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 ErosionThe 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 erosionPhysical 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 erosionChemical 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 WaterLiquid 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).• 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. For example, 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 WindWind 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 IceIce, 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 modern 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, for example. 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 ErosionThermal 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 ErosionSome 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 to 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 other 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 to 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 PeopleDeposition, Soils, and SedimentsEroded 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 blown into and suspended in its water. The fertile lands around the Yellow River have been among China’s most productive for thousands of years.Erosion ControlErosion 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.
The sun itself is actually an instrument of erosion! As rocks heat up, they expand. Expanding rocks can sometimes crack and crumble away.Eroding AnimalsBurrowing animals, such as beetles and worms, contribute to erosion by displacing soil.
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.
Term Part of Speech Definition Encyclopedic Entry accumulation Noun
a buildup of something.
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.
the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).
Encyclopedic Entry: agriculture array 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.
a dip or depression in the surface of the land or ocean floor.
Encyclopedic Entry: basin batter Verb
to beat and cause damage.
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.
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.
underground chamber that opens to the surface. Cave entrances can be on land or in water.
a soft mineral. Also called limestone and calcium carbonate.
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.
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.
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.
outer boundary of a shore.
deep crack, especially in a glacier.
Encyclopedic Entry: crevasse crevice Noun
crack in a rock.
Encyclopedic Entry: crop cumulative Adjective
growing in quantity or strength.
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.
area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.
Encyclopedic Entry: desert desert varnish Noun
dark, hard layer of yellowish or blackish oxides formed on exposed rock surfaces in windblown, arid regions.
individual or distinct.
to fall apart and disappear.
to break up or disintegrate.
to break up or disintegrate.
period of greatly reduced precipitation.
Encyclopedic Entry: drought dry season Noun
time of year with little precipitation.
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.
soil or dirt.
having to do with money.
community and interactions of living and nonliving things in an area.
Encyclopedic Entry: ecosystem endanger Verb
to put at risk.
person who plans the building of things, such as structures (construction engineer) or substances (chemical engineer).
to wear away.
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.
person who cultivates land and raises crops.
able to produce crops or sustain agriculture.
industry or occupation of harvesting fish, either in the wild or through aquaculture.
long, narrow ocean inlet between steep slopes.
Encyclopedic Entry: fjord floating island Noun
a mass of soil and plants torn from a coast.
overflow of a body of water onto land.
Encyclopedic Entry: flood flood plain Noun
flat area alongside a stream or river that is subject to flooding.
Encyclopedic Entry: flood plain fluid Noun
material that is able to flow and change shape.
ecosystem filled with trees and underbrush.
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.
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.
water found in an aquifer.
Encyclopedic Entry: groundwater gully erosion Noun
removal of soil along drainage lines by surface water runoff.
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.
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.
process of a substance or solution chemically combining with water.
process in which a compound is split into other compounds by reacting with water.
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.
small indentation in a shoreline.
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.
inorganic material that has a characteristic chemical composition and specific crystal structure.
material, such as earth, sand, and gravel, transported by a glacier.
Encyclopedic Entry: moraine natural hazard Noun
event in the physical environment that is destructive to human activity.
Northern Hemisphere Noun
half of the Earth between the North Pole and the Equator.
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.
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.
to make smooth and shiny by rubbing.
all forms in which water falls to Earth from the atmosphere.
Encyclopedic Entry: precipitation prone Adjective
vulnerable or tending to act in a certain way.
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.
natural substance composed of solid mineral matter.
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.
small, loose grains of disintegrated rocks.
sand dune Noun
mound of sand created by the wind.
region and name for some countries in Northern Europe: Iceland, Norway, Sweden, Finland, and Denmark.
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.
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.
line of bushes and trees forming a boundary.
type of plant, smaller than a tree but having woody branches.
end of a glacier.
top layer of the Earth's surface where plants can grow.
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.
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.
waves as they break on the shore or reef.
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.
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.
study of the shape of the surface features of an area.
the most valuable, upper layer of soil, where most nutrients are found.
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.
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.
all the plant life of a specific place.
measurement of the rate and direction of change in the position of an object.
rock that has been shaped by wind-driven sand, dust, or ice particles.
chemical compound that is necessary for all forms of life.
moving swell on the surface of water.
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.
structure that serves to interrupt an air current or flow of wind.