The
Dust Bowl, also known as the
Dirty Thirties, was a period of severe
dust storms that greatly damaged the ecology and
agriculture of the
US and
Canadian prairies during the 1930s; severe
drought and a failure to apply
dryland farming methods to prevent wind erosion (the
Aeolian processes) caused the phenomenon. The drought came in three waves, 1934, 1936, and 1939–40, but some regions of the high plains experienced drought conditions for as many as eight years. With insufficient understanding of the ecology of the plains, farmers had conducted extensive
deep plowing of the virgin
topsoil of the
Great Plains during the previous decade; this had displaced the native, deep-rooted
grasses that normally trapped soil and moisture even during periods of
drought and high winds. The rapid mechanization of farm equipment, especially small gasoline tractors, and widespread use of the
combine harvester contributed to farmers' decisions to convert arid grassland (much of which received no more than 10 inches (250 mm) of precipitation per year) to cultivated cropland.