Erosion

Erosion is the way that water, wind, and other natural forces move soil and rocks from one place to another on the Earth's surface. Unlike weathering, which breaks down rocks but doesn’t move them, erosion carries these materials away. This can happen in many ways, such as rain washing soil into rivers, rivers wearing away rock, or wind blowing sand across deserts.

Many things can cause erosion, including rainfall, rivers moving over bedrock, the action of waves along coastlines, glaciers scraping and carrying rock, and even landslides. The speed of erosion depends on the slope of the land and the weather conditions, like how much rain falls or how strong the wind is. Over time, erosion shapes the land, creating valleys, canyons, and other features we see today.

While erosion is a natural part of the environment, human activities have made it happen much faster. Farming, cutting down forests, building roads, and other changes to the land can cause soil to erode quickly. This fast erosion can harm farms, damage rivers, and lead to problems like deserts spreading. Learning about erosion helps us understand how to protect our land and keep it healthy for the future.

Physical processes

Rainfall and surface runoff

Rainfall and the water that flows over the land after rain can cause different types of soil erosion. The first and least serious type is splash erosion, where raindrops hit the soil and throw small pieces into the air. Next is sheet erosion, where thin layers of soil are carried away by flowing water. Rill erosion creates small channels in the ground as water flows over it. The most serious type is gully erosion, where deeper channels form after heavy rain or melting snow.

Rivers and streams

Rivers and streams erode the land by moving water and carrying away soil and rocks. This can create deep valleys and change the shape of the land over time. Sometimes, pieces of rock and sand can also help wear away the land as they move with the water.

Coastal erosion

Coastal erosion happens when waves and currents wear away the land along the shore. This can create cliffs, beaches, and other landforms. Sometimes, pieces of rock are broken off and carried away by the water.

Chemical erosion

Chemical erosion happens when water dissolves parts of the land, like rocks. This can create special landforms such as sinkholes.

Glaciers

Glaciers erode the land by scraping and moving rocks as they flow. This can create U-shaped valleys and leave behind piles of rocks and dirt when they melt.

Floods

Very large floods can create powerful swirling waters that erode the land quickly, forming deep holes and changing the landscape.

Wind erosion

Wind can also erode the land, especially in dry areas. It can pick up loose soil and carry it away, wearing down surfaces over time.

Mass wasting

Mass wasting is when soil and rocks move downhill due to gravity. This can happen slowly or very quickly, sometimes causing landslides.

Submarine sediment gravity flows

In the ocean, fast-moving mixtures of water and sediment can erode the sea floor, creating deep channels and canyons. These flows can also trigger underwater landslides.

Factors affecting erosion rates

Climate

The amount and intensity of precipitation is the main climatic factor that affects how soil wears away. Heavy rain, especially when the ground isn’t protected by plants, can cause more erosion. Wind can also move soil, especially when there’s little vegetation and the ground is dry. Other weather patterns, like temperature, can also play a role by affecting plants and soil.

In some places, like the mid-western US, heavy rain is the biggest cause of erosion. Bigger, faster-falling raindrops can move soil farther. In other areas, like western Europe, it’s the total amount of rain, not just how hard it falls, that matters most. Climate change may increase erosion in Europe by 13–22.5% by 2050. In Taiwan, more frequent storms have led to more soil being carried into rivers and reservoirs.

Vegetative cover

Plants help protect soil. They let water soak into the ground, reducing runoff, and shield the soil from wind. Plant roots also hold the soil together, making it harder for water or wind to move it. When plants are removed, erosion increases.

Topography

The shape of the land affects erosion. Longer, steeper slopes without enough plants can erode quickly during heavy rain. Steep areas are also more likely to experience landslides and other types of erosion.

Tectonics

Movements deep inside the Earth can change how quickly erosion happens. When parts of the land rise or fall, it changes the slope, which affects erosion rates. Erosion can also influence these movements by removing weight from the Earth’s surface, which can cause the land to rise again in some areas.

Development

Human activities like farming and building can greatly increase erosion and the movement of soil. In Taiwan, increases in soil carried by rivers match the timeline of development. The deliberate removal of soil by people is a type of erosion called lisasion.

Erosion at various scales

See also: denudation and planation

Mountain ranges can change a lot over millions of years because of erosion. It takes a very long time—more than 450 million years—for big mountain areas like the Himalaya to become flat, if the sea level does not change much. Erosion can make mountains look the same height across their tops. Some old mountain ranges, like the Timanides in Northern Russia, have been worn down a lot. Their broken pieces are now found far away, showing how long erosion has been happening.

Erosion of soil is a natural thing, but people have made it happen much faster—10 to 40 times faster than before. When soil erodes too quickly, it can hurt farms and nature. It can make it hard to grow food and can damage rivers and lakes. Both water and wind are big reasons why land can get damaged, and this is one of the biggest problems for the environment around the world. In the United States, farmers who work on land that erodes easily need to follow special plans to get help.

Consequences of human-made soil erosion

Main articles: Human impact on the environment, Environmental impact of agriculture, Soil retrogression and degradation, and Land degradation

When people harm the land, it can speed up natural soil loss. Farming, building, and other activities sometimes remove plants that hold soil in place, letting wind and water carry the soil away faster. This can make the land less fertile and harder to use for growing food or other purposes.