Geology Reference
In-Depth Information
Geo-Focus
Windmills and Wind Power
Whoosh, whoosh, whoosh. Ah, the
gentle sound of a windmill's blades
turning in the wind. The image most
people associate with windmills is one
of a pastoral landscape in Holland
dominated by a classic Dutch windmill
crafted of wood (
◗
Figure 1), or perhaps
Don Quixote tilting at windmills in the
famous novel
Don Quixote de la Mancha
by Miguel Cervantes. Today, instead of a
whoosh, whoosh, whoosh, the sound of
modern electricity-generating windmills
in a wind farm is more like a woomph,
woomph, woomph (
Figure 2).
As early as 5000 B.C., people began
to harness the power of wind to propel
boats along the Nile River. The Chinese
used windmills to pump water for
irrigating crops as long ago as 200 B.C.
Wind power was used in the Middle
Ages in Europe, particularly in Holland,
where windmills have played an impor-
tant role in society. Windmills were fi rst
used to grind corn, which is where the
term “windmill” originally came from.
Later windmills were used to drain
lakes and marshes from the low-lying
districts, and to saw timber. Settlers in
the United States in the late 19th and
early 20th centuries used this technol-
ogy to pump water and generate elec-
tricity in the Great Plains.
With the application of stream power
and industrialization in Europe and
later the United States, the use of wind-
mills rapidly declined. However, indus-
trialization led to the development of
◗
◗
Figure 1
Five traditional Dutch windmills lined up along
a canal at Kinderdiik, the Netherlands.
◗
Figure 2
A windmill farm in Alameda County, California. California
has more windmills than any other state in the United States.
causes most of the erosion in deserts. The dry conditions
and sparse vegetation characteristic of deserts enhance water
erosion. If you look closely, you can see the evidence of ero-
sion and transportation by running water nearly everywhere
except in areas covered by sand dunes.
Most of a desert's average annual rainfall of 25 cm or
less comes in brief, heavy, localized cloudbursts. During
these times, considerable erosion takes place because the
ground cannot absorb all of the rainwater. With so little
vegetation to hinder the fl ow of water, runoff is rapid, espe-
cially on moderately to steeply sloping surfaces, resulting in
fl ash fl oods and sheet fl ows. Dry stream channels quickly fi ll
with raging torrents of muddy water and mudfl ows, which
carve out steep-sided gullies and overfl ow their banks. Dur-
ing these times, a tremendous amount of sediment is rapidly
transported and deposited far downstream.
Although water is the major erosive agent in deserts
today, it was even more important during the Pleistocene
Epoch when these regions were more humid (see
Chapter 23). During that time, many of the major topographic
features of deserts were forming. Today that topography is
modifi ed by wind and infrequently fl owing streams.
Most desert streams are poorly integrated and fl ow only
intermittently. Many of them never reach the sea because the
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