AQA Geography Coastal systems and landscapes

Sediment cell

A stretch of coastline bordered by 2 prominent headlands. They are regarded as closed systems as sediment is not usually transferred from one to the other.

What is a system?

A set of interrelated components working together towards some kind of process.

Open system

Where matter and energy can be transferred from the system across and beyond the boundary.

Closed system

These have transfers of energy both into and beyond the system but not transfer of matter.

Isolated system

No interactions with anything outside the system boundary.

What is dynamic equilibrium?

The balanced state of a system when it's inputs and outputs are equal. If one element changes because of an external influence, this affects the internal equilibrium and affects other components of the system. By a process of feedback, the system adjusts to the change and regains equilibrium.

Positive feedback

Where the effects of an action are amplified by secondary knock-on effects.

Negative feedback

Where the effects of an action are nullified by its secondary knock-on effects.

What are the 4 coastal zones

Backshore: Area between high water mark (HWM) and the landward limit of marine activity. Changes normally take place here only during storm activity.
-Foreshore: Area lying between HWM and the low watermark (LWM). Most important to marine processes in times that are not influenced by the storm.
-Inshore: Area between LWM and the point where the waves cease to have any influence on the land beneath.
-Offshore: Area beyond the point where waves cease to impact upon the seabed and in which activity is limited to depositions of sediments

The inputs of a coastal environment (4)

1. Energy from wind, waves, tides and currents

2. Sediment from rivers, cliff erosion, wind, LSD

3. Sea level change

4. Human activity

Flows and transfers in a coastal environment (4)

1. Erosion

2. Weathering

3. Mass movement

4. Longshore drift

Outputs of a coastal environment (3)

1. Dissipation of wave energy

2. Accumulation above tidal limit

3. Evaporation

Explain wind as an input of energy in a coastal system. (4)

• Prevailing wind direction - controls the direction waves approach the coastline.

• Fetch - Distance of open water which a wind blows. Determines the magnitude and energy of waves.

• Frictional drag - Waves are created by transfer of energy from wind blowing over the sea surface.

• Wind can pick up and remove sediment from the coast.

Explain how waves are formed.(4)

Wave formation - wind moves across the surface of the water, causing frictional drag.

The strength of the wind and fetch affect the size of the wave.

As energy moves through the water, the water moves in orbital motions.

When waves reach shallow water, friction with the seabed slows the base of the wave, causing it to rise and break.

Characteristics of constructive waves. (6)

• Low height

• Long wavelength

• Low frequency

• Flat beach gradient

• Deposition exceeds erosion

• Stronger swash and weaker backwash

Characteristics of destructive waves. (6)

• High height

• Short wavelength

• High frequency

• Steep beach gradient

• Erosion exceeds deposition

• Weaker swash and stronger backwash

Wave refraction (4)

It occurs when waves change direction as they approach an irregular coastline.

The part of the wave that reaches shallow water first slows down due to friction, whilst the rest of the wave keeps moving fast.

This causes the waves to bend and align more parallel to the coastline.

Wave energy become concentrated on headlands and dissipated in bays.

Explain currents.(4)

Currents are permanent or seasonal movement of surface water in seas.

• Longshore currents - Occur when waves hit coastline at an angle, generating a flow of water running parallel to the shoreline.

• Rip currents - Strong currents moving away from shoreline. Develop when seawater is piled up along the coastline by incoming waves.

• Upwelling - When winds push warm surface water away, allowing colder water from deeper in the ocean to rise

Explain tides. (3)

Tides are The periodic rise and fall of sea levels caused by the gravitational pull of the sun and moon.

• Spring tides - Occur twice a month when the sun and moon align on the same side of the Earth. Largest tidal range.

• Neap tides - Occur twice a month when the sun and moon are at right angles to the Earth. Smallest tidal range

Storm surges

Pushing of water against a coastline at abnormally high levels - low pressure and high tides.

Factors affecting rate of erosion (4)

1. Wave type

2. Beach - absorbs wave energy for cliffs

3. Subaerial processes - weakening of cliffs

4. Rock type

Hydraulic action

When the force of waves compresses air in crack in a cliff face, increasing the pressure, weakening the cliff and eventually breaking pieces of rock off the cliff.

Wave quarrying

When high energy waves crash into a cliff face, they have the power to remove chunks of rocks and widen joints through vibrations.

Abrasion

When waves pick up sediment and hurl them at the cliff, causing the cliff to break.

Attrition

When the rocks in the sea hit each other, slowly wearing down into smaller and more rounded pieces.

Corrosion(solution)

When weak acids in seawater chemically react with and dissolve soluble rocks.

Salt crystallisation

When seawater gets into the crack of rocks. The evaporation leads to crystallisation of slats. It increases volume on a surface which puts pressure onto the rock, weakening it.

Longshore drift(LSD)

Where waves approach the shoreline at an angle, swash and backwash then transport material in a zig zag motion in the direction of the prevailing wind.

Marine deposition

When sea deposits material when there is a reduction in energy resulting from a decrease in velocity or volume of water.

When does deposition occur? (4)

• When sand + shingle accumulate faster than they are removed

• As waves slow following breaking

• As water pauses at the top of the swash before backwash begins

• When water percolates into the beach material as backwash takes it back down the beach

Aeolian deposition

The transportation of sediment by the wind

What are sub-aerial processes?

Operate on the land but affect the shape of the coastline. Material is broken down in situ remaining in or near its original position

What is sub-aerial weathering?

The breakdown or decay of rock in situ

Freeze-thaw weathering

Water enters cracks in the rock. The water then freezes and expands, putting pressure on the rock. As the process repeats, the cracks widen and pieces of rock start to break off. This is an example of mechanical/physical weathering.

Biological weathering + example

The breakdown of rocks by the action of vegetation and coastal organisms (flora +fauna).
E.g. Plant roots grow in cracks + roots, exerting pressure and widening them

Chemical weathering + 3 examples

The decomposition and decay of rocks caused by chemical reactions.

• Hydration: Addition of water to the rock --> expands + causes stress, causing the rock to disintegrate. This weakens the rock + creates cracks / widens joints, allowing further chemical weathering to occur.

• Hydrolysis: Mildly acidic water reacts with minerals in rock, creating clays + dissolvable salts, degrading the rock.

• Carbonation: co2 dissolved in rainwater makes weak carbonic acid. This reacts with the calcium carbonate in rocks to create calcium bicarbonate which dissolves easily in water.

Landslides

Heavy rainfall leads to water between joints and bedding planes in cliffs, causing large blocks of rock to slide downhill.

Rock fall

Large boulders break away from a cliff often due to freeze thaw weathering. This leaves piles of rock at the bottom of the cliff called scree.

Mud flows

Occurs when soil or weak rock has become saturated. They occur on steep slopes. It’s a rapid sudden movement when there is not enough vegetation to hold the soil in place

Rotational slip/slumping

They can occur after periods of heavy rain, when the water saturates softer material overlying much more resistant material,  making it liable to slide. With great amount of lubrication, whole sections of the cliff may move downwards with a concave slide plane, producing a rotation movement.

Soil creep

Damp soil moves very slowly down the slope as the weight of water pushes it forward. It happens on gentle slopes and produces a wavy surface. This occurs when there is a continuous movement of soil particles.

Discordant and concordant coastline

Discordant is when rocks run at right angles to the coastline.

Concordant is when rocks lie parallel to the coastline.

How do headlands and bays form.

Forms in areas with alternating more and less resistant rock on a discordant coastline.

Erosional processes are at the strongest at the areas with the less resistant rock, forming bays.

This leaves the more resistant rock protruding out to sea as it erodes at a much slower rate, forming a headland.

Wave-cut platform formation.

• When high + steep waves break at the foot of cliff their energy is concentrated into a small area of the rock face --> the base of the cliff is undercut, forming wave-cut notch.

• Further erosion increases stress on the cliff above and over time it will collapse.

• The cliff line will begin to retreat and after successive collapses a gently eloping wave-cut platform is formed at base of the cliff.

Formation of crack, cave, arch, stack and stump.

• Cracks in the base of the cliff are enlarged through hydraulic action and wave quarrying. They are enlarged by weathering as well.

• Cracks widen and a cave is formed through abrasion and hydraulic action.

• Waves may cut through the other side of the cave, creating an arch.

• Over time the roof can be weakened through weathering. The arch will collapse on its own weight forming a stack.

• Eventually, wave cut notches will form and the stack will collapse forming a stump.

Swash aligned beach. (4)

• Produced when waves break parallel to the coastline

• Experience minimal LSD

• They are found on irregular coastlines

• Form shingle beaches with large particle size

Spit formation

• Prevailing wind pushes the waves at an angle towards the shore, picking up sediment and depositing further down. In a zig zag movement - longshore drift.

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

• The spit often has a curved end due to secondary prevailing wind.

Tombolo

When a spit forms and joins the main land to an island.

Barrier beaches

Form as an extension from a spit between two headlands. It is a sand or shingle bar above high tide and separated from it by a separated lagoon.

Lagoon

A small body of water that is cut off from the sea. They may form behind a bar or tombolo.

Embryo dunes

Form when sea wood, driftwood or litter provides a barrier to trap sand.

Yellow dunes (fore dunes)

As pioneer plants take hold, they bind together the sand and form low sand dunes. Marram grass grows. 80% of sand is vegetated.

Grey dunes

As the marram grass and grass dies, it adds humus to the sand, creating soil. Plants such as gorse develop.

Dune slack

These are depressions between dune ridges that can dip below the water table, creating water-logged freshwater habitats.

Mature dunes

When the dunes are fully stable and reaches climax vegetation. Trees and shrubs can grow here.

Mud flats formation

Mudflats are formed in sheltered areas with low wave energy.

They develop where rivers carry a significant amount of fine sediment from upstream erosion.

At high tide the sediment is carried into the mudflat zone. At low tide the particles settle onto each other.

Salt marsh formation

Colonisation of mudflats by pioneer plants. These help trap more sediment and can tolerate salty environments.

Vegetation slows down water flow, allowing more sediment to be deposited.

As sediment accumulates and the land rises, other plant species establish behind the pioneer zone.

Eustatic change

A global change in sea level from an actual fall or rise in the level of sea itself.

Isostatic change

Local changes in sea level resulting from the land rising or falling relative to the sea.

Rias

This is a drowned river valley. As sea levels rise they flood the river valleys, leaving only the high land visible. Landform of submergence

Dalmatian coast

A coastline of long, narrow islands running parallel to the mainland. Landform of submergence.

Fjords

This is a drowned glacial valley. Through plucking and abrasion U-shaped valleys are formed. As sea levels rise, U-shaped valleys left by glaciers are submerged. Landform of submergence.

Raised beach

A beach that sits above current sea level. Landform of emergence.

Relict cliffs

An old coastal cliff located above the current sea level, marking a former shoreline.

Hard engineering

Making a physical change to the coastal landscape using resistant materials, like concrete, boulder, wood and metal.

Soft engineering

Using natural systems for coastal defences, such as beaches, dunes and salt marshes, which can absorb and adjust to wave and tide energy. It involves maintaining these systems.

Sea walls

They aim to dissipate wave energy. Their recurved structure throws waves back out to sea into the path of the next incoming wave, reducing its wave impact.

They also provide a physical barrier to flooding by raising the height of the coastline and must have a continuous facing because any slight gap will get exploited by waves.

Rock armour

Consists of large boulders placed in front of a cliff or sea wall to take the full force of the waves. The boulders are deliberately left angular in appearance to create a large surface area to block the waves.

Gabions

Small boulders are contained within steel wire mesh cages, connected together to make large walls or structures.

Groynes

Wooden, stone or steel breakwaters built perpendicular to  the coastline. They are built to controlling longshore drift by trapping sediment to create higher and wider beaches.

They also break up the waves, as they hit the coast.

Revetment

Concrete or wooden structures placed across a beach or coastline to take the full force of the wave energy, preventing further erosion of the coast.

Beach nourishment

Aims to replace material that has been lost through longshore drift.

Local councils may move material from one end of a beach to the other before the start of the tourist season.

Dune regeneration

They aim to replant vulnerable areas with plants such as marram grass and stabilising the surface with sacking or wire mesh.

1. Afforestation with conifers

2. Selective grazing

3. Restricting access by fencing off areas

4. Providing boardwalks for tourists

5. Educating tourists about the dunes

Managed retreat

Abandoning the current line of sea defences and developing the exposed land in some way - creating salt marshes, to reduce wave power.

Low lying land will be flooded . This will be reclaimed naturally by marsh plants, acting as a sea defence for the waves.

Land-use management (3)

If flooding or erosion is inevitable in the future, a local authority may mitigate the impacts.

They can educate the local community.

They can give land at risk from flooding for cattle instead of farming as they can be moved.

They can have caravan park at cliff edge as it can be moved.

Do nothing coastal management

It is cheaper to let nature do its thing.

You can compensate people for their homes, so there isn’t an outrage.

Shoreline management plans(SMPs) 4key policies

1. Hold the line -maintain current defences to stop erosion.

2. Advance the line -Build new defences seaward to reclaim land.

3. Management realignment -Allow the shoreline to move, creating natural, sustainable defences.

4. No active intervention -No coastal processes or investment

Integrated Coastal Zone Management(ICZM)

A long term approach to coastal planning that manages the entire coastal zone(land and sea) as one system.