QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
Unit 5.3
Name:
2013-2014 S3 Geography
(
)
S.3(
)
What are the causes and effects of landslides?
Key Questions:
1.
2.
3.
4.
5.
6.
7.
What is a landslide?
What are the main types of landslide?
Why do slopes collapse?
Where do landslides commonly occur in Hong Kong?
What are the causes of landslides in Hong Kong?
What are the effects of landslides?
How do we prepare for and respond to landslides?
Preparatory task
Find out the meaning of the BOLD words. Write down the definition in Chinese in the boxes below.
1.
Landslides refer to the sudden and rapid movement of soil or rocks from slopes. When the
(1) gravitational force is greater than the (2) resisting force, slopes become unstable and collapse.
2.
Resisting force includes (3) cohesion of slope materials and (4) friction.
3.
Heavy rainfall, (5) human activities, (6) poor maintenance of man-made slopes, steep slopes and
loose soil and rock materials are the causes of landslides in Hong Kong.
4.
(7) Weathering is the breaking down or decay of rock. Many areas in Hong Kong are made up of
(8) granite. It is a type of hard rock but it is easily weathered.
5.
(9) Strengthening and monitoring slopes, (10) setting up laws and regulations and education are
the (11) preventive measures to landslides.
6.
(12) Setting up warning systems is one of the ways to reduce loss made by landslides.
English
Chinese
1.
gravitational force
引力
2.
resisting force
抗力
3.
cohesion
內聚力
4.
friction
摩擦力
5.
human activities
人類活動
6.
poor maintenance
缺乏保養
7.
weathering
風化作用
8.
granite
9.
strengthening and monitoring slopes
10. setting up laws and regulations
11. preventive measures
12. setting up warning systems
花崗岩
加強及監察斜坡
立法及規例
預防措施
設立警告系統
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
2013-2014 S3 Geography
(
)
S.3(
)
Name:
1. What is a landslide? (Textbook, p.26)
The following photo is taken in Hong Kong. Study the photo and answer the following
questions.
i)
Is the above natural event regarded as natural hazard? Why?
Yes, it is. It is because it causes loss of life and property.
ii) Name and define the above natural hazard.
The natural hazard is landslide.
A landslide refers to the sudden and rapid movement of soil or rocks from slopes.
2. What are the main types of landslide?
The following diagrams show two main types of landslide. Name the types of landslide.
Diagram 1: landslide
Diagram 2: Rockfall
2
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
Name:
2013-2014 S3 Geography
(
)
S.3(
)
3. Why do slopes collapse? (Textbook, p.26-28)
Watch the video ‘What causes a slope to collapse?’ and answer the following questions.
i)
What is the relationship between the slope angle and speed of the can moving down the
slope?
 When the slope angle increases, the speed of the can moving down the slope
(increases / decreases).
ii)
How does water in the sand help the movement of the can?
 When water adds weight to the can, it reduces the friction
These make the can move down the slope more easily.
of the surface.
iii) How does the surface of the sloping plane affect the downslope movement of the can?
 A rough surface (increases / decreases) the friction and reduces the downslope
movement of the can.
iv) What forces affect the movement of slope materials?
 Slope materials are affected by two sets of forces. They are gravitational force and
resisting force.
 Gravitational force is created due to the weight of slope materials. It pulls the
materials downslope.
 Resisting force includes
cohesion of slope materials
and
friction. This force holds slope materials together and prevents slope materials
from falling down.
>
Slope becomes
unstable and collapse
Landslide
3
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
Name:
2013-2014 S3 Geography
(
)
S.3(
)
4. Where do landslides commonly occur in Hong Kong? (Textbook, p.24-25)
The following maps show the distribution of landslides and built-up area in Hong Kong.
Study the maps and answer the following questions.
Figure 1
Distribution of reported landslides in Hong Kong between 1982 and 2004
Figure 2
Built-up area of Hong Kong
i) Describe the distribution of landslides in Hong Kong.
 Landslides occurred over an extensive area in Hong Kong.
 Most of them are found close to or in the built-up area.
ii)
Do you think landslides area threat to Hong Kong people? Why?
Yes, Hong Kong is hilly and many slopes are developed for urban uses. Moreover,
population density is high. When a landslide occurs, it causes a great threat to many
people.
4
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
2013-2014 S3 Geography
(
)
S.3(
)
Name:
5. What are the causes of landslides in Hong Kong? (Textbook, p.28-30)
Below figures show the causes of landslides in Hong Kong. Study the figures and answer
the following questions.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
5
QESOSA Tong Kwok Wah Secondary School
2013-2014 S3 Geography
Living with natural hazards 
Name:
(
)
S.3(
)
i) Describe and explain the causes of landslides in Hong Kong by completing the table
below.
Figure
Description
Explanation
1
Heavy rainfall
 Hong Kong is humid and rainy in summer. When rainwater
infiltrates into slope material, it reduces the
of the slope and

This reduces
cohesion
friction
of slope materials.
slope stability.
Or
2
Human activities

Rainwater adds

This reduces

In Hong Kong, many slopes in urban areas are cut to
weight
to the slope materials.
slope stability.
build roads and buildings.

This increases slope gradient
and adds weight to
slopes.

This makes it easier to
pull the slope materials downslope.
Or

When farming

Without
is carried on slopes, vegetation is removed.
plant roots
to hold the slope materials,
the slope becomes unstable.
3
Poor-maintenance
of man-made
slopes

maintained
slope
broken drainage channels
cover
and
will allow more water
to seep into the soil.

4
Poorly
Loose soil and rock 
materials

This reduces friction
and cohesion
of slop materials.
Many areas in Hong Kong are made of
granite.
It is a type of hard rock but is easily weathered by
weathering and becomes a loose material.
5
Steep slopes

It is prone to

In Hong Kong, about 40% of the natural slope is at an angle,
landslides.
between 20°and 30°
of it is at an angle

and 20%
between 30°and 45°
.
Gravitational force increases with
increasing gradient.

iii)
The danger of landslides is high for many slopes.
Use a graphic organizer ( ________________ ) to show the causes of landslides in
Hong Kong. Complete it in Notebook.
6
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
Name:
2013-2014 S3 Geography
(
)
S.3(
)
6. What are the effects of landslides? (Textbook, p.31.)
Task 1: Study the following information and answer the following questions.
i)
What were the causes of the landslides?
Intense rain, loosened slope materials, removal of trees on slopes and poor urban
planning were the causes.
ii) What were the effects of the landslides?
The caused deaths and injuries, destroyed buildings and caused great economic
loss.
iii) How did people respond to the landslides?
Open answer. ( Through this question, it is hoped that students will develop a sense
of belonging to our nation and a caring attitude towards the suffering of people
living in places far away from Hong Kong.
Explore further
Since 1947, over 470 people died in landslides in Hong Kong. This most serious
landslide in Hong Kong occurred in 18 June 1972 in the squatter areas at Sau Mau Ping,
killing 71 people. On the other hand, the Shum Wan Road landslide is the largest rapid
slope failure within a hillside. During this landslide, about 26,000m3 of soil and rock
debris failed from the slope.
7
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
2013-2014 S3 Geography
(
)
S.3(
)
Name:
7. How do we prepare for and respond to landslides? (Textbook, p.32-35)
Task 1: Below figures show some measures carried out in Hong Kong to response to
landslides. Study the figures and name the measures.
Measure 1: Strengthening and monitoring slopes
Install soil nail to support slope Plant grass on slope to provide Construct retaining wall to
support steep slope
and cover slope surface with surface protection
masonry
Cover slope with shotcrete to
Prevent water from seeping
into the slope
Measure 2: Setting up laws and regulations Measure 3: education Measure 4 : Setting up warning
systems
Task 2: Classify the above measures based on the following criteria.
Criteria
Measures
Preventive measures
1, 2, 3
Ways to reduce loss
4
Task 3: Use a graphic organizer ( ________________ ) to show how we prepare for and
respond to landslides. Complete it in Notebook.
8
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
Name:
2013-2014 S3 Geography
(
)
S.3(
)
 Resisting force
 It holds slope materials together and prevents slope materials from falling down.
 It includes cohesion（內聚力）of slope materials and friction（摩擦力）
 Gravitational force
 It pulls slope materials downslope
9
QESOSA Tong Kwok Wah Secondary School
Living with natural hazards 
Name:
2013-2014 S3 Geography
(
)
S.3(
)
10