Coastal Processes (DP IB Geography)

Revision Note

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

Flowchart categorizing types of weathering: Physical (wetting and drying, exfoliation, salt crystallization, frost), Chemical (oxidation, hydration, carbonation, solution), Biological (vegetation, animals, humans).
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

Diagram explaining freeze-thaw weathering: water enters rock cracks, freezes and expands causing larger cracks. Repeated cycles of freezing and thawing break rock apart.
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

Diagram explaining types of mass movement: fall (rock fragments break from cliff), slide (blocks of rock slide downhill), flow (saturated soil flows), slump (soil slumps along a curve).
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

Diagram showing longshore drift: waves move material up the beach at an angle (swash) and gravity pulls it back down straight (backwash), moving it along the shore.
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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