MASS MOVEMENT

• Mass movement

  The movement of loose, weathered material called scree or regolith downslope under the influence of gravity
• Mass movement


  • Can occur rapidly or slowly
  • Can be wet or dry
• Water content


  Makes the scree/regolith heavier and acts as a lubricant, so particles separate and move downhill more easily
• Vegetation

  • The roots of plants bind soil particles together and help prevent mass movement
  • If vegetation is removed, the soil particles are free to move easily
• Human activity


  Can undermine the base of a slope by undercutting, making the slope unstable and causing mass movement
• Slope gradient


  The steeper the slope, the faster the soil and rocks will move
• When steep slopes, high water content (after rain) and lack of vegetation combine, severe mass movement occurs
• Types of mass movement

  • Soil creep
  • Landslide
  • Bog burst
  • Mudflow
• Soil creep


  Slow movement of soil downslope, evidence includes leaning telegraph poles, broken tree trunks, tension cracks in roads
• Bog burst


  Occurs when peat becomes saturated with rainwater, causing the wet and heavy peat to move quickly downslope, destroying everything in its path
• Bog burst


  • Shass Mountain, Leitrim, Ireland, June 2020
• Landslides can have several causes, including human activity like deforestation and earthquakes
• Landslide


  • Malin village, India, leaves 17 dead and 200 missing
• Mudflow

  • Occurs when soil is saturated with water following heavy rainfall, forming a mud that moves very rapidly downslope
  • Can also occur following volcanic activity
• Mudflow


  • Atami, Japan, July 2021, 21 people missing/presumed dead
• Preventing mass movements


  1. Planting vegetation to stabilise slopes

  2. Terracing to break up slopes

  3. Drainage to reduce water content

  4. Concrete walls to support slope base
• Climate change will lead to increased and heavier rainfall, making mass movements more likely
• Deforestation causes mass movements, but governments need to balance this with providing land for people
• Mass movements can cause loss of life and damage to property and infrastructure
• Understanding the factors that cause mass movements allows us to make better decisions about where to locate buildings, roads, etc.