What are the sub-aerial processes ? Flashcards
What does sub-aerial mean?
Under the air
What does weathering mean ?
The breakdown of rocks in-situ
What are the three types of weathering ?
- Mechanical
- Chemical
- Biological
Give four types of weathering ?
- Freeze-thaw
- Wetting and drying
- Exfoliation
- Salt crystallisation
What is freeze-thaw ?
Water enters the cracks in the rocks, expands by 10%, puts pressure on the rocks until they crack and break. The shattered angular fragments are found at the base as scree.
What is wetting and
drying ?
Common on the coastline in the inter-tidal zone, with clay and shale which expands when wet an contracts when dry. This provides cracks which are vulnerable.
What is exfoliation ?
Rocks under considerable heat will expand and then cooled by the sea causing rapid contraction. This repeated process causes the outer layer to crack and peel off (onion skin weathering)
What is salt crystallisation ?
Similar to freeze-thaw, salt crystals are deposited in cracks and accumulate under drier conditions, over time it applies pressure to the rocks and they crack.
Give two example of chemical weathering ?
- Carbonation
- Oxidation
What is carbonation ?
Sea and rain absorbs carbon dioxide forming carbonic acid which them dissolve the calcium carbonate in rocks such as limestone or chalk into calcium bicarbonate, especially in cracks and joints.
What is oxidation ?
Rocks containing iron compounds experience this when turning into a ferric state (rusting) when oxygen and water are available, leading to disintegration.
Give an example of biological weathering ?
- Plant roots
- Piddock
What is plant root weathering ?
Growing plant roots wien cracks in windy conditions these can widen.
What is piddock
weathering ?
On the coastline Piddock drills holes in the rock, puffins excavate nests and seaweed can move in storm conditions weakening rock.
