1. Agenda 2/10
Warm-Up: Have you ever seen geologic problems in California on the news? What types of events make life more challenging on the West Coast?
Soil Reading/WS
Mass Movement Notes
Mass Movement flipbook

2. Mass Movements at Earth’s Surface
Part 1

3. Mass Movements
Mass movement: downslope movement of loose sediments and weathered rock resulting from the force of gravity
All occur on slopes; since very few places on Earth are flat, almost all Earth’s surface undergoes mass movement
Range from extremely slow motions
to sudden slides, falls, and flows
Materials moved: fine mud to
large boulders

4. Variables that influence Mass Movements:
Material’s weight resulting from gravity
Material’s resistance to sliding or flowing (friction between material and slope)
Trigger: such as an earthquake
Erosion and undermining of soil increase potential for earth’s materials to move downhill

5. Other Variable: Water
Too little water: prevents sediment from holding together at all
Too much water: can make slope unstable increasing weight of soils and sediment
In this case: water not involved as transport agent; moves along with materials vs. materials moving along with water

6. Types of Mass Movements: Creep
Creep: slow, steady downhill flow of loose, weathered materials (soils)
Move few cm per year
Effects seen over long periods of time
Can cause tilting of utility poles, fences, bending of trees, cracking of walls, breaking of underground pipelines
Solifluction: slow, downhill movement of loose, water-logged materials in regions of permafrost (mudlike liquid)

7. Types of Mass Movement: Flows
Flows: can move slowly as a few cm per year or hundreds of km per hour
Earth flows: slow movements of soil
Mudflows: swiftly moving mixtures of mud and water triggered by earthquakes (common in volcanic regions and sloped semi-arid regions)
Los Angeles Basin (southern CA) slopes left with little vegetation, heavy rains fall, cause mudflows

8. Types of Mass Movement: Slides
Landslide: rapid downslope movement of materials that occurs when thin block of soil, rock, and debris separates from underlying bedrock Rock Slide: type of landslide that occurs when sheet of rock moves downhill on sliding surface Very destructive form of mass movement!

9. Types of Mass Movement: Slumps
Slump: when mass material in landslide rotates and slides along a curved surface
Occur in areas that have thick soils and on moderate to steep slopes
Common after rains because water reduces friction between grains of soil; weight of additional water pulls it downhill
Triggered by earthquakes

10. Types of Mass Movement: Avalanches
Avalanches: landslides occur in mountainous areas with thick accumulations of snow
Usually occur on slope
10,000 avalanches each year in mountains of western US
Sun melts surface snow, then refreezes at night, snow falls on top builds up heavy, slip, slide down slope as avalanche

12. Rock Falls
Occur at high elevations, steep road cuts, on rocky shorelines
Rocks loosened by physical weathering and plant growth
Rocks break up and fall downward

13. Mass Movements Affect People
Dangerous Mudflows: widespread loss of human life primarily result of location of villages both high up and in steep terrain and at foot of unstable, saturated slopes
Reducing the Risks: avoid building structures on such steep and unstable slopes
Trenches used to divert water from a slope and control drainage
Covering steep slopes with steel nets and protective fences

14. Mass Movement flipbook
Make a 6 flap foldable (like our Extreme Weather foldable). Each flap will have the name of one mass movement: Creep, Slump, Flow, Slide, Avalanche
Use your notes/internet searches to fill in your foldable
Front Flap: Title and Picture of the mass movement
Inside: definition, effects/trigger, what caused by, where these movements occur most often, and any other information you may want to add.