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Wind as an Agent of Change


    1.    Describe how wind shapes Earth's surface.

    2.    Identify landforms formed by wind erosion.



Just as water weathers and erodes the face of the Earth, the wind can also cause significant change in dry areas.  Although in deserts and coastal regions the change caused by the wind are most dramatic, dust storms can be seen across the plains as well.

Any time a large amount of silt and clay is lifted into the atmosphere it is called a dust storm.  Dust storms can move materials massive distances and leave areas depleted of loose topsoil.  Some of the factors dust storms are:

size of the loose topsoil
silt - smallest/can be carried many miles in the atmosphere
clay - still considered small and easily carried by wind
sand - not easily carried by wind / requires a wind of at lease 18km/hr to move

Some of the effects of dust storms are:

Deflation - the removal of loose particles of soil by the wind
creates desert pavement - area of only larger pebbles and rock
can cause hollows (blowouts)
if the hollow reaches the water table a pond is formed (desert oasis)

(nwgeoscience.com/dunes/photos/ images/deflation.jpg)

caused primarily by the movement of sand across a surface
abrasion occurs making the windward side of objects smooth
the resulting structure is called a ventifact (object created by the wind)


are unlayered deposits of silt and clay deposited after wind movements
much of the great plains area has loess soil
very fertile







(www.cis.umassd.edu/~gleung/ xshan34.jpg)


Sand Dunes
are large deposits of sand moved by strong winds in desert and coastal regions
the shape tells you the direction of the wind
gently sloping on the windward side & steep on the leeward side
the overall shape depends on the amount of sand and the strength of the wind
produced in areas of limited sands
the ends point downwind

(earthsci.terc.edu/.../images/ es1603_p4_brachandunes_c.jpg)
parabolic dunes
formed in areas where blowouts occur
the ends point upwind

Figure 24.Air photo of the parabolic (U-shaped) dunes on Provincetown Spit.

(pubs.usgs.gov/gip/capecod/ images/dunwa200.jpg)

transverse dunes
occur in areas with abundant sand
dunes can be hundreds of meters long and high
sand forms parallel bands at right angles to the wind

(geography.massey.ac.nz/papers/ 121311/Desertdune4.JPG)

longitudinal dunes
occur in deserts with moderate amounts of sand
sand piles in parallel bands in the same direction as the wind

(rst.gsfc.nasa.gov/Sect17/ ev5372_PIA02656_md.jpg)










Last modified: November 21, 2003