Geology 1 MT2 mass movements

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Geology 1 MT2 mass movements
2011-05-09 13:58:17
Geology MT2 mass movements

Geology 1 MT2 mass movements
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  1. 4 resisting factors that add stability to mass movements:
    • material strength/cohesion of soils
    • vegetation
    • slope angle
    • small amount of water (adhesion+cohesion)
  2. 2 driving factors that decrease stability of mass movements
    • water saturation
    • gravity
  3. slope stability equation
    • forces pulling slope downward [gravity, water saturation]...
    • ...must be matched or exceeded by forces holding slope in place [cohesion, friction, angle of repose]
    • F driving ≤ F resisting
  4. role of water in mass movements:
    • a little water adds stability through cohesion (surface tension attraction of water molecules)
    • too much water decreases stability because of the effect of water pressure
  5. angle of repose
    • the maximum angle at which a slope will be stable
    • ~30˚ for most slopes
  6. 2 types of SLOW mass movements:
    • creep
    • lateral spreading
  7. 4 types of FAST mass movements:
    • rock falls
    • slides/slumps
    • flows
    • subsidence/sinkholes
  8. freeze/thaw creep of mass movement
    • when water in soils freeze, they expand; inflates slope
    • when thaws, it contracts; gravity pulls slope down
    • signs of creep: bent trees, bent rock layers
  9. lateral spreading of mass movement
    spreading of ground surface due to strong rock layers sinking into weaker ones
  10. fall of mass movement
    vertical transport of material, mostly free-fall
  11. slides, of mass movement
    • failure occurs on a surface
    • planer surface is a slide (transitional or daylighting)
    • curved surface is rotational
  12. flow of mass movement
    a mass movement where the material behaves in a fluid-like manner
  13. long-runout landslides
    • sturtzstroms
    • runout is significantly longer than the fall height
    • possible causes: water lubrication?, heat generates steam?, friction melting of material?, acoustic fluidization?
  14. subsidence; mass movement
    lowering of the ground surface due to withdrawal of underground fluids [oil, water]
  15. sinkhole; mass movement
    • ground surface collapses into an underground cavity
    • typically form in areas with limestone bedrock [carbonic acid dissolution]