Weathering

Miss Johnstone’s Expectations

Arriving and leaving the classroom

Presentation

Underline your titles

Always put the date

Draw in pencil

Draw a line under previous lessons work and carry on

Learning Objectives

To be able to define weathering.

To be able to identify the three different

types of weathering.

To be able to explain the three types of

weathering.

What is Weathering?

Weathering is the breakdown of rocks by

three different processes – biological,

chemical and physical. Weathering takes

place where the rock is – no movement

is involved.

Weathering

Chemical

Limestone, Chalk or Marble

Biological

Plants and Animals

Physical

Onion Skin(Exfoliation)

Freeze-Thaw

Chemical Weathering(Order the statements)

Limestone, chalk or marble is dissolved or weakened.

The rocks are worn away or broken up.

Carbon dioxide mixes with rainwater to create a weak acid.

The weak acidic rain attacks the rocks.

Chemical Weathering(Order the statements)

3. Limestone, chalk or marble is dissolved or weakened.

4. The rocks are worn away or broken up.

1. Carbon dioxide mixes with rainwater to create a weak acid.

2. The weak acidic rain attacks the rocks.

Biological Weathering - Animals

Biological Weathering(Order the Statements)

Animals dig under the rocks.

Rocks collapse or fall apart.

Rocks are undercut and cracks are widened.

Plants grow into cracks in the rocks.

Rocks loosened and broken up.

Biological Weathering(Order the Statements)

2. Animals dig under the rocks.

5. Rocks collapse or fall apart.

3. Rocks are undercut and cracks are widened.

1. Plants grow into cracks in the rocks.

4. Rocks loosened and broken up.

Onion Skin Weathering (Exfoliation)

• Onion-skin weathering is

also known as exfoliation.

• During the day the

temperature rises

• The outer layers of the rock

heat up and expand

• This cycle continues to

widen the cracks in the

outer layer.

• Eventually, the outer layers

‘peel’ off like an onion.

• The pealed layers remain

where they fall.

• During the night the

temperatures fall.

• The expanded layers of the

rock cool down and

contract.

• Cracks form in the outer

layers of the rock.

Freeze-Thaw Weathering

• Cracks in the rocks get wet and filled with water.

• At night the temperature drops below 0oC.

• The water in the cracks freezes.

• As the water freezes, it expands.

• The cracks become wider.

• The temperature rises above 0oC.

• The ice thaws and contracts.

• This cycle continues widening and enlarging the cracks.

• This continuous process causes rocks to be broken up

For both chemical and physical weathering

(You can leave biological)

1. At what temperature and rainfall levels does the strongest chemical or

physical weathering occur?

2. Suggest a country where this might be, i.e. the Sahara

Desert will have very strong onion skin weathering.

Due: Tuesday 3rd February