Impacts of Erosion

Time: Two or three fifty-minute class periods

Objectives: Students will be able to recognize areas where erosion occurs. Students will make a model of an area that has been exposed to the forces of erosion to explain what will become of eroded materials.

Purpose: The purpose of the following lessons and activities is to familiarize students with cycles of the earth's minerals and for them to realize that erosion is an ongoing process.

Materials: Student workbooks, environmentally safe paint, rulers, paper or plastic bags, rubber gloves, a digging utensil if loose soil cannot be located (outside), pencils, paper.

Procedure: Human impact on erosion is a big environmental issue. Even in the times of Washington these processes occurred. Students should realize that erosion could have affected the surveying outcomes such as boundaries (ex. rivers, creeks, and gullies). What George Washington surveyed at Popes Creek Plantation (George Washington Birthplace National Monument) is not the same landscape we see today. Potomac shoreline erosion has changed the size and shape of the landscape (fields near the tidal water). How can erosion and plants (plants, stems, and roots can hold the soil and plants can be transported by erosion) create new land? (Deltas)

The topic of how land was affected by erosion impact in earlier times is of great importance when you look at how land was surveyed. George Washington used trees as reference points or as boundaries to survey land. You should be able to understand how big of a problem this could be if the trees died, were cut down, or the whole area was clear-cut (including removing the roots of the trees in order for crops to be planted) to obtain farm land. The effects of erosion would be as follows: If an area of land is cleared of all vegetation (any plant organism), the surrounding land will change. Ask the students to hypothesize why? (Hints to them include: What do plants have? Responses should be leaves, trunks, flowers, stems and roots). Point out to the students that no matter what the plant (tree, grass, flower, or weed), they all have roots. Where do roots grow? This should lead into a discussion of how the absence of vegetation can increase erosion. Roots bind (hold) soil; stems/leaves slow the energy of rain drops and flowing water. Ask, "Are there any ways to prevent erosion?" If so, what are they? Students should be able to respond that erosion cannot be prevented because it is a natural process of the earth. However, we can slow the processes of erosion by not clear-cutting forestland and by planting vegetation in areas prone to erode like hillsides or barren soil. This discussion should take an entire class period.

Activities:

1.) Have the students conduct a small experiment that will take two days. Put students into groups of 3-4. Have each group gather the following materials that you have gotten together: any type of environmentally safe paint, rulers to measure widths and lengths of the marks you will make, pencil and paper to record the measurements. Have the students go outside to conduct this activity in two different locations. First, all groups should go to a sandy area like the corner of a sports field or playground. In an inconspicuous area mark with paint a line about ten inches long and three inches wide. Mark each group's line with their group number. Second, mark a line for each group in a nearby area on the grass. The next day return to the marks to observe any changes. The more significant changes should be in the lines on the sand (especially if it was rainy or windy). The lines should have decreased in size or disappeared. The paint on the grass should be traceable to nearly the same measurements. (To encourage erosion if nothing has changed, use a cup of water to sprinkle on the painted areas.) The main idea should be that soil with no vegetation is more likely to erode faster than soil that has roots, just as the painted areas with the roots holding the blades of grass lasted longer than the sandy area. This lesson should be conducted as a lab requiring the students to put their results in the following format: Hypothesis, Materials, Procedure, Experiment, Results, and Conclusion. Any lab write-up format that you have taught the students is acceptable, but this is necessary for them to learn to organize their information. Each student will be required to turn in an individual written report.

2.) Put students into groups of four. Assign students their own job of gathering either sand, soil, pebbles, or gravel. Take the students outside to get these items. Keep them in their groups and have them put the materials in order from least amounts of erosion to most amounts of erosion. In general, the least amount of erosion should have occurred in the largest piece of rock (the gravel) and the most amount of erosion should have occurred in the smallest piece of rock (the soil). The pebbles and sand should be in order of their size. Ask the students to tell you why the larger particles show less erosion. The response should be "because erosion is based on time; it takes longer to get something eroded to the smallest grain in your examples."

Homework: Have the students complete the "Erosion Review Student Worksheet" for homework. This can be a graded assignment.