Mass wasting
Slope failures occur when the shear stress is greater than the shear strength.
Shear Stress (on a free standing body) - The force on a body that causes slippage or translation.
Shear Strength - The internal resistance of a body to movement.
Types of mass wasting movements:
Creep - slow downhill movement. Happens as particles lifted then fall down slope. Will happen by any process that causes volume change in earth mass on a slope such as:
wetting and drying
freeze thaw
animals
Earthflows, mudflows and debris flows - slightly more rapid. Steep slopes in humid regions. Dense mixtures of unconsolidated sediment, water and air that are moving like a liquid.
Slump - slow to moderately rapid. Soil or rock moves downslope with rotational movement as large mass or block.
Rockslide
& Debris slide - moving on an inclined surface.Landslides - avalanches, slides, falls. Characterized by sudden rapid movement. These are often disasters.
Rock fall - Free falling bodies. Steep slopes where rock outcrops.
Subsidence and collapse- when subsurface supporting material removed
Triggers:
heavy rains
earthquakes
unloading or undercutting bottom of stable slopes