1. Earth Science Chapter 8 Section 1
Mass Movements
Earth Science
Chapter 8
Section 1

2. Mass Movements Landforms change through processes involving
Wind
Water
Ice
Gravity
Down slope movement of soil and weathered rock from the force of gravity is called Mass Movement

3. Mass Movement Climate has an effect on weathering in certain areas
Climatic conditions determine the extent of mass movement
Mass movement can
Be barely detectable
Sudden slides, falls and flows
Materials range in size from mud to boulders

4. Factors that influence Mass Movements
Material’s weight
Materials’ resistance to sliding or flowing- friction
How cohesive the material is or if it is anchored to bedrock
Triggers- shake the material loose
Mass movements occur when the force pulling the material down slope that is stronger than the force holding it in place.

5. Creep Slow steady downhill flow of loose weathered material
May be only a few centimeters a year
Noticeable over long periods of time
Solification- creep that occurs in areas of permafrost
Mud-like liquid when water is released from melting permafrost
Saturates the surface
Unable to drain
Surface area slides

6. Mudflows Mud flow Swiftly moving mixtures of mud and water
Triggered by earthquakes or similar vibrations
Common when volcanoes melt snow
Water fills spaces in sediment and allows them to slide down hill
Common in sloped, semi arid areas that experience intense rain fall

7. Lahar Type of mud flow that occurs after a volcanic eruption
Melted snow mixes with ash and flows downslope

8. Slides Landslide Rapid downslope movement of material
Thin block of soil, rock and debris separate from underlying bedrock
Material slides as one block with little internal mixing
Common on steep slopes after saturation

9. Slides Rock slide Sheet of rock moves downhill on a sliding surface
Triggered by earthquakes
Move a large amount of material

10. Slumps Material moves along a curved surface
Material at the top moves downhill and slightly inward
Material at the bottom moves slightly outward
Occurs with thick soils on moderate to steep slopes
Common after rains
Can be triggered by earthquakes
Leave a crescent shape scar on slope

11. Avalanches Occur in mountains with thick accumulation of snow
Sun melts surface which refreezes at night- icy crust
Snow falls on this crust and builds up
Becomes heavy and slides down slope
Triggers
Vibrations as slight as a single skier

12. Rock Falls Rocks are loosened by physical weathering processes
Rocks break loose and fall directly downward
They bounce and roll
Produce a cone shaped pile of coarse debris at the base of the slope- called a talus
Common at high elevations in steep cut roads and rocky shorelines
Less likely in humid regions- rocks are covered with soil

13. Mass Movements Affect People
Mass movements are natural processes, however humans can contribute
Construction of buildings and roads- make slopes unstable
Poor maintenance of septic systems- leaks

14. Reducing the Risk
Catastrophic mass movements occur on slopes greater than 25 ° that experience annual rainfall of 90 cm
Risk can be reduced by
Digging trenches to divert water
Not building at the base of a slope
Covering steep slopes with nets
Contructing fences along highways where movement is common
Prevention measures are only temporarily successful