Images from the Dust Bowl, 1930s
The Dust Bowl, or the Dirty Thirties, was a period of severe dust storms causing major ecological and agricultural damage to American and Canadian prairie lands in the 1930s. The phenomenon was caused by severe drought combined with a failure to apply dryland farming methods to prevent wind erosion. Extensive deep plowing of the virgin topsoil of the Great Plains in the preceding decade had displaced the natural deep-rooted grasses that normally kept the soil in place and trapped moisture even during periods of drought and high winds. Rapid mechanization of farm implements, especially small gasoline tractors and widespread use of the combine harvester, were significant in the decisions to convert arid grassland (much of which received no more than 10 inches (250 mm) of precipitation per year) to cultivated cropland.