1. 5th year Geography
Mass Movement

2. Causes of Mass Movement Different types of Mass Movement
Learning Outcomes
Causes of Mass Movement
Different types of Mass Movement
Case Studies of Mass Movement
Impact of Human Activities on Mass Movement

3. Mass Movement
The movement of material downhill under the influence of gravity.
The loose material is called regolith.

4. Triggers of Mass Movement
Natural
Torrential rain
Heavy snow
Earthquakes
Volcanoes
Human
Road building across hills and mountains
Waste being piled on unstable slopes
Quarry blasting
Deforestation
Skiing

5. Factors Affecting Mass Movement
Gravity
Slope
Water
Vegetation
Human Activities
Type of Material

6. Classifying Mass Movements
Can be grouped according to;
Speed
Water Content

7. Types of Mass Movement Very Slow Fast and Dry Fast and Wet Soil Creep
Solifluction
Fast and Dry
Rock Falls
Avalanches
Fast and Wet
Mudflows
Bogbursts
Lahars
Landslides
Slumps

8. Chapter 10: Mass Movement
Soil creep
Very slow movement
Underlying rock becomes heavily saturated following periods of heavy rainfall
Water can no longer pass through the rock
Soil particles expand and later contract when they dry out
Causes soil particles to creep slowly downhill under the influence of gravity

9. Soil Creep

10. 2. Slump-rotational slide
Loosely consolidated rock layers moves down slope
Influence of gravity
Moderate speed
May be an isolated occurrence or they may occur in large areas
Often associated with areas which have been affected by human activities
E.g. during the construction of roads where the land has been too steepened and has been left unstable
Also linked to coasts and river banks where, due to erosion, slopes have been undercut
Also associated with landscapes following heavy rain

11. 3. Earthflow
Water saturated material (fine sand, silt and clay) flows downslope
Influence of gravity
Moderate speed
Generally occur on hilly slopes
Associated with heavy rain
Speed at which they travel varies from several cm per year to hundreds of metres per day
More common in humid areas
Tend to have a lower water content than mudflows

12. 4. Rockfall
Rocks fall downslope
Influence of gravity
Rapid speed
Occur following periods of heavy rain and frost weathering
Strong earthquakes may also cause rock falls to occur
Caused by either a biological or a climatic event changing rock stability

13. Rock Fall

14. Movement of rocks, soil and debris mixed with ice or water or both
5. Debris avalanche
Movement of rocks, soil and debris mixed with ice or water or both
Rapid movement
Material transported liquefies
Rapid speed
Can move further than the foot of a slope due to their rapid speed

15. Saturated regolith flows rapidly downslope Influence of gravity
6. Mudflow
Saturated regolith flows rapidly downslope
Influence of gravity
Associated with steep slopes and deep soils
Fast speed
Soil becomes waterlogged and saturated if there is an impermeable rock layer beneath
Can be of speeds in excess of 100 km per hour
Can occur as a result of volcanic activity – known as lahars
Volcano with snow on its top erupts, the melting snow and ice cause a mudflow

16. Chapter 10: Mass Movement
Mudflow case study
15 June 1991, Mount Pinatubo, Philippines
Volcanic eruption deposited more than 5 cubic kilometers of volcanic ash and rock fragments on the volcano slopes
Heavy rains washed this material down into the surrounding lowlands in giant, fast-moving lahars
The next four rainy season’s lahars carried about half of the deposits off the volcano, causing even more destruction in the lowlands

17. 7. Bogburst
An area of bog moves downslope
Influence of gravity
Slow to fast speed
Tend to occur mostly during autumn and winter due to high precipitation levels
Periods of very heavy rain after long periods of very dry weather seem to be associated with the occurrence of bog bursts
Human activity is also linked to the occurrence of bog bursts, e.g. peat cutting, draining of land for agriculture and the construction of wind farms

18. Chapter 10: Mass Movement
Bogburst case study
Derrybrien, Slieve Aughty Mountains, Co. Galway
16 October 2003: bog had been affected by a dry spell during the summer and when heavy rain fell, the peat became saturated
Resulted in local roads being closed
Lough Cutra river system was polluted
Thousands of fish killed when some 70 acres of bogland flowed down river
Triggers- Human Activity & Heavy Rain

21. Avalanche Very rapid movement of snow downslope
May occur due to either natural events or human activity
Fast speed
Usually occur on mountain slopes
Occur when the weight of the snow is too much for the slope to hold

22. Avalanche

23. Major causes of avalanches may include the following:
Weather – they are most likely to occur after a heavy snowstorm
Snowfall – recent snowfall exerts increased pressure on existing snow deposits
Temperature – warmer temperatures experienced over several days may cause upper layers of snow to melt and weaken
Wind direction – snow may be packed unevenly on the leeward side of a mountain due to prevailing wind direction
Slope angle – most avalanches occur on slopes of between 30 and 45 degrees
Slope orientation – most avalanches occur on slopes facing north, north-east and east
Human activities – deforestation and tourist activity may lead to the occurrence of avalanches

24. 9. Landslide
Slope stability changes from stable to unstable
Causes may be loss of vegetation, erosion of slope, weakening of slope, earthquake activity, volcanic eruptions and human activities
Fast speed

25. Damage caused during brazilian landslides (Jan 2011)

28. Impact of overcropping Impact of deforestation
Human activities can impact on the operation of surface processes
Impact of overgrazing
Impact of overcropping
Impact of deforestation

29. Sahel case study
Areas that are most affected by desertification are regions/areas that are on the edges of deserts
Sahel Region lies to the Southern end of the Sahara Desert in Africa
Covers an area of approximately 1000 km in total
Stretches from the Atlantic Ocean coast to the Red Sea coast and is located at the southern end of the Sahara desert
Desert is growing at a rapid rate
Experienced an increase in population in recent years

30. Sahel case study (continued)
High birth rate and immigration rates are also high
High population growth increases the demand for food
Increased demand for food and for land to cultivate
Growth of farming and cultivation has led to soil becoming exhausted and exposed to erosion
Increase in the number of animals required for food has also resulted in overgrazing
Cattle are also seen as a sign of wealth in the region.
Energy needs are satisfied by cutting down trees

31. Chapter 10: Mass Movement
Sahel case study (continued)
Vegetation, along with the trees, bind the soil together
When removed, the soil becomes weak and dry
When extra land is needed, a practice of ‘slash and burn’ has been used and has increased the barrenness of the region
The Sahel Region has experienced long periods of drought
Also experiences spots of unpredictable heavy rainfall
This type of rain can damage crops
When land experiences desertification, fertility is reduced and this has a direct effect on food supply; it may lead to famines

32. Saharan Desertification
Video Clip
Saharan Desertification
Millions of years ago the Sahara was a green and pleasant land, but over the centuries desertification changed its climate.

33. Exam Questions
Examine how human processes can impact on the process of mass movement. (30m)
Describe and explain any one process of mass movement. (30m)