Loess: Wind-Blown Dust

Wind not only deposits sand in sand dunes; it also deposits accumulations of silt and clay (dust) called loess. Loess blankets many regions throughout the world. It is composed mostly of silt-sized grains, but clay particles may also be present. Loess deposits are commonly found away from deserts, because the loess is blown away from them.

Why does dust travel out from the deserts, but sand is deposited within the deserts?
 

Sand is heavier and it settles out first. The dust is finer and much lighter. It can travel in the wind for hundreds of kilometers before it finally settles out.

Because loess is not deposited in dry desert areas, it often ends up in areas with sufficient precipitation to support vegetation. Loess is often rich in nutrients, so it makes some of the world’s best agricultural soil. Loess plains in northern China originate from wind-blown dust from the Gobi Desert. On these plains, the rich soil gave rise to the first Chinese culture in the fifth century B.C. Today, loess-rich soils in the U.S. are also highly productive agricultural land.