Unit 3 topic 2

• Weathering refers to the weakening, breaking up, and disintegration of rocks that form the land's surface of the land and lie exposed to the weather elements in situ
• In situ


  A Latin phrase which means 'in its original place' or stationary
• Weathering


  The breaking down of rocks that happens in a stationary position
• Erosion


  The washing away of the topsoil by wind, water or ice
• Weathering is mostly caused by differences in temperature and acid rain, whereas erosion is caused by the movement of water, wind and ice
• Weathering produces inselbergs and karst landscapes, whereas erosion produces gullies and dongas
• Physical weathering (also known as mechanical weathering)


  The disintegration of rock into smaller pieces by mechanical processes
• No change occurs in the chemical composition of the rock during physical weathering
• Physical weathering


  • Most common in arid climates such as deserts, arctic regions and areas with little vegetation
  • Produces sandy soils
• Exfoliation


  Occurs when heated rocks expand and contract when cooled
• Exfoliation


  1. Outer layers of the rock expand faster than the inner layers during the day

  2. Outer layers cool faster than the inner layers at night

  3. Causes stress in the rock, resulting in the outer layers peeling off like the rings of an onion
• Thermal expansion/insulation weathering


  Different minerals within the rock expand and contract at different rates depending on their physical characteristics, resulting in granular disintegration within the rock
• Freeze-thaw weathering


  • Occurs in rocks with crevices and joints and little vegetation cover
  • Requires temperatures to fluctuate around 0°C
  • Water enters crevices during the day and freezes at night, expanding and shattering the rock
• Salt crystallisation


  Saline water evaporates, leaving salt crystals that exert stress on the rock, causing it to disintegrate
• Pressure release


  • Intrusive landforms such as batholiths are formed deep below the surface and under intense pressure
  • Removal of the overburden causes fractures to develop, especially on the top layers of the rock, in a process referred to as sheeting

  
• Chemical weathering


  The process by which rainwater, a weak carbonic acid, chemically attacks and erodes rock
• Processes of chemical weathering


  • Carbonation
  • Hydration
  • Oxidation
  • Hydrolysis
• Carbonation


  Rainwater absorbs carbon dioxide from the air and forms a weak carbonic acid that can dissolve rocks, especially limestone
• Hydration


  Rock minerals and water combine, causing the minerals to expand and the rock to shatter
• Oxidation


  Rock minerals chemically combine with oxygen in water or air, causing discoloration and weakening of the rock
• Hydrolysis


  Acidic water acts on rock-forming minerals, forcing them out of the rock and causing it to disintegrate and create clay
• Biological weathering


  The actions of flora and fauna, such as plant roots growing in cracks and burrowing animals
• Factors affecting the rate of weathering


  • Climate
  • Relief
  • Vegetation
  • Rock type
  • Exposure
• Peltier diagram


  Shows how weathering rates are related to water availability and average annual temperatures