Blowing sand entered the news headlines in March 2003 when sand- and duststorms added an unwelcome weather element to the Iraq war. Blowing dust and sand are no strangers to the headlines, however. Both the United States and Canada consider the Dust Bowl years of the 1930s and the accompanying black blizzards among the century's most significant weather stories.
The duststorm headlines are not all from distant lands or the distant past. Spread by strong winds, blowing dust affected a wide section of the American Southwest from New Mexico and through much of western Texas in mid-April of 2003. The storm forced road closures and caused a ten-car pileup that killed two.
We know that in duststorms and sandstorms, great quantities of dust and sand are carried by the wind. How does it get born aloft?
Dust borne on the wind is with us almost all the time. Aeolian or Eolian transport (after Aeolus, a Greek god of the wind) is the term used to describe particles carried by the wind and are held aloft through suspension. The Aeolian process usually starts when strong, often gusty, winds cross an arid landscape picking up small particles such as sand, dust, soil and other debris. The wind then moves the particles in one, or a combination, of three ways: suspension, saltation, or creep.
Suspension
The smallest dust particles are carried through the air by suspension. Suspension occurs when the dust is lofted into the air and held there by upward air currents strong enough to support the weight of the particles. Typical surface wind speeds can suspend dust particles with diameters less than 0.2 millimetres (8/1000 inch) and carry them short distances. Severe windstorms, however, can not only hold large particles aloft for some time, but may also push them to very high altitudes, which enhances their travel distance. Under strong winds, suspended dust particles may be lifted thousands of metres upward and drift thousands of kilometres downwind -- even crossing the oceans.
Saltation
The term "saltation" comes from the Latin word for "leaping," an apt description of what dust and sand particles do at high wind speeds. In saltation, the particles advance forward through a series of jumps or skips, like a game of progressive leap-tag. The wind lifts the first particle into the air to a height of around a metre or two (3-7 ft). Those particles too heavy to remain suspended, drift downwind a distance of approximately four times the height they attained above the ground (e.g., one metre up moves four metres
