Encyclopedic Entry

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.

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.

Vocabulary

Term Part of Speech Definition Encyclopedic Entry

accumulate

Verb

to gather or collect.

air

Noun

the layer of gases surrounding Earth.

Encyclopedic Entry: air

blanket

Verb

to cover entirely.

calcium carbonate

Noun

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

cliff

Noun

steep wall of rock, earth, or ice.

Encyclopedic Entry: cliff

crystal

Noun

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

desert

Noun

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

Encyclopedic Entry: desert

dust

Noun

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

Encyclopedic Entry: dust

erode

Verb

to wear away.

extensive

Adjective

very large.

fertile

Adjective

able to produce crops or sustain agriculture.

fine

Adjective

very thin.

glacier

Noun

mass of ice that moves slowly over land.

Encyclopedic Entry: glacier

grass

Noun

type of plant with narrow leaves.

Great Plains

Noun

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

loess

Noun

windblown soil or silt.

Encyclopedic Entry: loess

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.

sediment

Noun

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

Encyclopedic Entry: sediment

silt

Noun

small sediment particles.

Encyclopedic Entry: silt

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.

Credits

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Writer

Kim Rutledge
Melissa McDaniel
Diane Boudreau
Tara Ramroop
Santani Teng
Erin Sprout
Hilary Costa
Hilary Hall
Jeff Hunt

Illustrator

Tim Gunther
Mary Crooks, National Geographic Society

Editor

Kara West
Jeannie Evers

Educator Reviewer

Nancy Wynne

Producer

Caryl-Sue, National Geographic Society

Sources

Dunn, Margery G. (Editor). (1989, 1993). "Exploring Your World: The Adventure of Geography." Washington, D.C.: National Geographic Society.

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