Geology Reference
In-Depth Information
Box 12.2
THE DUST BOWL
The natural vegetation of the Southern Great Plains
of Colorado, Kansas, New Mexico, Oklahoma, and
Texas is prairie grassland which is adapted to low rain-
fall and occasional severe droughts. During the 'Dirty
Thirties', North American settlers arrived from the east.
Being accustomed to more rainfall, they ploughed up
the prairie and planted wheat. Wet years saw good
harvests; dry years, which were common during the
1930s, brought crop failures and dust storms. In 1934
and 1935, conditions were atrocious. Livestock died
from eating excessive amounts of sand, human sickness
increased because of the dust-laden air. Machinery was
ruined, cars were damaged, and some roads became
impassable. The starkness of the conditions is evoked
in a report of the time:
are generally similar to those of snow blizzards. The scenes are
dismal to the passerby; to the resident they are demoralizing.
(Joel 1937, 2)
The results were the abandonment of farms and an
exodus of families, remedied only when the prairies
affected were put back under grass. The effects of the
dust storms were not always localized:
On 9 May [1934], brown earth from Montana and Wyoming
swirled up from the ground, was captured by extremely high-
level winds, and was blown eastward toward the Dakotas.
More dirt was sucked into the airstream, until 350 million
tons were riding toward urban America. By late afternoon the
storm had reached Dubuque and Madison, and by evening
12 million tons of dust were falling like snow over Chicago -
4 pounds for each person in the city. Midday at Buffalo on
10 May was darkened by dust, and the advancing gloom
stretched south from there over several states, moving as fast
as 100 miles an hour. The dawn of 11 May found the dust set-
tling over Boston, New York, Washington, and Atlanta, and
then the storm moved out to sea. Savannah's skies were hazy all
day 12 May; it was the last city to report dust conditions. But
there were still ships in the Atlantic, some of them 300 miles
off the coast, that found dust on their decks during the next
day or two.
The conditions around innumerable farmsteads are pathetic.
A common farm scene is one with high drifts filling yards,
banked high against buildings, and partly or wholly cover-
ing farm machinery, wood piles, tanks, troughs, shrubs, and
young trees. In the fields near by may be seen the stretches of
hard, bare, unproductive subsoil and sand drifts piled along
fence rows, across farm roads, and around Russian-thistles and
other plants. The effects of the black blizzards [massive dust
storms that blotted out the Sun and turned day into night]
(Worster 1979, 13-14)
the prevailing wind, and
V
is a measure of the vegetation
cover. Although this equation is similar to the ULSE, its
components cannot be multiplied together to find the
result. Instead, graphical, tabular, or computer solutions
are required. Originally designed to predict wind ero-
sion in the Great Plains, the WEQ has been applied
to other regions in the USA, especially by the Natural
Resources Conservation Service (NRCS). However, the
WEQ suffered from several drawbacks. It was calibrated
for conditions in eastern Kansas, where the climate is
rather dry; it was only slowly adapted to tackle year-
round changes in crops and soils; it was unable to cope
with the complex interplay between crops, weather, soil,
and erosion; and it over-generalized wind characteristics.
Advances in computing facilities and databases have
prompted the development of a more refined
Wind
Erosion Prediction System
(
WEPS
), which is designed
to replace WEQ. This computer-based model simulates
the spatial and temporal variability of field conditions
and soil erosion and deposition within fields of vary-
ing shapes and edge types and complex topographies.
It does so by using the basic processes of wind ero-
sion and the processes that influence the erodibility
of the soil. Another
Revised Wind Erosion Equa-
tion
(
RWEQ
) has been used in conjunction with GIS
databases to scale up the field-scale model to a regional
model (Zobeck
et al
. 2000). An
integrated wind-
erosionmodelling system
, built in Australia, combines a
