LO 1.2 - Physical factors in soil formation

Question 1

What is Weathering?

Answer 1

Weathering:

Is a process by which rock is broken into smaller particles by physical, chemical or biological agents. Nutrients such as phosphorus, potassium and sulphur are released which become available to plants.

Question 2

What is Erosion?

Answer 2

Erosion:

Is the movement of rock particles and soil, due to action of wind, water, ice and gravity.

Question 3

Consider this

Weathering and erosion are two separate processes although they often happen at the same time.

Answer 3

Question 4

What are the different kinds of Physical Weathering?

Answer 4

• Heating/cooling
• Freezing/thawing
• Wetting/drying
• Expansion of plant roots
• Abrasion

Question 5

What are the different kinds of Chemical Weathering?

Answer 5

• Acids
• Dissolution
• Oxidation
• Plants/fungi/lichens

Question 6

What physical or chemical weathering processes can be considered biological?

Answer 6

Question 7

Consider this

Physical weathering: heating/cooling

Answer 7

• Different minerals expand at different rates when heated.
• When rocks composed of different minerals are heated, the different minerals undergo different rates of expansion.
• ‘Onion-skin weathering’ happens when outer parts of a rock are at different temperature from inner parts.

Question 8

Consider this

Physical weathering: freezing/thawing & wetting/drying

Answer 8

• Water penetrates small cracks in rocks.
• Water can then freeze and expand.
• This is known as ‘frost shattering’.
• Some minerals swell when exposed to water and shrink on drying

Question 9

Consider this

Physical weathering: expansion of plant roots

Answer 9

• Roots grow into small cracks and crevices in rocks.
• They grow and expand and widen the cracks which exposes the rock to surface elements.

Question 10

Consider this

Physical weathering: abrasion

Answer 10

Water or air/wind carrying rock fragments ‘scours’ or ‘sand-blasts’ the surface of rocks.

Fast-flowing streams/rivers and seas carry stones/pebbles that are tumbled against each other.

Glaciers carry particles of varying sizes that scour the rock below, wind carries sand.

Gravity can contribute to abrasion too – rocks falling or sliding down a slope scrape against each other and against bedrock.

The physical force of water alone is also a powerful agent of weathering, including rivers/streams and waves along shorelines.

Question 11

Physical Weathering: Abrasion

How do animals cause this?

Answer 11

• Abrasion also happens when animals (including humans) repeatedly pass over an area of rock.
• Burrowing animals can have a similar effect below ground.