Shaping Earth's Surface (Lori Belateche)
Title: Shaping Earth's Surface
Principle(s) Investigated: Earth materials are eroded (moved) by flowing water. Earth materials are deposited once moving water has slowed down or stopped.
2. Topography is reshaped by the weathering of rock and soil and by the erosion and deposition of sediment. As a basis for understanding this concept:
a.Students know water running downhill is the dominant process in shaping the landscape, including California’s landscape.
b.Students know rivers and streams are dynamic systems that erode, transport sediment, change course, and flood their banks in natural and recurring patterns.
Materials: Sand and clay mixed together. Stream table (you can also use long aluminum pans), rulers, plastic bowls with holes punched in the bottom, a wedge or other material to prop up one end of the stream table, water.
Procedure:
1. Mix together the sand and clay
2. Put into stream table. Move the sand/clay mixture to the end of the stream table that does not have a hole. Create a "plateau" of sand/clay. The plateau should be flat and even.
3. Put a wedge or other item under the end with the plateau so that the stream table is elevated.
4. Place a ruler across the width of the stream table about 5 cm from the elevated end.
5. Place the plastic bowl with the hole in the bottom on the ruler. Balance the bowl on the end of the steam table and the ruler. Make sure the hole in the bottom of the bowl is open and placed over the sand/clay material.
6. Fill up the bowl with water and observe the flow of water over the plateau.
7. When all the water has drained from the bowl, remove the ruler and bowl. Observe the plateau and the rest of the stream table.
8. When the teacher instructs you to do so, visit all the other stream tables to see there land surfaces.
Student prior knowledge: Students have already learned that rocks are weathered by physical and chemical processes. Now they will learn how earth materials are transported and deposited by water.
Explanation: Rocks are WEATHERED by physical and chemical processes. Weathering means to break the rocks into smaller and smaller pieces. Once rocks are weathered, they can be ERODED by water and wind.
Water always flows down hill, due to gravity. As it flows downhill, it erodes loose rocks and sediment and carries the sediment along with the water. As long as the water is flowing quickly, the water will carry the sediment. As soon as the water slows down due to a lower gradient, the sediment drops out of the water and is deposited. The larger grains of sand are deposited first with the smaller grains of silt and clay being deposited much farther down stream.
Questions & Answers:
Q. How did the plateau change once the water was flowing across its surface? A. The plateau developed a crack which widened and became a valley or a canyon.
Q. What shapes did you find in the plateau after the water had flowed across its surface? A. The shapes were V like structures -- valley or canyon shapes.
Q. What happened to the soil and rock that had been in the plateau? A. The soil and rock that had been in the plateau was transported down slope.
Q. Did all the eroded material end up in the same place? A. No, the heavier material fell out of the water first. But the lighter clay material traveled farther and some even ended up in the basin at the end of the stream table.
Q. Why did the water in the catch basin turn a different color from the initial water? What caused the color change? A. The water started out transparent. However, as the water moved over the plateau, small pieces of silt and clay were eroded. Because they are such fine earth materials, they stay suspended in the water for a longer period of time.
Applications to Everyday Life:
1. When you buy a house in a flood plain, you may experience flooding during high water volume events. You should check flood maps if you are living near a flood plain.
2. After a fire, a hillside may not have any plant life. During a rainstorm (especially heavy rain) the soil will be transported down the hill and extensive erosion can occur.
3. Farmers soil is enriched by regular flood plain deposits.
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos: There are a number of videos on youtube. However, I found this one to be very clear and concise.
This video illustrates the set up for each step.