The work of rivers 2

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  • 1. The Work of RiversThe erosional work of streams/rivers carves and shapes the landscape through which they flow.3 functions of riversc. Erosiond. Transportatione. Deposition
  • 2. The Work of RiversA. Erosion•A river may erode in 4 ways3.Abrasion/corrasionLoad carried by a river will grind against itsbed and sides.This process slowly wears the bed and sidesaway.
  • 3. The Work of RiversA. Erosion2. AttritionWhen thrown against the sides and bed ofrivers, the load gets broken into smallerpieces.
  • 4. The Work of RiversA. Erosion3. Hydraulic actionThe work of turbulence in the water.Running water causes friction in the joints ofrocks in a stream channelJoints may be enlargedLoosened fragments of rocks get swept away.
  • 5. The Work of RiversA. Erosion4. Solution/CorrosionCertain minerals in rocks like limestone canbe dissolved in water.Rocks are then eroded.
  • 6. The Work of RiversRelationship of velocity and sediment size toerosion
  • 7. The Work of RiversB. Transportation (4 ways)
  • 8. The Work of RiversB. Transportation (4 ways)•TractionLarger and heavier rocks/gravels are dragged orrolled along the bed.
  • 9. The Work of RiversB. Transportation (4 ways)2. Saltation (saltim: by leaps/jumps)Smaller and lighter rock fragments and sandhop and bounce along the river bed.At times, the distinction between traction andsaltation may be difficult to determine.
  • 10. The Work of RiversB. Transportation (4 ways)3. SuspensionSome of the load like silt and clay (fine-grained) will float along.They may only be deposited when streamvelocity reaches near 0.Turbulence in the water is crucial in holding aload of sediments.
  • 11. The Work of RiversB. Transportation (4 ways)4. SolutionSome minerals are transported in dissolvedform.Especially chemical solution derived fromminerals like limestone or dolomite.
  • 12. The Work of RiversC. DepositionA river will drop its load when:c. Volume decreasesd. Speed decreases
  • 13. The Work of RiversC. DepositionA river’s volume decreases when• Dry season• Dry region with high evaporation• Presence of permeable rocks• Receding flood waters
  • 14. The Work of RiversC. DepositionA river’s speed decreases when• It enters a lake• It enters a calm sea• It enters a gently sloping plain
  • 15. The Work of RiversThe work of a river depends on its energyEnergy a function ofc. Volume of waterd. Speed of water flow (dependent on gradient)