Landslides Causes

Is landslide a natural process?

Climatic graph of Hong Kong

Any relation between rainfall and landslides?

Rain washes away the soil

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

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

Water acts as a lubricant

Unweathered & weathered granite

How is granite weathered?

Thick layer of soil

Rocks change to soil by weathering

Soil is removed by water or rain

Let’s do a demonstration

Steep slopes are common in Hong Kong

Houses are built on steep slopes

Houses are so close to steep slopes

Can you recognize this place?

Can you recognize this place?

Slopes are oversteepened

Landslides usually occur on steep slopes

Should human be responsible for landslides?

Trees on the slope are removed. Slope lacks protection.

Heavy traffic causes vibration.

Road cutting oversteepens the slope.

Can you name some highways running beside steep slopes?

Leakage of water pipes reduces the strength of slopes.

Buildings add weight to the slopes.

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