• 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.

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

  • Term Part of Speech Definition Encyclopedic Entry
    accumulate Verb

    to gather or collect.

    air Noun

    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


    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.