Weathering Erosion in Glaciers: How does a river make a trench?

Purpose/Hypothesis

In this experiment you will investigate the effects that glaciers, rivers of ice, have on the landscape, such as forming trenches and moraines, arc-shaped ridges of rocky debris. Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of glaciers. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:

• the topic of the experiment
• the variable you will change
• the variable you will measure
• what you expect to happen

A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "Ice flow causes sediment erosion."

In this case, the variable you will change is the presence of an ice flow, and the variable you will measure is the movement of soil in the ice flow's path. You expect the ice flow to cause erosion.

As a control experiment, you will set up one tray of sand with no ice flow in it. That way, you can determine whether the sand moves even with no ice flow. If the sand moves under the ice flow, but not in the control tray, your hypothesis will be supported.

Level of Difficulty

Moderate.

Materials Needed

• 10 pounds (4.5 kilograms) play sand for sandboxes
• 24-inch (60-centimeter) square of window screening
• two 8 x 24-inch (20 x 61-centimeter) plastic trays (Liners for window boxes are ideal.)
• water
• freezer
• ruler
• bucket

Approximate Budget

$15.

Timetable

30 minutes to set up; 5 minutes a day to add water over a 30-day period.

Step-by-Step Instructions

1. Place the screening over the bucket and sift the sand by pouring it through the screen. Save any sand that remains on the screen. Discard any sand that goes through the screen.
2. Pour the sand that remained on the screen into both plastic trays.
3. Using the side of the ruler, smooth the surface of the sand in the trays and measure the depth of the sand. Make sure the sand is the same depth in both trays.
4. Using your finger, make a well in the sand at one end of both plastic trays.
5. Place the trays inside the freezer and prop up the ends with the well about 1 inch (2.5 centimeters).
6. Pour 0.25 cup (60 milliliters) of water into the well of one tray (the experimental tray) and close the door. The control tray will have no water—and thus no ice. Add another 0.25 cup (60 milliliters) of water to the experimental tray daily for 30 days.
7. After 30 days, record the length of the ice flow that formed in the experimental tray.
8. Carefully remove both trays from the freezer.
9. Allow the ice flow to melt 6 to 12 hours.
10. Diagram the pattern the ice caused in the sand; describe the sand pattern in the control tray.
11. Measure the depth of the sand in the trench and at the end of the ice flow in the experimental tray. Measure the sand depth at both ends of the control tray. Record your findings.

Summary of Results

Organize your data on a chart that shows the sand levels in both trays at the beginning and the end of the experiment. Compare your end results. Did the ice flow move sediment? Did erosion take place in the control tray? Write a paragraph summarizing what you found.

Change the Variables

You can change the variables in this experiment by using different soils. You might try top soil or a more rocky soil. Also, you can change the angle of the slope and see how the depth of the trench is affected. Gravity plays a large role in soil movement. The steeper the slope, the greater the pull of gravity.

Source: Experiment Central. U·X·L, 2000.