Geography (What are the causes and effects of landslides?)

Question 1

What and when do landslides occur?

Answer 1

Landslides are the collapse of slopes. They occur when a mass of soils and rock of all sizes move down a slope rapidly due to gravity.

Question 2

In HK, natural terrain covers about ___% of tte total land area. Each year, about ____ landslides occur on natural terrain. Some landslides occur on __________ slopes. These slopes are found in built-up areas.

Answer 2

1. 60%
2. 300
3. man-made

Question 3

Explain how landslides affect us.

Answer 3

+Landslides in built-up areas cause injuries and even deaths
+Landslides may bury buildings and damage infrastruture such as water pipes, and
powerlines. The supply of these services will be cut off.
+Landslides often block roads and stop traffic. This greatly disrupts peoples daily lives.

Question 4

When a slope is ____, it will not collapse. Slope stability is controlled by the balance of the ____ force and the _____ force.

Answer 4

1. stable
2. driving
3. resisting

Question 5

What is driving force?

Answer 5

Driving force drives movement. It pulls slope materials downhill under the force of gravity. It is mainly controlled by slope gradient and weight of slope materials.

Question 6

What is resisting force?

Answer 6

Resisting force resists movement down the slope. It prevents slope materials from sliding down. It is affected by the cohesion of slope materials and the force of friction.

Question 7

When the ____ force is greater than the ____ force, the slope is stable. In contrast, when the _____ force is greater than the _____ force, the slope is unstable and may collapse.

Answer 7

1. resisting
2. driving
3. driving
4. resisting

Question 8

What are the causes of lanslides in HK. Explain why.

Answer 8

Heavy rainfall:
+Heavy rainfall adds much weight to the slope. Therefore, slope materials are more
likely to fall down.
+Large amount of rainwater seeps into the soil or rock on slopes. The reduces the
cohesion of slope materials and the force of friction. Therefore, the resisting force
decreases.

Strong weathering:
+Many areas in HK is made out of granite which can easily be wethered, especially in
HK’s weather. This means HK is often deeply weathered, which leaves a thick layer of
loose materials on slopes. The resisting force of those loose materials is small, so
landslides occur easily as a result.

Large slope gradient:
+HK has a hilly relief.~60% of natural terrain in HK has slopes>20. The larger the slope
gradient, the larger the force pulling slope materials downhill. Risk of landslides are
high when slope gradient>30

Question 9

What human activities increase the risk of landslide. Explain why.

Answer 9

Human activties on slopes:
+Many slopes in built-up areas are cut and filled to build roads and buildings
This increases the slope gradient and therefore the driving force.
+Vegetation on slopes is often completely removed. This may also adversely affect slope
stability.
+In the past, some cut slopes in Hk were developed without taking adequate preventive
measures.This raised the risk of lanslides. Nowadays there are stricter laws and better
slope management, cutting slopes in HK is safe.

Poor mainteneance of man-made slopes:
+A man-made slope will break after some time if there is no proper maintenance
+Cracked slope surface and drainage channels allow more water to seep into the soil.
This increases driving force and decreases resisting force, Landslides may occur as a
result.

Question 10

Name 5 preventive measures. Explain how it helps.

Answer 10

Building barriers
+Barriers prevent slope materials from rushing down to settlements.
+Barriers can be built on the slope or at the bottom of the slope.
/_This reduces the loss of life and property

Strenghtening and monitoring slopes
+Reduce risk of landslides on manmade slopes by strengthening them.
/_Either by reducing driving force or increasing resisting force
*Retaing wall (Increase resisting force)
*Gabion wall (Increase resisting force)
*Drainage channel (Increase resisting force+Decrease driving force)
*Soil nails (Increase resisting force)
*Shotcrete+Weephole (Increase resisting force+Decrease driving force)

Setting up laws
+Restrict development on steep slopes. ( Cant be cut without careful study and
government authorisation)
+Owners are required to carry out proper slope maintenance measures.

Setting up warning systems
+Landslip warning
/_Reduce the publics exposure to potential landslides+Stay away from slopes.

Education
+Educates the public about appropriate actions to take when landslip warning is in force