1. Weathering

2. 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

3. 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.

4. 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.

5. Weathering Chemical Limestone, Chalk or Marble Biological Plants and Animals Physical Onion Skin (Exfoliation) Freeze-Thaw

7. 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.

8. 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.

10. Biological Weathering - Animals

11. 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.

12. 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.

14. 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.

16. Freeze-Thaw Weathering Cracks in the rocks get wet and filled with water. At night the temperature drops below 0 o C. The water in the cracks freezes. As the water freezes, it expands. The cracks become wider. The temperature rises above 0 o C. The ice thaws and contracts. This cycle continues widening and enlarging the cracks. This continuous process causes rocks to be broken up

17. 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 3 rd February