supply of sand,
*A large tidal range, so there is time for the sand to dry,
*An onshore wind to move sand to the back of the
beach,
*An obstacle such as drift wood for the due to form against
How do sand dunes form?
- Sand dunes develop in areas with a plentiful supply of sediment
- This sediment is moved on shore by strong winds.
- A large tidal range favours sand dune development as the sand can dry out allowing the wind to move
it. - Sand particles are transported through saltation and suspension.
- When sand particles meet a barrier e.g. a piece of driftwood they will start to develop around it.
- Pioneer species start to grow in the sand and bind the it together, forming an embryo dune.
- Embryo dunes are mobile and can be blown inland by the wind, they will be colonized by other salt
tolerant species e.g. marram grass – this leads to the development of fore dunes and later yellow dunes
behind them. - Yellow dunes can be 30-40 years old and are very tall.
- Behind yellow dunes, we see the formation of grey dunes. These are further from the shore, meaning
less saltwater inundation. This means that a greater variety of plant species can grow here. These dunes
are called grey dunes as the soil is darker in colour due to an increase in nutrient rich material. - Behind grey dunes are the mature dunes. These can be as old as 250 years. Here vegetation succession
has allowed for the development of a climax community – in the UK this tends to be deciduous
woodland.
Holderness coast, costal erosion and management case study
Geology of the coastline: Holderness is mostly boulder clay that was deposited during the last ice age. This material is soft rock and so is easily eroded by the action of the sea.
Processes of erosion and weathering:
The cliff foot erosional processes of hydraulic action and abrasion undercut the cliffs at their base and erode the soft material.
Rain water saturates the boulder clay at the top
of the cliff and lubricates a slip plane.
The processes of undercutting and weathering cause material to become unstable - eventually cliff material slips down into the sea under the force of gravity (cliff slumping).
The strong currents of the North Sea rapidly transport material along the shore (longshore drift operates from north to south along this coastline).
This leaves little opportunity for beach development and as a result cliffs are exposed to the action of the sea.
Today, Holderness is one of the fastest eroding coastlines in the world.
Variation in recession along the coastline: Most of Holderness is comprised of soft boulder clay, however, the northern most part of the coastline is made up of chalk.
Chalk is a more resistant rock and so less easily
Eroded.
Therefore, to the north of the coast we find a headland (Flamborough Head), this area protrudes out to sea as it erodes much more slowly.
Effects of cliff recession
Not cost effective to protect areas of low land values.
Resulted in 14 villages being lost from the coastline since Roman times.
Many farmers have also lost their livelihoods, been forced to migrate or diversify. For example, Ringborough Farm has lost 145 acres since 1939, meaning that half of the farm’s land has been lost to the sea. The farmer has moved his farm buildings back from the coast (they are now
considered to be 300 years away from being lost as a result of recession).
The rapid rate of cliff recession has meant that there has been a need to protect areas of high value with hard engineering defences e.g., the settlement of Hornsea on the Holderness Coast.
The problem with this is that it can speed up the processes of erosion further along the coast (where there is an absence of protection). Groynes, such as those at Hornsea, trap sediment and reduce the amount of material reaching the natural spit at the southern end of Holderness (Spurn Point). Without replenishment, Spurn Point may erode; this area is an SSSI (site of special scientific interest) and it is an important habitat for many bird species (e.g., oystercatchers).
Costal managment not a case study
Defences in Holderness
use of groynes to trap moving beach material and provide a protective beach in front of
the cliff
the construction of seawalls and revetments as wave-resistant structures at the base of
the cliffs
artificial off-shore breakwaters like tyres and concrete blocks, forcing waves to break
off-shore.
sea wall used to protect Easington Gas Station (cost 4.5 million)
Defences in Mappleton
- In 1991 a rock revetment and two rock groynes were built to encourage the buildup of beach material by trapping material transported by longshore drift. This means that waves break on the beach rather than attacking the cliffs, as a result sand accumulated and halted erosion.
- However, south of Mappleton, the rate of erosion has increased significantly.
- Material that usually moves south via longshore drift is becoming trapped within the groynes. Now there is no beach to protect the cliffs in these areas - the sea reaches the base of the soft cliffs and erosion occurs.
Managed retreat
Smaller villages and farmland do not typically receive protection – at least not from costly hard engineering schemes such as groynes, sea walls and rock armour. For example, the local authority has decided not to defend the village of Kilnsea (population 80) as it is not seen to be cost effective. This has left villagers feeling abandoned and it is likely that This settlement will eventually be lost to the sea.
At Sandy Beaches Caravan Park the authorities have been practising managed retreat. The caravan site has already lost 50 bases to the sea. It is participating in the local council’s roll back scheme. For every 4 bases that are lost the council provides the funds to buy 5 more bases. The site owner purchases land from farms further inland, rolling back the development.
Hurricane Katerina case study
Impacts:
*Katrina was a category 4 storm.
* Storm surges reached over 6 metres in height.
*New Orleans was one of the worst affected areas because it lies below sea level and is protected by levees. These protect it from the Mississippi River and Lake Pontchartrain. The levee defences were unable to cope with the strength of Katrina, and water flooded into the city.
*Despite an evacuation order, many of the poorest people remained in the city.
*People sought refuge in the Superdome stadium. Conditions were unhygienic, and there was a shortage of food and water. Looting was commonplace throughout the city. Tension was high and many felt vulnerable and unsafe.
*1 million people were made homeless and about 1,200 people drowned in the floods.
*Oil facilities were damaged and as a result petrol prices rose in the UK and USA.
Responses
$50 billion in aid was given by the government.
The UK government sent food aid during the early stages of the recovery process.
The National Guard was mobilised to restore and maintain law and order in what became a
hostile and unsafe living environment.
Possible exam questions:
- For a named area you have studied, explain the hazards faced by coastal communities as a result of natural processes (7)
- For a named area which you have studied, describe the impacts of a tropical
storm (7)
The Great Barrier Reef, north-eastern coast of Australia
Mini case study
- A barrier reef is a reef that runs parallel to the shore but is separated from it by a channel of deep water.
- The Great Barrier Reef sits on what is the remains of the sediments of the Great Dividing Range, a huge
mountain system, off the northeastern coast of Australia. - All reefs, including the Great Barrier Reef, form from a single organism called a coral polyp. Polyp attached
themselves to the sediments of the Great Dividing Range. After they settled the polyps secreted calcium
carbonate, which hardened to form the bony white structure, or skeleton, that formed the shape of the coral
itself. Polyps live on the outside of this bony structure, where more of the same species joined it, becoming one
organism. - The Great Barrier Reef is the largest and longest reef complex in the world, extending for more than 1,250
miles, at an offshore distance ranging from 10 to 100 miles. It has been characterised as the largest structure
ever built by living creatures. - Off the coast of Queensland there is little annual variation in sea temperature, this has been important for the
development of the reef as the optimum temperature for growth is 22-25 degrees Celsius. The waters in this
regions of the southwestern Pacific are generally crystal-clear, with submarine features clearly visible at depths of 100 feet. This is important as coral feed on algae, that are housed within the coral, and so clear water enables sunlight to penetrate to enable the algae to photosynthesize. - Being the world’s most extensive coral reef system, the Great Barrier reef is extremely biodiverse, containing
400 types of coral, 1,500 species of fish and 4000 types of mollusk. It also holds great scientific interest as the
habitat of species such as the dugong (sea cow) and the large green turtle, which are threatened with
extinction.
