3.3 Slope Processes and Development

• Affects of Rock Type on a slope

  Faulting can produce steep valley sides like a rift valley.

  
  

  Folding can produce either steep or gentle slops depending on the angle of dip.

  
  

  Vulcanicity produces instrusions of igneous rock which is hard and resistant. Igneous surrounded by other kinds of rock leads to steep slopes and certain rocks erode faster than others.
• Affects of Climate of Slopes

  Arid regions - Slopes are jagged or straight due to mechanical weathering and sheetwash.

  
  

  Humid Regions - Slopes are roudner due to chemical weathering, soil creep and fluvial transport.

  
  

  Humid Tropics - Chemical weathering dominates due to hot, wet conditions where organic acids are available.
• Affects of Regolith


  The layer of unconsolidated rocky material covering bedrock.

  
  

  It is prone to downslope movement. Weight of deep regolith will increase likelihood of instability.

  
  

  Clay-rich regoliths are particularly unstable because of their ability to retain water.
• Affects of Soil


  Soil structure and texture will determine how much water it can hold .

  
  

  Clay soils hold more water than sandy soils.

  
  

  Deep clay will provide little resistance to mass movement.
• Affect of Aspect


  Refers to the direction the slope faces.

  
  

  Climactic conditions can vary on aspect of a slope e.g. the affect of freeze-thaw weathering as some areas remain in shade for longer.
• Vegetation


  Decreases runoff through interception and storage both above and below ground.

  
  

  Deforested slopes are exposed to intense erosion and gulleying.

  
  

  Vegetation can increase chance of landslips due to roots displacing soil and the added sheer stress due to weight.
• Causes of Mass Movements

  Most important factors are gravity, slope angle and pore pressure.

  
  

  Slopes fail when the sheer stress exceeds the sheer strength of the slope, where gravity acts as a slide component by dragging loose material downwards.
• Heave


  Individual soil particles are pushed to the surface by wetting, heating or freezing of water.

  
  

  They move at right angles as it is path of least resistance.

  
  

  When particles dry or cool, they move a small distance under influence of gravity.
• Falls


  Occur on steep slopes greater than 40deg.

  
  

  Initial fall caused by freeze-thaw or disintergration.

  
  

  Rocks fall under influence of gravity and distance of fall dictates type of slope formed.

  
• Slides


  Includes rockslides and landslides of any material.

  
  

  Rotational slides which produce massive terraces.

  
  

  Occur with a combination of weak rocks, steep slopes and active undercutting.
• Slip Planes


  Occur at:

  Junction of two layers.

  At a fault line.

  Where there is a joint.

  Along a bedding plane.

  At the point beneath the surface where the shear stress outgrows the shear strength.
• Slumps and Flows


  Occur with weaker rock like clay and have a rotational movement.

  
  

  Clay absorbs water, becomes saturated and exceeds liquid limit. Material then flows along a slip plane.

  
  

  They have a higher water content and smaller particles than landslides.
• Avalanches


  Rapid movements of snow, ice, rock or earth down a slope.

  
  

  Occur on slopes over 22deg when new snow slips off of older and compacted snow.

  
  

  Often associated with saturated ground conditions.