The natural movement of soil from wind and water is referred to as soil erosion.  Soil erosion has been around millions of years and it will continue to happen as long as the ground is covered with soil.  The wind and water remove soil from the earth nearly at the same rate that soil is formed, but Accelerated Soil erosion occurs it is far much more of a problem due to the soil is being removed much faster than it is being formed. 

Causes of Soil Erosion:

Water:
Soil erosion by water is usually caused by rain.  The rain can cause the soil to be move directly from the drops of water hitting the ground and moving the soil.  This process is not as critical because the “splash erosion” can only move the soil a few centimeters, inches at most, which means that most of the soil that is moved will probably distribute back out to where it was from the start.  The only exception to this is when the soil is on the side of mountains and slopes.

The other form of soil erosion from water is indirectly from the runoff of water in rills and gullies (small and large channels).  This happens when the ground has soaked up as much rain as possible and the excess will begin to run downhill due to gravity and which carried the soil downhill with it.  This is the more dominate form of soil erosion by water.

Wind:
Soil erosion by wind is generally the removal of the most fertile part of the top soil by wind.  There are roughly 70 million acres of land across the US that is affected by wind erosion.  About 10% of the land affected by wind erosion receive moderate to severe damage. 

Effects of Soil Erosion:
The effects of soil erosion take effect in two areas, on-site and off-site.

On-Site:
On-site effects are both where the soil erosion occurs and where the soil ends up.  When soil erosion occurs, the top, nutrient filled, layers are the ones that are moved which then causes the origin to be less fertile.  With the ground being less fertile, it makes it nearly impossible to grow crops/plants. The eroded soil, where the soil ends up, tends to be too fertile to allow for plant growth, which also reduces the ability for water to be held by the soil.

Off-Site:
The main off-site effect is from water erosion.  The movement of sediment and agricultural pollutants into the water courses cause dams to silt up,  the contamination of drinking water, and cause bodies of water, (lakes, rives, etc) to flood resulting in abnormal behavior of the ecosystem.