• erosion
    The beach beneath this beach house has eroded away

    Solar Erosion
    The sun itself is actually an instrument of erosion! As rocks heat up, they expand. Expanding rocks can sometimes crack and crumble away.

    Eroding Animals
    Burrowing animals, such as beetles and worms, contribute to erosion by displacing soil.

    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.

     
    Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind or water. A similar process, weathering, breaks down or dissolves rock, but does not involve movement.
     
    Erosion is the opposite of deposition, the geological process in which earthen materials are deposited, or built up, on a landform.
     
    Most erosion is performed by liquid water, wind, or ice (usually in the form of a glacier). If wind is dusty, or water or glacial ice is muddy, erosion is taking place. The brown color indicates that bits of rock and soil are suspended in the fluid (air or water) and being transported from one place to another. This transported material is called sediment.
     
    Physical and Chemical Erosion
     
    The process of erosion is often broken down into two forms: physical erosion and chemical erosion. They often work together, as well as with other geological processes such as weathering and sedimentation.
     
    Physical erosion
    Physical erosion describes the process of rocks changing their physical properties without changing their basic chemical composition. Physical erosion often causes rocks to get smaller or smoother. Rocks eroded through physical erosion often form clastic sediments. Clastic sediments are composed of fragments of older rocks that have been transported from their place of origin.
     
    Landslides and other forms of mass wasting are associated with physical weathering. These processes cause rocks to dislodge from hillsides and crumble as they tumble down a slope. 
     
    Plant growth can also contribute to physical erosion in a process called bioerosion. Plants break up earthen materials as they take root, and can create cracks and crevices in rocks they encounter.
     
    Ice and liquid water can also contribute to physical erosion as their movement forces rocks to crash together or crack apart. Some rocks shatter and crumble, while others are worn away. River rocks are often much smoother than rocks found elsewhere, for instance, because they have been eroded by constant contact with other river rocks.
     
    Chemical erosion
    Chemical erosion describes the process of rocks changing their chemical composition as they erode. Chemical erosion almost always refers to rocks interacting and undergoing a chemical reaction with water.
     
    The most familiar form of chemical erosion is probably rust, the product of a process called oxidation. During oxidation, rocks interact with oxygen in the presence of water. The amount of water required for oxidation is minimal, often the amount of water present in the atmosphere. Iron is the most familiar mineral to undergo oxidation and rust.
     
    Carbonation is another form of chemical erosion. During carbonation, rocks interact with carbon dioxide in the presence of water. In rocks such as chalk, carbonation can create a weak acid (carbonic acid) that erodes the surface of the rock. 
     
    Hydration is a form of chemical erosion in which the chemical bonds of the mineral are changed as it interacts with water. One instance of hydration occurs as the mineral anhydrite reacts with groundwater. The water transforms anhydrite into gypsum, one of the most common minerals on Earth.
     
    Another familiar form of chemical erosion is hydrolysis. In the process of hydrolysis, a new solution (a mixture of two or more substances) is formed as chemicals in rock interact with water. In many rocks, for example, sodium minerals interact with water to form a saltwater solution.
     
    Erosion by Water
     
    Liquid water is the major agent of erosion on Earth. Rain, rivers, floods, lakes, and the ocean carry away bits of soil and sand, and slowly wash away the sediment.
     
    Rainfall produces four types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. 
    • Splash erosion describes the impact of a falling raindrop, which can scatter tiny soil particles as far as .6 meters (2 feet). 
    • Sheet erosion describes erosion caused by runoff. 
    • Rill erosion describes erosion that takes place as runoff develops into discrete streams (rills). 
    • Finally, gully erosion is the stage in which soil particles are transported through large channels. Gullies carry water for brief periods of time during rainfall or snowmelt, but appear as small valleys or crevasses during dry seasons.
     
    Valley erosion is the process in which rushing streams and rivers wear away their banks, creating larger and larger valleys. The Fish River Canyon, in southern Namibia, is the largest canyon in Africa and a product of valley erosion. Over millions of years, the Fish River wore away at the hard gneiss bedrock, carving a canyon about 160 kilometers (99 miles) in length, 27 kilometers (17 miles) wide, and 550 meters (1,084 feet) deep. 
     
    The ocean is a huge force of erosion. Coastal erosion—the wearing away of rocks, earth, or sand on the beach—can change the shape of entire coastlines. During the process of coastal erosion, waves pound rocks into pebbles and pebbles into sand. Waves and currents sometimes transport sand away from beaches, moving the coastline farther inland. 
     
    Coastal erosion can have a huge impact on human settlement as well as coastal ecosystems. The Cape Hatteras Lighthouse, for example, was nearly destroyed by coastal erosion. The Cape Hatteras Lighthouse was built on the Outer Banks, a series of barrier islands off the coast of the U.S. state of North Carolina, in 1870. At the time, the lighthouse was nearly 457 meters (1,500 feet) from the ocean. Over time, the ocean eroded most of the beach near the lighthouse. By 1970, the pounding surf was just 37 meters (120 feet) away and endangered the structure. Many people thought the lighthouse would collapse during a strong storm. Instead, it was moved 880 meters (2,900 feet) inland. 
     
    The battering force of ocean waves also erodes seaside cliffs. The action of erosion can create an array of coastal landscape features. Erosion can bore holes that form caves. When water breaks through the back of the cave, it can create an arch. The continual pounding of waves can cause the top of the arch to fall, leaving nothing but rock columns called sea stacks. The seven remaining sea stacks of Twelve Apostles Marine National Park, in Victoria, Australia, are among the most dramatic and well-known of these features of coastal erosion.
     
    Erosion by Wind
     
    Wind is a powerful agent of erosion. Aeolian (wind-driven) processes constantly transport dust, sand, and ash from one place to another. Wind can sometimes blow sand into towering dunes. Some sand dunes in the Badain Jaran section of the Gobi Desert in China, for example, reach more than 400 meters (1,300 feet) high. 
     
    In dry areas, windblown sand can blast against rock with tremendous force, slowly wearing away the soft rock. It polishes rocks and cliffs until they are smooth—giving the stone a so-called “desert varnish.” Wind is responsible for the eroded features that give Arches National Park, in the U.S. state of Utah, its name. 
     
    Wind can also erode material until little remains at all. Ventifacts are rocks that have been sculpted by wind erosion. The enormous chalk formations in the White Desert of Egypt are ventifacts carved by thousands of years of wind roaring through the flat landscape.
     
    Some of the most destructive examples of wind erosion are the dust storms that characterized the “Dust Bowl” of the 1930s in North America. Made brittle by years of drought and agricultural mismanagement, millions of tons of valuable topsoil were eroded away by strong winds in what came to be known as “black blizzards.” These dust storms devastated local economies, forcing thousands of people who depended on agriculture for their livelihoods to migrate.
     
    Erosion by Ice
     
    Ice, usually in the form of glaciers, can erode the earth and create dramatic landforms. In frigid areas and on some mountaintops, glaciers move slowly downhill and across the land. As they move, they transport everything in their path, from tiny grains of sand to huge boulders. 
     
    Rocks carried by glaciers scrape against the ground below, eroding both the ground and the rocks. In this way, glaciers grind up rocks and scrape away the soil. Moving glaciers gouge out basins and form steep-sided mountain valleys. Eroded sediment called moraine is often visible on and around glaciers.
     
    Several times in Earth’s history, vast glaciers covered parts of the Northern Hemisphere. These glacial periods are known as ice ages. Ice Age glaciers carved much of the northern North American and European landscape. 
     
    Ice Age glaciers scoured the ground to form what are now the Finger Lakes in the U.S. state of New York. They carved fjords, deep inlets along the coast of Scandinavia. The snout of a glacier eroded Cape Cod Bay, Massachusetts, and formed the recognizable fishhook shape of Cape Cod itself.
     
    Today, in places such as Greenland and Antarctica, glaciers continue to erode the earth. Ice sheets there can be more than a mile thick, making it difficult for scientists to measure the speed and patterns of erosion. However, ice sheets do erode remarkably quickly—as much as half a centimeter (.2 inch) every year. 
     
    Other Forces of Erosion
     
    Thermal erosion describes the erosion of permafrost along a river or coastline. Warm temperatures can cause ice-rich permafrost to break off coastlines in huge chunks, often carrying valuable topsoil and vegetation with them. These eroded “floating islands” can disintegrate into the ocean, or even crash into another piece of land—helping spread new life to different landscapes.
     
    Mass wasting describes the downward movement of rocks, soil, and vegetation. Mass wasting incidents include landslides, rockslides, and avalanches. Mass wasting can erode and transport millions of tons of earth, reshaping hills and mountains and, often, devastating communities in its path.
     
    Factors Impacting Erosion
     
    Some of the natural factors impacting erosion in a landscape include climate, topography, vegetation, and tectonic activity.
     
    Climate is perhaps the most influential force impacting the effect of erosion on a landscape. Climate includes precipitation and wind. Climate also includes seasonal variability, which influences the likelihood of weathered sediments being transported during a weather event such as a snowmelt, breeze, or hurricane.
     
    Topography, the shape of surface features of an area, can contribute to how erosion impacts that area. The earthen flood plains of river valleys are much more prone to erosion than rocky flood channels, which may take centuries to erode. Soft rock like chalk will erode more quickly than hard rocks like granite.
     
    Vegetation can slow the impact of erosion. Plant roots adhere soil and rock particles, preventing their transport during rainfall or wind events. Trees, shrubs, and other plants can even limit the impact of mass wasting events such as landslides and natural hazards such as hurricanes. Deserts, which generally lack thick vegetation, are often the most eroded landscapes on the planet.
     
    Finally, tectonic activity shapes the landscape itself, and thus influences the way erosion impacts an area. Tectonic uplift, for example, causes one part of the landscape to rise higher than others. In a span of about 5 million years, tectonic uplift caused the Colorado River cut deeper and deeper into the Colorado Plateau, 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 and People
     
    Deposition, Soils, and Sediments
    Eroded sediments have profoundly influenced the development of civilizations around the world. 
     
    Agricultural development is often reliant on the nutrient-rich soils created by the accumulation of eroded earth. When the velocity of wind or water slows, eroded sediment is deposited in a new location. The sediment builds up in a process called sedimentation, and creates fertile land. 
     
    River deltas are made almost entirely of sediment that has eroded from the banks and bed of a river. The rich delta soils of the San Joaquin and Sacramento rivers in northern California, for example, have created one of the most agriculturally productive areas in the world.
     
    Loess is an agriculturally rich sediment made almost entirely of wind-blown, eroded sediment. The Yellow River in central China gets its name from the yellow loess suspended in its water. The fertile lands around the Yellow River have been among China’s most productive for thousands of years.
     
    Erosion Control
    Erosion is a natural process, but human activity can make it happen more quickly. 
     
    Human activity altering the vegetation of an area is perhaps the biggest human factor contributing to erosion. Trees and plants hold soil in place. When people cut down forests or plow up grasses for agriculture and development, the soil is more vulnerable to washing or blowing away. Landslides become more common. Water rushes over exposed soil rather than soaking into it, causing flooding. 
     
    Global warming, the current period of climate change, is speeding erosion. The change in climate has been linked to more frequent and severe storms. Storm surges following hurricanes and typhoons can erode kilometers of coastline and coastal habitat. These coastal areas are home to residences, businesses, and economically important industries, such as fisheries.
     
    The rise in temperature is also quickly melting glaciers. The slower, more massive form of glacial erosion is being supplanted by the cumulative impact of rill, gully, and valley erosion. In areas downstream from glacial snouts, rapidly melting glaciers are contributing to sea level rise. The rising sea erodes beaches more quickly. 
     
    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 also includes physically changing the landscape. Communities often invest in windbreaks and riparian buffers to protect valuable agricultural land. Windbreaks, also called hedgerows or shelterbelts, are lines of trees and shrubs planted to protect cropland from wind erosion. Riparian buffers describe plants such as trees, shrubs, grasses, and sedges that line the banks of a river. Riparian buffers help contain the river in times of increased stream flow and flooding. 
     
    Living shorelines are another form of erosion control in 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.
  • Term Part of Speech Definition Encyclopedic Entry
    accumulation Noun

    a buildup of something.
    adhere Verb

    to stick to or support.
    aeolian landform Noun

    geographic feature created by wind.
    agricultural development Noun

    modern farming methods that include mechanical, chemical, engineering and technological methods. Also called industrial agriculture.
    agriculture Noun

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

    		 Encyclopedic Entry: agriculture
    array Noun

    large group.
    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    		 Encyclopedic Entry: atmosphere
    avalanche Noun

    large mass of snow and other material suddenly and quickly tumbling down a mountain.

    		 Encyclopedic Entry: avalanche
    bank Noun

    a slope of land adjoining a body of water, or a large elevated area of the sea floor.
    barrier island Noun

    long, narrow strip of sandy land built up by waves and tides that protects the mainland shore from erosion.
    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.
    beach Noun

    narrow strip of land that lies along a body of water.

    		 Encyclopedic Entry: beach
    bedrock Noun

    solid rock beneath the Earth's soil and sand.

    		 Encyclopedic Entry: bedrock
    bioerosion Noun

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

    deep, narrow valley with steep sides.

    		 Encyclopedic Entry: canyon
    carbonation Noun

    absorption of, or reaction with, carbon dioxide.
    carbonic acid Noun

    chemical produced as carbon dioxide dissolves in water.
    cave Noun

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

    a soft mineral. Also called limestone and calcium carbonate.
    channel Noun

    waterway between two relatively close land masses.

    		 Encyclopedic Entry: channel
    chemical bond Noun

    attraction between atoms, ions or molecules that enables the formation of chemical compounds.
    chemical erosion Noun

    process of rocks changing their chemical composition as they erode.
    chemical reaction Noun

    process that involves a change in atoms, ions, or molecules of the substances (reagents) involved.
    civilization Noun

    complex way of life that developed as humans began to develop urban settlements.

    		 Encyclopedic Entry: civilization
    clastic sediment Noun

    rock composed of fragments of older rocks that have been transported from their place of origin.
    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
    climate change Noun

    gradual changes in all the interconnected weather elements on our planet.

    		 Encyclopedic Entry: climate change
    coastal erosion Noun

    wearing away of earth or sand on the beach by natural or man-made methods.
    coastline Noun

    outer boundary of a shore.
    crevasse Noun

    deep crack, especially in a glacier.

    		 Encyclopedic Entry: crevasse
    crevice Noun

    crack in a rock.
    crop Noun

    agricultural produce.

    		 Encyclopedic Entry: crop
    cumulative Adjective

    growing in quantity or strength.
    current Noun

    steady, predictable flow of fluid within a larger body of that fluid.

    		 Encyclopedic Entry: current
    delta Noun

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

    		 Encyclopedic Entry: delta
    deposition Noun

    process of silt and sediment building up in an area.
    desert varnish Noun

    dark, hard layer of yellowish or blackish oxides formed on exposed rock surfaces in windblown, arid regions.
    discrete Adjective

    individual or distinct.
    disintegrate Verb

    to fall apart and disappear.
    dissolve Verb

    to break up or disintegrate.
    dissolve Verb

    to break up or disintegrate.
    drought Noun

    period of greatly reduced precipitation.

    		 Encyclopedic Entry: drought
    dry season Noun

    time of year with little precipitation.
    dune Noun

    a mound or ridge of loose sand that has been deposited by wind.

    		 Encyclopedic Entry: dune
    dust Noun

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

    		 Encyclopedic Entry: dust
    Dust Bowl Noun

    (1930-1940) term for the Great Plains of the U.S. and Canada when severe dust storms forced thousands of people off their farms.
    dust storm Noun

    weather pattern of wind blowing dust over large regions of land.
    earth Noun

    soil or dirt.
    economic Adjective

    having to do with money.
    ecosystem Noun

    community and interactions of living and nonliving things in an area.

    		 Encyclopedic Entry: ecosystem
    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.
    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
    floating island Noun

    a mass of soil and plants torn from a coast.
    flood Noun

    overflow of a body of water onto land.

    		 Encyclopedic Entry: flood
    fluid Noun

    material that is able to flow and change shape.
    forest Noun

    ecosystem filled with trees and underbrush.
    frequent Adjective

    often.
    frigid Adjective

    very cold.
    gabion Noun

    wire frame filled with rock.
    geological process Noun

    method by which the Earth changes.
    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
    gouge Noun

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

    water found in an aquifer.

    		 Encyclopedic Entry: groundwater
    gully erosion Noun

    removal of soil along drainage lines by surface water runoff.
    habitat Noun

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

    		 Encyclopedic Entry: habitat
    hedgerow Noun

    line of bushes and trees forming a boundary.
    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.
    hydration Noun

    process of a substance or solution chemically combining with water.
    hydrolysis Noun

    process in which a compound is split into other compounds by reacting with water.
    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
    landform Noun

    specific natural feature on the Earth's surface.

    		 Encyclopedic Entry: landform
    landscape Noun

    the geographic features of a region.

    		 Encyclopedic Entry: landscape
    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
    loess Noun

    windblown soil or silt.

    		 Encyclopedic Entry: loess
    mass wasting Noun

    downward movement of rock, soil, and other material.
    mineral Noun

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

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

    		 Encyclopedic Entry: moraine
    Northern Hemisphere Noun

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

    substance an organism needs for energy, growth, and life.

    		 Encyclopedic Entry: nutrient
    oxidation Noun

    chemical process of a substance combining with oxygen to change the substance's physical and molecular structure.
    permafrost Noun

    permanently frozen layer of the Earth's surface.

    		 Encyclopedic Entry: permafrost
    physical erosion Noun

    process of rocks and earthen materials breaking apart and being transported without changing their chemical composition.
    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.
    precipitation Noun

    all forms in which water falls to Earth from the atmosphere.

    		 Encyclopedic Entry: precipitation
    rill Noun

    very small stream.
    rill erosion Noun

    process of soil removal by water running through little streamlets, or headcuts.
    riparian buffer Noun

    area of grass, trees, or shrubs near a river bank.
    rock Noun

    natural substance composed of solid mineral matter.
    runoff Noun

    overflow of fluid from a farm or industrial factory.

    		 Encyclopedic Entry: runoff
    rust Noun

    red or orange coating that forms on the surface of iron when it is exposed to oxygen and moisture. Also called iron oxide or ferric oxide.
    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 rise Noun

    increase in the average reach of the ocean. The current sea level rise is 1.8 millimeters (.07 inch) per year.
    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
    sedimentation Noun

    process of accumulating small solid deposits.
    sheet erosion Noun

    removal of soil in thin layers by the forces of rain and stream flow.
    shelterbelt Noun

    line of bushes and trees forming a boundary.
    shrub Noun

    type of plant, smaller than a tree but having woody branches.
    snout Noun

    end of a glacier.
    soil Noun

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

    substance in which a gas, liquid, or solid is evenly distributed in another medium.
    splash erosion Noun

    soil displacement by the impact of a falling raindrop.
    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.
    tectonic activity Noun

    movement of tectonic plates resulting in geologic activity such as volcanic eruptions and earthquakes.
    tectonic uplift Noun

    movement of plates beneath the Earth's surface that causes one part of the landscape to rise higher than the surrounding area.
    temperature Noun

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

    		 Encyclopedic Entry: temperature
    thermal erosion Noun

    erosion of permafrost by the combined thermal and mechanical action of moving water.
    topography Noun

    study of the shape of the surface features of an area.
    topsoil Noun

    the most valuable, upper layer of soil, where most nutrients are found.
    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.
    valley Noun

    depression in the Earth between hills.
    valley erosion Noun

    process in which rushing streams and rivers wear away their banks, creating larger and larger valleys.
    vegetation Noun

    all the plant life of a specific place.
    velocity Noun

    measurement of the rate and direction of change in the position of an object.
    ventifact Noun

    rock that has been shaped by wind-driven sand, dust, or ice particles.
    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.
    windbreak Noun

    structure that serves to interrupt an air current or flow of wind.

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Caryl-Sue, National Geographic Society

Last Updated

March 20, 2018

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