Erosion and Deposition

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Erosion and Deposition
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Two Important Definitions

• Erosion the removal of weathered rock and soil
  from its original location
• Deposition the dropping of eroded material in a
  different location (when you make a deposit at
  the bank you are leaving money here rock is
  deposited in a new place)

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Gravity

• The power behind most erosional agents
• Rock is pulled downslope by the force of gravity

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4 Types of Erosion

1. Erosion by Water
2. Erosion by Glacier
3. Erosion by Wind
4. Erosion by Living Things

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1. Erosion by Water

• Rill Erosion when a narrow stream cuts a small
  channel into the land (think narrow stream)
• Gully Erosion stream of water has gone beyond
  Rill Erosion and now the stream of water is deep
  and wide (think wider stream)

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1. Erosion by Water- Rivers and Streams

• Each year streams carry billions of metric tons
  of sediments and weathered material to the
  coastal areas
• Over time, the build up of sediment produces
  deltas (example Colorado River Delta-right
  Mississippi River Delta - left)

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1. Erosion by Water- Waves

• Sand on an ocean shoreline is repeatedly picked
  up, moved, and deposited
• Constant movement of water is a continuous
  erosional process
• Deposits can lead to sand bars and barrier
  islands (example Outer Banks of N.Carolina)

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2. Glacial Erosion

• Currently cover 10 of the Earths surface
• Once covered 30
• Scraping and gouging the earth as they move huge
  rock and piles of debris over great distances
• Glacial movements scratch and grind surfaces and
  deposit material over long distances

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3. Wind Erosion

• Moves fine, dry particles a great distance
• Most common in areas without vegetation holding
  the soil into places
• Can be prevented with a wind barrier (stand of
  trees or other vegetation planted perpendicular
  to the direction of the wind)

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4. Erosion by Living Things

• Examples of Erosion by living things
• Excavating land
• Planting a garden
• Developing land
• Building a highway
• All of these can lead to erosion

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Mass Movement

• Downslope moving of soil and weathered rock
  resulting from the force of gravity
• ALL mass movements occur on slopes

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Factors that Influence Mass Movement

1. Materials weight
2. Materials resistance to sliding or flowing
3. Trigger (like at earthquake)
4. Water

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Classification of Mass Movement

• Creep slow, steady downflow of loose weathered
  material
• a) slowly creep can cause once vertical utility
  poles and fences to tilt

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• 2) Flows slow movements of soil
• a) mudflows swiftly moving mixtures of mud
  and water

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Mudflow

• http//www.youtube.com/watch?vn1cCs-S5EKc

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• 3) Slides top layers of soil are thin and move
  downslope rapidly
• a) Landslides
• b) Slumps (landslide on a curved surface)
• c) Avalanche (snow melts in sun, refreezes at
  night and the fallen snow moves downslope)

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Avalanche

• http//www.youtube.com/watch?v99j17GL3qlE

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• 4) Rockfalls rocks are loosened by physical
  weathering,
• they then break loose and fall downslope
• a) less likely in humid climates where a layer of
  soil and vegetation cover the rock

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Rock fall

• http//www.youtube.com/watch?vZVYGJYnJTi0

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People

• Humans can minimize the destruction caused by
  mass movement by not building near the base of
  unstable slopes
• gt25o slopes are at the greatest risk of a
  catastrophic mass movement