Mass Wasting

Objectives

DefinitionTypes and RatesCauses or Factors InvolvedEffectsSignificance

DefinitionsMass movement/wasting involves down slope movement of rock, regolith, and soil under the direct influence of gravity. The earth materials behave as solids or viscous masses, and may be consolidated (compacted and cemented) or unconsolidated (loose and uncemented). Movement occurs when the force or gravity exceeds the resisting force (slope stability). Angle of repose refers to the natural angle formed by loose, unconsolidated materials (gravel, sand, soil, etc.). The angle of repose is the angle at which loose material sits at rest. Typically 25 - 40 degrees.

Types of Mass Wasting

Types (cont.)

Rates of Mass WastingRapid Movement (1 m/sec to >100 km/hr)RockfallsMudflowsDebris flowsRock slides or rock avalanches Moderate Movement (1 cm/day to 1 cm/sec)SlumpsEarthflowsDebris slides

Slow Movement (1 mm/yr to 1 mm/day)CreepSolifluction

Causes/FactorsOversteepening of Slopes/Slope Gradient By humans (road building, etc.) Natural processes (i.e. tectonics, stream and wave erosion, etc.)Addition of water to a slope Adds weight (~8 lbs/gal) Lubricates loose material, reduces friction Adds pressure called pore water pressure Reduces cohesion by displacing air and destroying surface tensionRemoval of vegetation Decreases soil cohesion when roots decay Plants adsorb water, decreasing saturation limit of the slope material

Causes/Factors (cont.)Overloading weight of buildings or other structures Dumping, filling, or piling up material Geology rocks dipping (incilned) in the same direction as the slope Bedding planes and Fractures serve as zones of weaknessTriggering Mechanisms Excessive amounts of water Earthquakes Volcanic eruptions Vibrations Noise

What Can Be Done?Slope DewateringSlope ReductionCut and FillBenchingStabilizing StructuresRetaining WallsRock Bolts

SummaryMass wasting is the movement of earth materials downslope under the influence of gravityControls and Triggers include: water, oversteepened slopes, removal of vegetation, earthquakes, rock type, land use types, etc.Types include: slumps, slides, flows, and fallsThe rate of mass movement may be rapid, moderate, or slow depending on the type of material

http://www.youtube.com/watch?v=0FRf6FF6KxA&feature=related http://www.youtube.com/watch?v=4PF4Y3P88GQ&feature=related http://www.youtube.com/watch?v=B4XjmIAxOfA&feature=related http://www.youtube.com/watch?v=AiczROnfGbc&feature=related http://www.youtube.com/watch?v=KGh4g399wpc&feature=related http://www.youtube.com/watch?v=pJF-RhL4TvE http://www.youtube.com/watch?v=jHrPwzbqNyM&feature=related Mass Wasting Video Links: