MASS WASTING AND MASS MOVEMENT
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mass movement - a general term used to describe the downhill movement
of material that are known as slides, falls, slumps, flows, and creep
MASS WASTING AND MASS MOVEMENT
1. unconsolidated material - those that are loose or uncemented, such as sand
and soil
2. consolidated material - those that are compacted, cemented, or vegetated
soils
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Factors That Influence Mass Movement
1.slope of material - the steepness of a slope influences instability in mass
movement
i. the steepness of a pile of loose material such as sand has a distinct limit angle of repose
ii. once the angle of repose is reached, addition of more sand will make the
pile broader but not taller
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Factors That Influence Mass Movement
2. internal friction - a material’s total resistance to movement
i. consolidated dry materials are held together by cohesion
(attraction of like particles) and adhesion (attraction of unlike
particles)
ii. cementation
iii. plant roots
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Factors That Influence Mass Movement
3.
surface tension
4.
moisture content
i.
too little limits vegetation
ii.
too much can push grains apart, add weight, or provide
lubrication
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Factors That Influence Mass Movement
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Triggers of mass movement
1.
sudden addition of moisture
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Triggers of mass movement
2.
shaking of the ground - liquefaction
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Classification of mass movement
1.
Based upon
i.
nature of the material (rock or unconsolidated)
ii.
speed of movement
iii.
nature of movement (sliding, falling, or flowing)
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Rock Mass Movement
1.
rockfall - free fall of boulders from a cliff
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Rock Mass Movement
2.
rockslides - sliding of rock down an incline
i.
usually due to rock breaking from its host material along a bedding
plane, joint, or other structural weakness
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Rock Mass Movement
3.
talus - debris at the bottom of the slope in a broken mass due to
rockfalls and rockslides
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Rock Mass Movement
4.
rock avalanche - rock becomes broken into pieces before it
reaches the foot of a slope
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Unconsolidated Material Mass Movement
1.
creep - extremely slow, almost imperceptible downslope
movement of soil and rock debris
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Unconsolidated Material Mass Movement
2.
solifluction (soil flowage) - special type of creep that is common in
polar regions where groundwater in the pore spaces of soil and rock is
permanently frozen
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Unconsolidated Material Mass Movement
3.
earthflows and debris flows - consist of mixtures of rock fragments,
mud, and water that flow downslope as viscous fluids
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Unconsolidated Material Mass Movement
3.
earthflows and debris flows - consist of mixtures of rock
fragments, mud, and water that flow downslope as viscous fluids
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Unconsolidated Material Mass Movement
4.
mudflows - a variety of debris flow that consist mostly of small silt and
clay-sized particles
i.
usually occur after heavy rain
ii.
as much as 30% water content
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Unconsolidated Material Mass Movement
5.
debris avalanche - fastest unconsolidated mass movement
i.
on steep slopes in humid areas
6.
slumps and debris slide - movement of material in which the material
is not rearranged
Debris Slide
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Plate Tectonics
1.
OC - CC boundary
i.
causes steep slopes
ii.
volcanic activity and earthquakes
Gros Ventre
•1925
•80 km / hr
•Buried 30 m thick
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Impact of Human Activities on Mass Movement
1.
road construction
2.
reservoirs