Slope, processes & development lesson 8


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Slope, processes & development lesson 8

  2. 2. SLOPE A small strip or patch of the land surface that is inclined from the horizontal is mantled with regolith, which grades down into, unaltered rock called bedrock Regolith provides the source f sediment, which consists of rocks and mineral particles Soil and regolith blanket the bedrock, except in a few places where bedrock is particularly hard projects in the form of outcrops
  3. 3. Slope Models1. Convex slope segments2. Concave slope segments3. Rectilinear slope segments
  4. 4. Convex slope segments Form on the upper parts of slopes Inresponse to soil creep and rain splash When slopes are below the threshold for rapid mass wasting
  5. 5. Concave slope segments Slopesegments that form near the base of slopes Inthe absence of removal waste (e.g. river downcutting) With increasing run off downslope, velocity and sediment transport can be maintained over increasingly lower slope
  6. 6. Concave or convex?
  7. 7. Concave or convex?
  8. 8. Rectilinear Slope segments Straight section of a profile May develop on uniform rock type where there is only very thin covering debris
  9. 9. Factors controlling slopeform and development 1. Climate 2. Geological structure 3. Nature of regolith 4. Vegetation
  10. 10. Climate Different processes operate in different climate zones and produce different slope forms and shapes Humid areas – slopes are frequently rounded due to chemical weathering Arid region – slopes are jagged or straight owing to mechanical weathering and sheetwash Heavy rain and meltwater both add volume and weight to the soil  increases erosive power  make slope less stable Heavy snowfall add weight  conducive to rapid movement (Avalanche)
  11. 11. Geological structureRock type affect vulnerability to weathering  resistant to down slope movement
  12. 12. Nature of the regolith Includes soil, scree, weathered bedrock and deposited material. Unconsolidated nature  prone to downslope movement Increase weight of deep regolith will increase the likelihood of instability Clay rich regoliths – unstable because the ability to retain water In a non saturated soil- increases cohesion and reduce soil movement In saturated soil – the pore water pressure forces the particle apart, causing soil movement
  13. 13. Vegetation Can decrease overland run off Lack of vegetation means there are fewer roots to bind the soil together
  14. 14. How do we get slope failure? When the gravitational force acting on a slope exceeds its resisting forces, slope failure (mass wasting occur)
  15. 15. What is a shear strength? The resisting forces that help to maintain slope stability include the slope material’s strength and cohesion The amount of internal friction between grains and any external support of the slope known as shear strength
  16. 16. How does the force gravityresulted in slope failure?  Gravity operates vertically but has a component acting parallel to the slope causing instability  The steeper the slope angle the greater the component of force acting parallel to the slope and greater the chances for mass wasting
  17. 17. Define angle of repose The steepest angle that a slope can maintain without collapsing Angle of repose for unweathered solid rock steeper than 40 degrees
  18. 18. What does it mean by “when aslope is in a constant state ofdynamic equilibrium”? Means that they are constantly adjusting to new conditions