Few ecological disasters in US history have left a deeper mark on the country than the Dust Bowl of the 1930s.

The advent of gasoline-powered tractors and combine harvesters early in the 20th century had made large-scale cultivation of the Great Plains possible for the first time. When wheat prices skyrocketed in the aftermath of WWI, thousands rushed to cultivate the prairies.

But as farmers converted grasslands to cropland, they eliminated the native grasses whose roots kept the topsoil in place.

When drought hit in the 1930s, the unanchored topsoil blew away in huge dust storms like the one pictured above. The resulting ecological disaster ravaged 100 million acres of land and contributed to the displacement of 3.5 million Americans.