Erosion and Deposition

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Erosion and Deposition

• Agents, Forces, and Results

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What Caused This?
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What is Erosion?

• Erosion - moving of rock material (sediment) from
  one place to a new location
• For erosion to occur three processes must take
  place detachment of particles, lifting them, and
  transporting them
• Many agents of erosion - flowing water, moving
  ice, waves, gravity, or wind
• Sand consists of small pieces of rock that have
  been weathered from a parent rock, eroded, and
  deposited somewhere else

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What Is Wind Erosion?

• Wind - responsible for wearing away rocks and
  creating great deserts like the Sahara Desert and
  Gobi
• Most effective in moving loose material
• Two main effects (1) Wind causes small particles
  to be lifted and moved away. (2) Suspended
  particles may impact on solid objects causing
  erosion by abrasion (rubbing).
• Occurs in areas where there is not enough
  rainfall to support vegetation

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What Is Water Erosion?

• Water - most influential force in erosion
• Ability to move materials from one location to
  another over long distances
• The faster water moves in streams the larger
  objects it can pick up and transport
• Responsible for wearing away of rocks in rivers,
  lakes, and the oceans

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What Is Wave Erosion?

• Waves - relentless pounding
• Erodes the softer, weaker parts of the rock
  first, leaving harder, more resistant rock behind
• Can take over 100 years to erode a rock to sand
• Energy of waves along with the chemical content
  of the water erodes the rock off the coastline

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What Is Gravitational Erosion?

• Mass movement - downward movement of rock and
  sediments, mainly due to the force of gravity.
• Moves material from higher elevations to lower
  elevations where streams and glaciers can pick up
  the material and move it to lower elevations
• Process is occurring continuously on all slopes,
  some act very slowly while others occur very
  suddenly until equilibrium is reached

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What Is Glacial Erosion?

• Ice - moves and carries rocks, grinding the rocks
  beneath the glacier
• Glaciers pluck and abrade to cause erosion
• Plucking occurs when water enters cracks under
  the glacier, freezing, and breaking off pieces of
  rock that are then carried by the glacier.
• Abrasion cuts into the rock under the glacier,
  smoothing and polishing the rock surface

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What is Deposition?

• Deposition - laying down of sediment that has
  been transported by something such as wind,
  water, or ice
• Process of erosion stops when the moving
  particles fall out of the transporting medium and
  settle on a surface. This settling is deposition.
• If the speed of the medium slows or the
  resistance of the particles increases, the
  balance changes and causes deposition.
• Speed can be reduced by large rocks, hills,
  vegetation, etc.

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Deposition - Wind

• Wind speed can be related to variations in
  heating and cooling
• Wind can transport fine particles in suspension
  hundreds of km from its original source in the
  desert.
• Heavier material may be blown along the ground.
• Material is eventually deposited when the wind
  changes direction or loses its strength.
• Obstacles, whether natural of man-made, will
  often decide where the deposition occurs and the
  nature of the feature formed.

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Deposition - Water

• Running water enters a large, fairly still body
  of water and its speed decreases.
• As speed decreases, water's ability to carry
  sediments decreases
• Sediments carried by running water are deposited
  where the slowing water can no longer move them.
  Largest particles are deposited near the shore.
  Increasingly smaller particles settle out farther
  from the shore where the water is calmer
• Occurs in streams, rivers, oceans, etc.

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Deposition - Ice

• Glacial flows of ice - become slower when the ice
  begins melting
• Deposits left by glaciers are called moraines
  and
• outwashes
• Moraines are large chunks of broken rock left
  at the base
• and sides of the glacier as it melts and
  recedes
• Finer material is carried in the rivers that form
  when the glacial ice melts. The deposits of these
  rivers look similar to normal river deposits and
  are called outwashes

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Whats the Difference?

• WEATHERING - think weather wearing rock down
• EROSION - think of a road and traveling
• DEPOSITION think of depositing money in a bank