(9) Mass Wasting T3

Question 1

Definition

Answer 1

Gravitational transfer of earth materials down a slope; a ‘landslide’ is a general term for rapid mass movement

Question 2

Controlling Factors

Answer 2

• Gravity and slope (main)
• Earth Materials
• Water
• Vegetation
• The other factors influence susceptibility of areas to mass movement, speeds of movement, sizes of affected areas, and frequency

Question 3

Earth Materials: Unconsolidated Sediment

Answer 3

• Main control is ‘angle of response’ – max slope angle at which material is stable
• 25-40 degrees in general
• Coarser/rougher materials can maintain steeper slopes

Question 4

Earth Materials: Rocks

Answer 4

• Massive uniform textures rocks with interlocking grains are more stable; granite, basalt, quartzite, limestone
• Rocks that are fractured schistosity/cleavage layered; provide ‘slip zones’ or ‘planes of weakness’ along which movement can occur

Question 5

Water

Answer 5

• Can act as a lubricant
• Adds weight
• Clays absorb water and swell = plastic and weak
• Unconsolidated sediments the amount of water can be very important
  o Moisten: surface tension holds grains together
  o Saturate: decreased tension = lubricant

Question 6

Vegetation

Answer 6

• Bind loose material, but weathers with roots and weakens material

Question 7

Initiating causes

Answer 7

• Conditions favouring mass wasting may exist for long periods of time without movement; it usually requires an additional ingredient to initiate movement
  1. Removal of supporting materials near base of slopes; man-made road cuts, riverbanks
  2. Overloading; material added on to the slope; avalanches, ‘Panama canal’ (remove material from the bottom and piling on top)
  3. Reducing friction by adding water; rainfall, leakage from reservoirs, ‘sprinkler’
  4. Earthquake initiation; ‘sensitive clays’

Question 8

Falls

Answer 8

• Near vertical free fall (topple)

- Talus slopes (chucks fall off)

Question 9

Slides/glides and slumps

Answer 9

• ‘Frank, Alberta slide
• ‘Avalanche’
• Slump (Red River): movement along a curved plain
• Rock slide

Question 10

Flows

Answer 10

• Water influence

- Mud/earth flows

Question 11

Creep

Answer 11

• Slowest

- Gentle slopes

Question 12

Preventative measures

Answer 12

• Terrain analysis – ask a geologist
• Reduce weight on slope
• Flatten/reduce slope angle – terraces
• Plant vegetation
• Aid water drainage
• Retaining walls and rock bolts (tie backs and shear pins)
• Add material to hold the bottom

Question 13

Landslides happen when…

Answer 13

• By removing components: minerals/water/oil etc.
  • Karst terrain, groundwater/ice removal, oil removal, etc.
• Liquefaction; ‘sensitive clays’
• ‘Shrink and swell clays’ (when wet)
  • Winnipeg – lake Agassiz clays, glacial ‘flour’