Earth Science: Geology, the Environment, and the Universe

Chapter 7: Weathering, Erosion, and Soil

Problem of the Week

Where Has All the Soil Gone?

Erosion by water and wind are naturally occurring processes that have formed many of the natural wonders that we treasure and seek to preserve in our national parks. Erosion by water was the sole creator of the Grand Canyon and the intricately beautiful landscape called the Badlands National Park in South Dakota. Winds have carried tons and tons of sand to create the area we call Great Sand Dunes National Park in Colorado and it has sculpted many of the desert monuments in Monument Valley throughout Utah and Arizona.

These wonders of nature are treasures to humans. Yet the word erosion often carries with it a negative connotation, doesn’t it? When we think of erosion we think of beach erosion and soil erosion, two processes that humans fight to prevent with various methods, some more successful than others.

Soil formation, as you know, is a slow process. "Soil-making processes are notoriously slow, requiring from 200 to 1,000 years to form 2.5 centimeters of topsoil under normal agricultural conditions." And due to various activities of humans and "depending on the region, topsoil is currently being lost 16 to 300 times faster than it can be replaced." This is a dismal set of statistics to be sure, but there are efforts taking place to conserve soil through various means. No one soil conservation management system works in every area due to differences in soil type, topography, type of farming operation, and climate. Conservation practices, which reduce wind speed, reduce rate and amount of water movement, and/or increase soil organic matter levels, continue to spread worldwide, giving soil a chance to remain where it is and to remain fertile.

With this in mind take a look at the map below to see how our country fares in the area of wind and soil erosion:

First lets look at what this map shows:

  • Estimated water and wind erosion on cropland or agricultural land only.
  • The gray areas are Federal lands and are not included in the data though erosion is happening on those lands as well.
  • Each blue dot represents 200,000 tons of average annual erosion due to water (1,068 million tons per year).
  • Each red dot represents 200,000 tons of average annual erosion due to wind (840.5million tons per year).

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Problem:

  • Locate the region of the country that you live in. How would you describe the soil erosion problems in your area based on this map?

  • What pattern do you note for the relationship between water erosion and river watershed areas?

  • In what areas of the country is wind erosion common? Are there any patterns discernable here?

Think About This:

Looking at the water erosion areas and their relationship to rivers:

  • Where does all of this soil go?

    • Does it make it to the oceans?

    • If it does, what landforms are created at the mouths of rivers as the stream flow decreases and the soil carried by the water is deposited there?

    • Why are these areas so fertile?

Another thought:

Much of the East Coast of the United States has beach erosion problems. Normally this sediment reaches the coast and provides sand for beaches. However, today, this natural flow of sediment has been interrupted or halted in many areas.

  • What factors may cause the disruption of sediment reaching the coasts?

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