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What is Soil Erosion? - Definition and Causes

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  • 0:06 What Is Soil Erosion?
  • 1:23 Water Erosion &…
  • 2:21 Types of Water Erosion
  • 4:47 Wind Erosion
  • 5:35 Tillage
  • 6:16 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

With soil erosion, the top layer of soil is worn away due to factors such as water, wind and tillage of farmland. Learn about soil erosion and how natural elements and human activities break up and transport soil.

What Is Soil Erosion?

When things erode, they wear away due to some force acting on them. Just look at any coastline, and you will notice how the constant pounding force from wind and waves causes erosion of the rocky structures, leaving behind all kinds of interesting cliffs, caves and structures. Soil is not immune to erosion, and like rocks along a coastline, soil can erode due to the effects of forces, such as water, wind and farming practices. In this lesson, we will learn about soil erosion and the factors that cause it.

Soil is naturally created when small pieces of weathered rocks and minerals mix with organic materials from decaying plants and animals. Soil creation is a slow process, taking many years. However, the soil that is created is constantly subjected to natural and manmade forces that disrupt it.

Soil erosion is defined as the wearing away of topsoil. Topsoil is the top layer of soil and is the most fertile because it contains the most organic, nutrient-rich materials. Therefore, this is the layer that farmers want to protect for growing their crops and ranchers want to protect for growing grasses for their cattle to graze on.

Water Erosion and Surface Water Runoff

One of the main causes of soil erosion is water erosion, which is the loss of topsoil due to water. Raindrops fall directly on topsoil. The impact of the raindrops loosens the material bonding it together, allowing small fragments to detach. If the rainfall continues, water gathers on the ground, causing water flow on the land surface, known as surface water runoff. This runoff carries the detached soil materials away and deposits them elsewhere.

There are some conditions that can accentuate surface water runoff and therefore soil erosion. For example, if the land is sloped, there is a greater potential for soil erosion due to the simple fact that gravity pulls the water and soil materials down the slope. Also, water will have an easier time running across the surface, carrying topsoil with it, if the ground is already saturated due to heavy rains or the soil lacks vegetation to keep the soil in place.

Sheet Erosion

There are different types of soil erosion caused by water. Sheet erosion is erosion that occurs fairly evenly over an area. As raindrops loosen soil, the surface water runoff can transport topsoil in a uniform fashion, almost like a bed sheet sliding off of a bed. This can be so subtle that it might not even be noticed until much of the valuable, nutrient-rich topsoil has already been washed away. If a farmer heads out to his field and sees an accumulation of soil and crop residue at one end of his field, he should be worried about sheet erosion.

Rill Erosion

Rill erosion is erosion that results in small, short-lived and well-defined streams. When rainfall does not soak into the soil, it can gather on the surface and run downhill, forming small channels of water called rills. You can use this fact as a memory jogger if you remember that 'a little rill will run downhill.' A rill will dry up after the rainfall, but you may still see the stream bed that was created by the temporary stream.

Gully Erosion

Gully erosion can be thought of as advanced rill erosion. In fact, if rills are not addressed, they will grow into larger gullies. Gully erosion can spell big problems for farmers because the affected land is not able to be used for growing crops, and the big ditches create a hazard for the farmer driving his farm machinery over the fields.

Bank Erosion

Bank erosion is another type of water erosion and is defined as erosion of the bank of a stream or waterway. As you learned, surface water runoff always moves toward the lowest level due to gravity. Therefore, low-lying streams, rivers and even constructed drainage channels collect water runoff. However, over time, this water activity and other forces naturally wear down the banks lining the waterways.

Like other types of erosion, bank erosion needs to be managed. Otherwise, it can reduce productive farmland and pose a threat to the structural integrity of roads or bridges located near the waterway. This can end up causing the loss of money for farmers and big repair bills for communities. In other words, bank erosion leads to the loss of money or, in slang terms, with bank erosion, you are 'losing bank.'

Wind Erosion

Of course, water is not the only element that can lead to erosion. We also see wind erosion. Wind erosion is simply the loss of topsoil due to wind. Wind has more of a chance of eroding soil if the area does not have a lot of vegetation, which tends to lock the soil in place.

Soil that has a high sand content is also more vulnerable to wind because sand particles are not held together as tightly as other types of soil. Therefore, sand can be more easily picked up and carried by the wind. Think about the shifting sand dunes at the beach, and you will be thinking of a type of wind erosion. Small sand particles are not the only type of soil that can be eroded by wind. Given the right conditions, even large soil particles can be picked up and redistributed by the wind.

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