Weathering

• Weathering - the breakdown of rock, where it is, which is caused by day-to-day changes in the atmosphere.
• Two types of weathering:

  Mechanical weathering - the breakdown of rocks by turning them into smaller pieces.

  OR

  Chemical weathering - dissolvement of rock or minerals, due to chemical changes, such as acidic rainwater
• Freeze-Thaw Weathering ~ (mechanical):

  1. Rain collects in cracks.
  2. Temperature drops below 0°C, so water freezes and expands, putting pressure on the rock, so crack expands.
  3. Temperature rises above 0°C, and ice melts.
  4. This repeats until rock splits.
• Salt weathering ~ (mechanical) :

  1. Seawater which contains salt, is left behind when water evaporates.
  2. These salt crystals grow in holes and cracks, and expand.
  3. This puts pressure on the rocks, weakening its structure.
  4. Overtime the rock may start to break and flake off.
• Carbonation ~ (chemical) :

  1. Rainwater absorbs CO2 and becomes slightly acidic.
  2. Acid rain falls on alkaline rocks (e.g. chalk and limestone).
  3. A chemical reaction occurs, which causes rock to dissolve.
• Types of mass movement:

  • Sliding (Mudflow) ~ saturated soil and weak rock flows down a slope
  • Sliding (Landslide) ~ rock slides downhill
  • Slumping ~ saturated soil and weak rock slumps along a curved surface
  • Rockfall ~ bits of rock break away from cliff, due to freeze-thaw