16'1 Erosion by Wind

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16.1 Erosion by Wind

• By,
• Sara Rosenthal, Danielle Wisdom,and Nicole Casado

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Wind Erosion

• Wind erodes dry land more effectively then wet
  land
• Wind moves sand and dust in different ways wind
  cannot keep aloft even the smallest particle of
  sand, so sand grains are moved along by a series
  of jumps and bounces, much like pebbles in a
  stream. This is called saltation. This means that
  the wind speed is great enough to roll sand
  grains along the ground, and when the sand grains
  collide with one another some sand grains bounce
  up When in the air a sand grain moves a short
  distance and then falls. As it falls it strikes
  other sand grains which may be thrown into the
  air or rolled ahead by the impact
• However, dust can be lifted by the wind and
  carried high into the air. Even gentle air
  currents can keep dust particles suspended in the
  air

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Wind Erosion 2

• Volcanic dust may remain in the atmosphere for
  several years before falling to the ground
• Strong winds may lift enormous amounts of dust
  into the atmosphere and create large dust storms
  which can cover hundreds of square kilometers and
  darken the sky for several days

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Effects of wind erosion

• Deflation the most common form of wind erosion
• It occurs when wind removes the top layer of fine
  rock or soil particles then the left behind
  fragments form desert pavement a hard surface
  of closely packed rocks that protect the land
  from erosion
• Deflation hollow- shallow depression left by
  topsoil that has been stripped off.

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Wind Deposition

• All material is eventually eroded and deposited
  by the wind
• The size of the particles carried by the wind
  depends on the wind speed. As the speed increases
  it is able to carry large particles. If it
  decreases the heavier part of the load drops
  forming a deposit
• If deposits are not carried away by a later
  strong wind they are covered by future deposits
• This can form sedimentary rocks.

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Dunes

• Dunes are mounds of windblown sand
• They form where there are strong winds and the
  soil is dry and unprotected such as deserts and
  shores of lakes and oceans

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How Dunes form

• Wind blown sand will build up around a barrier
  such as a large rock, grass or a fence
• The barrier slows the wind speed and the wind
  deposits more sand on the sheltered side or
  slipface and at the base of the exposed side or
  the windward side of the dune
• The dune becomes a barrier and covers the
  original border
• The gentlest slope facing the wind and being
  reshaped and the opposite side having a steep
  slope

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Different types of Dunes

• Barchan - crescent shaped dunes
• Parabolic - crescent shaped dune with the open
  side of the dune facing the wind
• Transverse forms at a right angle to the wind
  in a wavelike pattern
• Longitudinal forms in the shape of a ridge and
  lies parallel to the wind

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Types of dunes
Barchan dune
Parabolic dune
Longitudinal dune
Transverse dunes
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Dune Migration

• Occurs when sand is blown off the windward side
  over the crest and builds on the slipface
• In level areas dunes will continue to migrate
  until they reach a barrier

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Dune migration
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Loess

• A loess is thick deposits of yellowish fine
  grained sediment than can be formed by the
  accumulation of windblown dust and is known by
  its German name loess meaning loose
• It is soft and easily eroded and can break into
  vertical slabs
• It sometimes forms steep bluffs and its deposits
  are extremely fertile

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Loess