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Deflation
Deflation (dih-FLAY-shuhn) is the removal of loose rock
particles by the wind. In many desert areas the sands and
clays formed by weathering are blown away by winds,
leaving pebbles and boulders. The resulting surface is
called desert pavement. The surface shown in the
photograph below is desert pavement. Desert pavement
protects the materials beneath from further deflation.
Stony surfaces of this type are common in the deserts
of the southwestern United States and in the Sahara
in Africa.
In semiarid regions, such as the Great Plains, deflation
has formed thousands of hollows called blowouts. Most of
these are shallow and small, but some are many thousand meters long and
about a hundred meters deep. Blowouts form in dry regions with patchy
vegetation. A small irregularity on the ground causes winds to focus on a
small area. Over time, these winds remove more and more sands or clays
from the area. If the bottom of the blowout reaches the water table, the wet
ground stops deflation. The growth of vegetation also halts deflation. In
desert regions, oases sometimes are found in deep blowouts that were
formed by deflation.
Image not available.
Please refer to the
image in the textbook
or on the eEdition CD.
BLOWOUT Deflation caused by wind
erosion has formed a blowout in the
Sand Hills of Nebraska.
Abrasion
Windblown silt and clay particles are too small, and often too soft, to wear
away most rocks. Sand grains, however, are larger and tend to be made of
more abrasive materials. Sand grains driven by winds grind and scour most
surfaces they hit. Quartz sand grains, in particular, can wear away many
materials. In some desert areas, rocks and telephone poles may be
undercut at the base by windblown sand.
Blasts of desert sand grind boulders and small rocks into shapes called
ventifacts (VEHN-tuh-FAKTS). The shape of a ventifact gives a clue about
the direction of the wind that formed it. As shown in the photograph below,
the side of a ventifact that faces the prevailing wind is worn into a smooth,
flat surface. A second facet may form if the wind blows from different
directions at different times of
the year or if the boulder is
turned so that a new side faces
the wind.
CLASSZONE.COM
Observe an animation showing the
formation of an arch.
Keycode: ES1601
The word ventifact comes from the
Latin word for wind, ventus, and the
Latin word factum, which refers to
something that has been made.
Image not available.
Please refer to the
DEATH VALLEY, CALIFORNIA
Wind-driven sands have weathered the
windward sides of these ventifacts. The
wind has also blown away sands and
clays from the ground, leaving desert
pavement around the ventifacts. Sand
has piled up behind the ventifacts.
image in the textbook
or in the eEdition CD.
Chapter 16 Wind, Waves, and Currents
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