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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.
The Loess Hills of western Iowa are more than 61 meters (200 feet) thick.
Photograph by Phil Scherme
Yellow River
The Yellow River gets its name from the yellow loess suspended in the water.
accumulate
Verb
to gather or collect.
blanket
Verb
to cover entirely.
calcium carbonate
Noun
chemical compound (CaCO3) found in most shells and many rocks.
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.
erode
Verb
to wear away.
extensive
Adjective
very large.
fertile
Adjective
able to produce crops or sustain agriculture.
fine
Adjective
very thin.
grass
Noun
type of plant with narrow leaves.
Great Plains
Noun
grassland region of North America, between the Rocky Mountains and the Mississippi River.
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.
skeleton
Noun
bones of a body.
soil
Noun
top layer of the Earth's surface where plants can grow.
till
Noun
rock, earth, and gravel left behind by a retreating or melting glacier.
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.
