1. Landslides
Causes

3. Is landslide a natural process?

4. Climatic graph of Hong Kong

5. Any relation between rainfall and landslides?

6. Rain washes away the soil

7. Describe and explain the rainfall characteristics of Hong Kong.
Heavy
Prolonged
Intense
Because HK belongs to tropical monsoon climate, which is hot and wet.

8. How does rain cause landslides?
Rain acts as a lubricant
which reduces friction
Soil becomes loose
Soil becomes saturated
Weight increases
 unstable slopes

9. Water acts as a lubricant

10. Unweathered & weathered granite

11. How is granite weathered?

12. Thick layer of soil

13. Rocks change to soil by weathering

14. Soil is removed by water or rain

15. Let’s do a demonstration

16. Steep slopes are common in Hong Kong

17. Houses are built on steep slopes

18. Houses are so close to steep slopes

19. Can you recognize this place?

20. Can you recognize this place?

21. Slopes are oversteepened

22. Landslides usually occur on steep slopes

23. Should human be responsible for landslides?

24. Trees on the slope are removed. Slope lacks protection.

25. Heavy traffic causes vibration.

26. Road cutting oversteepens the slope.

27. Can you name some highways running beside steep slopes?

28. Leakage of water pipes reduces the strength of slopes.

29. Buildings add weight to the slopes.

30. Summary: Conditions for landslides
Physical Factors – amount + duration + intensity of rain, thickness of soil layer, steepness of the slope
Human Factors – removal of vegetation, urban development, lack of maintenance, road cutting