Geology 1 MT2 mass movements

• material strength/cohesion of soils
• vegetation
• slope angle
• small amount of water (adhesion+cohesion)

• water saturation
• gravity

• 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

• 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

• the maximum angle at which a slope will be stable
• ~30˚ for most slopes

• creep
• lateral spreading

• rock falls
• slides/slumps
• flows
• subsidence/sinkholes

• 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

spreading of ground surface due to strong rock layers sinking into weaker ones

vertical transport of material, mostly free-fall

• failure occurs on a surface
• planer surface is a slide (transitional or daylighting)
• curved surface is rotational

a mass movement where the material behaves in a fluid-like manner

• sturtzstroms
• runout is significantly longer than the fall height
• possible causes: water lubrication?, heat generates steam?, friction melting of material?, acoustic fluidization?

lowering of the ground surface due to withdrawal of underground fluids [oil, water]

• ground surface collapses into an underground cavity
• typically form in areas with limestone bedrock [carbonic acid dissolution]