In some parts of the world, windblown dust and silt blanket the land. This layer of fine, mineral-rich material is called loess.

Loess is mostly created by wind, but can also be formed by glaciers. When glaciers grind rocks to a fine powder, loess can form. Streams carry the powder to the end of the glacier. This sediment becomes loess.

Loess ranges in thickness from a few centimeters to more than 91 meters (300 feet). Unlike other soils, loess is pale and loosely packed. It crumbles easily; in fact, the word “loess” comes from the German word for “loose.” Loess is soft enough to carve, but strong enough to stand as sturdy walls. In parts of China, residents build cave-like dwellings in thick loess cliffs.

Extensive loess deposits are found in northern China, the Great Plains of North America, central Europe, and parts of Russia and Kazakhstan. The thickest loess deposits are near the Missouri River in the U.S. state of Iowa and along the Yellow River in China.

Loess accumulates, or builds up, at the edges of deserts. For example, as wind blows across the Gobi, a desert in Asia, it picks up and carries fine particles. These particles include sand crystals made of quartz or mica. It may also contain organic material, such as the dusty remains of skeletons from desert animals.

On the far side of the desert, moisture in the air causes the particles and dust to settle on the ground. There, grass and the roots of other plants trap the dust and hold it to the ground. More dust slowly accumulates, and loess is formed.

Loess often develops into extremely fertile agricultural soil. It is full of minerals and drains water very well. It is easily tilled, or broken up, for planting seeds. Loess usually erodes very slowly—Chinese farmers have been working the loess around the Yellow River for more than a thousand years.

loess
The Loess Hills of western Iowa are more than 61 meters (200 feet) thick.

Yellow River
The Yellow River gets its name from the yellow loess suspended in the water.

accumulate
Verb

to gather or collect.

Noun

layer of gases surrounding Earth.

blanket
Verb

to cover entirely.

calcium carbonate
Noun

chemical compound (CaCO3) found in most shells and many rocks.

Noun

steep wall of rock, earth, or ice.

crystal
Noun

type of mineral that is clear and, when viewed under a microscope, has a repeating pattern of atoms and molecules.

Noun

area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.

Noun

tiny, dry particles of material solid enough for wind to carry.

erode
Verb

to wear away.

extensive
Adjective

very large.

fertile
Adjective

able to produce crops or sustain agriculture.

fine
Adjective

very thin.

Noun

mass of ice that moves slowly over land.

grass
Noun

type of plant with narrow leaves.

Great Plains
Noun

grassland region of North America, between the Rocky Mountains and the Mississippi River.

Noun

windblown soil or silt.

mica
Noun

type of mineral that can be split into thin, see-through sheets.

mineral
Noun

inorganic material that has a characteristic chemical composition and specific crystal structure.

Missouri River
Noun

(4,382 kilometers/2,723 miles) river in the western United States.

moisture
Noun

wetness.

organic
Adjective

composed of living or once-living material.

pale
Adjective

nearly white or lacking in color.

particle
Noun

small piece of material.

quartz
Noun

common type of mineral.

rock
Noun

natural substance composed of solid mineral matter.

root
Noun

part of a plant that secures it in the soil, obtains water and nutrients, and often stores food made by leaves.

sand
Noun

small, loose grains of disintegrated rocks.

Noun

solid material transported and deposited by water, ice, and wind.

Noun

small sediment particles.

skeleton
Noun

bones of a body.

soil
Noun

top layer of the Earth's surface where plants can grow.

stream
Noun

body of flowing fluid.

till
Noun

rock, earth, and gravel left behind by a retreating or melting glacier.

wind
Noun

movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

Yellow River
Noun

(5,464 kilometers/3,395 miles) river in China. Also called the Huang River.