River Processes

• Types of weathering (in situ break down of rock)


  • Mechanical weathering
  • Chemical weathering
  • Biological weathering
• Mechanical weathering


  • Freeze-thaw is most common in colder climates
  • When water freezes in joints and faults it expands and causes the faults and joints to widen and eventually break away
• Chemical weathering


  • Rocks' mineral composition is changed
  • Granite contains feldspar which turns to clay when it reacts with water making it easier to erode
  • Limestone is dissolved by carbonation as it is alkali and water is acidic
• Biological weathering


  • Caused by plants and animals
  • Trees roots can cause cracks and faults to be created
• Types of mass movement

  • Sliding/creeping
  • Slumping
• Mass movement


  The downhill movement of material under the influence of gravity
• Types of transportation


  • Traction
  • Saltation
  • Suspension
  • Solution
• Traction


  Large boulders are rolled along the river bed
• Saltation


  Smaller stones are bounced along the river bed
• Suspension

  Sand and small particles are carried along in the flow
• Solution


  Some minerals are dissolved in water
• Processes of river erosion (breakdown and removal of rock)

  • Hydraulic action
  • Abrasion
  • Attrition
  • Solution
• Hydraulic action


  The force of the water on the bed/banks of the river
• Abrasion


  The rivers bedload scrapes the banks and bed of the river
• Attrition


  Rocks and pebbles collide
• Solution


  Chemical action by water, dissolves minerals in rocks
• Deposition


  When the river loses energy it may drop some of its load