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
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
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
Types of mass movement
Exam Tip
To help you remember the different types of mass movement, try splitting them up into these four categories: fall, slide, flow and slump.
