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Chapter 5 Mass Movements and Subsidence

Chapter 5 Mass Movements and Subsidence. Causes vs. Triggers. Cause – situation that leads to failure Trigger – event that produces failure Natural geologic – fractures, layers Physical Natural morphology Heavy rainfall/rapid snowmelt

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Chapter 5 Mass Movements and Subsidence

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  1. Chapter 5Mass Movements and Subsidence

  2. Causes vs. Triggers Cause – situation that leads to failure Trigger – event that produces failure Natural geologic – fractures, layers Physical Natural morphology Heavy rainfall/rapid snowmelt Uplift (tectonic or volcanic) Rapid drawdown Subsurface erosion Earthquake Vegetation loss (fire, drought) Volcanic eruption Freeze-thaw action Flooding Human Human Excavation or loading Explosions Deforestation Mining Irrigation or water leakage

  3. Resolution of forces on a slope Driving force – downhill component Resisting force – depends on underlying material Safety factor = resisting force/driving force if > 1, slope is stable if < 1, failure can occur

  4. Angle of repose

  5. Bedding planes on a slope

  6. How stable is this house?

  7. Classification of Mass Movements • Falls – free fall • Rock • Debris • Slides and slumps • Rotational • Translational • Flows • Mudflow or earthflow • Creep

  8. Free fall

  9. Cause of slope failure • 1- steepening of slope • 2- removal of toe support • 3- addition of mass at top

  10. Rotational slide Crown Head scarp Basal surface Toe

  11. Anchorage AlaskaMarch 1964 Earthquake

  12. Translational slide

  13. Types of flows – notice differences Debris flow Earthflow

  14. Creep

  15. Turtle Mtn/Frank Slide, Alberta1903

  16. Mass movements of other material • Snow avalanches • Submarine slumps – largest mass movements on Earth, but not seen

  17. Subsidence • Downward movement of ground surface • Not reversible once it occurs • Causes • Removal of water or oil • Compaction of clay materials (deltas) • Solutioning of limestone by CO2

  18. Alabama 1972130 m long - 46 m deep

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