1. Chapter 5.3
Mass Movements

2. Triggers of Mass Movements
What force causes material to move down slope?
Movement of rock and soil down slope due to gravity is called mass movement

3. Mass Movement
This home in Pacific Palisades, California, was destroyed by a landslide triggered by the January 1994 Northridge earthquake

4. Q & A Are snow avalanches a type of mass movement?
Yes. These thundering down slope movements of snow and ice can also transport large quantities of rock, soil, and trees. 10,000 snow avalanches
occur each year in the mountainous western United States.

5. Triggers of Mass Movement
Water
Oversteppened slopes
Removal of vegetation such as plants and trees
Earthquakes

6. Triggers of Mass Movement
Water
Heavy rains and rapid melting of snow can trigger mass movement by saturating soil particles on the surface with water

7. Triggers of Mass Movement
Oversteepened Slopes
Loose soil particles are stable until a certain angle. When this angle is exceeded mass movement of soil particles occurs.

8. Triggers of Mass Movements
Removal of plants
Plants make slopes more stable because their roots bind soil together
When plants are removed by human activities mass movement increases

9. Triggers of Mass Movement
Earthquakes are one of the most dramatic triggers of mass movements
An earthquake and its aftershocks can dislodge enormous amounts of rock and unconsolidated material

10. Types of Mass Movements
Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of movement
Five kinds of mass movement
Rockfalls
Slides
Slumps
Flows
Creep

11. Rockfalls
A rockfall occurs when rocks or rock fragments fall freely through the air
Common on slopes that are too steep for loose material to remain on the surface

12. Slides
In a slide, a block of material moves suddenly along a flat, inclined surface
Slides that include segments of bedrock are called rockslides
Often occur in high mountain areas
Reaching speeds of over 124 mph

13. Slumps
A slump is the downward movement of a block of material along a curved surface
As the block moves, its upper surface sometimes tilts backward and leaves a crescent-shaped cliff just above the slump

14. Flows
Flows are mass movements of material containing a large amount of water that move downslope as a thick fluid
Example-
Mudflows move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete

15. Creep
Creep is slowest, downhill movement of soil (only travels a few inches per year)

16. Creep

17. Review What is mass movement? How does water trigger mass movements?
The transfer of rock and soil down slope due to gravity
Water fills the pores in soil particles, allowing the particles to slide past one another more easily

18. Review What is the slowest type of mass movement?
When highway engineers build a road in a mountainous area, they insert drainage pipes into the slopes alongside the road. Explain why.
Creep
The pipes allow water to drain out of the soil and regolith in the slopes, reducing the chance that a mass movement will carry slope material onto the road.