flows

• what are flows?


  occur when an entire mass of material is deformed internally through liquefaction and flows downslope, behaving as a viscous fluid
• speed of flows

  • wettest movements with speeds ranging from slow to fast
  • materials move at differing velocities due to frictional differences
  • materials directly in contact with slope experience more friction and move slower
• causes of flows


  intense saturation of soil due to intense storms (humid climates)/ high amount of meltwater from snow
• location of flows

  • originate on gentle slopes of 5-6 degrees
  • more common on slopes of moderate steepness of up to 35 degrees
  • usually localised movements that occur at one part of the slope
• what are the types of flows?

  • earthflow
  • mudflow
  • debris flow
• how are the types of flows categorized

  according to the type of material that is displaced
• speed of earthflow


  move at a rate of 1m/year to 100km/hr
• materials involved in earthflow

  • fine clay sized particles where 80% of the material is less than 2mm in size
  • involves soil and other loose sediments moving downhill as a viscous mass
• location of earthflow

  • more likely in areas that experience periods of dryness but still allow build up of regolith (like wet and dry savannahs)
  • confined within a specific area and loses velocity quickly when it reaches a flat surface
• evidence of earthflow

  • changes the way a slope looks
  • at the top, material slumps away leaving a scarp (curved wall)
  • longitudinal profile from head (top) to toe (leading edge), earthflow is concave upward near the head and convex upward near the toe
• speed of mudflow

  • rate of 1-100km/hr
  • lahars-> originate from volcanic activities
• materials involved in mudflow

  • mixture of fine textured material (sand, silt, clay)
  • contain up to 60% water by weight
• causes of mudflow

  • created when fine material mix with large volume of water
  • formed following intensive rainfall which falls faster than it can be absorbed by the soil
  • as water runs downslope -> forms thin mud which picks up additional sediment as it flows, becoming thicker
  • follows the contours of river valleys and slopes
• location of mudflow

  • gentler slopes than earthflow
  • common in areas with sparse vegetation that experience torrential rainfall
  • arid tropics when sudden intense rainfall lead to rainwash combining with fine material -> fast flows pick up and incorporate large material as they travel downslope
  • mudflows in desert wadis can be 2m thick and may move so fat that they have waves on their surface
• speed of debris flow

  rate of flow varies from 1m/year to 100km/h
• materials involved in debris flow

  • variety of materials -> small and large rock fragments, organic material
  • mostly corse (20%-80% >2mm)
  • proportions of moisture and solids in debris flows vary from between 10% to more than 30% by weight and 35%-90% respectively
  • appear like moving masses of wet concrete, carrying large cobbles and boulders
• location of debris flow

  • commonly occur in mountainous areas in humid and arid tropics -> high- intensity rainfall encourages downslope movement
  • debris flows in arid regions of high relief can transport large amounts of sediment during rare high intensity rainfall events
• evidence of debris flow

  • tongue like front
  • displaced material is dissected by ridges and furrows