Coasts Flashcards
the littoral zone
The little zone is the zone of dynamic equilibrium with many inputs, processes and outputs causing rapid change. It consists of factual, for sure, near sure and offshore zones.
offshore
zone furthest out
nearshore
between the offshore and the foreshore: where the sea bed begins to slope upwards and flatten
foreshore
between the nearshore and backshore: swash and backwash zone
backshore
zone inland: the beach
advancing and retreating coasts
classifying coasts into advancing and retreating combines shorter-term erosion and deposition with longer-term changes in sea and land level. Resistant rocks (geology) can also reduce erosion, slowing the rate by which coast retreat down.
what’s the difference between a high and low energy coast?
The amount of energy in the coastal environment determines the coastal landscape.
Characteristics of high energy coasts:
– waves: more powerful waves (destructive), conditions, longer factors
– processes: erosion and transport; sediments from eroded land, mass movement and weathering, supplied by offshore current
– landforms: cliffs, wave cup platforms, arches, Caves, stacks.
– General location: exposed to largest waves, Highland and lowland coasts, Rocky landscape
Characteristics of low energy coasts:
– waves: less powerful waves (constructive), storm conditions, long fetches
– processes: deposition and transport; settlement from rivers, longshore drift and natural currents
– landforms: beaches, spit, bars, sand dunes, mudflats so washes
– general location: sheltered from large waves; lowland coasts, coastal plain landscapes
what effect does geological structure have on the type of coast?
geological structure determines whether the coasts are concordant or discordant, influences dalmatian and half coastline types (concordant) and headlands and bays (discordant), and the formation of cliff profiles (cliff cross sections) and microscale features (e.g. caves).
concordant coasts
- concordant coast occur where the folding or arrangement of alternating hard and soft rocks is parallel to the coast (Dalmatian coastline type)
– this means more resistant rocks form elongated islands, while less resistant rocks from long inlet or coves.
discordant coasts
– Discordant coasts occur where the folding or arrangement of alternating hard and soft rocks is in right angles to the coast (Atlantic coastline type)
– this means more resistant rocks for headlands, while less resistant rocks form bays or inlets
haff coastline
these are a type of concordant coastline found on the southern Baltic coastline. Long ridges of mud and sand form parallel to the shoreline, with lagoons (haffs) behind them.
headlands and bays
wave refraction explains why headlands are eroded more than bays: wave energy is focused on headlands and reduced in bays. Overtime the coastline ‘smooths’.
cliff erosion diagram
what do rates of coastal erosion depend on?
Rates of coastal recession and stability depend on bedrock lithology, differential erosion and – on Sandy Coast – the role of vegetation.
lithology
rock types and their characteristics
how does lithology influence coastal recession?
– Igneous rocks (e.g. granite) are more resistant to erosion and weathering than less resistant sedimentary rocks (e.g. limestone)
– Metamorphic rocks are formed from sedimentary and igneous rocks subjected to intense heat and pressure (e.g. marble), making them more resistant.
– superficial deposits made by rivers, wind and glaciers can overlay bedrock. These are unconsolidated and usually easily eroded.
strata
layers of rock
what is differential erosion?
cliffs can have alternating strata of different rock types, with differing resistance to weathering and erosion. This makes for a complex cliff profile and influences recession rates because erosion happens at different rates.
what influences differential erosion?
– A cliff with a permeable rock strata above an impermeable, weekly consolidated rock strata is vulnerable to mass movement. This is because rainwater is percolating into the upper strata creating instability.
– some types of rock contains soluble minerals of vulnerable chemical weathering
– strata of rocks may erode faster than other strata, as chemical weathering gradually weakens the rock
what is the stabilising role of vegetation?
– Plant roots bind the sediment together so they are less likely to be eroded.
– plant leaves slow down windspeeds at ground level reducing erosion and increasing deposition.
– as plants lose leaves and as they die they add organic material to the sand which eventually forms soil
what is plant succession?
succession refers to the way the vegetation on a sandy coastline changes overtime, from pioneer species, which initially colonise the bare sand or mud, to the climax seal stage.
– Plants especially adapted to the salty conditions (they are halophytes) and the dry conditions and rapidly draining sand dunes (they are xerophytes)
– sand and salt marshes both have plants succession that stabilise the soil
what are halophytes?
plants that are specially adapted to salty conditions
what are xerophytes?
plants specially adapted to sandy conditions (dry)
what are the stages of dune succession? what vegetation do you find at each stage? could be useful to draw a diagram and fill in anything missing.
how is the effectiveness of marine erosion determined? (what factors make an area around the sea erode… essentially what causes the erosion?)
– Wave type
– wave size
– tide level
– the shape of the coastline and lithology of the rock
– the mineral composition
– angle of bedding
– jointing of a rock
how are waves formed?
– Waves result from friction between the wind and the sea surface.
– the potential energy of a wave is proportional to its height
destructive waves
- backwash is stronger than swash, removing sediment from the beach
constructive waves
- swash is stronger than backwash, depositing sediment on the beach
what are the 4 wave erosion processes?
Attrition
Abrasion
Corrosion
Hydraulic action
attrition
waves continually move rocks, pebbles, and sand, especially in the surf zone. As the sediments move, projecting angular corners are knocked away producing stones.
abrasion
destructive waves pick up sand and pebbles (or larger rocks) and scrape or throw them against the rock, abrading it.
corrosion
water from waves may react with rock minerals and dissolve them. The minerals are carried away in the seawater.
hydraulic action
A large destructive wave breaking on a cliff exerts considerable pressure. May be compressed into cracks or joints in the rock. The sudden release of pressure can shatter the rocks.
how can you measure waves? (like literally if you want to know frequency or something)
Time the frequency of the waves over effect period using a stopwatch to time the gap between the arrival of each wave crest. Use a fixed point on the beach to give a reference point. This would give you the data for a measure of central tendency. The main frequency of the waves would tell you if they were constructive or destructive.
formation of a wave cut platform
cave arch stack stump sequence
what is a sediment cell?
> along the section of coastline, erosion, transport and deposition processes operate in a linked system.
– a sediment cell has sources, transfers and sinks: in theory it is a close system
– erosion in one place in the system (the source) is balanced by deposition in another (a sink), with transfers of sediment within the cell by processes such as longshore drift and current
– the amount of sediment gained from sources and loss to sinks can be calculated: sediment budget.
– It is a useful concept for assessing the extent of coastal change and for a evaluating coastal management strategies
how many sediment cells are there in the UK?
11
sediment cell example
sediment cell sources, transfers and sinks
sources: erosion of cliffs, land sediments transported by rivers, wind-blown sediment from the land, onshore currents bringing sediment to shore
transfers: long shore drift, waves, tides, currents and wind
sinks: depositional features on the backshore (dunes), foreshore (beaches) and nearshore (bars) and offshore
dynamic equilibrium in a sediment cell
- negative feedback tends to maintain equilibrium, for example where wave erosion causes rockfalls, which then protect the base of the cliff from further erosion.
– positive feedback tends to increase change in the system into a new equilibrium is reached, for example a ‘blowout‘ in a sand dune allows more sand to be eroded by the wind, reducing vegetation cover further.
longshore drift
- the strongest longshore drift occurs when waves approach the beach at a 30° angle
- The swash carries beach sediment up the beach at the same angle as the waves approach.
– the backwash carries the sediments back down the beach at right angles to the shore, under the influence of gravity. This moves sediment along the coastline until it meets an obstacle
– the predominant wind direction determines the direction of longshore drift.
transport process landforms
types of weathering
what are the 3 types of weathering processes?
mechanical
chemical
biological
what are subareial processes?
a combination of weathering and mass movement that alter the shape of the coastline
what is mass movement?
– Mass movement is the movement downslope of rocks, sand, clay or soil.
– it is caused by gravity once a slow post become unstable: after waves have undercut resistant rocks or when water enters unconsolidated rocks and forces particles apart
– water content determines the type of mass movement
– slope angle and vegetation is also important in determining slope stability
mass movement landforms: Talus scree slopes
mass movement landform: rotational scars and terraced cliff profiles
mass movement landform: block falls
mass movement landform: mudflows
what is eustatic change?
a change in sea level
what is isostatic change?
a change in the land level - also linked to ice on the land
- when ice is km thick, its weight pushes the land down
- britains north was glaciated and pushed down, the south was ice free and so tilted up
- when ice sheets melted at the end of an ice age, the land that had been pushed down rebounded back up and land that tilted up started to sink back; this is called post glacial adjustment
- sediment eroded from sinking land will be redeposited on coasts; this is called accretion
what is post glacial adjustment?
when ice sheets melted at the end of an ice age, the land that had been pushed down rebounded back up and land that tilted up started to sink back
tectonic change
– As tectonic plates moving and collide, some continental shelves and areas of land are pushed upwards, or sink downwards.
– volcanic islands may create new coast lines, for example island arcs
– tectonic activity can produce tsunamis, which threaten coastal areas
emergent coastlines
these are often the result of isostatic rebound:
– Raised beach: a form of beach that is now above the high tide line. Some raised beaches may consist of several different levels, each indicating different stage of uplift. Features such as rounded boulders and pebbles may be present.
– Fossil cliffs: near-vertical slopes initially formed by marine processes but now found some distance in land. They may still have visible marine erosion features such a sea caves and wave-cut platforms
submergent coastlines
submarine coasts are often the result of sea level rise or isostatic sinking.
– A ria is a flooded river valley. The valley sides may be steep due to their being formed in periglacial conditions, when the soil was frozen.
– a fjord is a flooded glaciated (U-shaped) valley: very deep water with steep sides
– Dalmatian Coast are concordant coast where the sea has flooded the landscape of alternating hills and valleys create long bays and parallel hilly Islands.
How has climate change caused sea level rise?
– As the sea heats up, it’s volume increases (thermal expansion). This currently contributes to over 50% of sea level rise.
– in the future, melting ice from glaciers, Greenland and Antarctica could increase sea level rise significantly.
– The rate of sea level rise is increasing as the ocean warm and polar ice melting exceeds expected rates.
– erosion rate and coastal change will be intensified by climate change and sea level rise
what are 3 possible coastal impacts of climate change?
- low lying islands and eco systems will disappear
- stronger storms will create larger more destructive waves causing increased erosion
- wave height will increase in the arctic as sea ice disappears causing increased erosion
how do human actions affect the sediment cell system?
Why does coastal recession happen?
coastal recession (retreat) is the result of natural factors such as geology, marine processes and sub-aerial processes.
Human actions can sometimes alter these processes.
what physical factors affect rapid recession?
what local factors increase the risk of coastal flooding?
- height of an area
- degree of subsidence (isostatic sinking)
- vegetation removal
why do humans live on the coast
sea and river trade
farming (deltas have very fertile soil)
how do mangroves reduce coastal flooding
- they reduce the height of the waves reducing wave erosion at the coast
- their roots trap sediment raising the height of the coast
- they reduce storm surge levels - by 0.5m for every 1km of forest the seawater has to pass through
what are storm surges and how do they form
storm surges are linked to low pressure weather systems, particularly tropical cyclones and depressions.
- Low air pressure over the sea allows water to bulge upwards in a dome.
- The lower pressure, the higher the dome
- Storm surges are made worse by wins on top of the jam, which increases the height of the water at the coast, increasing the risk of flooding.
- When the low pressure system moves towards the coast, the dam of seawater surge of shore.
- The shape of the coastline can also increase storm surges if it acts to funnel storm towards an area of shallow offshore water.
consequences of coastal recession: economic
these include cost of repairs and rebuilding, loss of jobs and income and the money and resources needed in form of aid
– in the UK the government does not pay compensation to people who lose their homes to coastal erosion.
– most coastal erosion happens over a long period of time and affect where to be few people. The properties affected lose their value.
– sudden economic losses from coastal recession to happen but rare.
consequences of coastal recession: social
these are the losses directly affecting people, for example having to relocate temporarily or permanently or losses of amenity areas.
– Coastal recession can produce a less aesthetically attractive coastline with boarded up properties and closed roads. - – Coastal recession can lead to conflict: example of people experiencing coastal erosion blame the construction of seed defences up drift
– living with coastal erosion can impact on health because of stress of property losing value, insurance increases, etc
how many environmental refugees are there and how will this change going into the next few decades?
– Around 22.5 million people have been displaced due to climate related events between 2008 and 2016.
– a world bank study estimated that more than 100 million people will be pushed into poverty by climate change by 2030
– rising sea levels are a major factor for example by 2050 years estimated up to 18 million people may be displaced in Bangladesh by rising sea levels
what are some different hard engineering strategies?
what are some different hard engineering strategies?
what are some different soft engineering strategies?
what are some features of sustainable management?
– The full environmental impact of new developments on the coast needs to be evaluated before developments can proceeded.
– waste in coastal environments needs to be minimised.
– everyone affected by new developments on the coast needs to be involved in the decision making about the developments
– new economic developments on the coast should provide some benefits for the local community.
– the exploitation of coastal resources must be avoided.
– working with physical processes where possible to reduce unsustainable spending on hard engineering coastal defences
– adaptation to future changes/threats
what is managed retreat and how does it work?
Ministry is an example of a sustainable approach to coastal defence in areas where costs of hard or soft engineering significantly exceeds the benefits. This may conflict with the wishes of local people.
How it works:
areas a set aside for the C2 Flood or a road. For example, for assault marshes that are now farmland may be allowed to flood again.
Benefits:
– can avoid the construction and maintenance costs of hard engineering.
– can stand valuable and natural ecosystems
– and adaptation response to sea level rise
Costs:
– requires the agreement of affected landowners and property owners.
– may only be medium term solution if sea levels continue to rise further.
– defences often need to be constructed around the edge of the flooded area to protect property
what are some adaptation strategies
- restoring mangroves: effective against storm surges, boost fish numbers, benefit local communities.
- Zoning areas of coast: threatened by sea level rise to prevent further development there which avoids increasing risk
- elevating critical infrastructure: for example power stations to protect them from flooding
what is ICZM and what does it do?
ICZM stands for integrated coastal zone management.
– A process for planning and coordinating how coastal resources are used and developed.
– integrated means it looks at the coast as a whole system and brings together all of the stakeholders with the aim that everybody benefits including human and physical marine and terrestrial processes.
– coastal zones are littoral cells which is a similar concept of sediment cell
what is ICZM and what does it do?
ICZM stands for integrated coastal zone management.
– A process for planning and coordinating how coastal resources are used and developed.
– integrated means it looks at the coast as a whole system and brings together all of the stakeholders with the aim that everybody benefits including human and physical marine and terrestrial processes.
– coastal zones are littoral cells which is a similar concept of sediment cell
what are SMPs and what do they do
SMP stands for shoreline management plan
– SMP‘s are examples of ICZM
– there is an SMP for each littoral cell.
– putting together an SMP involves consultation with scientific advisors and many groups of local stakeholders: resident associations, landowners, farmers, wildlife organisations, local leisure clubs, local tour sports, chamber, and utility companies
– S&P identify the risk associated with coastal processes operating in the littoral cell and make decisions about how to manage them
what is an SMP coastal defence evaluation and what are the 4 policy choices?
what are some implications of policy decisions?
Some places have seen an SMP policy decision change from holding the existing shoreline to no active intervention or manage retreat.
– this usually followed a cost benefit analysis: comparing the cost of coastal defences with the value of the land be protected.
– places with low lying land had difficulty qualifying for government money to pay for sea defences.
– this affected property values in these places and also had social impacts – communities felt less secure
what are some factors affecting policy decisions?
although the economic value of the land is often the most significant factor and decisions to hold the existing shoreline, there are others:
– coastal sites that have strategic importance for national infrastructure, such as nuclear power stations or gas terminals
– coastal areas with historical sites, areas of archaeological significance are important cultural value
– coastal areas that provide habitats for rare plants and animals.
– places that mount effective publicity campaigns for coastal protection or effective lobbying of their MP
what is coastal management in developing countries and how can it be challenging?
coastal management is challenging where:
– coastal erosion is rapid.
– coastal communities are vulnerable because of poverty and lack of opportunity.
– local people have no legal rights to the coastal land they depend on.
– coastal regions are controlled by elites who look after their own interests only
What is the littoral zone
A way to classify the coast into subdivisions: the back shore, foreshore, nearshore and offshore
It is a zone of dynamic equilibrium with many inputs, outputs and processes that cause rapid change
What are inputs?
sediment brought in through various ways, and energy from waves, wind, tides, and currents
What are outputs?
includes sediment leaving through the action of waves, deposition, and transportation
What are the flows/transfers/processes?
refer to erosion, weathering, transportation, and deposition
What are transfers?
has stores/components, which are the landforms that store sediment, such as spits
What’s a high energy coast? (How can it be classified)
More powerful waves, calmer conditions and long fetches
Erosion and transport, sediments from eroded land, mass movement and weathering from offshore currents
Cliffs, wave cut platforms, arches, sea caves and stacks
Exposed to largest waves, highland and lowland coats and rocky landscapes
What’s a low energy coast? (How can it be classified)
Less powerful constructive waves, storm conditions, long fetches
Deposition and transport, sediments from rivers, longshore drift and nearshore currents
Beaches, spits, bars, sand dunes, mud flats and salt marshes
Sheltered from large waves, lowland coasts, coastal plain landscapes
How can coasts be classified into advancing and retreating?
Combines short term erosion and deposition with longer term changes in sea level and land level
> resistant geology can also have an impact on erosion
What are concordance coastlines?
Occurs where the folding of arrangement of hard and soft rocks is parallel to the coast (Dalmatian)
This means more resistant rocks for elongated islands while less resistant ones form coves
What’s a discordant coastline?
Alternating bands of hard and soft rock at right angles to the coast
This means more resistant rocks form headlands while less resistant rocks form bays or inlets
What’s a haff coastline?
A type of concordat coastline found on the southern Baltic coastline. Long ridges of mud and sand form parallel to the shore with lagoons (haffs) behind them
How does wave refraction explain how coasts become smoothed over time?
Wave refraction explains why headlands are eroded more than bays: wave energy is focused on headland and reduced in bays meaning overtime they smooth to the same level
How does rock strata influence a cliff profile?
———————
Uniform horizontal strata produces steep cliffs
<
Rocks dip gently seaward with near vertical joints causing rocks to fall of en masse when the joints are opened by weathering
/
A steep Sea ward dip causes small amounts to break off and slide down
\
an inland strata dip produces a stable steady cliff profile
X
Rocks dip inland but have well developed joints at right angles that act as a slide plane
What factors affect the rate of coastal erosion?
Lithology
Strata
Permeable and impermeable rock
Stabilising vegetation
How does lithology and coastal recession impact coastal erosion?
Lithology refers to rock types and their characteristics
Igneous rocks are more resistant to erosion and weathering than less resistant sedimentary rocks
Metamorphic rocks are formed from sedimentary rocks and igneous rocks being subjected to intense heat and pressure making them more resistant
Superficial deposits made by rivers, wind and glaciers can overlay bedrock. These are in consolidated and therefore usually easily eroded.
What does lithology mean?
Rock types and their characteristics
How do metamorphic rocks form?
From sedimentary and ingenious rocks subjected to intense heat and pressure making
What’s an example of a sedimentary, igneous and metamorphic rock?
Limestone
Granite
Marble
What’s differential erosion?
Cliffs can have alternating strata of different rock types with differing resistance to weathering and erosion.
This causes a complex cliff profile and influences recession rates
How does the permeability of a rock impact differential erosion?
A cliff with a permeable rock strata above an impermeable, weakly consolidated rock is vulnerable to mass movement. This is because rainwater can percolate the rock which can make it unstable.
What can make a rock more likely to erode chemically? How does think link to strata?
The presence of certain soluble minerals that can be very vulnerable to chemical weathering
> strata of such rocks may erode faster than other strata as chemical weathering works by gradually weakening the rock
What is strata?
Layers of rock
How can vegetation help to bind together sandy coastlines?
Plant roots bind the sediment together so they are less likely to be eroded
Plant leaves slow down wind speeds at ground levels which reduces erosion and increases deposition
As plants lose leaves and as they die they add organic matter so the sand which forms soil
What is plant succession?
The way the vegetation on a sandy coastline changes over time from pioneer species which initially colonise the bare sand or mud
> sand dunes and salt marshes both have this
What are halophytes?
Plants adapted to salty conditions
What are xerophytes?
Plants adapted to dry conditions
What are the stages of sand dune succession? What plants to you get at each stage?
Embryo dune (pioneer plants)
Yellow dune (marram grass)
Mature or grey dunes (gorse)
How does a wave occur?
They result from friction between the wind and the sea surface
The potential energy of a wave is proportional to its height
What’s a destructive wave?
Weak swash, strong backwash
More frequent
Deeper nearshore
What’s a constructive wave?
Strong swash, weak backwash
Less frequent
Shallow nearshore
What are the 4 wave erosion processes?
Attrition
Abrasion
Corrosion
Hydraulic action
What is attrition?
Waves continually move rocks, pebbles and sand, especially in the surf zone. As the seiners move, projecting and angular corners are knocked away
What’s abrasion?
Destructive waves pick up sand and pebbles and scrape or throw them against the rock, abrading it
What’s corrosion?
Water from waves may react with rock minerals and dissolve them. The minerals are carried away in the seawater
What’s hydraulic action?
A large destructive wave crashing against a cliff and exerting considerable pressure on it causing air to be compressed into joints or cracks. The sudden release of pressure can cause the rock to shatter
What are some landforms of coastal erosion?
Wave cut notches
Wave cut platforms
Cliffs
Cave, arch, stack, stump systems
What’s a wave cut notch and how does it form?
At high tide, destructive waves can reach the base of a cliff
Abrasion and hydraulic action can erode the rock creating a small notch along the length of the cliff with an overhang above
Sea caves may form at weaker points along the line
What’s a wave cut platform and how can this cause cliff retreat?
Above the wave cut notch there is an overhang of unsupported rock.
As the overhang continues to be undercut, mass movement of the unsupported rock occurs and the cliff retreats. Lithology can affect this.
As the cliff retreats it leaves behind a flat or slightly sloped area between the high and low tide levels: a wave cut platform
How does the cave arch stack stump sequence occur?
A small fault in a headland forms from hydraulic action and abrasion which grows into a cave
The back of the cave is eventually eroded through creating a tunnel, the top of which will eventually collapse creating a stack
Further erosion leaves a stump
What’s a sediment cell?
Various transport processes move sediment across a coastline.
Along a section of coastline, erosion, transport and deposition processes operate in a linked system, this is a sentient cell
What is longshore drift?
The swash carries sediment up the beach at the same angle the wave approaches
> the strongest longshore drift occurs when the wave approaches at a 30° angle
The backwash carries the sediments back down the beach at right angles to the shore under the influence of gravity which moves sediment along the shoreline until it meets an obstacle
> wind direction determines the direction of the drift
What’s the sediment cell concept?
A sediment is a closed system (theoretically) of sources, transfers and sinks
Erosion happens in one place (source) and is balanced by deposition in another place (sink) with transfers of sediment within the cell by processes such as longshore drift and currents
The amount of sediment gained from sources and lost to sinks can be calculated
> sediment budget
Sediment cells are useful for assessing coastal change and deciding on appropriate management strategies
What’s a source in the sediment cell concept?
Erosion of cliffs, land sediments transported by rivers, wind blown sediments from the land, onshore currents bringing sediment to the shore
What’s a transfer in the sediment cell system?
Longshore drift, waves, tides, currents and wind
What’s a sink in the sediment cell concept?
Depositional features on the back shore (dunes), foreshore (beaches) and nearshore (bars) and offshore
What’s dynamic equilibrium and how does negative and positive feedback affect this?
Negative feedback maintains equilibrium, for example where wave erosion causes rock falls which then protect the base of the cliff from further erosion
Positive feedback tends to increase changes in the system until a new equilibrium is reached, for example a blow out in sand dunes allowing more sand to be eroded by the wind and reducing vegetation cover further
What is an offshore bar?
A long ride of sand or pebbles formed a short distance out to sea, in shallow water where destructive waves break down before reaching the beach. These waves scour the seabed and throw materials forwards into a heap. Currents in the sea also supply sediments.
What’s a barrier beach?
A beach that connects two areas of land with a lagoon forming behind. They form with a plentiful supply of sand or shingle, waves with enough energy to move material and a rising sea level to push sediment towards the shore. They also require a shallow nearshore area.
What’s a nearshore bar?
These are similar to barrier beaches, but smaller. They commonly form in the surf zone where storm waves break and scoop up sediment, adding them to onshore transport to pile them up in a long ridge, parallel to the coast. Bars may be attached to the shore in some places.
What’s a Tombolo?
A tombolo forms after longshore drift carries sediment across a gap between the mainland and an island, forming a narrow low ridge of sand and pebbles
What’s a spit?
Spits form where there is a dominant longshore drift direction, plenty of sediment from mass movement and erosion and a gap in the coastline such as an estuary or bay.
When transported sediments reach the gap in the coastline, they are carried for a short way in the same direction until they are deposited on the sea bed.
Over time so much sediment is deposited that a narrow strip of land forms across part of the bay or estuary
The shelter provided by the spit means that sediment can be deposited behind it to form mudflats, upon which, salt marshes can develop.
As the spit grows longer, the tides, river currents and other wave directions turn the end of the spit into a hook
What’s a double spit?
Double spits may form where there are local variations in longshore drift and strong river currents. Spits form on either side of a large bay, but do not join because river currents pass out into the sea between the splits
What’s a cuspate foreland?
This is a low lying, roughly triangular, headland that probably develops when longshore drift from two opposite directions forms two spits across a bay. These meet and shelter the bay behind them, which fills with sediments. Mudflats and salt marshes form and deposition creates a new low land area
What are the 5 types of chemical weathering
Salt crystallisation
Freeze thaw
Oxidation
Seaweed acids
Boring molluscs
What are subaerial processes?
A combination of weathering and mass movement that alter the shape of a coastline, as distinct from marine erosion, transport and deposition processes
What 3 categories does weathering fall into?
Mechanical, chemical or biological
Why is weathering important and what can impact it?
It is important in sediment production and influences rates of recession
Climate change is an important influence on weathering as it determines temperatures and moisture levels
What is salt crystallisation?
When waves break or splash cliffs on coastal rocks, the water evaporates leaving behind magnesium and sodium in joints and cracks. These salt crystals grow and create pressure forcing rocks apart
This causes angular rock fragments to fall and create scree slopes at the base of the cliff
What is freeze thaw weathering?
When water seeps into cracks and joints in the rock and freezes when it expands, exerting pressure and forcing the rock apart.
This creates angular parts to fall away creating scree slopes are the base of the cliff
What is oxidation?
Oxygen combines with iron based minerals in a rock, causing a chemical breakdown of the minerals as shown by a red orange rust colour on a rock face.
The rock minerals will no longer be bonded together so the rock will crumble
What is seaweed acids?
Some seaweed cells contain pockets of sulphuric acid. When these cells break contact with rock, the acid will dissolve some rock minerals
Rock minerals will no longer be bonded together so parts of the rock will crumple
What are boring molluscs?
Many marine molluscs live on coastal rocks, scraping away at the rock surface for food or boring a hole in the rock to make a home.
Holes provide weak points for other weathering processes to act
What is mass movement?
The movement downslope of rocks, sand, clay, till or soil.
It is caused by gravity once a slope has become unstable: after waves have undercut resistant rocks or when rainwater enters unconsidered rocks and forces particles apart.
Water content determines the type of mass movement
Slope angle and vegetation cover is also important in determining slope stability.
What landforms does mass movement create?
Talus scree slopes, rotational scars, and terraced cliff profiles
Different types of mass movement create different landforms
What are talus scree slopes?
Steep fan shaped slopes of angular material
They have large boulders at their core with other smaller materials on top
The slope of the talus scree is usually between 34 and 40 degrees, depending on the size of the fragments
What are rotational scars?
In unconsolidated sands and clays, mass movement occurs in the form of rotational slumps, slips or mudflows
Rotational slumping is where a section of cliff stays intact but falls down a cliff along a curved slid plane, often with a vegetation layer on top intact also
This leaves a crescent shaped rotational scar above it on the cliff
What’s a terraced cliff profile?
When a sequence of slumps creates terraces in the cliff profile
What’s blockfall?
When ‘blocks’ of a cliff separate from the rest of the cliff and slide, intact, down a curved slip plane
This occurs on steep slopes as a cliff face is weathered which can loosen and dislodge whole blocks of rock
What are mudflows?
Where there is plentiful water and a higher clay content, mudflows may result which spill over the foreshore
What is eustatic change?
A change in sea level
> as ice melts sea levels rise
What is isostatic change? What is post glacial adjustment?
A change in land level
> when ice is km thick it pushes down land due to its weight
> Britain’s north was glaciated and pushed down, the south which was ice free was tilted up
When the ice sheets melt at the end of an ice age, the land that has been pushed down rebounds upwards and land that tilted upwards starts to sink back
> this is post glacial adjustment
What is post glacial adjustment?
When the ice sheets melt at the end of an ice age, the land that has been pushed down rebounds upwards and land that tilted upwards starts to sink back
What is tectonic change?
A tectonic plates move and collide, some continual shelves and areas of land are pushed upwards or sink downwards (subsidence)
Volcanic islands may create new coastlines
> volcanic arcs
Tectonic activity can also produce tsunamis which threaten coastal areas
What are emergent coastlines?
The result of isotonic rebound
Raised beaches
Fossil cliffs
What is a raised beaches?
a former beach that is now above the high tide line. Some raised beaches may consist of several different levels, each indicating a different stage of uplift. Features such as rounded boulder and pebbles may be present
What is a fossil cliff?
A near vertical slope that was initially formed by marine processes but is now found some distance inland. They may still have visible marine erosion features like sea caves and wave cut platforms.
What is a submergent coastline?
The result of isostatic sinking or sea level raise
Rias and fjords are an example as well as Dalmatian coasts
What’s a ria?
A flooded river valley. The valley sides may be steep due to their being formed in periglacial conditions, when the soil was frozen
What’s a fjord?
A flooded glaciated U shaped valley with very deep water and very steep sides
What’s a Dalmatian coast?
A concord and coast where the sea has flooded the landscape of the alternating hills and valleys to create long bays and parallel hilly islands
What’s climate change and how does this link to sea level rise?
As the atmosphere heats up so does the sea. This causes its volume to increase due to thermal expansion
> currently this is attributing to over 50% of sea level rise
In the future melting glaciers could increase sea level rise significantly
The rate of sea level rise is increasing as the oceans warm and polar ice melts exceeding expected rates
> a sea level rise of 2m by 2100 is predicted
Erosion and coastal change will be intensified by climate change and sea level rise
What are 3 possible impacts of climate warming?
Low lying islands like the Maldives are at risk of disappearing
Wave heights in the arctic will increase as sea ice disappears
Stronger storms will create larger and more destructive waves
What are some physical factors that affect recession?
Marine processes
Geology
Subaerial processes
How do marine processes impact coastal recession ?
Wave type - destructive and high energy waves, prevailing winds, fetch, winter storms
Tides - high tides may mean waves reach the back shore
Submerging coastlines - exposes cliffs to more erosion
How does geology impact coastal recession?
Less resistant rocks are eroded more quickly
Jointed rock and rock with bedding layers also eroded more quickly
How do subaerial processes impact coastal recession?
Processes like weathering (cliffs susceptible to crystallisation for example) and mass movement (permeable over impermeable strata) can speed up coastal recession
How can human actions change sources, transfers or sinks that impact the rate of recession in a sediment cell?
Coastal defences built at one location will stop or limit the supply of sediment to a cell meaning that another place down drift may not receive sediment for beach building. This means the beach will get narrower and lesson able to absorb wave energy. Waves that hit will erode the backshore with greater force.
Offshore dredging removed sand and gravel which also reduces the supply of sediment to beaches making them less able to absorb wave energy. Dredging may also allow waves to maintain their circular motion and energy closer inshore meaning they have a more destructive impact on the coast.
Why is coastal flooding a concern?
A lot of people around the world are settled at the coast, many of which in lowland areas. This is because of livelihoods centred around the sea as well as river trade and farming (on deltas)
What are some local factors that increase flood risk?
Height: flood risk is worse for low lying areas
Degree of subsidence: areas that are experiencing isostatic sinking are more vulnerable to coastal flooding as are areas where drainage has caused land shrinkage
Vegetation removal: ecosystems such as salt marshes and mangrove forests are very important in reducing flood risk but may be removed
How do mangroves reduce coastal flooding?
Reduce wave height, preventing the coast from being eroded
Their roots trap sediment, raising the heights of the coast
They reduce storm surges
> 1km of mangrove reduces wave height by 0.5m
What are storm surges?
Linked to low pressure weather systems, especially tropical cyclones and depressions.
Low air pressure over the sea allows the water to bulge upwards into a dome. The lower the pressure, the higher the dome. Storm surges are made worse by storm winds on top of the dome which increase the height of the water at the coast, increasing the risk of flooding.
When the lower pressure system moves towards the coast, the dome of sea water surges ashore. This shape of the coastline can also increase storm surges if it acts to funnel the storm surge towards an area of shallow offshore water.
What are some economic consequences of coastal recession?
The costs to repair and rebuild as well as losses of jobs and income, not to mention the money and resources needed for aid
In the uk the government does not pay compensation to people that lose
their homes to coastal erosion
Most coastal erosion happens over a long period of time and affects relatively few people. The properties affected lose their value.
What are some social consequences of costal recession?
These are losses directly affecting people, for example having to relocate temporarily or permanently or losses of amenity areas
Coastal recession can produce a less aesthetically pleasing coastline with boarded up properties and closed roads. Coastal recession can lead to conflicts: for example of people experiencing coastal erosion blame the construction of sea defences up drift
Living with coastal erosion can impact health due to the stress of properties losing value and insurance costs
What are environmental refugees and how many of them are there?
Around 22.5 million people who have been displaced between 2008-16
A world bank estimate states that more than 100 million people will be pushed into poverty by climate change by 2030
Rising sea levels are a major factor
> by 2050 up to 18 million people are estimated to be displaced in Bangladesh alone
What are some coastal adaption strategies?
Restoring mangroves - effective against storm surges, boost fish numbers and benefit local communities
Zoning areas of the coast - places threatened by sea level rise can be prevented from being built on which avoids further increasing risk
Elevating critical infrastructure - things like power stations can be raised to prevent them from flooding
What is managed retreat? How does it work?
An example of a sustainable approach to coastal defence in areas where costs of hard or soft engineering significantly exceed the benefits. This often conflicts with the wishes of local people.
Areas are set aside for the sea to flood or erode. For example former salt marshes that are now farmland.
What are the benefits of managed retreat?
Can avoid the construction and maintenance costs of hard engineering
Can extend valuable natural ecosystems
An adaption response to sea level rise
What are the costs of managed retreat?
Requires agreeement of affected land and property owners
May only be a medium term solution if sea levels continue to rise further
Defences often need to be constructed around the edge of the flooded area to protect property
What is a groyne? How does it work? What are the benefits and costs?
Barriers on a beach that sit at a right angle to the sea and slow down longshore drift. They make a beach wider and higher so that waves experts energy on it rather than on the back shore
Maintain the side of the beach
Protect the coast
Enhance the beach as a recreational amenity
Less expensive than a sea wall
Expensive
May hinder people walking up the beach
Reducing longshore drift can worsen it elsewhere (more erosion down drift)
What is a sea wall? How does it work? What are the benefits and costs?
Recurved sea walls reduce wave energy by reflecting waves back on themselves
Stepped sea walls dissipate wave energy
Very effective at preventing erosion
Prevents high water from moving inland
Gives people a sense of security
Very expensive
Greatly reduces supply of sediment to the sediment cell
May be considered ugly
What is Rip rap? How does it work? What are the benefits and costs?
Boulders usually granite or concrete tetrahedrons that are resistant to erosion and have a large surface area to dissipate wave energy
Long lasting and flexible
Can be placed at susceptible points along the coast
Expensive
Seawater can get through gaps which can allow some types of erosion
May look unsightly
What are revetments? How does it work? What are the benefits and costs?
Sloped walls placed parallel and in front of backshore. they take the force of breaking waves and reduce erosional power
Absorb wave energy and trap sediment
Longshore drift can continue
Cheaper than sea walls
Still expensive
Need constant maintenance as they can rot
Reduce access from backshore to beach
What are offshore breakwaters? How does it work? What are the benefits and costs?
Boulders dropped in shallow nearshore waters and aligned parallel to the shore. They absorb wave energy and dissipate waves before they can damage the back shore or foreshore.
Allow longshore drift to continue
Can create sheltered water areas behind them for water sports
Proven to protect vulnerable areas
Expensive
May create increased deposition on the and side which can reduce longshore drift
Other defences may be needed for gaps inbetween
What is beach nourishment? How does it work? What are the benefits and costs?
Replaces beach sediments eroded or transported by longshore drift. A large beach will absorb wave energy and portage back shore from erosion.
Used natural sediment so the beach still looks the same
Provides an amenity for recreation and so supports the local tourist industry
Cheap compared to some hard engineering options
May have to be replaced frequently mid sediment comes from offshore it can alter sediment cells and remove natural habitats
What is soft engineering?
Working with physical systems and processes to protect coasts and manage changes in sea level
What is cliff regrading? How does it work? What are the benefits and costs?
Regrading an unstable cliff which is prone to collapse creates a new slope angle that is stable for the rock type
Creates a natural looking slope
Will remain stable as long as the base of the slope is protected from marine erosion
Large cost
Other defences needed to protect the cliff base
Cliff drainage may also be required
What is cliff drainage? How does it work? What are the benefits and costs?
Where the cliff lithology has permeable above impermeable rock, drains with gravel are inserted to drain the cliff quickly
Reduces the risk of mass movement after heavy rainfall
Looks natural once revegetated as the engineering is not generally visible
Only reduces the risk of mass movement does not prevent it
Implementing across whole cliff system disturbs the cohesion of the rock layers
What is dune stabilisation? How does it work? What are the benefits and costs?
Dunes can provide a natural barrier to sea level rise and storm waves but are fragile. Monitoring their condition and replacing them with a geo fabric or plants helps to keep them in place
Looks natural and works as an effective barrier
Provides a natural ecosystem and recreation area
Can be used to restore dunes lost to storm surges or blow outs
High cost
May need to be fenced while plants grow
Powerful storms can destroy
What is sustainable management?
Sustainable coastal management plans to provide ways to continue to using coastal and marine resources that will not reduce the ability of future generations to use them in the same way
What are some features of sustainable coastal management?
The full environmental impact of new developments on the coast needs to be evaluated before developments proceed
Waste in coastal environments needs to be minimised
Adaptation to future changes and threats (relocate developments rather than protect them)
Work with physical processes where possible to reduce unsustainable spending on hard engineering coastal defences
The over exploitation of coastal resources must be avoided
New economic developments in the coast should provide some benefits for the local community
Everyone affected by new developments on the coast needs to be involved in decision making
What is ICZM?
Integrated coastal zone management - a process for planning and coordinating how coastal resources are used and developed
What is ICZM based off of? (Hint - sediment cells)
Littoral cells
What does integrated mean in ICZM?
It looks at the coast as a whole system and being together all the stakeholders with the aim that everyone benefits, including human, physical and terrestrial processes
Why is having littoral tears useful?
They mean all the different physical processes and human activities are considered over a long timescale
What are SMPs?
Shoreline management plans
- there is one for every littoral cell
- they involve consulting with scientific advisors and many groups of local stakeholders
- they identify the risks associated with coastal processes operating in a littoral cell and make decisions about how to manage them
What are the 4 policy choices for SMPs?
Hold the existing shoreline
Advance the existing line (building new defences closer to the sea)
Managed realignment of the shoreline (natural processes allowed to operate without interference but carefully monitored)
No active intervention (no investment in defences or maintenance)
What’s the key feature of SMPs?
Coastal defences
Evaluated to be:
Appropriate for the physical processes in operation in the cell
Environmentally acceptable
Feasible to build
Economically, socially and politically viable
Sustainable in the long term
What is an EIA?
An environmental impact assessment that analyses the predicted environmental consequences of the proposed defences
What are the implications of policy decisions in terms of coastal management?
Some places have seen SMP policy decisions change from holding the existing shoreline to no active intervention or managed retreat
This is usually followed by a cost benefit analysis: comparing the cost of coastal defences with the value of the land to be protected
Places with low land value has difficulty qualifying for government money to pay for sea defences
This affected property value in these areas and also has social impacts as communities feel insecure
What factors affect policy decisions in terms of shoreline management plans?
The economic value of the land is usually the most significant factor but it’s also worth considering
Coastal sites that have value in terms of national infrastructure like nuclear power stations or gas terminals
Sites with historical or archeological importance
Areas that prove habitats for plants and animals
Places that mount effective public campaigns for coastal protection or effectively lobby their MP
When is coastal management challenging?
When erosion is rapid
When communities are vulnerable becasue of poverty and lack of opportunity
When local people have no legal rights to the land they’re dependent on
Coastal regions are controlled by elites who look after their own interests only
