Subaerial:rain/weathering/surface runoff/throughflow – causing mass
movement
Wave pounding
Hydraulic Pressure
Attrition
Abrasion/Corrasion
Corrosion/Solution
Attrition
Hydraulic Action
Abrasion
Corrosion
Processes of Erosion
•Abrasion/Corrasion
This is the process by which the coast is worn down by material carried by the waves. Waves throw these particles against the rock, sometimes at high velocity.
•Hydraulic Action
This process involves the force of water against the coast. The waves enter cracks (faults) in the coastline and compress the air within the crack. When the wave retreats, the air in the crack expands quickly causing a minor explosion. This process is repeated continuously.
•Corrosion
This is the chemical action of sea water. The acids in the salt water slowly dissolve rocks on the coast. Limestone and chalk are particularly prone to this process.
•Attrition
Material carried by the waves bump into each other and so are smoothed and broken down into smaller particles.
This is the headland which is made from more resistant rock than the bay.
This is the bay which is made from less resistant rock, and therefore erodes more quickly.
wave attack
Plan view
An example of headlands and bays on the Dorset coastline…….
chalk
clay
limestone
Swanage Bay
Wave Refraction
What else protects the bay from erosion?
Wave fronts
Waves travel more slowly in the shallow water near the headlands. This causes the waves to bend and concentrate their energy on the headlands. This, in turn, protects the bay from the full force of the waves.
Why don’t the bays erode completely back over a short period of time?
The waves attack the base of the cliff through the processes of abrasion, corrosion, hydraulic action and attrition.
Over time the cliff will be undercut and a wave cut notch is formed.
Eventually the cliff becomes unstable and collapses. Further cliff retreat will form a wave cut platform.
High tide
Low tide
wave cut notch
Wave cut platform
Old
Cliff Recession
Caves, Arches, Stacks and Stumps
•The waves erode faults (cracks) in a headland through the processes of erosion. The faults eventually widen into a CAVE.
•The waves eventually erode through the headland to form an arch.
•The waves undercut the arch base and it becomes widened. After a time the arch becomes unsupported and collapses to form a STACK.
•The stack erodes to become a STUMP.
If these photos were taken of one headland over time,
which of these landforms would be the first to be formed?
Sub aerialSub aerial RainwashRainwash Surface run-offSurface run-off WeatheringWeathering Mass movementMass movement
Human activity can also cause change to the physical nature of the coast. In what ways?
What do these features have in What do these features have in common?......common?......
Features formed by erosionFeatures formed by erosion
Headlands and baysHeadlands and bays Geo, W-C Notch, Cave, Arch, Stack , Geo, W-C Notch, Cave, Arch, Stack ,
(stump) & W-C Platform(stump) & W-C Platform
What combination of factors led to these features?
Draw a labelled diagram showing the sequence of formation and the processes occurring
Concordant coastline: This is a coastline where bands of different rock run parallel to the shore. They are usually of alternating resistance creating features like coves (e.g Lulworth Cove)
Factors affecting rates of erosionFactors affecting rates of erosion
Factors affecting rates of erosionFactors affecting rates of erosion
Breaking point of waveBreaking point of wave Wave steepnessWave steepness Length of fetchLength of fetch Configuration of Configuration of
coastlinecoastline Supply of beach materialSupply of beach material Beach widthBeach width Rock resistanceRock resistance Rock structureRock structure
Write an explanation of Write an explanation of each stating why they each stating why they would affect the rate of would affect the rate of erosionerosion
WavesWaves
How are they created?How are they created? What are the factors that are responsible What are the factors that are responsible
for the size/strength of waves?for the size/strength of waves?
Destructive waves:Destructive waves:
•BackwashBackwash much stronger than swash. They much stronger than swash. They remove material from the beach.remove material from the beach.
•Frequent. 10-15 per minute.Frequent. 10-15 per minute.
•High. Scouring of beach material.High. Scouring of beach material.
•They create a They create a steep narrow beachsteep narrow beach
Constructive waves:
• Swash > Backwash Therefore – beach built up - deposition.
• Not so frequent – 6-9 waves per minute.
•Long waves ‘roll’ onto the beach rather than crashing onto it.
•create a wide, gently sloping beach.
What features and processes can you identify on this picture?
Coastal landforms resulting from sea level change - THE CYCLE:
Glaciers and ice sheets growGlaciers and ice sheets grow
Sea level falls.Sea level falls.
Coast advances, and continental shelf is uncovered. Coast advances, and continental shelf is uncovered. Process = regression.Process = regression.
Ice thickness increases and land lowers isostaticallyIce thickness increases and land lowers isostatically
Temperatures riseTemperatures rise
Ice melts and sea levels rise eustaticallyIce melts and sea levels rise eustatically
Melting releases pressure and land rises isostaticallyMelting releases pressure and land rises isostatically
This process creates 2 different types of
coastline...
SUBMERGED COASTLINES• These are coastlines that have been formed due to rising sea levels (eustatic).
Fjords
Valleys that have been Valleys that have been created by the slow created by the slow progression of glaciers progression of glaciers & then subsequently & then subsequently filled with rising sea filled with rising sea water.water.
NorwayNorway
RiasRias
Rias are similar to Fjords. However rather than being a Rias are similar to Fjords. However rather than being a drowned glacial valley, they are drowned river valleys. drowned glacial valley, they are drowned river valleys. The shape of the Ria depends on the structure of the The shape of the Ria depends on the structure of the coastline. Examples can be seen along the south-west of coastline. Examples can be seen along the south-west of Ireland as well as the Dalmatian coast of CroatiaIreland as well as the Dalmatian coast of Croatia
Raised BeachesRaised BeachesGlacial ice melted here Glacial ice melted here 15,000 years ago, returning 15,000 years ago, returning the water which had been the water which had been locked up in the ice to the locked up in the ice to the sea. Consequently sea levels sea. Consequently sea levels rose rapidly and prominent rose rapidly and prominent beaches were cut all round beaches were cut all round Cowal. With the removal of Cowal. With the removal of the ice load, however, the ice load, however, Central Scotland has lifted Central Scotland has lifted up since the Ice Age, thus up since the Ice Age, thus raising the earlier levels raising the earlier levels into the well known 'raised into the well known 'raised beaches'beaches'
EMERGENT COASTLINEThese are coastal landforms created as a result of isostatic changes.
