Chapter 5 Mass Movements and Subsidence
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Transcript of Chapter 5 Mass Movements and Subsidence
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Chapter 5
Mass Movements and Subsidence
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Causes vs. TriggersCause – situation that leads to failure Trigger – event that produces
failureNatural geologic – fractures, layers PhysicalNatural morphology Heavy rainfall/rapid snowmelt Uplift (tectonic or volcanic) Rapid drawdown Subsurface erosion Earthquake
Vegetation loss (fire, drought) Volcanic eruption Freeze-thaw action FloodingHuman Human Excavation or loading Explosions Deforestation Mining Irrigation or water leakage
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Resolution of forces on a slope
Driving force – downhill componentResisting force – depends on underlying
material
Safety factor = resisting force/driving forceif > 1, slope is stableif < 1, failure can occur
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Angle of repose
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Bedding planes on a slope
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How stable is this house?
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Classification of Mass Movements
• Falls – free fall• Rock• Debris
• Slides and slumps• Rotational• Translational
• Flows• Mudflow or earthflow
• Creep
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Free fall
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Cause of slope failure 1- steepening of
slope
2- removal of toe support
3- addition of mass at top
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Toe
Crown
Basal surface
Head scarp
Rotational slide
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Anchorage AlaskaMarch 1964 Earthquake
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Translational slide
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Types of flows – notice differences
Debris flow Earthflow
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Creep
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Turtle Mtn/Frank Slide, Alberta1903
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Mass movements of other material
Snow avalanches Submarine slumps – largest mass
movements on Earth, but not seen
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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
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Alabama 1972130 m long - 46 m deep