Weathering & Mass Movement

• Weathering is the breaking down of rocks where they are (in situ)
• Mechanical weathering sees rocks disintegrate into fragments due to pressure from temperature or salt
• Chemical weathering sees slightly acidic rainfall dissolves certain rocks, e.g., limestone
• Biological weathering sees animals burrow into or plants grow through rocks creating cracks
• This is how freeze-thaw weathering (mechanical) works:

  1. During the day, water enters cracks in rock
  2. During the colder nights, water freezes into ice, expands and widens the crack
  3. During the warmer day, ice melts (thaws) and more water enters an enlarged crack
  4. Repeated freezing and thawing over years causes rock to break apart

  
• Rockfalls:

  • Freeze-thaw = water expands into ice in cracks​
  • Thaws into water and repeats​
  • Free-fall = gravity​
  • Scree slope (fallen rock) at cliff base

  
• Sliding:

  • Heavy rain soaks soil via infiltration​
  • Percolates into rock​
  • Wave splash into cracks​
  • Steep cliff heavier​
  • Slips quickly in straight line

  
• Slumping:

  • Heavy rain​
  • Water saturates softer rock = heavy​
  • Undercutting at base by waves
  • Curved slip in stages = gravity