Mass Movements

Question 1

Define a mass movement

Answer 1

the downhill transfer of slope materials as a coherent body

Question 2

When do mass movements occur?

Answer 2

when the downslope forces exceed the upslope forces.

Question 3

What are the ultimate causes of mass movements?

Answer 3

1. A reduction in the internal resistance (shear strength) of the slope
2. An increase inshear stress(i.e. the forces acting on a slope that may lead to MM)

Question 4

Name 2 trigger mechanisms of mass movements?

Answer 4

1. Precipitation

2. Seismic activity

Question 5

What are the 5 physical factors contributing to slope instability?

Answer 5

1. Steep gradient
2. Rock type
3. Geological structure
4. Water content and permeability
5. Slope undercutting

Question 6

Physical factors contributing to slope instability

steep gradient

Answer 6

Steeper the slope, the more effective the downward pull of gravity

Question 7

Physical factors contributing to slope instability

geology - rock type

Answer 7

• Granite and limestone vs sandstone and clay / unconsolidated vs consolidated
• Rock juxtaposition – weaker on top of stronger may be prone to sliding over underlying strata

Question 8

Physical factors contributing to slope instability

geology - geological structure

Answer 8

Heavily fractured / jointed rocks more prone to weathering processes e.g. freeze thaw

Question 9

Physical factors contributing to slope instability

geology - water content and permeability

Answer 9

water decreases friction and lubricates the slope

Question 10

Physical factors contributing to slope instability

slope undercutting

Answer 10

By natural processes e.g. fluvial / marine erosion

Question 11

Name 2 human factors contributing to slope instability

Answer 11

1. Removal of vegetation

2. Human actions/ development

Question 12

How does removal of vegetation contribute to slope instability?

Answer 12

Vegetation intercepts rainfall and binds soil and rock particles together. Removal decreases shear strength of slope.

Question 13

Give 3 examples of human actions/ developments and explain how they contribute to slope instability

Answer 13

1. Settlement
2. Mining
3. Infrastructure (roads)

• increases weight on slopes ( increases shear stress acting on slope)
• digging of foundations mades material more unconsolidated, this reduces the shear strength of the slope
• interference of natural drainage systems results in higher water content in slopes which acts as a lubricant
• road building steepens slope

Question 14

What are the 3 geographical issues associated with mass movements?

Answer 14

1. Impact on human activities
2. Human activities causing slope destabilisation
3. Physical geography causing landslides