Coasts

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Lesson notes

What is Coastal Erosion?

Coastal erosion is the loss or displacement of land along the coastline due to waves, currents, tides, wind-driven water, and storms.
It involves the long-term removal of sediment and rocks, causing the shoreline to retreat landwards.
Erosion can be measured over different timescales, from individual tides to seasons and longer cycles.
On coasts with rocks of varying resistance, softer areas erode faster, creating landforms like tunnels, bridges, columns, and pillars.
Over time, the coast tends to even out as softer areas fill with sediment from harder rocks, and rock formations are worn away.
Erosion is common where there are strong winds, loose sand, and soft rocks; blowing sand grains create a sandblasting effect that smooths and polishes rocks.
According to the IPCC, sea level rise caused by climate change will increase coastal erosion worldwide, significantly changing coasts and low-lying areas.

Processes of Coastal Erosion

Hydraulic action: waves strike a cliff face, compressing air in cracks; this exerts pressure, splintering and removing rock pieces, and over time can form caves.
Attrition: loose rock debris (scree) collides and grinds against itself, becoming smaller, smoother, and rounder; it also chips the cliff base.
Solution: acids in seawater dissolve certain rocks, such as chalk and limestone.
Abrasion (also called corrasion): waves break on cliff faces and use scree to batter and break off rock pieces from higher up the cliff.
Corrosion: seawater with a pH below 7.0 corrodes rocks, particularly limestone; wave action removes reacted material, increasing the reaction rate.

Factors Influencing Erosion Rates

Primary factors include the hardness of sea-facing rocks (controlled by rock strength and presence of fissures, fractures, and non-cohesive materials like silt and fine sand).
The rate at which cliff fall debris is removed depends on wave power; debris lobes can persist for many years if wave energy is insufficient.
Beaches dissipate wave energy and protect the land behind them; a stable, wide foreshore reduces the number and power of waves reaching the cliff.
The adjacent bathymetry (seafloor configuration) controls wave energy arriving at the coast; shoals and bars cause storm waves to break and dissipate energy before reaching shore.
Changes in the location of shoals and bars can shift the focus of erosion along the shore.
Secondary factors include weathering and transport slope processes, slope hydrology, vegetation, cliff foot erosion, cliff foot sediment accumulation, and resistance of cliff foot sediment to attrition and transport.
Tertiary factors include resource extraction and coastal management.

Landforms of Erosion

Headlands and bays form where rocks of different resistance meet the sea; softer rocks erode faster to form bays, while harder rocks remain as headlands.
Cliffs are steep rock faces formed by wave erosion at the base, causing the cliff to collapse over time.
Wave-cut platforms are flat, rocky areas left at the base of cliffs after the cliff has retreated.
Caves form when hydraulic action and abrasion exploit weaknesses in a headland, hollowing out the rock.
Arches form when a cave is eroded through a headland to the other side.
Stacks are isolated pillars of rock left standing in the sea after an arch collapses.
Stumps are the remains of stacks that have been eroded down to just above sea level.

Longshore Drift and Landforms of Deposition

Longshore drift is the movement of sediment along the coast by waves approaching at an angle, driven by the prevailing wind.
Sediment is carried up the beach at an angle by swash and returns straight back down by backwash, creating a zigzag movement.
Beaches are accumulations of sand and shingle deposited by constructive waves; they dissipate wave energy and protect the coast.
Spits are ridges of sand or shingle that extend into the sea, formed by longshore drift where the coastline changes direction.
Bars form when a spit grows across a bay, cutting off the water behind it to form a lagoon.

Coastal Management

Hard engineering involves building structures to prevent erosion, such as sea walls, groynes, and rock armour.
Soft engineering works with natural processes, for example beach nourishment and dune stabilisation.
Relocation (managed retreat) allows the coastline to erode naturally in some areas, often with compensation for landowners.
Hard engineering can be expensive and may cause increased erosion elsewhere by disrupting longshore drift.
Soft engineering is often cheaper and more environmentally friendly but may need ongoing maintenance.

UK Coastline Case Study

The UK has a diverse coastline with many examples of erosion and deposition landforms.
The Holderness Coast in Yorkshire is one of Europe's fastest eroding coastlines, with soft boulder clay cliffs.
Erosion at Holderness leads to the loss of farmland and properties, and contributes to the growth of Spurn Head spit.
Coastal management at Holderness includes hard engineering (sea walls, groynes) and soft engineering (beach nourishment).
The Jurassic Coast in Dorset is famous for its erosional landforms, including Lulworth Cove, Durdle Door arch, and Old Harry Rocks stacks.

Slides

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Practice questions

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1.Which process describes waves compressing air in cracks in a cliff face, causing pieces of rock to splinter and break off?
Easy
- AHydraulic action
- BAttrition
- CSolution
- DLongshore drift
2.Which erosion process involves loose rock fragments colliding with each other and becoming smaller, smoother and rounder?
Easy
- AAbrasion
- BAttrition
- CSolution
- DHydraulic action
3.Which coastal erosion process is also known as corrasion and involves waves using sediment to batter and break off pieces of rock from a cliff face?
Easy
- AAttrition
- BSolution
- CAbrasion
- DHydraulic action
4.Which type of rock is most affected by solution because acids in sea water dissolve it?
Medium
- AGranite
- BChalk or limestone
- CBasalt
- DSlate
5.Which statement best explains why softer rock layers erode faster than harder rock layers along a coast?
Medium
- AHarder rocks are more resistant to erosion, so softer areas are worn away first, creating features such as bays and headlands.
- BSofter rocks are more resistant to erosion, so they stand out as headlands.
- CAll rocks erode at the same rate regardless of hardness.
- DHarder rocks dissolve more easily in sea water.
6.Which human activity is listed as a tertiary factor influencing coastal erosion?
Medium
- AVegetation growth
- BCoastal management
- CSlope hydrology
- DCliff foot sediment accumulation
7.Which of the following are processes of coastal erosion? (select all that apply)
Medium
- AHydraulic action
- BAttrition
- CLongshore drift
- DSolution
- EDeposition
8.Which of the following are hard engineering methods used to control coastal erosion? (select all that apply)
Medium
- ASea walls
- BGroynes
- CBeach nourishment
- DRock armour
- EManaged retreat

Revision notes

## Coasts — KS3 Geography Revision ### Waves - **Constructive waves** build up beaches; **destructive waves** erode the coast. - Wave energy depends on factors like rock hardness, beach width, and the seafloor shape (bathymetry). ### Coastal Erosion Processes - **Hydraulic action**: waves compress air in cracks, splintering rock and forming caves. - **Attrition**: rock debris (scree) collides, becoming smaller, smoother, rounder. - **Solution**: acids in seawater dissolve rocks like chalk or limestone. - **Abrasion (corrasion)**: waves pound cliffs and use scree to batter and break off rock. - **Corrosion**: seawater with pH below 7.0 corrodes rocks, especially limestone. ### Landforms of Erosion - **Headlands and bays**: form where rock layers have varying resistance; softer rock erodes faster. - **Cliffs and wave-cut platforms**: cliffs retreat, leaving a flat platform at their base. - **Caves, arches, stacks, stumps**: formed as waves exploit cracks and weaknesses in headlands. ### Longshore Drift and Deposition - **Longshore drift** moves sediment along the coast in a zigzag pattern. - **Beaches**: areas of deposited sand and shingle. - **Spits and bars**: formed by deposition where the coastline changes direction. ### Coastal Management - **Hard engineering**: sea walls, groynes, rock armour — expensive, can affect other areas. - **Soft engineering**: beach nourishment, dune stabilisation — more natural, less durable. - **Relocation**: moving people and buildings away from the coast. ### UK Coastline Case Study - The UK has a varied coastline with many examples of erosion and deposition landforms. - Rising sea levels due to climate change are increasing coastal erosion worldwide. ### Key Idea - Coastal erosion is the loss or displacement of land due to waves, currents, tides, wind, ice, and storms. - Over time, the coast generally evens out as softer areas fill with sediment from harder areas. ### Exam Tips - Link processes to landforms: e.g., hydraulic action and abrasion create caves, arches, stacks. - Use named examples for management strategies. - Remember: beaches dissipate wave energy and protect the land behind them.

Coastal erosion: The loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms.
Hydraulic action: Occurs when waves strike a cliff face, compressing air in cracks, exerting pressure and progressively splintering and removing pieces of rock.
Attrition: Occurs when waves cause loose pieces of rock debris (scree) to collide with each other, grinding and chipping each other, progressively becoming smaller, smoother and rounder.
Solution: The process in which acids contained in sea water dissolve some types of rock such as chalk or limestone.
Abrasion (corrasion): Occurs when waves break on cliff faces and slowly erode them, using scree to batter and break off pieces of rock.
Corrosion: Occurs when the sea's pH (anything below pH 7.0) corrodes rocks on a cliff face; limestone is particularly affected.
Longshore drift: The movement of sediment along the coast by wave action, often in a zigzag pattern.
Spit: A landform of deposition formed by longshore drift where the coastline changes direction.
Bar: A landform of deposition formed when a spit joins two headlands.
Hard engineering: Coastal management using man-made structures like sea walls, groynes, and rock armour to prevent erosion.
Soft engineering: Coastal management using natural methods like beach nourishment and dune stabilisation to reduce erosion.
Relocation: A coastal management strategy involving moving people and buildings away from the coast.

Flashcards

What is coastal erosion?

The loss or displacement of land, or the long-term removal of sediment and rocks along the coastline, due to the action of waves, currents, tides, wind-driven water, waterborne ice, or storms.

What is hydraulic action?

When waves strike a cliff face, air in cracks is compressed, exerting pressure on the surrounding rock and progressively splintering and removing pieces. Over time cracks can grow, sometimes forming a cave.

What is attrition?

When waves cause loose rock debris (scree) to collide with each other, grinding and chipping each other so the pieces become smaller, smoother and rounder.

What is solution (as a coastal erosion process)?

The process in which acids contained in sea water dissolve some types of rock, such as chalk or limestone.

What is abrasion, also known as corrasion?

When waves break on cliff faces and slowly erode them, using scree to batter and break off pieces of rock from higher up the cliff face.

What is corrosion in coastal erosion?

Chemical weathering where the sea's pH (below pH 7.0) corrodes rocks on a cliff face; limestone cliffs are particularly affected, and wave action increases the rate of reaction by removing reacted material.

On non-rocky coasts, why do landforms such as tunnels, bridges, columns and pillars form?

Because the coastline contains rock layers or fracture zones with varying resistance to erosion: softer areas erode much faster than harder ones.

How does a sandblasting effect contribute to coastal erosion?

In areas with strong winds, loose sand and soft rocks, millions of sharp sand grains are blown against rock, helping to erode, smooth and polish it.

What is grinding in the context of coastal erosion?

The wearing away of rock surfaces through the mechanical action of other rock or sand particles.

How does the hardness of sea-facing rock affect erosion rates?

Rock strength and the presence of fissures, fractures and beds of non-cohesive materials such as silt and fine sand control how erodible the rock is.

How do beaches affect wave energy and coastal protection?

Beaches dissipate wave energy on the foreshore and provide a measure of protection to the adjoining land.

Why does a stable foreshore reduce cliff erosion?

Once stable, the foreshore should widen and become more effective at dissipating wave energy, so fewer and less powerful waves reach beyond it.

How does the adjacent bathymetry influence cliff erosion?

The configuration of the seafloor controls the wave energy arriving at the coast; shoals and bars offer protection by causing storm waves to break and dissipate energy before reaching the shore.

Why can debris lobes at the base of a cliff persist for many years?

The waves crossing the beach must reach a critical energy level to remove material from the debris lobe, so lobes can be very persistent and take many years to disappear completely.

How is climate change expected to affect coastal erosion?

According to the IPCC, sea level rise caused by climate change will increase coastal erosion worldwide, significantly changing coasts and low-lying coastal areas.

Name the three common forms of coastal erosion control methods.

Soft-erosion controls, hard-erosion controls, and relocation.

Give examples of secondary factors that influence coastal erosion rates.

Weathering and transport slope processes, slope hydrology, vegetation, cliff foot erosion, cliff foot sediment accumulation, resistance of cliff foot sediment to attrition and transport, and human activities.

Give examples of tertiary factors that influence coastal erosion rates.

Resource extraction and coastal management.

How has rising sea level affected coastal erosion in Florida?

Florida has noticed increased coastal erosion, and the state and its individual counties have increased budgets to replenish eroded sands that attract visitors and support its tourism industries.

What is the difference between the primary and secondary factors influencing erosion rates?

Primary factors are the direct controls on wave erosion such as rock hardness, debris removal, beach protection, foreshore stability and bathymetry; secondary factors include weathering and slope processes, slope hydrology, vegetation, cliff foot erosion and sediment accumulation, and human activities.

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