Page 331 - Fundamentals of Geomorphology

314 PROCESS AND FORM

Box 12.2

THE DUST BOWL

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