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 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 of precipitation to cultivated cropland. During the drought of the 1930s, the unanchored soil turned to dust, which the prevailing winds blew away in huge clouds that sometimes blackened the sky. These choking billows of dust – named "black blizzards" or "black rollers".'' The swirling dust proved deadly. Those who inhaled the airborne prairie dust suffered coughing spasms, shortness of breath, asthma, bronchitis and influenza. Much like miners, Dust Bowl residents exhibited signs of silicosis from breathing in the extremely fine silt particulates, which had high silica content. Dust pneumonia, called the “brown plague,” killed hundreds and was particularly lethal for infants, children and the elderly. One monster dust storm reached the Atlantic Ocean. While “black blizzards” constantly menaced Plains states in the 1930s, a massive dust storm 2 miles high traveled 2,000 miles before hitting the East Coast on May 11, 1934. For five hours, a fog of prairie dirt enshrouded landmarks such as the Statue of Liberty and the U.S. Capitol, inside which lawmakers were debating a soil conservation bill. For East Coasters, the storm was a mere inconvenience—“Housewives kept busy,” read a New York Times subhead—compared to the tribulations endured by Dust Bowl residents. The Dust Bowl was both a manmade and natural disaster. Beginning with World War I, American wheat harvests flowed like gold as demand boomed. Lured by record wheat prices and promises by land developers that “rain follows the plow,” farmers powered by new gasoline tractors over-plowed and over-grazed the southern Plains. When the drought and Great Depression hit in the early 1930s, the wheat market collapsed. Once the oceans of wheat, which replaced the sea of prairie grass that anchored the topsoil into place, dried up, the land was defenseless against the winds that buffeted the Plains.