Activity: Erosion

Materials:

PER GROUP

Deli containters

Soil

Grass clippings

Dead twigs

Bottle with a spray nozzle

Trowel

Reusable aluminum trays (used for a couple weeks for same activity).

Procedure:

  1. Each group will need three packed deli cups of dirt. The same three containers can be used over and over. You will need to flip them upside down like a jello mold.
  2. Leave the first mound as is. This will be your area of completely deforested land.
  3. Cover the second mound with grass clippings and stick in a few (3-4) broken twigs This is an area that has been cut for timber selectively.
  4. The third pile should get twig trees stuck into it thickly like a forest, then top it with a blanket of lawn clippings in between. This is an uncut forest.
  5. Using bottle on the widest spray pattern, spray the three mounds evenly. Spray them until tiny streams of water are running down the unprotected mound. Turn off the water. (You might want to have the kids take turns spraying each mound three times and then passing it to the next kid. Examine in between.)
  6. Examine the three mounds. How did they each fare under the spray? Did the unprotected mound wash away with no vegetation to protect it? Did the timbered mound have less erosion than the unprotected mound? How did the forested mound do? Can you guess how a clear-cut forest would do in a big rainstorm?

Background:

Without human activities, losses of soil through erosion would in most areas probably be balanced by the formation of new soil. On virgin land a mantle of vegetation protects the soil. When rain falls on a surface of grass or on the leaves of trees, some of the moisture evaporates before it can reach the ground. Trees and grass serve as windbreaks, and a network of roots helps to hold the soil in place against the action of both rain and wind. Agriculture and lumbering, as well as housing, industrial development, and highway construction, however, partially or wholly destroy the protective canopy of vegetation and greatly speed up erosion of certain kinds of soils. Erosion is less severe with crops such as wheat, which cover the ground evenly, than with crops such as corn and tobacco, grown in rows.

Overgrazing, which in time can change grassland to desert, and careless cultivation have had disastrous effects in certain parts of the United States (as in theDust Bowl). Some historians believe that soil erosion has been a determinant in the complex of causes underlying various population shifts and the fall of certain civilizations. Ruins of towns and cities have been found in arid regions, such as the deserts of Mesopotamia, indicating that agriculture was once widespread in the surrounding territory.