• erosion
    Wind and water eroded these hoodoos.

    Photograph by George F. Mobley

    Far-Flung Dust
    Wind is a powerful force. It can carry huge amounts of dust over long distances. In the winter and spring of 2004, winds eroded 45 million tons of dust from a spot called the Bodele Depression in the desert of northern Chad all the way across the Atlantic Ocean to Brazil.

    Super Sediment
    Most sediment is small, often nothing more than a grain of sand. But glaciers can sometimes carry huge boulders hundreds of kilometers from their source. These boulders often sit on top of the ground, looking like they fell from the sky. These supersized sediments are called erratic boulders. One of the world's largest erratic boulders, the Big Rock, sits in Alberta, Canada. It is 41 meters (135 feet) long and 9 meters (30 feet) high.

    Erosion is the act in which earth is worn away, often by water, wind, or ice. A similar process, weathering, breaks down or dissolves rock, weakening it or turning it into tiny fragments. No rock is hard enough to resist the forces of weathering and erosion. Together, they shaped the sharp peaks of the Himalaya Mountains in Asia and sculpted the spectacular forest of rock towers of Bryce Canyon, in the U.S. state of Utah.

    The process of erosion moves bits of rock or soil from one place to another. Most erosion is performed by water, wind, or ice (usually in the form of a glacier). These forces carry the rocks and soil from the places where they were weathered. If water is muddy, it is a sign that erosion is taking place. The brown color indicates that bits of rock and soil are suspended in the water and being transported from one place to another. This transported material is called sediment.

    When wind or water slows down, or ice melts, sediment is deposited in a new location. As the sediment builds up, it creates fertile land. River deltas are made almost entirely of sediment. Delta sediment is eroded from the banks and bed of the river.

    Erosion by Water

    Moving water is the major agent of erosion. Rain carries away bits of soil and slowly washes away rock fragments. Rushing streams and rivers wear away their banks, creating larger and larger valleys. In a span of about 5 million years, the Colorado River cut deeper and deeper into the land in what is now the U.S. state of Arizona. It eventually formed the Grand Canyon, which is more than 1,600 meters (1 mile) deep and as much as 29 kilometers (18 miles) wide in some places.

    Erosion by water changes the shape of coastlines. Waves constantly crash against shores. They pound rocks into pebbles and reduce pebbles to sand. Water sometimes takes sand away from beaches. This moves the coastline farther inland.

    The Cape Hatteras Lighthouse was built in 1870, on the Outer Banks, a series of islands off the coast of the U.S. state of North Carolina. At the time, the lighthouse was nearly 1,000 meters (3,300 feet) from the ocean. Over time, however, the ocean eroded most of the beach near the lighthouse. By 1999, the surf endangered the structure. Many people thought it would collapse during a strong storm. The lighthouse was moved 880 meters (2,900 feet) inland.

    The battering of ocean waves also erodes seaside cliffs. It sometimes bores holes that form caves. When water breaks through the back of the cave, it creates an arch. The continual pounding of the waves can cause the top of the arch to fall, leaving nothing but rock columns. These are called sea stacks. All of these features make rocky beaches beautiful, but also dangerous.

    Erosion by Wind

    Wind is also an agent of erosion. It carries dust, sand, and volcanic ash from one place to another. Wind can sometimes blow sand into towering dunes. Some sand dunes in the Badain Jaran area of the Gobi Desert in China reach more than 400 meters (1,300 feet) high.

    In dry areas, windblown sand blasts against rock with tremendous force, slowly wearing away the soft rock. It also polishes rocks and cliffs until they are smooth.

    Wind is responsible for the dramatic arches that give Arches National Park, in the U.S. state of Utah, its name. Wind can also erode material until nothing remains at all. Over millions of years, wind and water eroded an entire mountain range in central Australia. Uluru, also known as Ayers Rock, is the only remnant of those mountains.

    Erosion by Ice

    Ice can erode the land. In frigid areas and on some mountaintops, glaciers move slowly downhill and across the land. As they move, they pick up everything in their path, from tiny grains of sand to huge boulders.

    The rocks carried by a glacier rub against the ground below, eroding both the ground and the rocks. Glaciers grind up rocks and scrape away the soil. Moving glaciers gouge out basins and form steep-sided mountain valleys.

    Several times in Earth's history, vast glaciers covered parts of the Northern Hemisphere. These glacial periods are known as ice ages. Glaciers carved much of the northern North American and European landscape. They scoured the ground to form the bottom of what are now the Finger Lakes in the U.S. state of New York. They also carved fjords, deep inlets along the coast of Scandinavia.

    Today, in places such as Greenland and Antarctica, glaciers continue to erode the earth. These ice sheets, sometimes more than a mile thick, carry rocks and other debris downhill toward the sea. Eroded sediment is often visible on and around glaciers. This material is called moraine.

    Erosion and People

    Erosion is a natural process, but human activity can make it happen more quickly. Trees and plants hold soil in place. When people cut down forests or plow up grasses for agriculture or development, the soil washes away or blows away more easily. Landslides become more common. Water also rushes over exposed soil rather than soaking into it, causing flooding.

    Erosion control is the process of reducing erosion by wind and water. Farmers and engineers must regularly practice erosion control. Sometimes, engineers simply install structures to physically prevent soil from being transported. Gabions are huge wire frames that hold boulders in place, for instance. Gabions are often placed near cliffs. These cliffs, often near the coast, have homes, businesses, and highways near them. When erosion by water or wind threatens to tumble the boulders toward buildings and cars, gabions protect landowners and drivers by holding the rocks in place.

    Erosion control can also be done by physically changing the landscape. Living shorelines, for example, are a form of erosion control for wetland areas. Living shorelines are constructed by placing native plants, stone, sand, and even living organisms such as oysters along wetland coasts. These plants help anchor the soil to the area, preventing erosion. By securing the land, living shorelines establish a natural habitat. They protect coastlines from powerful storm surges as well as erosion.

    Global warming, the latest increase in temperature around the world, is speeding erosion. The change in climate has been linked to more frequent and more severe storms. Storm surges following hurricanes and typhoons threaten to erode miles of coastline and coastal habitat. These coastal areas have homes, businesses, and economically important industries, such as fisheries.

    The rise in temperature is also quickly melting glaciers. This is causing the sea level to rise faster than organisms can adapt to it. The rising sea erodes beaches more quickly. In the Chesapeake Bay area in the eastern United States, it is estimated that a rise in sea level of 8 to 10 centimeters (3 to 4 inches) will cause enough erosion to threaten buildings, sewer systems, roads, and tunnels.

  • Term Part of Speech Definition Encyclopedic Entry
    adapt Verb

    to adjust to new surroundings or a new situation.

    agriculture Noun

    the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

    Encyclopedic Entry: agriculture
    anchor Verb

    to hold firmly in place.

    arch Noun

    shape that looks like an upside-down "U."

    basin Noun

    a dip or depression in the surface of the land or ocean floor.

    Encyclopedic Entry: basin
    batter Verb

    to beat and cause damage.

    bioerosion Noun

    the process in which a living organism wears away at rock or another hard substance.

    bore Verb

    to drill or tunnel into something.

    boulder Noun

    large rock.

    Bryce Canyon Noun

    large rock formations (not a canyon) in the U.S. state of Utah.

    cave Noun

    underground chamber that opens to the surface. Cave entrances can be on land or in water.

    Chesapeake Bay Noun

    large, shallow estuary of the Susquehanna and other rivers that flow through the U.S. states of Maryland, Virginia, West Virginia, Delaware, Pennsylvania, and New York and the capital of Washington, D.C., before emptying in the Atlantic Ocean.

    cliff Noun

    steep wall of rock, earth, or ice.

    Encyclopedic Entry: cliff
    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    coastline Noun

    outer boundary of a shore.

    debris Noun

    remains of something broken or destroyed; waste, or garbage.

    delta Noun

    the flat, low-lying plain that sometimes forms at the mouth of a river from deposits of sediments.

    Encyclopedic Entry: delta
    deposit Verb

    to place or deliver an item in a different area than it originated.

    development Noun

    growth, or changing from one condition to another.

    Encyclopedic Entry: development
    dissolve Verb

    to break up or disintegrate.

    dust Noun

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

    Encyclopedic Entry: dust
    earth Noun

    soil or dirt.

    economic Adjective

    having to do with money.

    endanger Verb

    to put at risk.

    engineer Noun

    person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).

    erode Verb

    to wear away.

    erosion Noun

    act in which earth is worn away, often by water, wind, or ice.

    Encyclopedic Entry: erosion
    erosion control Noun

    process of preventing or reducing erosion by wind and water.

    farmer Noun

    person who cultivates land and raises crops.

    fertile Adjective

    able to produce crops or sustain agriculture.

    Finger Lakes Noun

    series of thin, deep lakes in the U.S. state of New York.

    fishery Noun

    industry or occupation of harvesting fish, either in the wild or through aquaculture.

    fjord Noun

    long, narrow ocean inlet between steep slopes.

    Encyclopedic Entry: fjord
    flood Noun

    overflow of a body of water onto land.

    Encyclopedic Entry: flood
    forest Noun

    ecosystem filled with trees and underbrush.

    frequent Adjective

    often.

    gabion Noun

    wire frame filled with rock.

    glacial period Noun

    time of long-term lowering of temperatures on Earth. Also known as an ice age.

    glacier Noun

    mass of ice that moves slowly over land.

    Encyclopedic Entry: glacier
    global warming Noun

    increase in the average temperature of the Earth's air and oceans.

    Encyclopedic Entry: global warming
    Gobi Desert Noun

    large desert in China and Mongolia.

    gouge Noun

    hand tool with a partly curved blade, used for carving.

    Grand Canyon Noun

    large gorge made by the Colorado River in the U.S. state of Arizona.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    highway Noun

    large public road.

    Himalaya Mountains Noun

    mountain range between India and Nepal.

    hurricane Noun

    tropical storm with wind speeds of at least 119 kilometers (74 miles) per hour. Hurricanes are the same thing as typhoons, but usually located in the Atlantic Ocean region.

    ice Noun

    water in its solid form.

    Encyclopedic Entry: ice
    ice age Noun

    long period of cold climate where glaciers cover large parts of the Earth. The last ice age peaked about 20,000 years ago. Also called glacial age.

    ice sheet Noun

    thick layer of glacial ice that covers a large area of land.

    Encyclopedic Entry: ice sheet
    indicate Verb

    to display or show.

    inlet Noun

    small indentation in a shoreline.

    island Noun

    body of land surrounded by water.

    Encyclopedic Entry: island
    landslide Noun

    the fall of rocks, soil, and other materials from a mountain, hill, or slope.

    Encyclopedic Entry: landslide
    lighthouse Noun

    structure displaying large, bright lights to warn and help ships navigate coastal waters.

    living shoreline Noun

    method of creating coastal land by using stones and marine grasses to trap soil, sand, and mud.

    Encyclopedic Entry: living shoreline
    moraine Noun

    material, such as earth, sand, and gravel, transported by a glacier.

    Encyclopedic Entry: moraine
    mountain range Noun

    series or chain of mountains that are close together.

    Northern Hemisphere Noun

    half of the Earth between the North Pole and the Equator.

    Outer Banks Noun

    barrier islands off the coast of the U.S. state of North Carolina.

    oyster Noun

    type of marine animal (mollusk).

    peak Noun

    the very top.

    plow noun, verb

    tool used for cutting, lifting, and turning the soil in preparation for planting.

    polish Verb

    to make smooth and shiny by rubbing.

    reduce Verb

    to lower or lessen.

    remnant Noun

    something that is left over.

    rock Noun

    natural substance composed of solid mineral matter.

    sand Noun

    small, loose grains of disintegrated rocks.

    sand dune Noun

    mound of sand created by the wind.

    Scandinavia Noun

    region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark.

    scour Verb

    to rub harshly, often to polish.

    sea level Noun

    base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle.

    Encyclopedic Entry: sea level
    sea stack Noun

    column-shaped rock formation created by waves eroding parts of coastal cliffs.

    sediment Noun

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

    Encyclopedic Entry: sediment
    sewer Noun

    passageway or holding tank for liquid waste.

    shore Noun

    coast.

    soil Noun

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

    spectacular Adjective

    dramatic and impressive.

    storm Noun

    severe weather indicating a disturbed state of the atmosphere resulting from uplifted air.

    storm surge Noun

    abnormal rise in sea level accompanying a hurricane or other intense storm. Also called a storm tide.

    Encyclopedic Entry: storm surge
    stream Noun

    body of flowing fluid.

    surf Noun

    waves as they break on the shore or reef.

    suspend Verb

    to temporarily stop an activity.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    tremendous Adjective

    very large or important.

    typhoon Noun

    tropical storm with wind speeds of at least 74 miles (119 kilometers) per hour. Typhoons are the same thing as hurricanes, but usually located in the Pacific or Indian Ocean region.

    Uluru Noun

    large sandstone rock formation in central Australia. Also called Ayers Rock.

    valley Noun

    depression in the Earth between hills.

    vast Adjective

    huge and spread out.

    volcanic ash Noun

    fragments of lava less than 2 millimeters across.

    Encyclopedic Entry: volcanic ash
    water Noun

    chemical compound that is necessary for all forms of life.

    wave Noun

    moving swell on the surface of water.

    weathering Noun

    the breaking down or dissolving of the Earth's surface rocks and minerals.

    Encyclopedic Entry: weathering
    wetland Noun

    area of land covered by shallow water or saturated by water.

    Encyclopedic Entry: wetland
    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.

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