Chapter 5.3

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 isslowest, 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.

19. http://www.youtube.com/watch?v=w40JgaKNihY http://www.youtube.com/watch?v=aajUXQmec-Q http://www.youtube.com/watch?v=4H1jGry5biU