factors influencing movement of materials

• what are the factors influencing movement of materials on slopes?

  • natural: climate (rainfall, vegetation), slope characteristics, rock characteristic ,natural hazards
  • human: human activity
• which is more significant factor influencing mass movement on global scale

  climate as it greatly influences the amount of rainfall an area receives and amount of vegetation cover on slopes
• which factor influence mass movement most on regional and local scale?

  • slope and rock characteristics, and humans activity -> affect type, nature, frequency of mass movement and water erosion on slopes
  • what causes mass movement not the result of a single factor
• climate (rainfall) affecting mass movement

  • mass movement occur more frequently in humid tropics due to greater, more consistent presence of rainfall
  • small amount of water aids soil cohesion, too much water increase pore water pressure and reduce friction between soil particles allowing them to move and slide easily, reducing shear stress
  • water increase weight of slop material-> increase shear stress
• how climate (rainfall) in humid tropics affect mass movement

  • plentiful rainfall -> slope failure common esp in tropical rainforests or wet season for tropical monsoon and savannah regions
  • mass movement occur during or following a conventional or tropical storm that bring huge volumes of rain in relatively short period of time or failure may occur at end of rainy season as moisture accumulates
• how climate (rainfall) in arid tropics affect mass movement

  • generally dry but sporadic and intense rainfall can trigger water erosion and mass movements esp when there are high levels of rapid runoff -> associated with lack of vegetation cover, thin/absent soils in such areas
• climate (vegetation cover) affecting mass movement

  • determined by its climate
  • plentiful rainfall and warm temps are conducive to vegetation growth
  • wetter climate zone, denser vegetation cover
• climate (vegetation cover) in humid tropics affecting mass movement

  • tree foliage intercepts rainfall and protects slope against rain splash erosion while roots extract water binding soil particles together -> increase shear strength
  • huge tree roots can wedge rocks apart exposing them to chemical weathering reducing shear strength
  • tall, heavy trees add weight to slope imposing high lateral stresses in strong winds
  • greater coverage of vegetation may increase shear stress, promote shear strength->slope stability
• climate (vegetation cover) in arid tropics affecting mass movement

  • lack of vegetation leave slopes vulnerable to water erosion and mass movement
  • rainfall intensity reaching the surface is higher + without roots binding soils together -> rainsplash more effective in detaching particles from the surface
  • large volumes of runoff during heavy rainfall -> rills and gullies
• how can slope characteristics be categorised?

  • gradient
  • amount of weathered material
• gradient (slope characteristics) affecting mass movement

  • steeper the slope, higher the shear stress, greater likelihood of mass movement
  • areas of high relief with steep slopes experience falls and landslides most frequently esp when combined with other contributing factors
  • certain mass movements (creep, flow) can also occur on gentle slopes
  • steeper slopes: runoff flow faster increasing effectiveness of overland flow in eroding slope surface
  • undercut slope by natural (stream and marine erosion) or human activity (road building) -> lose stability
• amount of weathered material (slope characteristics) affecting mass movement

  • amount of weathered material and rate produced determines degree to which shear strength of slope material is reduced as it is broken down
  • rate and extent of weathering in humid tropics -> mass movement more likely in humid
• how can rock characteristics be categorised into?

  • rock type
  • presence of joints
• rock type (rock characteristics) affecting mass movement

  • rocks differ in ability to hold a slope
  • slopes where weak rocks lie on top of stronger rocks are more prone to slides as weak rocks have lower shear strength
  • slopes composed of loose and unconsolidated rocks are less stable as they have lower shear strength and more prone to overland flow
• presence of joints (rock characteristics) affecting mass movement

  • increase likelihood of slides as they provide ready made shear planes
  • heavily jointed rocks will have higher secondary permeability -> more prone to weathering processes-> weaken and lose shear strength, reducing stability
  • high permeability -> rock is favourable to water accumulation -> add shear stress to slope
• natural hazards affecting mass movement

  • earthquakes and volcanic activity
  • -> shocks and vibrations trigger mass movement
  • -> earthquake events-> intense shaking cause build up of pore water pressure -> liquefaction
  • present in both humid and arid tropics -> impact not limited to specific climatic regions
• human factors (human activity) affecting mass movement

  • increasing shear stress: residential development and construction on slopes cause overloading -> add weight to slope
  • reduce shear strength: use of machineries cause shock and vibrations, cutting or excavating land removes underlying support of the slope
  • affecting vegetation cover: landuse change via deforestation or overgrazing -> reduce protective cover of vegetation on slopes -> more vulnerable to water erosion
  • takes place in both humid and arid tropics -> extent of contribution depends on many factors