MASS WASTING AND MASS MOVEMENT

• mass movement - a general term used to describe the downhill movement of unconsolidated material that are known as slides, falls, slumps, flows, and creep
• unconsolidated material - those that are loose or uncemented, such as sand and soil
• consolidated material - those that are compacted, cemented, or vegetated soils

• mass wasting - all processes by which masses of rock and soil move downhill under the influence of gravity, eventually to be carried away by other transporting agents

• Factors That Influence Mass Movement
• slope of material - the steepness of a slope influences instability in mass movement
• the steepness of the a pile of loose material such as sand has a distinct limit - angle of repose
• once the angle of repose is reached, addition of more sand will make the pile broader but not taller
• internal friction - a material's total resistance to movement
• consolidated dry materials are held together by cohesion (attraction of like particles) and adhesion (attraction of unlike particles)
• cementation
• plant roots

• surface tension
• moisture content
• too little limits vegetation
• too much can push grains apart, add weight, or provide lubrication

• Triggers of mass movement
• sudden addition of moisture
• shaking of the ground - liquefaction

• Classification of mass movement
• Based upon
• nature of the material (rock or unconsolidated)
• speed of movement
• nature of movement (sliding, falling, or flowing)

• Rock Mass Movement
• rockfall - free fall of boulders from a cliff
• rockslides - sliding of rock down an incline
• usually due to rock breaking from its host material along a bedding plane, joint, or other structural weakness

• talus - debris at the bottom of the slope in a broken mass due to rockfalls and rockslides
• rock avalanche - rock becomes broken into pieces before it reaches the foot of a slope

• Unconsolidated Material Mass Movement
• creep - extremely slow, almost imperceptible downslope movement of soil and rock debris
• solifluction (soil flowage) - special type of creep that is common in polar regions where groundwater in the pore speaces of soil and rock is permanently frozen
• earthflows and debris flows - consist of mixtures of rock fragments, mud, and water that flow downslope as viscous fluids
• mudflows - a variety of debris flow that consist mostly of small silt and clay-sized particles
• usually occur after heavy rain
• as much as 30% water content

• debris avalanche - fastest unconsolidated mass movement
• on steep slopes in humid areas

• slumps and debris slide - movement of material in which the material is not rearranged

• Plate Tectonics
• OC - CC boundary
• causes steep slopes
• volcanic activity and earthquakes

• Impact of Human Activities on Mass Movement
• road construction
• reservoirs