1 A blizzard struck the city of Phoenix, Arizona, on July 5, 2011. But it wasn’t a frozen, white, swirling kind of blizzard. This storm was gritty, dark, and smothering. It was known as a “black blizzard.” “Black blizzard” is an American nickname for a dense cloud of dry particles that blankets a large area. It is commonly called a dust storm. The Phoenix blizzard towered 5,000 feet into the air, stretched 100 miles across, and plowed a 150-mile path before it finally calmed down. During the storm, visibility was nearly zero. 2 It’s common to see a swipe of dust, dirt, or sand stirred up by a gust of wind. A black blizzard is the same experience multiplied many times over. Such storms are powered by high winds. Like water flowing in a river, fast air currents pick up and transport loose, dry soil. Lighter particles are swept up and carried for miles. Heavier particles are pushed forward by saltation. Saltation happens when blowing particles knock into stationary particles on the ground. The blowing particles set them in motion, too. Soon many particles bounce along by a series of skips and jumps. Saltated particles can work together to nudge pebbles and other objects. The nudging action is called creep. Saltation and creep come together to move massive amounts of material. In September 2009, a giant dust storm moved five million tons of red outback soil through Sydney, Australia! Watch Out . . . 3 Dust storms can severely affect whatever or whoever gets in their way. The grinding blast damages crops, livestock, buildings, and vehicles. Dust storms can have harmful effects on human health, too. They make breathing illnesses much worse. Dust storms stir up bacteria, molds, and fungi, which can cause “valley fever,” an infection that often follows dust storms in Phoenix. Virologists believe valley fever is caused by a soil fungus. . . . For a Dust Storm Near You 4 The threat of dust storms is greatest in Earth’s dry regions. what sentence from the article best states the central idea