8.2 Characteristics and formation of coastal landforms

• what is a concordant coastline?

• What is a discordant coastline?

• concordant = bands of rock run parallel to the coast

• Discordant = bands of rock run perpendicular to the coast

Name the three types of rock and give examples of each

→ structure of each rock type

• igneous = granite, basalt

  → interlocking crystals which allow for high resistance to erosion

• Metamorphic = slate, marble

  → crystal all orientated in the same direction, resisting erosion

• Sedimentary = limestone

  → lots of faults making them weak and vulnerable to erosion

What coastal formations form on a discordant coastline?

• headlands: reduced rate of erosion compared to softer rock

• Bays: increased rate of erosion on softer rock

What coastline does a cove form on:

• how do they form?

• EXAMPLE

Coves = concordant coastline

• a crack in the outer hard rock is attacked by waves

• Crack penetrates to softer rock, where the rate of erosion by water increase dramatically

• This forms a cove, that looks like a bay, but it is set back by 1 band of harder rock

• EXAMPLE = Lulworth Cove, UK: Portland limestone outer rock, then clays, then chalk cliff face again

Name 6 factors that influence cliff shape

• hard rock = vertical shape

• Soft rock = gently sloping

• Dip to sea = slopes towards sea

• Dip from sea = vertical + rugged

• Impermeable base, porous top = unstable

• Raised beach = modern cliff degrades cliff line above it

What is a salt marsh?

• EXAMPLE

• an area in a sheltered bay or behind a spit

• Salt and minerals will build up

• Vegetation may establish and through vegetation succession stabilise the salt marshes

• EXAMPLE = Medmerry Nature Reserve, West Sussex

Name the 5 stages of salt marsh succession

1. Algal stge

2. Pioneer stage

3. Establishment stage

4. Stabilisation

5. Climax vegetation

Explain plant adaptations for salt marshes

• found in temperature regions, these grassy marshland are adapted to saline conditions

• Dominated by salt tolerant plants e.g. cordgrasses

What vegetation would be present in the algal stage?

Gut weed and blue green algae establish as they can grow on bare mud. Their roots help bind together the mud

What vegetation would be present in the pioneer stage?

Cordgrass and glasswort grow, their roots establish the mud allowing the estuarine to grow

What vegetation would be present in the establishment stage?

Salt-marsh grass and sea asters (floral plants) grow. This creates a layer of vegetation and so the height of the salt marsh increases

What vegetation would be present in the stabilisation stage?

Sea thrift, scurvy grass and sea lavender grow. This means salt rarely gets submerged beneath the marsh

What vegetation would be present in the climax vegetation stage?ph

Rush, sedge and red fescue grass grow because the salt marsh is only submerged 1-2x a year

What are mangroves?

• EXAMPLE

• trees adapted to grow in saline, low oxygen conditions

• Develop in swamps in tropical regions. This means the environment constantly changes with the tides

• Mangroves can stabilise shorelines with roots and protect areas from erosion, as well as providing an environment for wildlife.

• Reduce pollution in coastal areas

• EXAMPLE = Everglades, Florida

Key mangrove facts

• store of carbon (Carbon sink)

• Store 20bn tonnes of carbon = 2x annual greenhouse gas emissions

• Cover 0.1% of the worlds surface

What is tidal sedimentation? Where does it occur?

Occurs in estuaries due to change in water velocity from a river to ocean

• when the water that flows from the river meets the incoming tide and waves from the sea the water virtually stops. The water can then no longer carry its sediment in suspension.

• over time this small fine sediment builds up until it is above the water level.

• deposition occurs as a result of flocculation

• Pioneer plants colonise the area leading to more sediment becoming trapped

• Example: chichester harbour

Explain plant adaptations for mangroves

• found in tropical regions, mangroves have unique adaptations like aerial roots and salt filtering system (which keeps out up to 90% of the salt)

• Mangrove seeds (propagules) start to grow and develop roots on the parent plant → propagules fall into the water and float to shallow areas where their roots can anchor in mud

• Leaves have glands which secrete salt, leaving salt crystals on the leaf surface

• These adaptions allow them to thrive in intertidal zones with varying salinity

Benefits of mangroves

1. Biodiversity and carbon storage: provide habitats, act as long-term carbon sinks by storing carbon in the soil

2. Economic opportunities: estimated economic benefit of £27,000-£45,000 per hectare per year, provides productive fishing areas.

3. Coastal protection: reduces damage caused by coastal flooding, less expensive to restore mangfrove belts.

Threats to mangroves

• overfishing

• Pollution

• Forest clearance

• River discharge changes

• Soil erosion

• Climate change

• Loss of other marine habitats

Explain why pollution is a threat to the mangrove coastline

• Species are covered by oil pollution and microplastics can be ingested by fauna.

• Fertilisers and pesticides used in agriculture are present in run off and can change the pH and toxicity of the mangrove habitat.

Explain why forest clearance is a threat to the mangrove coastline

• natural resources are taken for fuel wood and charcoal production

• Space is cleared for waterfront development for tourist activities, port infrastructure, legal and illegal shrimp farming, and salt harvesting

Explain why loss of other marine habitats is a threat to the mangrove coastline

• a decline in the number of coral reefs can affect the mangrove ecosystem.

• Coral reeds provide a natural barrier that protects mangroves from high waves and strong currents

• Removal of coral reeds reduces the supply of fine sediment in which mangrove seedlings grow = more difficult for mangrove forests to become established and reduces the nutrients that are available to them.

Explain why river discharge changes is a threat to the mangrove coastline

• the amount of freshwater reaching mangrove habitats is reduced by damming rivers upstream and by increasing irrigation for agriculture.

• A decrease in freshwater supply increases the salinity of the water surrounding mangrove forests and may cause the mangrove ecosystem to dry out.

Explain why climate change is a threat to the mangrove coastline

• rising sea levels and increased extreme storm events make mangrove forests more vulnerable to coastal flooding

Explain why soil erosion is a threat to the mangrove coastline

• deforestation increases the soils susceptibility to erosion

• This increases the sediment in both rivers and coastal areas

• Mangroves cannot filter this additional sediment and are in danger of silting up.

Why does sea level change?

1. Short period of time

2. Long period of time

1. Tides, low pressures during storm surges (atmospheric pressure changes), wind

2. Climate change, global warming, isostatic and eustatic change in sea level

What can cause sea levels to rise?

Change in the level of the actual sea OR a downward or upward movement of the land which means that the sea level relative to the land has changed.

Name the 3 scenarios that can lead to a FALL in relative sea level

1. Sea level falls and land either rises, stays still or subsides at a slower pace

2. Sea level remains fixed with the land rises

3. Sea rises but the land rises at a greater pace

Name the 3 scenarios that can lead to a RISE in relative sea level

1. Sea level rises and land either subsides, stays still or rises at a slower pace

2. Sea level remains fixed whilst the land subsides

3. Sea level falls and the land subsides at a greater pace

What is an isostatic change?

Local-scale sea level changed caused by either depression or elevation of the Earth’s crust in one particular place

→ due to isostatic subsistence (dropping land) (always to do with the weight of ice)

State an example of isostatic change due to tectonic activity.

Bandeh Aceh, Sumatra: 2004, Earthquake, caused the land to fall 0.5 metres, Indian Ocean

What is isostatic rebound/recovery

When the ice melts and the land rises

Explain isostatic changes in Britain

• In the ice age Scotland had more ice than the south of Great Britain.

• As the ice melted isostatic rebound occurred which caused the land to rise up.

• North/west of Scotland are still getting 2mm a year of isostatic rebound due to ice melting.

What is an eustatic change?

Global-scale sea level change caused by a change in the volume of water in the ocean store

Example of eustatic change

• Thermal expansion (when water is warmed)

• Thermal contraction (when water is cold)

• Cold temperatures → increase in number of glaciers and amounts of sea ice = sea level will drop

Definition of emergent landforms

Occur where there has been relative FALL in sea level (marine regression) / land has raised in relation to coastline

→ raised beaches, relic cliffs

Definition of raised beach

Flat or gently inclined surface that is above the high tide level formed due to isostatic rebound.

Common on the West coast of the UK.

How does a raised beach form?

Beach deposits and shell beds would have been formed when the sea was previously at a higher level and subsequently fallen.

These raised shore platforms create a terrace, an area of flat land, which is backed by the relic cliffs. The presence of the raised platform indicates that before sea level fell, the sea must have been at a relatively fixed level for a considerable period of time to have allowed that platform to develop.

Example of a raised beach

Tongue Bay, Sunderland, UK

What is a relic cliff?

An old cliff displaying features such as caves, arches and stacks

Definition of submergent landforms

→ examples?

• Occur where there has been a RISE in relative sea level (marine transgression) / coastline has lowered

• Sea may isolate some ares of land to form islands

→ rias, fjords, Dalmation coasts

What are rias? Give an example

• Submerged river valleys that have been submerged during a period of marine transgression.

• The lowest part of the river’s course and the floodplains alongside the river may be completely drowned, but the higher land remains exposed

→ example = Sydney Harbour, Australia

How do rias form?

• When sea levels were lower than present, base level was lowered, giving rivers a renewed potential energy to cut downwards. Rivers will therefore erode deep river valleys during these times of lowered sea levels

• When sea levels rise, the deepened segments of the rivers situated at the coast are filled as the sea level increases, creating the drowned river valley with its characteristic dendritic drainage pattern.

What is the pattern of a rias?

Dendritic pattern (branching)

Where are rias most common?

Along discordant coastlines where geological strata, mountains and hills trend at right angles to the coastline.

What coastline do Dalmatian coastlines form on?

• What are Dalmatian coasts

• Give an example

Dalmatian coastlines = concordant coastlines

• Wide, open bodies of water called sounds develop, which have islands or ridges of raised land between them due to the land being flooded.

• EXAMPLE = Croatian Dalmatian coasts

How do Dalmatian coast form?

• waves travel at an angle to the bands of rock

• Increased rates of erosion on softer rocks leave behind only the harder bands of rock

What are fjords? Give an example

Drowned glacial valleys which have been shaped by the action of ice and submerged during the Holocene (the time since the last Ice Age)

→ Milford Sound, New Zealand

How do fjords form?

• deep, steep-sided glacial troughs carved out by moving ice are submerged as sea levels rise

• Deep troughs are best formed at higher altitudes where the effects of ice have been more profound.

Characteristics of a fjord

• steep valley sides

• Fairly straight and narrow

• U-shaped cross-section with hanging valleys on either side

• Shallower section at the mouth called a threshold → due to reduced glacial erosion as the glacier came into contact with the sea.

What is a beach?

→ how are they created?

A depositional landform that stretched from roughly the low tide to high tide line

→ created when sediment is deposited near the coastline when waves lose their energy

→ backwash is often weaker than the swash - water percolates into the sand → as backwash is not powerful the larger sediment remains at the top od the beach

What is prevailing wind?

A wind from the direction that is predominant or most usual at a particular place or season

What is a swash aligned beach

→ characteristics

Example

• where waves and wave crests approach parallel to the coast

• Form when energy is low

• Limited longshore drift = sediment does not travel far as little horizontal/lateral movement

• Wave refraction may reduce the speed of high energy waves leading to the formation of a shingle beach with larger sediment

  → example = Lulworth Cove

Why do different beach types occur?

The effectiveness of transportation is dependent on the angle of prevailing wind in relation to the land

What is a drift aligned beach?

→ example

• waves approach at a significant angle due to longshore drift

• Larger sediment found at start of the beach

• Weathered sediment travels further: small sediment at end of beach

→ Chesil Beach, Dorset

What is a spit?

• EXAMPLE

• a long narrow strip of land formed from longshore drift

• Causes beach to extend out to sea usually due to a change in direction of the coastline

• EXAMPLE = Hayling Island

Explain how spits are formed

• sediment is transported by waves along s coastline by longshore drift

• When the coastline changes direction the waves no longer have the energy to carry the sediment and it is deposited

• The build up of deposited sediment out to sea, often into an estuary, is called a spit

• The spit often has a curved end or hooks due to a secondaey prevailing wind

How does the spit formation lead to salt marsh

• sediment projection can create a salt marsh due to the sheltered, saline environment where water flow is lower, allowing deposition of finer sediments to occur.

Characteristics of a spit

• Behind the spit (leeward side) salt marshes can form: saline, slow moving water, deposition

• Opposite = windward side

• Length of the spit will depend on changing currents or rivers but will never extend across an estuary

What forms a recurved end to form on a spit?

A change in wind/wave direction/current/weather can cause the end of a spit to curve

What is a compound spit?

• EXAMPLE

A spit with multiple recurved ends

• Hurst Spit

What is an offshore bar?

→ how do they form?

→ example

Can be formed in different ways:

1. when the waves do not have enough energy to carry sediment to shore

2. Formed when the wave breaks early, instantly depositing its sediment - this loose sediment builds an offshore bar

3. They may also be formed as a result of backwash from destructive waves which remove sediment from the beach

→ outer banks, North Carolina, USA

What do offshore bars do?

• absorb energy

• Reduce erosion in some areas

What is a tombolo?

→ how do they form?

EXAMPLE?

• A spit that connects the mainland to an offshore island and may be covered at low tide

→ formed due to wave refraction off the coastal island reducing wave velocity - meaning deposition is able to occur

→ EXAMPLE = Chesil Beach, Dorset

What is a barrier beach?

• occurs when a beach or spit extends across a bay to join 2 headlands

• Traps water behind it (creating a brackish (salty water) lagoon)

• Form due to longshore drift

When does a barrier island form?

When a barrier beach becomes separated from the mainland forming a barrier island.

EXAMPLE of:

1. a barrier beach

2. A barrier island

1. Slapton Sands, Devon

2. Scolt Head Island

How do sand dunes form?

• EXAMPLE

• occur and form when prevailing winds blow sediment to the back of a beach

• West Wittering

What conditions are needed for dunes to form

• Formation of dunes requires large quantities of sand and a large tidal range → means sand is dry enough and light enough to be picked up by the wind and carried to the back of the beach

• Frequent onshore winds are necessary

• Dunes develop further as a process of a vegetation succession

Name of dunes starting with the dune closest to the sea

SEA

• Embryo dune

• Fore dune

• Yellow dune

• Grey dune

• Mature dune

How do the following change as you move from the dune closest to the sea to the dune furthest away from the sea:

1. organic matter

2. Number of plant species

3. Water content

4. Influence from the sea

1. Increases

2. Increases

3. Increases

4. Decreases

What is wave refraction?

• The process by which waves turn and lose energy around a headland on uneven coastlines

• Wave energy is focused on the headlands, creating erosive features

• Energy is dissipated in bay leading to features associated with lower energy environments such as beaches

Where do cave, arch and stack form?

• explain the formation

• EXAMPLE

At a headland, where the rock is hard, erosion is slow where wave refraction concentrates wave energy onto the headland

• joints in the headland are susceptible to erosion by hydraulic action and abrasion

• Over time the joints widen forming a cave which is enlarged by hydraulic action and abrasion

• Eventually marine erosion + sub-aerial processes cuts through the headland forming an arch

• The roof of the cave is unstable and will eventually collapse due to gravity and the lack of support

• This leaves a stack which over time will be eroded by weathering, abrasion and hydraulic action to form a stump

EXAMPLE = Old Harry Rocks

How do wave cut platforms form?

• powerful destructive waves attack the base of the cliff at high tide

• The hydraulic action and abrasion create a wave-cut notch which over time increases in size → undercutting

• Eventually the overhang created by the undercutting collapses due to weathering anf gravity

• The cliff retreats, leaving a wave cut platform that is exposed at low tide

What is an estuary?

The point where a river meets an ocean

When does deposition of sedimentation occur in the estuary?

• deposition occurs in river estuaries due to a change in water velocity from a river to an ocean when the flow of water from the river meets with the incoming tides and waves from the sea, the water flow practically ceases.

• As a result, the water can no longer carry the sediment in suspension and therefore it gets deposited.

Name 3 factors that affect the process of sedimentation in estuaries

• tides and waves

• Water density

• Vegetation

Explain how tides and waves can affect the process of sedimentation in estuaries

• tidal currents provide a steady source of energy for sediments moving both into and out of an estuary with flood waves carrying in a large volume of material in suspension.

• During storm events: waves entering the estuary entrances can stir up huge amounts of sediment + with oncoming tides this moves into the estuary

• Waves generated inside the estuary basin can also scour sediment from the areas

• As most of the sediment is small and fine it leads to a build-up of mud which, overtime builds up until it is above water level

Explain how water density can affect the process of sedimentation in estuaries

• fresh water is less dense than seawater and floats over it

• When sediment enters the estuary it remains in suspension with the river water and can be flushed out to sea quite quickly

• However, heavier particles fall out of suspension and sink to the bottom as the flow meets saltwater

• This is why sediment deposition in greatest near the upper reaches of the estuary

Explain how vegetation can affect the process of sedimentation in estuaries

• vegetation within the estuary causes deposition as it slows down the speed of the water, increasing rates of deposition

• Over time, the surface of the mudflats may become higher than the surface of the estuary and can be colonised by terrestrial species

• Mud flats and salt marshes may develop as a result of sedimentation which is increased by their relatively sheltered nature, providing low energy environments in which sedimentation is deposited as it cannot be carried any longer.

Give an example of where tidal sedimentation occurs in estuaries

• Crow Stone, London

• Langstone Harbour