Flashcards in Coastal Zone Deck (71):
What is a coast?
A coast is the boundary or interface between land and the sea.
What is a wave?
A wave is a long body of water, curling into an arch form and breaking on the shore.
How do waves form?
As wind passes over the surface, via friction and pressure, energy is transferred to the topmost layers of the water. These forces create a disturbance that are transported through the sea water and develop into waves. WAVES MOVE NOT THE WATER!
What determines the size or waves?
-Wind speed: greater with powerful storms.
-Wind duration: succession of storms in winter 2013-2014.
-Fetch: distance of open water over which the wind can blow (longer=more powerful).
Why do waves break?
1. The sea becomes shallower.
2. Friction against seabed slows the BOTTOM of wave.
3. Top of wave is not slowed down by friction.
4. Close to the shore the wave becomes increasingly elliptical (curved).
5. Top of wave is mover much faster than the bottom causing the wave to break.
6. Water rushes up beach (swash).
7. Water returns down the beach due to gravity (backwash).
What are the properties of constructive waves?
-Lower, limited energy.
-Small height, flat (1m)
-Well spaced apart
-Strong swash (pushes material UP beach).
The beach is built up as a result.
What are the properties of destructive waves?
-Large height and steeper (3-4m)
-Close together (usually interfere)
-Strong backwash (removes materials)
The beach is destroyed as a result.
What is mass movement?
The downhill movement of material under the influence of gravity
What is slide?
Blocks of consolidated rock/earth slide downhill along a straight plane e.g. landslide
What is slump?
Slumping of saturated soil and weak rock on a curved surface e.g. rotational slip.
What is rockfall? (MM)
When fragments of rock ofter breakaway from the cliff face, often due to freeze thaw weathering.
What is landslide? (MM)
When material blocks of earth slide downhill along a rupture surface.
What is mudflow? (MM)
The movement of earth that behaves more like liquid because of saturation. Can be very slow (a creep) or very rapid.
What is rotational slip/slump? (MM)
The slumping of unsaturated soil and weak rock e.g. clay along a curved surface. This can be caused by undercutting at the base of a slope.
What is mass movement affected by?
-Amount of precipitation (soil saturated with water).
-Geology (solid rock or loose earth)
-Antecedent (previous) weather conditions (hot, dry, freezing, wet etc.)
What is weathering?
The disintegration or decay of rock ins situ or close to the ground surface.
What are the different types of weathering?
-Physical/Mechanical: disintegration of rock without any chemical change. e.g. freeze thaw weathering.
-Chemical: The decomposition of rocks is caused by a chemical reaction within the rock. e.g. acid rain can dissolve certain ricks and minerals.
-Biological: Involves the actions of fauna or flora e.g. plant roots expanding cracks in rocks or rabbits burrowing into weak rocks such as sand stone.
Describe freeze thaw weathering
1. Water permeates into the rock and collects in pores and cracks.
2. When the temperature falls below freezing at night the water freezes to form ice it expands by approximately 9% causing pressure in the rock and so the crack enlarge.
3. When temperature rises above zero degrees, the ice melts releasing pressure. (The water thaws and contracts).
4. After repeated freezing and thawing, the cracks widen and the water can seep deeper into rock. Eventually fragments of rock will fall from the main body of rock as scree.
Where is freeze thaw weathering most common?
Common where temperatures fluctuate repeatedly above and below freezing point.
Freezing occurs mostly at night.
Mid latitude and lots of rain.
Describe chemical weathering
-Rainwater has CO2 dissolved in it, making weak carbonic acid.
-Carbonic acid reacts with rocks that contain calcium carbonate e.g. carboniferous limestone and so the rocks are dissolved by the rainwater.
What are different forms of erosion?
-Hydraulic Power: as the sheer power of waves smash onto a cliff, trapped air is blasted into holes and crash on the rock. Eventually through repetition, the rocks break apart. The explosive force of the trapped air operating in a crack is called cavitation.
-Abrasion: the 'sand papering' effect of rocks rubbing against the rock surface often causing it to become smoother.
-Attrition: rock fragments carried by the sea knock against on another causing them to become smaller and more rounded.
-Solution: weak carbonic acid in seawater causes some rocks e.g. chalk and limestone to be dissolved.
-Corrasion: fragments of rock are hurled by the sea at the cliff, the rocks act as erosive tools by scraping and gouging at the rock.
What is a concordant coastline?
Concordant coastlines have the same type of rock along the coastline.
What is a discordant coastline?
Discordant coastlines are coastlines where the geology alternates between bands of hard and soft rock.
How are headlands and bays formed?
1. Headlands (steep sides) and bays (gentle slope) are formed where the geology alternates between hard and soft rock at right angles to the coast (discordant coastlines).
2. The harder rock is more resistant to erosion and so forms headlands which protrude out to sea.
3. In contrast the softer rock is less resistant to erosion and so the waves erode this area more rapidly, forming bays that are set back from the coast.
Describe the formation of a wave cut platform
1. At the base of the cliff waves hit between the high and low tide levels, this leads to coastal erosion occurring such as abrasion and hydraulic action, undercutting the cliff and forming a wave cut notch.
2. Over hundreds of years the overhanging cliff can no longer support itself and so collapses.
3. The sea continues to attack the cliff causing more wave cut notches to be formed.
4. After this process is repeated, the cliff line gradually retreats inland, leaving behind a gently sloping rocky surface at the foot of a cliff called a wave cut platform.
5. As it is below sea level at high tide it is usually eroded through hydraulic action and abrasion, causing it to be smooth.
Describe the formation of caves, stacks and stumps
1. Headlands made of resistant rock may have weakness in them such as cracks which are vulnerable to erosion by hydraulic action and abrasion.
2. Overtime this concentrated erosion (hydraulic action n and abrasion) creates a hollowed out feature in the cliff called a cave.
3. Two back to back caves may deepen further breaking through the headland due to erosion forming an arch.
4. Further erosion at base and weathering processes on its roof cause the arch enlarge and eventually they cause the arch to collapse as it is unstable.
5. This leaves an isolated pinnacle of rock sticking out from the sea called a stack.
6. The stack is further eroded by the waves leaving behind a stump which is only visible at low tide and covered by water at high tide.
What are the different types of coastal transportation?
-Traction: when heavy or large particles are carried along the seabed.
-Suspension: when lighter particles are carried within the water.
-Saltation: a 'hopping' or 'bouncing' of particles or pebbles (too heavy to be suspended) along the sea bed by the force of water.
-Solution: the transportation of dissolved chemicals.
What is longshore drift?
The transport of sediment along a stretch of coastline, caused by the waves approaching the beach at the same angle as the prevailing wind.
Describe longshore drift
1. Waves follow the direction of prevailing wind.
2. Usually hit the coast at an oblique angle.
3. Swash carries material up the beach in the same direction as the waves.
4. Backwash carries the material down the beach at right angle, back towards the sea.
5. Overtime material zig-zags along the coast.
Draw a diagram of longshore drift, spit, bar, tombolo and spit with river.
When does deposition occur?
-When there is too little energy to transport material so it is left behind e.g. where coasts are sheltered, so waves are not very powerful and there is less wind (e.g. bays).
-IN A BAY: When there is shallower water and the waves refract causing the energy of the wave to be more spread out causing deposition of sand and shingle.
-Where constructive waves are present and eaves have reach their carrying capacity.
-When groynes are present.
How is the amount of material deposited increased?
-When there is lots of erosion elsewhere on a coast so there lots of material is available. / large supply of sediment being brought down by rivers.
-When there is lots of transportation of material into an area (large supply).
When are coasts built up?
When the amount of deposition is greater than the amount of erosion
What are beaches?
Beaches represent the accumulation of material deposited between low tides and the highest point reached by storm waves.
What are properties of sandy beaches?
(flat and wide)
-Small sediment particles.
-Gentle gradient (usually under 5 degrees)
-Strong backwash as when sand is wet it becomes compact and allows very little energy to be lost by percolation. (little energy lost to friction). So material is carries down the beach.
-Found in sheltered areas as there is shallower water in a bay and the waves mirror the shape of the coast through wave refraction. This spreads out and reduces wave energy, leading to deposition of sand.
What are the properties of shingle beaches?
(steep and narrow)
- Generally larger particles (depends on geology of area and wave energy)
-Steeper gradient (usually 10-20 degrees)
-Weak backwash as water rapidly percolates through the shingle as there a more gaps. This means that very little material is moved down the beach.
-The larger the material the more energy is needed to transport it, so shingle is only moved when the waves are more powerful, hence they are thrown further up the beach.
-Found in less sheltered areas as the waves are more powerful and near cliffs as erosion takes place and fragments of rocks are eroded and fall down.
Describe the formation of a spit
-A spit is a finger of new land made of sand or shingle, jutting out into the sea from the coast
-It is a landform resulting from transportation and deposition along the coast.
1. LSD carries materials material in the direction of the prevailing wind.
2. When there is a break in the coast e.g. a river mouth or the coast changes direction , LSD still continues and sediment is still deposited, to build a long narrow ridge of the material projecting out into the sea or across an estuary.
3. Often at the end of a spit, a curved end is formed due to the second most dominant wind coming from another direction. This changes the direction of the LSD and therefore where the material is transported to and deposited.
Describe the formation of a bar
A bar is formed when a spit joins two headlands together, trapping the bay behind it. A lagoon forms behind the bar.
What is a tombolo?
A spit that joins an island to the mainland.
What is a major cause to rising sea levels?
-Thermal expansion: this occurs due to an increase of volume (or density) as a result of an increase of temperature in the water. As the air temperatures rise (due to climate change), the water temperatures rise, causing the water in the ocean to expand and therefore take up more space.
-Melting Ice Caps: ice sheets, ice caps and glaciers melting increases the volume of water in the ocean causing sea levels to rise.
What are the economic impacts of rising sea levels?
-Loss of tourism
-Loss of agricultural land (seawater has a high salt content, and this salt reduces soil fertility and so crop production can be affected for years after a flood)
What are the social impacts of rising sea levels?
-Water supply can be contaminated (floodwater can pollute drinking water with salt or sewage).
-Loss of housing
-Loss of jobs (coastal industries may be shut down because of damage to equipment and buildings e.g. fishing boats can be destroyed0.
What are the environmental impacts of rising sea levels?
-Ecosystems are affected (increased salt in sea water can damage or kill organisms in an ecosystem)
-Vegetation killed (the force of floodwater uproots trees and plants. Standing flood water also drowns some trees and plants.
-Increased erosion (a large volume of fast-moving water can erode lots of material, damaging the environment)
What are the political impacts of rising sea levels?
The government has to make policies to reduce the impacts of future flooding. They can do things like building more or better flood defences or they can manage the use of ares that might be flooded e.g. by stopping people from living there.
What are some facts about the Maldives?
-Group of 1190 islands in the Indian Ocean (119 inhabited)
-About 300,000 people population
-Capital Malé is densely populated
-1.5 m above sea level but 80% is below 1m. Predicted to be totally submerged in 50-100 years.
What are the economic impacts of coastal flooding in the Maldives?
-Loss of tourism: main source of income, with over 600,000 visitors annually, 30% of its GDP from tourism. Will loose their 5 airports (2 of which are by the coast), stopping international visitors and trade is harder.
-Disrupted fishing industry: second most important source of income, CF may damage fish processing plants, reducing the fish exports and therefore the country's income.
-Stronger waves will destroy fish habitats and damage the coral (tourist attraction).
What are the social impacts of coastal flooding in the Maldives?
-Loss of housing
-Less freshwater is available and so they may end up spending 85% of their income on bottled freshwater or rely on rainwater, supplies are already low and might be polluted with salty seawater, or will have to build expensive desalination plants to meet their water demands.
-May need to swim deeper for fish which gives a higher risk.
-If need to migrate, they will find hard as language barrier of Dhivehi is not spoken widely.
What are the environmental impacts of coastal flooding in the Maldives?
-Loss of beaches, CF wears away beaches at rapid rate, which destroys habitats and exposes the land behind the beach to the effects of flooding.
-Loss of soil, soil of most of islands is shallow and so CF could easily wash away the soil layer, which would mean that most plants would not be able to grow.
What are the political impacts of coastal flooding in the Maldives?
-Maldivian government asked Japan to give them $60 million to build 3m high sea wall around capital, Malé.
-Change environmental policies, pledge to become carbon neutral so it doesn't contribute to global warming and encouraging other governments to do the same.
-Long term thinking about buying land in countries like India and Australia and moving Maldivian's there before the islands become uninhabitable. (environmental refugees)
Describe a sea wall
-A concrete or rock barrier built at the foot of a cliff or top of a beach. Curved face to reflect waves back into the sea.
-Benefits: Stops coastal flooding by acting as a barrier, and prevents erosion of coast. Often has walkway.
-Negatives: obtrusive and unnatural, high maintenance and expensive (£6,000 per metre), does not absorb wave energy only reflects, creates strong backwash which erodes under the wall.
Describe rock armour
-Large boulders piled up along the coast or foot of a cliff. Force waves to break absorbing their energy and protecting the cliffs.
-Benefits: reduce erosion and flooding, relatively cheap (£4,000 per metre) and low maintenance, attracts fishing.
-Negatives: obtrusive, doesn't fit in with local geology, can be moved by strong waves so need to be replaced, expensive to transport from abroad.
-Wooden or stone fences built at right angles to the coast, from coast into the sea, trapping sediment transported by LSD, enlarging the beach. Wider beach acts as a buffer to waves reducing wave attack to coast.
-Benefits: create wider beaches which slow down the waves (absorbs wave energy), which gives greater protection from flooding and erosion, builds beach up enhancing the tourist attraction of the coast, relatively cheap (£10,000 each at 200m intervals), provides useful structures for fishermen.
-Negatives: interrupts LSD starving beaches further down the coast of sand, making them narrower which doesn't protect the coast as well leading to greater erosion and floods.
Describe beach nourishment
-Importing sand and shingle and piling on top of beaches to make it higher and broader.
-Benefits: creates wider beaches which slow down the waves giving greater protection from erosion and flooding (absorbs wave energy), relatively cheap £3,000 per metre, good for tourism.
-Negatives: taking material form seabeds can kill organisms, requires constant maintenance as only lasts a year.
Describe dune regeneration
-Planting vegetation (marram grass) to stabilise sand or nourish sand dunes as they are effective buffers to the sea.
-Benefit: provide a barrier between land and sea and the wave energy is absorbed which prevents flooding and erosion, stabilisation is relatively cheap at £2,000 per metre, maintains the natural environment for people and wildlife.
Describe marsh creation (managed retreat)
-Nature is allowed to take its course by allowing low-lying coastal areas to be flooded forming salt marshlands, which are effective barriers to the sea/ planting vegetation in mudflats along the coast.
-Benefits: introduces biodiversity and new habitats, reduces the speed of waves preventing flooding and erosion, cheap when the land is not built on £5,000 - £10,000 per hectare (farmland).
-Negatives: land (often agricultural) is lost as flooded by the sea, famers and land owners need to be compensated as livelihood is affected, marsh creation is hard if erosion rates are high as the marsh can then not establish itself, takes a long time.
Describe salt marshes
1.Often formed in sheltered areas, such as bays and the landslides of a spit. This is because the waves have lower energy, causing silt and mud to be deposited forming and intertidal mudflat.
2.Salt tolerant plants e.g. halophytes colonise on mudflats becoming the pioneer plant.
3.The level of mud rises and rainwater washes out the salt so conditions are less harsh and decomposing plant matter improves soil fertility of newly forming soil.
4.New plant species start to colonise and gradually over hundreds of years there is vegetation succession.
Use a case study to explain why a coastal habitat has distinct characteristics
-A salt marsh is a coastal ecosystem in the intertidal zone between the mainland and open salt water that is regularly flooded by tides.
-Essex Marshes are found all along the Essex coast from River Thames in the South to the River Stour and Harwich.
-Environmental characteristics: situated between high and low tide, salty water, wave action and water movement, cope with low oxygen levels, terrestrial herbivores and fire
How has the flora adapted to the Essex Salt marshes?
-Double rooted system, allow it to bind to surface and anchor it up to 2 metres deep into the sediment to prevent it from being washed away.
-xerophytic (able to tolerate dry conditions, concentrates salt into their roots to lower water potential, allowing osmosis to take place.
-Have aerenchyma (air channels in their leaves) which supply submerged portions with atmospheric oxygen as well as lower the metabolic demands of the plant.
-Halophytes (able to tolerate salt) by having special glands to release the excess salt.
How has the fauna adapted to the Essex Salt marshes?
-Long curved bill to allow it to probe deep into the mud, seeking worms, shellfish and shrimps.
-Long legs help them keep their body dry.
-Perfectly shaped bill allows it to prise open mussels and cockles.
Describe the management strategies in the Essex Salt marsh
-Need to protect Wallasea Island, 400 years ago 300,000ha but now only 2,500ha
-Wallasea Island Wild Coast project began in 2012 and likely to be complete by 2019.
-Strategy for Wallasea Island is managed realignment.
-Must be sustainable and managed realignment is as it greatly benefits the environment e.g. greater habitats for fish, which in turn may benefit local fishing economies.
What effects cliff collapse?
-Power of waves: causes undercutting at base of cliff making it unstable and overhand eventually collapses.
-Heavy rainfall: may add to weight of rock especially if soft and porous can cause landslides, slips and slumps.
Use a case study of an area of recent or threatened cliff collapse
-Jurassic Coast 2012
-The site is a 95 mile stretch of the south coast from exmouth in East Devon to Studland in Dorset.
-Predicted that rates of coastal erosion may increase with changing climate and associated sea level rise. Different rate of erosion on discordant coastline.
-Mass movement also common
Social impacts in Jurassic Coast
-Property loss and damage: mass movements at Monmouth Beach Lyme Regis caused £200,000 each beach huts to be damaged.
-Death: 25th July 2012 Charlotte Blackman killed on Burton Bradstock beach buried by tonnes of rock following cliff collapse onto the beach.
Economic impacts in Jurassic Coast
-2012 threat mass movements posed such a threat that Dorset and Devon authorities had to close man section of the beach and greatly reduce cliff access, impacted local economy (heavily dependent on tourism (jobs)).
Environmental impacts in Jurassic Coast
-Destruction of famous beauty spots which are iconic features of the British landscape and popular with tourists e.g. arch Durdle Door near Lyme Regis in Dorset will eventually collapse with continued erosion and cliff collapse.
-Alters landscape: 20m stretch of South-West Coastal Footpath gave way, leading to an estimated 400 tonnes of mud and rock falling form the top of the cliff and down onto the beach.
How did people worsen the situation in Jurassic Coast in 2012?
-Tourists rambling and hiking along cliff tops, ignoring warning signs can cause smaller rockfalls and landslips.
-Other people continue to search for newly exposed fossils at the base of recently collapsed cliffs at Lyme Regis (putting their lives at risk, although this did attract tourists to the area, which is famous for its fossils).
Describe the strategies put in place for the Essex Salt marsh
1. Salt marshes in the UK are disappearing due to the development pressures of tourism, industry and recreation as well as hand engineering flood management strategies
2. Wallasea Island in theEssex Saltmarshes
Why does the Wallasea Island need protecting?
-400 years ago there were 30,000ha of intertidal saltmarsh but now only 2,500ha remain
-This land is being claimed by agriculture and enclosed sea defences
-Consequently the marshes are diminishing by 100ha/yr and thus is certain t increase with the acceleration of sea level rise
How is Wallasea Island being protected?
1. Wallasea Island Wild Coast project is a landmark conservation and engineering scheme for the 21st century
2. AIM: combat the threats from climate change, coastal flooding and sea level rise by recreating the ancient wetland landscape of mudflats, salt marsh, lagoon and pasture
3. Began in 2012 likely complete by 2019
4. Strategy is managed realignment: turn 746haa of arable farmland into 320ha of mudflats, 160ha of saltmarsh, 96ha of shallow saline lagoons, 64ha of brackish grazing marshland and 129ha of pasture
5. Cost approximately £500,000 for designing engineering studies, and £12m to carry out project
6. Breaches in sea wall will be created, recreating an intertidal habitat
7. Landscape will be used for tourism and recreation as well as wildlife, 15km of new and improved access routes and eventually a range of visitor facilities will also be provided
How are the Essex marshes used sustainably?
1. Management strategies must cater for the people of today without compromising the ability of future generations to meet their own needs
2. Managed realignment schemes seem to be the beat management option as they greatly benefit the environment
3. Greater habitat for fish, which will also benefit local fishing economies
4. Increases in bird life, increasing the beauty and attraction of the area to tourists particularly bird-watchers