Coastal Processes (DP IB Geography)
Revision Note
Written by: Grace Bower
Reviewed by: Bridgette Barrett
Sub-aerial processes
Sub-aerial processes occur on the land
These processes shape our coastlines
Weathering
When weathered, rocks disintegrate or break down in situ
Weathering impacts sediment on the coastline
Weathering also influences the rate of recession
The different types of weathering are:
Mechanical (physical) – rocks fracture and break into pieces
Chemical – chemical reactions cause rocks to degrade
Biological – animals and plants cause rocks to weaken
The types of weathering and causes
Mechanical weathering
Freeze-thaw weathering occurs when water finds its way into the cracks in the rock
Water freezes and expands (roughly 10%), increasing the pressure on the surrounding rock
Water then thaws and moves further down into the gaps and cracks
As this process repeats, the rock will eventually give way and break
This typically occurs during colder months
The process of freeze-thaw weathering
Salt Crystallization
Salt crystals can enter cracks in the rock through deposition or evaporation
Water enters cracks at high tide and evaporates at low tide
This leaves salt crystals behind, which build up over time
The increase in salt can put pressure on the surrounding rock, causing it to break
Wetting and drying
This process typically affects clay-type rocks
Rocks get wet during high tide and expand
As they dry, they contract
As this process repeats, the rock can fragment and break
Chemical weathering
Oxidation – Oxygen can react with other chemicals, e.g. calcium to form iron oxide. This causes the rock to degrade
Hydration – rocks absorb minerals, which can create crystals. Just like salt crystals, they cause the rock to break
Carbonation – as carbon dioxide reacts with seawater, it produces carbonic acid, which damages the rock
Solution – some minerals can dissolve when they come into contact with water, causing the rock to break down. This is commonly seen with acid rain
Biological weathering
Animals, vegetation (and even humans) can cause rocks to break down
Tree roots can grow from small cracks in the rock and exert pressure. This causes the rock to break
Some creatures bore into rocks, causing weaknesses
Some plants and animals can produce acids that wear away the rock
Mass movement
Mass movement moves material downwards due to the force of gravity
There are many different types of mass movement
Factors determining the amount of mass movement include:
Sediment type or size
Amount of water
Presence of vegetation
Speed of movement (how steep the slopes are)
Soil creep
This is a very slow process
This occurs on gentle slopes
The material expands and contracts when in contact with water or ice
This expansion moves the material downwards
Earth flows and mudflows
Soil moves downhill when it has become saturated with water
Earth flows act like a liquid
This leaves behind a depression at the top and a lobe shape at the bottom
Mudflows occur when the material is extremely wet
Landslides
A large chunk of material moves down a slope
It splits into smaller pieces of material when it reaches the bottom of a slope
This is very common when slopes are steep
Slumping
Rotational slumping or slip is very common at the coastline
The material moves as a single piece downwards, leaving behind a curved gap
It occurs when weaker rocks or rocks made of unconsolidated materials become saturated with water
Rockfall
Rocks can fall downwards at steeper slopes
This is typically caused by freeze-thaw weathering
It leaves scree behind at the base
Types of mass movement
Examiner Tips and Tricks
To help you remember the different types of mass movement, try splitting them up into these four categories: fall, slide, flow and slump.
Wave processes
Wave processes transfer, erode and deposit material at the coast
Wave processes are responsible for shaping the coastline
Littoral drift
Littoral drift is also known as longshore drift
This is the main process in which waves transport and deposit sediment
Waves hit the coastline at an angle due to prevailing wind forces
Swash carries material up the shore and backwash brings the material back towards the sea at a right angle (gravity)
Material moves along the beach through the wave processes of:
Traction – large rocks roll along the seafloor
Saltation – smaller rocks or pebbles bounce on the seafloor
Suspension – small particles of sediment float in the water
Solution – the water carries dissolved material
Longshore (littoral) drift creates depositional landforms along the coast, such as spits
Examiner Tips and Tricks
make sure you know how the process of littoral drift works. You may be asked to describe what kind of landforms it creates!
The process of littoral drift
Hydraulic action
Destructive waves with high energy can cause the rock to break from the impact
Destructive waves can also force air into the cracks and faults in the rock
Changes in air pressure cause rocks to crack
This can cause pieces of rock to break off as the cycle repeats
Abrasion
Waves carry all types and sizes of sediment
Destructive, high-energy waves throw this sediment against the rock at the coastline
As this process repeats, chunks of rock break away
It mirrors sandpaper, where smaller pieces of sediment wear away the rock
Softer sedimentary rock is more affected by abrasion
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