Erosion and Streams

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Erosion and Streams
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Sediment Transport

• Dissolved load- ions dissolved in water
• Suspended load- clay and silt particles, some
  rivers carry sand depending on velocity
• Bed load- boulders and cobbles, sand

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Why is a rocky bottom stream rocky and a soft
bottom stream soft?
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Mississippi River Ex.- Note trend
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Erosion of stream channel- High gradient streams

• Downcutting- erosion deeper into bed
• Base level- as deep as the river can cut, sea (or
  lake) level or to the bedrock.
• What would happen if a stream eroded to below
  its base level?

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Niagara Falls

• Harder dolomite over soft shale
• Shale erodes and dolomite collapse
• Niagara falls move upstream
• 11,000 meters since formation! (1m. per year)

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Erosion and Deposition

• In fast flowing areas erosion occurs
• When the stream slows, deposition occurs
• What causes the stream to be fast flowing, or
  slow?

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Low gradient streams

• Lateral erosion- most of stream energy is
  directed against the banks, undercuts valley
  sides and widens stream valley/channel.
• Meanders- a series of bends in the stream

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Can form an oxbow lake
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Formation of oxbow lakes
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A lot of sediment? Stream can form several
channels- braided stream

• Why is this stream braided?
• Where does the sediment come from?

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At the end of the road. DEPOSITION

• Alluvial fan- when gradient abruptly changes
  (base of a mountain)

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Label EROSION and DEPOSITION(3 of each)
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Deposition cont.

• Delta- deposition where stream enters a lake or
  ocean (submarine delta)

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Largest deltas in the world!