Coasts Flashcards
How is a wave formed?
1) The wind blows over the sea
2) This creates ripples
3) These ripples become bigger swells
4) Swells approach land
5) The sea becomes shallower
6) The bottom of the wave slows due to friction
7) The top keeps going and forms a crest
8) The crest topples forming a breaking wave
Waves are created by:
The action of wind and its frictional drag on the surface of the sea.
Waves can be a product of:
Local winds (sea) or distant storms (swell).
Wave energy is determined by:
- Wind velocity (wind speed)
- Duration (period of time during which the wind blew)
- Fetch (distance over which the wind blew)
What are the two parts of a wave?
- Swash: the movement of the wave up the beach
- Backwash: the movement of the wave back down the beach
Wavelength:
the distance between two successive crests
Wave frequency:
number of waves per minute
Wave crest
highest point of a wave
Wave trough
lowest point of a wave
Wave steepness:
the ratio of the wave height to the wavelength
Wave period:
the time taken for a wave to travel between one wavelength
Wave energy:
a product of wind velocity, duration and fetch
Describe the features of a constructive wave:
- Created by short fetch
- Small, gentle waves with low energy
- Deposit sediment
- Swash is stronger than the backwash.
Describe the features of a destructive wave:
- Created by large fetch
- Big, strong waves with high energy
- Erode the coastline
- Backwash is stronger than the swash.
What is fetch?
Fetch is the distance the wind blows over the sea - the bigger fetch, the bigger wave.
Outline wave refraction
- As waves leave deep water they slowed by the frictional drag of contact with the bed
- Waves would ideally like to break parallel to the coast
- Irregular coastlines do not allow this – waves will slow in shallower water (approaching headlands) but remain unimpeded in deeper water (bays)
- Wave energy is therefore focused on the headlands
- Here the coastline is exposed to the full energy, velocity and power of the wave.
Outline the concept of sediment cells
A sediment cell (littoral cell) is section of coastline that is involved in the complete cycle of sediment transport and deposition.
Sediment budget describes the movement of sand sized particles and larger sediments into, within and out of a defined coastal segment (sediment cell).
There will be inputs of sediment (sediment sources) and outputs of sediment (sediment sinks).
What are tides?
Tides are the regular rising and falling of the surface of the sea
They are caused by the gravitational pull of the sun and moon on the ocean
What is the spring tide?
When the moon is between the Earth and sun their combined gravitational pull creates the biggest bulge of water and the highest tide.
At this time the high tides are at their highest and the low tides are at their lowest – so the tidal range is at its greatest.
What is the neap tide?
When the Earth, moon and sun form a right angle their gravitational pull interferes with one another giving the lowest high tides and highest low tides - small tidal range.
What is the tidal range?
The tidal range determines the vertical range of erosion and deposition and the length of time the littoral zone is exposed to subaerial weathering.
What are tidal bores?
When water from an open stretch of ocean is confined in narrow sections of estuaries the tide is amplified.
The Bristol channel narrows to become the Severn estuary.
When tides suddenly rise this sends on influx of water up the Severn River – known as the Severn Bore.
What is erosion?
EROSION IS THE WEARING DOWN OF ROCK BY MOVING FORCES.
This usually occurs at the base of our cliffs and by waves.
What is weathering?
WEATHERING IS THE WEARING DOWN OF ROCK ‘IN SITU’ BY ITS ENVIRONMENT.
Sub aerial forces (like rain, air and temperature) act on the cliffs to break them down.
What is mass movement?
MASS MOVEMENT IS THE MOVEMENT OF ROCK DOWNHILL UNDER GRAVITY.
Weathering and mass movement work together. The cliffs are weakened by weathering, pieces of rock are loosened and then they fall away from the cliff (this final stage is mass movement).
What is freeze-thaw?
Water repeatedly freezes and melts within rock joints in areas where diurnal range hovers around 0°C (as water freezes it expands and puts pressure on the rock, until it shatters e.g. Scottish Highlands)
What is pressure release?
Overlying soil or regolith is removed, this pressure release can open joints in underlying rock (e.g. granite tors, Dartmoor, UK)
What is biological weathering?
Organic agents (trees, animals) grow and burrow into rock.
What is chemical weathering?
Chemical weathering occurs where there is alternate wetting and drying of an area which leads to a chemical reaction or breakdown of the cliff face.
It is caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic.
What is mechanical weathering?
Mechanical weathering takes place when rocks are broken down without any change in the chemical nature of the rocks.
The rocks are essentially torn apart by physical force, rather than by chemical breakdown.
What is soil creep?
Slowest form of mass movement. Top soil moves downslope under gravity.
Wet and thawing periods add moisture and weight which increases creep (Trym valley, Bristol).
What is solifluction?
When an area begins to thaw, after a period of extended permafrost, the top soils can slide downslope as a whole layer (e.g. Start Point, Devon, after the last ice age)
What are mudflows?
Heavy rainfall saturates ground on steeper slopes and unconsolidated soils flow downslope
What are rockfalls?
Rapid falling of rock/debris down very steep slopes or cliffs, rocks weakened by chemical weathering.
What is run off?
Surface runoff has ability to move soil and debris downslope. Sheet flow is a continuous layer of runoff. Particularly vulnerable are areas with little vegetation.
What are slides and slumps?
Slides and slumps – Unlike mudflows, slides and slumps maintain the structure of the strata of soil and rocks as they rotate and slip along weak fissures.
What is hydraulic action?
Erosion of the cliffs caused by the force of water and air in the waves colliding against them.
What is abrasion?
Erosion of the cliffs as waves throw particles and rocks against them.
What is attrition?
Erosion of the material carried in the waves. The material in the waves is smoothed as it bumps into each other.
What is corrosion/solution?
Erosion of the cliffs by the salts and acids in sea water. Salts and acids are able to dissolve some rocks - limestone and chalk for example.
How does long shore drift occur?
1) Waves sometimes approach the coast at an angle
2) This causes the waves to break on the beach at an angle
3) The swash of the waves carries material up the beach at an angle
4) The backwash then flows back to down the beach in a straight line
5) This creates a zig zag movement of sediment down the beach called longshore drift
What is solution?
Minerals are dissolved in the water and carried along in solution.
What is suspension?
Fine light material is carried along in the water.
What is saltation?
Small pebbles and stones are bounced along the river bed.
What is traction?
Large boulders and rocks are rolled along the river bed.
What is deposition?
This is the dumping of sediment by the sea. It occurs when the waves lose energy, often when they enter a sheltered part of the coastline like a bay.
How are headlands and bays formed?
The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland.
The areas where the soft rock has eroded away, next to the headland, are called bays.
How are Cliffs, Wave Cut Notches and Wave Cut Platforms formed?
Over time the cliff will be undercut by hydraulic action and abrasion and a wave-cut notch is formed.
Eventually the cliff becomes unstable and collapses. Further cliff retreat will form a wave-cut platform.
Example - Burgh Island, Devon
How are Cracks, Caves, Arches, Stacks and Stumps formed?
The waves erode FAULTS (cracks) in the headland.
The waves eventually erode through the headland to form an ARCH.
The arch becomes unsupported and collapses to form a STACK.
A STUMP is formed from the collapsed stack.
What if offshore?
Beyond the influence of the waves
What is nearshore?
Where the friction with the seabed causes the waves to slow and begin to break
What is foreshore?
The zone of constant change. The swash and backwash operate here. Littoral drift occurs.
Berms, ridges and runnels are created by breaking waves and the action of the swash/backwash.
What is backshore?
Affected by the spring high tides that deposits larger calibre sediment here. Fairly stable, neap tides do not reach here.
Describe shingle beaches
Large material results in gaps between the particles which allows water to percolate through it resulting in less water returning to the sea.
This means the backwash is weak and has little energy to move material back down the beach.
Describe sand beaches
Small particles e.g. sand packs tightly together leaving few gaps for water to percolate between the particles.
This results in a compacted, wet surface that has little friction. Much of the swash returns to the sea as backwash carrying sand with it.
How are spits formed?
A change in the shape of the land (caused by the estuary) means longshore drift begins to deposit sediment out away from the coast.
A long tongue of sediment builds up, known as a spit. The end is curved by a secondary wind.
Salt marsh develops in the sheltered area behind the spit (e.g. Keyhaven Marshes behind Hurst Castle spit)
How are bars formed?
Bars form where a spit grows across two headlands, enclosing an area of water known as a lagoon. In the direction of the prevailing wind
How are tombolos formed?
Tombolos form where a spit grows away from a headland and links it to an offshore island.
How do salt marshes develop?
Salt marshes begin life as an accumulation of mud, sand and silt.
Salt tolerant plants like cordgrass then colonise (move into) the area. Cordgrass is called a pioneer
Over time more species move into the area, building up the vegetation. This is called succession.
What is succession?
Succession is a sequence of vegetation species that develops within an environment.
Over time vegetation will develop from small, tough plants to large, complex shrubs and trees.
Describe mudflats(stage 1):
Cordgrass begins to colourize - they must tolerate being submerged for up to 12 hours and saline conditions. Silt also accumulates around them.
Describe a low marsh (stage 2):
As mud builds up the new plants will spend less time submerged. Conditions have changed allowing plants such as sea lavender to colourise.
Describe high marsh(stage 3):
This area is only covered by spring tides - colourised by juncus. Area gradually rises above tidal influence.
Eustatic sea level rise:
Sea level change caused by change in volume due to ice caps melting.
Isostatic sea level rise:
Sea level change caused by change of weight as ice melts on land
Effects of sea level rise:
1) Increased cliff and beach erosion
2) Coastal flooding through storm surges
3) Salinisation of farmland
4) Salinisation of water supply
5) Destruction of coastal ecosystems and habitats
How does global warming cause sea level change?
- As temp rises, the sea absorbs heat from atmosphere
- When water absorbs heat, it expands, and therefore increase sea level.
What is post-glacial rebound?
- Ice physically pushes land down (glacial subsidence)
- When ice melts, the land bounces/rebounds back up
What effect does post-glacial rebound have on the UK?
- As the UK is a island, it acts like a seesaw.
- When the north rebounds, the south begins to sink causing them to be at risk of coastal erosion and flooding.
What are the two landforms associated with sea level change?
Submergent and emergent coastlines
What is a submergent coastline?
Areas of coastline that have been inundated and submerged by the sea due to rise in sea level.
Features of a submergent coastline includes drowned river valleys/rias, drowned glaciated valleys/fjords
What is a emergent coastline?
Areas of coastline that have been exposed by the sea by a fall in sea levels.
Features of a emergent coastline includes raised beaches/machair, wave cut platforms and sea caves.
Case study on how rising sea levels affect the coastal zone:
Tuvalu
Where is Tuvalu located?
Pacific ocean and is a polynesian island.
What are the threats to Tuvalu?
King tides
Storm surges
Ground water flooding
What are king tides?
The highest tide that Tuvalu has, increases 5mm per year.
What are storm surges?
Storms rage in the Pacific ocean and as they hit the shore, the surface of the sea rises, flooding the land.
What is ground water flooding?
Thin coral soils are porous which causes salty water to come up through pores in the ground and the salt contaminates the soil
Environmental impacts on Tuvalu:
When land is flooded by the sea, salt is left behind. This is known as salt water intrusion which affects ecosystems.
Flooding and storm surges erode soils. Thin soils support less plants and animals.
Coral reefs are being damaged. Coral provides an important marine habitat. Warmer temperatures bleach coral which kills it, and the organisms it supports.
Social impacts on Tuvalu:
Many Tuvaluans are being forced from their homeland (4,000 now live in New Zealand)
Families are being ripped apart and cultures and traditions are dying out as Tuvaluans are forced to emigrate to New Zealand
Health problems (stress, water borne diseases like typhoid) are more common as flooding damages infrastructure and contaminates water supplies.
Economic impacts on Tuvalu:
Island’s two industries are being hit.
1) Bleaching of coral reef ecosystems reduces fish stocks, hitting the fish industry.
2) Salt water intrusion is hitting farmers and agriculture.
Cash crops like pulaka (opposite) are killed by contaminated groundwater supplies.
Downturn in GDP (Gross Domestic Product) since 2002
Political impacts on Tuvalu:
The government has to plan the evacuation and migration of the remaining 10,000 inhabitants.
The government is campaigning and trying to get its voice heard (Tuvalu Protocol, Copenhagen 2009)
Tuvalu now relies on aid from New Zealand
Case study with a hard engineering based SMP:
Lyme Regis
Location information on Lyme Regis:
Located on jurassic coast
Geology: Topsoil, limestone, black ven Marl
Black ven marl does not allow rain to infiltrate, pressure increases, friction between layers decreases causing land to slide downhill - limestone slides down causes mass movement
Attack from below and above in Lyme Regis:
Suffers from heavy landslides and coastal erosion
Suffers from wave attacks - strong south westerly winds brings powerful destructive waves
Due to areas geology, landslides are major hazard.
Hard engineering strategies used in Lyme Regis:
Piling to secure limestone to Black Ven Marl
Rock armour extending Cobb.
Construction of a sea wall and existing sea wall repaired,
Drainage improvements
Soft engineering strategies used in Lyme Regis:
Beach nourishment
Landslide early warning system in areas where it is not feasible to carry out stabilisation works.
What have the advantages of Lyme Regis’ SMP been?
Safeguards 140 properties and businesses in Lyme Regis, secures income from tourism (worth £994 million a year to Dorset)
Safeguards beach – a major economic draw, improvements in amenities (beach huts and arcades installed on sea front) and access to sea front (promenade and Cobb Road improved)
What have been the disadvantages of Lyme Regis’ SMP been?
High cost £21 million
Substantial disruption to environmentally sensitive area, temporary eyesore – piling and nailing involved
Langmoor Gardens being ripped up, heavy maintenance burden, intensive changes to cliff habitats and coastal processes (i.e. breakwater and groynes alter currents),
Terminal groyne syndrome.
Case study with a soft engineering based SMP:
North Norfolk
Location information of North Norfolk:
The coastline of NE Norfolk consists of cliffs of unconsolidated (loose) glacial sands and clays and lower-lying areas of drained marshland.
How is North Norfolk vulnerable?
Weathering weakens the cliffs from above and makes them susceptible to landslides.
The geology of the cliffs - sand, tills and clay – are all very weak rock types.
Hydraulic action and abrasion erode the cliff bases forming wave cut notches.
Ostend clay forms impermeable horizon on top of which the Happisburgh Sand Member becomes prone to land slippage.
What was the main focus of North Norfolk’s SMP?
The main focus of the new plan is that of managed realignment and retreat of the present coastline.
Only the most important settlements will be protected
This has caused controversy amongst coastal communities.
What are the Hard Engineering methods used in North Norfolk?
Maintain existing coastal defences, no new ones. Including repairing sea wall.
What are the Soft engineering methods used in North Norfolk?
Beach nourishment and managed retreat/do nothing.
What are the advantages of coastal management in North Norfolk?
Beach nourishment protects tourism and the coastline as it absorbs wave energy. This coastal management is also easy to carry out and relatively cheap.
Managed retreat in North Norfolk allows the protection of more important areas further down the coast by allowing natural coastal erosion and flooding to occur.
What are the disadvantages of coastal management in North Norfolk?
Includes the relocation of residents from their homes and the loss of land caused by managed retreat and doing nothing.
Tourism will also be greatly affected due to maintenance of the original hard engineering strategies which will create an eyesore for North Norfolk.
