2.4. Weathering Flashcards
What is weathering?
The breakdown of rocks in situ (in the same place with no major movement of rock materials involved
What are sub-aerial processes?
Land based processes which alter the shape of the coastline.
These are a combination of weathering and mass movement.
What do all processes involve?
All processes involve energy transfer from the sun or rain.
Weathering is responsible for the transfer (flow) of material
What are the links to other natural systems?
- carbon cycle
- water cycle
What is an example of a positive feedback loop for weathering?
If the rate of debris removal exceeds the rate of weathering and mass movement, positive feedback may operate- rate of weathering and mass movement could increase
What is an example of a negative feedback loop for weathering?
If debris removal is slow and ineffective, it will lead to a build up of debris that reduces the exposure of the cliff face as it extends up the cliff face- weathering and mass movement rates decrease
What is biological weathering?
This involves the break up of rock by organic activity
BW- plant roots
- Thin plant roots grow into small cracks in cliff face
- Cracks widen as roots grow and break up rock
BW- decaying vegetation
Water running through decaying vegetation becomes acidic, which leads to increased chemical weathering
BW- birds and animals
Birds and animals dig burrows into cliffs
BW- marine organisms
Marine organisms are capable of burrowing into rocks or secreting acids
What is mechanical weathering?
The break up of rocks without any chemical changes taking place
What is freeze-thaw weathering?
- Mechanical
- water enters a crack or joint in rock when it rains and freezes in cold weather
- when frozen, water increases by approx 10%
- expansion exerts pressure on rock so crack widens
- with repeated freezing and thawing, fragments of rock break away and collect at the base of the cliff as scree
What is crystallisation?
- mechanical
- salt water evaporates, leaving salt crystals behind
- these can grow over time and exert stresses on the rock, causing it to break up
- salt can also corrode rock
What is wetting and drying?
- mechanical
- rocks rich in clay expand when they get wet and contract when they dry
- this causes them to crack and break up
What is chemical weathering?
Involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is then easily eroded
What is carbonation?
- chemical
- rainwater absorbs Co2 from air to form weak carbonic acid
- this reacts with calcium carbonate in rocks to form calcium bicarbonate, which is easily dissolved
-cooler the temp of rainwater, the more Co2 is absorbed
What is oxidation?
- reaction of rock minerals with oxygen
- e.g. iron reacts with oxygen to form rust red powder which leaves rocks more vulnerable to weathering
What is solution?
The dissolving of rock minerals, such as halite
