Soil erosion is the wearing away of the top layer of soil. It is a type of soil damage. This natural process happens because of the movement caused by different forces, such as water (like landslides or floods), ice (like glaciers), snow (like avalanches or snow sliding), air (like wind), plants (like trees being uprooted), and animals (including humans). Based on these forces, erosion is often grouped into types: water erosion, glacial erosion, snow erosion, wind erosion, erosion caused by animals, and erosion caused by human activities, such as farming. Soil erosion can happen slowly over time, or it can occur quickly, leading to the loss of valuable topsoil. Losing soil from farmland can reduce the size of farmland, lower crop production, harm water quality, and damage drainage systems. Soil erosion may also create sinkholes and soil tunnels that can grow into small channels and larger gullies.
Human activities have increased soil erosion worldwide by about 28 times compared to natural erosion rates. Too much erosion causes problems both where it happens and in other areas. Problems at the site of erosion include lower farming productivity and damage to natural landscapes because the top layer of soil, which is rich in nutrients, is lost. In some cases, this can lead to desert-like conditions. Problems away from the site include dirt blocking waterways, too many nutrients in water bodies, and damage to roads and homes from dirt. Water and wind erosion are the main causes of land damage; together, they affect about 84% of degraded land worldwide, making excessive erosion one of the most serious environmental issues.
Activities like farming, cutting down forests, building roads, acid rain, human-caused climate changes, and expanding cities are major human actions that increase erosion. However, there are many ways to prevent or reduce erosion of vulnerable soils.
Physical processes
If the soil is soaked, or if rain falls faster than the soil can absorb it, water flows over the ground as surface runoff. If this runoff has enough energy, it can carry loose soil particles (sediment) down a slope. Rain and the surface runoff it causes lead to four main types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. Splash erosion is usually the first and least serious stage of soil erosion. It is followed by sheet erosion, then rill erosion, and finally gully erosion, which is the most severe.
In splash erosion, the force of falling raindrops creates small craters in the soil, throwing soil particles into the air. These particles can travel up to 0.6 meters (two feet) vertically and 1.5 meters (five feet) horizontally on flat ground with no wind.
Sheet erosion happens when loose soil particles are moved by water flowing over the land.
Rill erosion refers to the formation of small, temporary water channels on slopes. These channels act as both sources and paths for soil movement. Rills are most active in disturbed upland areas where erosion is strongest. Water in rills is usually only a few centimeters (about an inch) deep, and the slope of the channel can be very steep. This makes the movement of water in rills different from water in larger, deeper river channels.
Gully erosion occurs when runoff water collects and flows quickly through narrow channels during or after heavy rain or melting snow, removing soil to a significant depth. Another cause of gully erosion is grazing, which can compact the ground. Compacted soil loses its ability to absorb water, leading to erosion in vulnerable areas.
Valley or stream erosion happens when water flows continuously along a linear feature, such as a river. This erosion deepens the valley downward and extends it backward into the hillside, creating steep banks and head cuts. In the early stages of stream erosion, the water mainly erodes vertically, forming valleys with a V-shaped cross-section and steep gradients. When the base level of the stream is reached, erosion shifts to sideways movement, widening the valley floor and creating a narrow floodplain. As the stream meanders, the gradient becomes nearly flat, and sediment is deposited along the edges. During floods, when water moves faster and carries more sediment, the most erosion occurs. In this process, water is not the only force at work—particles like pebbles and boulders carried by the water also erode surfaces through a process called traction.
Bank erosion refers to the wearing away of the sides of a stream or river. This is different from changes in the riverbed, which is called scour. To measure erosion on riverbanks, metal rods are inserted into the bank, and the position of the bank surface is marked at different times.
Thermal erosion happens when moving water melts and weakens permafrost (frozen ground). It occurs along rivers and coasts. For example, the Lena River in Siberia experiences rapid changes in its course due to thermal erosion, as parts of its banks are made of frozen, non-cohesive materials. When these weak banks collapse, large slumps form. Thermal erosion also affects Arctic coasts, where waves and warm temperatures undercut frozen cliffs, causing them to collapse. Between 1955 and 2002, erosion along a 100-kilometer (62-mile) section of the Beaufort Sea shoreline averaged 5.6 meters (18 feet) per year.
At extremely high water flows, large volumes of rushing water create spinning water currents called kolks. These cause intense local erosion, removing bedrock and forming rock-cut basins, which are similar to potholes. Examples of this can be seen in the channeled scablands of eastern Washington, created by floods from glacial Lake Missoula.
Wind erosion is a major force shaping the Earth’s surface, especially in dry and semi-dry areas. It causes land degradation, dust in the air, desertification, and damage to crops. Human activities like deforestation, farming, and building cities increase wind erosion beyond natural levels.
Wind erosion occurs in two main ways: deflation, where wind carries away loose particles, and abrasion, where surfaces are worn down by particles carried in the wind. Deflation has three types: (1) surface creep, where larger particles roll or slide along the ground; (2) saltation, where particles bounce and move short distances in the air; and (3) suspension, where tiny particles are lifted high into the air and carried far (e.g., dust from the Sahara). Saltation causes about 50–70% of wind erosion, followed by suspension (30–40%) and surface creep (5–25%). Silty soils, like loess, are most affected by wind erosion because their particles are easily moved.
Wind erosion is worse in dry areas and during droughts. For example, in the Great Plains, soil loss from wind erosion can be 6,100 times greater during drought years than in wet years.
Mass movement is the downward and outward movement of rock and soil on a slope, mainly due to gravity. It is an important part of erosion, especially in mountainous areas, where it moves weathered material to lower elevations. Other forces, like rivers and glaciers, then move this material further. Mass movement happens constantly on all slopes, some slowly and others suddenly, causing disasters. Any noticeable downslope movement is often called a landslide. Landslides can be classified based on the forces causing them and their speed. A slow form of mass movement is a scree slope, which is a pile of loose rock fragments at the base of a slope.
Slumping occurs on steep hillsides along cracks in materials like clay. Once the material starts moving, it can slide quickly downhill, forming a spoon-shaped depression. Slumping can be caused by water weakening the slope or by poor construction along roads.
Surface creep is the very slow movement of soil and rock debris by gravity, usually only noticeable over time. It can also describe the rolling of tiny soil particles (0.5 to 1.0 mm in size) along the ground by wind.
Tillage erosion happens in farmland when farming equipment moves soil. Evidence shows that tillage erosion is a major cause of soil loss in agricultural areas, sometimes more significant than erosion from
Factors affecting soil erosion
The amount and strength of rainfall are the main climate factors that influence soil erosion by water. This connection is especially strong when heavy rain falls on soil that is not protected by plants. This can happen during times when farming leaves the soil exposed or in dry areas where plants naturally grow in small numbers. Wind erosion happens when strong winds blow, especially during droughts when plants are scarce and the soil is dry and easier to move. Other climate factors, like average temperature and how much temperatures change, can also affect erosion by influencing plants and soil characteristics. In general, areas with more rainfall (especially heavy rain), more wind, or more storms are likely to have more erosion, assuming similar plants and ecosystems exist.
In some parts of the world, such as the Midwestern United States and the Amazon Rainforest, the strength of rainfall is the main factor that determines how much erosion happens. Stronger, heavier raindrops cause more erosion because they have more energy to move soil particles. The size and speed of raindrops also matter. Larger, faster raindrops push soil particles farther than smaller, slower ones.
In other regions, like western Europe, erosion happens when light, steady rain falls on soil that is already wet. In these cases, the total amount of rain, not its strength, is the main factor that determines how much erosion occurs.
Soil texture, how wet it is, and how tightly packed it is also affect how much erosion happens. Soils with more clay are harder to erode because clay helps hold soil particles together. Soils with more organic matter are also harder to erode because organic materials help soil particles stick together, making the soil stronger. The amount of water already in the soil before rain starts is important too. Wet soil cannot absorb as much water, leading to more runoff and more erosion. Soil that is packed tightly allows less water to soak in, increasing runoff and erosion.
Plants act as a barrier between the air and the soil. They help water soak into the soil, reducing runoff. They also protect soil from wind, which lowers wind erosion and improves the local climate. Plant roots hold soil together, creating a stronger structure that is less likely to erode. Removing plants increases the speed of soil erosion.
The shape of the land affects how fast water flows over the surface, which influences how much erosion happens. Long, steep slopes (especially without enough plants) are more likely to erode quickly during heavy rain than short, gentle slopes. Steeper areas are also more likely to experience landslides, mudslides, and other types of erosion caused by gravity.
Human activities that aid soil erosion
Unsustainable farming methods increase erosion rates by 10 to 100 times compared to natural erosion and exceed the rate at which new soil is created. Plowing soil, which breaks it into smaller pieces, is a major cause. Modern machinery allows deep plowing, increasing the amount of soil that can be moved by water. Other causes include growing only one crop type, farming on steep slopes, using chemicals that harm soil-binding organisms, row planting, and surface irrigation. Soil erosion can lead to uneven nutrient loss, as finer soil particles, which contain more phosphorus, are more easily carried away. This affects water systems because finer soil may hold less phosphorus than larger particles. Plowing also increases wind erosion by drying soil and breaking it into small pieces that wind can carry. Removing trees from farmland allows wind to move faster, increasing erosion. Overgrazing reduces plant cover and compacts soil, both of which worsen erosion.
In forests, mineral soil is protected by layers of leaves and organic material that cover the ground. These layers absorb rain impact and let water slowly soak into the soil instead of running off. Tree roots and fungi help hold soil together. Vegetation reduces the speed of raindrops before they hit the ground, lowering their energy. However, the forest floor, not the tree canopy, is most effective at preventing erosion. Raindrops reach their fastest speed after falling about 8 meters (26 feet). Since tree canopies are usually taller, raindrops may regain speed after hitting them. The forest floor, with its leaf litter and organic matter, still absorbs rain impact effectively.
Deforestation increases erosion by exposing soil, removing plants that hold soil together, and compacting soil from logging equipment. If the forest floor remains intact after trees are removed, erosion may be low. Severe fires can cause more erosion if heavy rain follows.
Globally, slash-and-burn farming of tropical forests is a major cause of soil loss. For example, in Madagascar’s high central plateau, much of the land is barren, with deep gullies over 50 meters (160 feet) deep and 1 kilometer (0.6 miles) wide. Shifting cultivation, which sometimes uses slash-and-burn, degrades soil fertility. There is debate about whether slash-and-burn farming with regrowing forests or permanent farming after logging causes more soil damage. Studies in Brazil show that after a few years of regrowth, erosion from slash-and-burn farming decreases, similar to natural forests. Another study found that 15 years of fallow land after slash-and-burn farming can restore soil conditions.
Human activities increase erosion by removing plants, altering water flow, and compacting soil during construction. Covering land with asphalt or concrete increases runoff and wind speeds. Runoff from cities often carries fuel, oil, and chemicals, polluting waterways and causing erosion. Increased water flow also erodes riverbanks.
Warmer temperatures may increase rainfall intensity, leading to more erosion. Rising sea levels from climate change also worsen coastal erosion. Studies suggest that more rainfall will increase erosion unless steps are taken. Erosion rates may change due to: a) changes in plant cover from shifts in plant growth; b) changes in leaf cover from altered decomposition and plant growth rates; c) changes in soil moisture affecting water infiltration and runoff; d) reduced soil organic matter making soil more erodible; e) winter rain replacing snow, which is less erosive; f) melting permafrost creating erodible soil; and g) land use changes due to climate shifts.
Studies by Pruski and Nearing suggest that a 1% increase in rainfall could lead to a 1.7% increase in erosion. Early 21st-century studies predicted a 17% increase in rainfall erosivity in the U.S., 18% in Europe, and 30–66% globally by the end of the century.
Global environmental effects
Because of how bad it is for the environment, erosion is one of the biggest environmental problems today. Water and wind erosion are the main causes of land damage. Together, they are responsible for 84% of land that has become degraded. Each year, about 75 billion tons of soil is lost from the land, which is 13–40 times faster than the natural rate of erosion. About 40% of the world’s farmland is seriously damaged. The United Nations says that every year, an area of fertile soil as large as Ukraine is lost because of drought, deforestation, and climate change. In Africa, if soil damage continues at current rates, the continent may only be able to feed 25% of its population by 2025, according to the United Nations University’s Institute for Natural Resources in Africa.
Recent studies have measured how strong rainfall is at causing erosion worldwide using detailed rainfall data collected over short time periods. A global effort created the Global Rainfall Erosivity Database (GloREDa), which includes erosion measurements from 3,625 stations in 63 countries. This database was used to create a map showing erosion rates across the world at a scale of about 1 kilometer. A study published in Nature Communications says that about 36 billion tons of soil is lost each year because of water erosion, and deforestation and other changes in how land is used make the problem worse. Scientists used high-resolution maps to study how soil erosion happens globally. This method allows researchers to include details about land use, farming areas, and how different farming practices affect erosion.
Soil erosion is a major cause of water pollution because it causes large amounts of soil to flow into rivers and lakes. This soil acts as a pollutant and carries other harmful substances, like pesticides and heavy metals. Too much sediment in water can harm aquatic ecosystems. Sediment can cover fish spawning areas, reduce their food supply, and damage their gills, making it hard for them to breathe. It also harms plants, algae, and small animals that live in water. Even though a sediment event may last only a short time, the damage to ecosystems can last for many years.
Before the 1980s, one of the worst erosion problems in the world was in China, along the middle part of the Yellow River and the upper part of the Yangtze River. The Yellow River carries over 1.6 billion tons of sediment into the ocean each year, mostly from erosion in the Loess Plateau region of northwest China.
Wind erosion can create air pollution in the form of dust. This dust often contains harmful chemicals, like pesticides or fuel, which can harm the environment and human health when they settle on the ground or are inhaled. Dust from erosion can also make the sky appear white instead of blue, causing more red sunsets. Dust events have been linked to the decline of coral reefs in the Caribbean and Florida since the 1970s. Similar dust from the Gobi Desert in Asia travels long distances and mixes with pollutants, reaching North America.
Monitoring, measuring and modelling soil erosion
Monitoring and modeling erosion helps people understand why soil erodes, predict how erosion might happen under different conditions, and plan ways to stop or fix erosion. However, erosion is complex, and many scientific fields must be studied to understand and model it, such as climate, water movement, rocks, soil, farming, and physics. This complexity makes accurate modeling difficult. Erosion models are also hard to use with numbers because they are non-linear, meaning small changes can lead to big results. This makes it hard to use data from small areas to predict erosion in large areas.
The most common model for predicting soil loss from water erosion is the Universal Soil Loss Equation (USLE), created in the 1960s and 1970s. It calculates the average yearly soil loss on small areas using factors like rainfall strength, soil type, land shape, land cover, and farming practices.
Even though the USLE was designed for small areas, it has often been used for larger areas like watersheds and continents. A major issue is that the USLE cannot predict gully erosion, which can make up 10–80% of total erosion on farmed or grazed land. This means gully erosion is not included in USLE-based studies.
Since the USLE was introduced, many other models have been developed. However, because erosion is complex, all models only roughly match real erosion rates when tested. This is why new models continue to be created. Some models still use USLE ideas, like the G2 model. Others, like the Water Erosion Prediction Project model, use fewer USLE elements, and models like RHEM do not use USLE at all. Global studies still often rely on the USLE.
For smaller areas, such as rivers, dams, or spillways, erosion models use soil properties like how easily soil erodes and the force needed to move it. These properties can be measured with tests like the hole erosion test or the jet erosion test.
Prevention and remediation
The most effective way to prevent erosion is to plant more vegetation on the land. This helps stop erosion caused by wind and water.
Terracing is a very useful method for controlling erosion. People have used this technique for thousands of years in many parts of the world. Terracing involves creating steps on sloped land to reduce soil movement.
Windbreaks, also called shelterbelts, are rows of trees and shrubs planted along the edges of farmland. These rows protect crops from strong winds. In addition to reducing wind erosion, windbreaks help crops grow better by creating more favorable conditions, provide homes for birds, help absorb carbon dioxide from the air, and improve the appearance of farmland.
Traditional farming methods, such as planting different crops together (instead of planting the same crop repeatedly) and changing the type of crop grown each year, can also reduce erosion.
Plant material left on the soil after harvesting, such as stems and leaves, helps prevent erosion when using conservation tillage methods. This material lessens the force of raindrops hitting the soil, which reduces soil breakdown.
Erosion is more likely to occur when growing potatoes compared to growing cereals or oilseed crops. Forage plants, which have many roots that spread through the soil, help prevent erosion by holding the soil in place and covering the land completely. In tropical coastal areas, mangroves have been studied for their ability to reduce erosion. Their roots help protect against storm waves and flooding, hold soil together, and slow water movement, which allows sediments to settle and reduces erosion. However, enough mangrove trees must be present to maintain a balance in sediment levels.
Agroforestry, which combines crops with trees, is a good way to reduce soil erosion. This method works well in tropical areas with heavy rainfall and in areas where the land has been badly damaged by farming. Trees help protect against wind and rain, reducing erosion caused by wind and the movement of water over the soil surface.