Sub-aerial Processes: Mass Movement

Question 1

What is mass movement?

Answer 1

• large scale downslope movement of material under the influence of gravity

Question 2

What are the 4 main areas that mass movement can be categorised into?

Answer 2

• heaves
• flows
• slides
• falls

Question 3

What is the type of mass movement dependent on?

Answer 3

• cliff/slope angle
• rock type
• rock structure
• vegetation
• saturation of ground
• presence of weathering

Question 4

What are the different types of mass movement?

Answer 4

• soil creep
• mudflows
• rockfall
• landslides + rockslides

Question 5

What is soil creep?

Answer 5

• particles pushed towards surface at right angles by wetting, + freezing, [e.g. freeze-thaw causes water to expand causing soil to bulge]
• then sinks down by gravity, slowly moving downslope
• creates shallow terracettes
• slowest + most prevalent form of mass movement

Question 6

What are mudflows?

Answer 6

• when an inc. in water content of soil, dec. friction as cohesive bonds break
  
  • leads to Earth + mud to flow over underlying bedrock, or slippery material
• water can get trapped within rock, inc. pore water pressure: forces rock particles apart, weakening slope
• can be v. fast flowing

Question 7

What are rockfalls?

Answer 7

• rocks falling under gravity on steep slopes >45° when exposed to mechanical weathering
• can be triggered by earthquakes
• leads to built up scree at base of slope

Question 8

What are landslides/rockslides?

Answer 8

• when heavy rainfall leads to water in joints + bedding planes in cliffs
  - dec. friction + leads to entire masses of material moving along a slip plane v. quickly
• it can break at bottom of slope + occurs on weak rocks w steep slopes that have active undercutting