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Water or air that moves over a soil surface applies forces to the soil
particles on the surface. If the forces are large enough, they move the
particles. The stronger the current or wind, the more particles are put
into motion. Larger and heavier particles tend to roll or hop near the
soil surface. Finer and lighter particles are carried upward from the
soil surface. In nature, the finest particles may be carried for hundreds
or even thousands of kilometers high in the atmosphere before they fall
out!
Soil erosion is a serious problem in many areas of the world. Soil takes
thousands of years to form, but much of it can be eroded by just a few
unusually heavy rainstorms or strong winds. Bare soil surfaces are very
likely to be eroded by a sudden heavy rainstorm. The running water can
cut a channel, called a gully, in the soil surface. Once the gully is
cut, the force of the water is focused there. This deepens the channel.
One very good way to reduce soil erosion is to keep the soil surface covered
with vegetation. Another way is to plant crops in rows that follow the
contours of the land surface rather than running up and down a slope.
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