the force rapidly increases. For instance, a doubling in wind velocity from 10 kph
to 20 kphquadruplesthe force of the wind so that seemingly small wind variations
can sometimes make significant differences in the work the wind performs. Along
land surfaces, wind is able to modify those surfaces by eroding soil and weathered
rock material already in small enough pieces to be moved. Known as deflation,
this is especially evident in arid areaswhere there is littlevegetationto hold the
material. Unlike water, air is not limited to channels and is frequently capable of
transporting materials uphill.
Aeolian transport has three modes depending on wind speeds and sizes of mate-
rials. The first mode is creep. Traction is when pieces are pushed along on the
landscape. The eddying nature of surface wind is able to concentrate energy onto
the surface and move materials. The second mode of transport, saltation, is the
“skipping” of somewhat smaller pieces over the landscape. The materials are
repeatedly picked up and dropped by whirling eddies that cause parabolic “skips”
ranging from a few meters to a few tens of meters. The third mode of transport is
suspension. This is generally reserved for materials less than 100 micrometers
across, and it is through this mechanism that wind can transport materials over
very long distances. For instance, satellite imagery observes dust from the Sahara
being blown to the Caribbean basin and Mongolian materials being transported
eastward far over the Pacific. When the aeolian material is concentrated it
becomes a dust storm, which can be hazardous to plants, animals, and people.
However, it has been found that aeolian materials deposited in the world’soceans
provide a source of nutrients for the oceanic food chain.
As wind transports materials away its erosion creates several types of land-
forms.Desertpavement is an arid land surface created by the wind-caused disap-
pearance of the finer materials leaving the larger size pieces behind; indeed, in
places it appears as if someone has carefully laid out pavement. Blowouts are
low places that are created when wind moves loose materials off of arid and semi-
arid surfaces. These basins are usually oblong. They are common on the U.S.
Great Plains and Big Hollow west of Laramie, Wyoming approximates 18 km long
by 6 km wide by 60 m deep. It is dwarfed by the Qattara Depression in Libya
encompassing 15,000 sq km.
When considering arid landscapes like mesas, buttes, and canyons such as
found plentifully in the American Southwest, one is tempted to ascribe many of
the landforms to the action of wind erosion. Rather than being the major cause
of these landforms, wind tends to put on the “finishing touches” by abrading surfa-
ces through sandblasting. Even on the world’s driest landscapes, it is actually
water that accomplishes the bulk of the erosion.
All wind-blown material eventually settles and deposition is significant on parts
of the landscape. Clearly visible are deposits of silts and sands. Silts are weathered
Wind Erosion and Deposition 365