Erosion Notes
Parent Material- The material from which soil is made. Parent material can be classified as either residual or
transported:
Residual soils- soils that have formed in their present location from the bedrock beneath.
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Bedrock – The solid rock beneath the soil.
Example – Sandstone soils form from sandstone bedrock producing dry coarse soil. (mountain ridges)
Examples – Limestone soils come from limestone bedrock producing soil good for farming. (Lancaster)
Transported soils- soils that have be moved from their original location.
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Glacial till- rocks and soils moved by glaciers
Aeolian- soil moved by wind
Colluvial- fallen rocks and soil along cliffs and slopes
Alluvial- soil moved by water (flooded stream banks)
What is Erosion?
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The movement of soil by wind or water to some new location.
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Naturally a slow process but speeds up quickly when it is exposed)
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Billions of tons of exposed topsoil are lost each year to erosion
Erosion History
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The invention of the plow greatly increased the amount of erosion by exposing large areas of farmland
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Early colonists would grow one crop (monoculture) in the same place every year until the nutrients
were used up and then they would move on leaving exposed soil behind.
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Colonists moved west to the great plains where the soil was rich in organic matter.
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Farmland increased rapidly and by the 1930’s giant dust clouds of soil blew across the county due to dry
exposed soil. (dust bowl)
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The government created the Soil conservation Service (SCS) (now the NRCS) within the Dept. of
Agriculture to conserve the nation’s soils.
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The NRCS maps and surveys soil to plan methods of soil conservation.
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Modern technology has allowed the U.S. to increase its production allowing it to produce more food
than needed.
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In the 70’s the U.S. started growing grains for other countries adding to the erosion problem (dust
storms in CA.)
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Many conservation practices are still ignored when using large machinery because many practices are
more difficult to do on a large scale.
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Besides farming, highway construction, building construction, overgrazing and some logging
activities all increase the rate of erosion
Types of erosion
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Rill erosion– occurs on gentle slopes of exposed soil. Water creates small channels a few inches deep.
It may turn into gully erosion on steeper slopes.
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Gully erosion– Occurs on steep slopes. Fast moving water cuts deep ditches into the soil that can
change the landscape.
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Sheet erosion– gradual removal of topsoil by wind or water. Occurs in thin layers on very gentle to
non-sloping exposed soils. It can be seen by blowing dust and muddy water.
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Mass erosion– Large movements of soil due to gravity (landslide in California)