What is the Cause of Plate Movement?
Name
Date
Purpose: To use a model to simulate the circulation in the asthenosphere that drives the movement of
lithospheric plates and to examine how uneven heating in Earth’s interior can affect patterns of
convection and plate movement.
Background: What is the cause of plate movement? When Alfred Wegener proposed the idea of
continental drift, he could not explain a viable mechanism for movement of the continents. Most
geologists now believe that the key to plate movement is in the asthenosphere. Temperature and pressure
increase with depth in Earth’s interior. Heat from Earth’s core is transferred outward through the mantle.
The plastic rock in the asthenosphere is unevenly heated,
creating temperature and density differences. Energy
transfer in the asthenosphere occurs by convection.
Heated material is less dense than surrounding cooler
material, so it rises. As it reaches the bottom of the
lithosphere, it spreads laterally away from the area of
upwelling area and slowly cools and become denser,
sinking back into the mantle. The brittle lithospheric
plates are carried along for the ride, interacting with other
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plates along their boundaries.
Procedure – Read and follow the procedure carefully! Do not skip steps.
Materials: 6 Styrofoam cups, plastic box, plastic dropper, food coloring solution, spoon, Styrofoam plate
fragments, white paper
Trial 1 – The Control
1. Fill the box to about an inch below the top with cold tap water. Set the box on the stand made of
inverted cups. Move the cups so they are as close to the corners of the box as possible. Adjust the
cups as needed to keep the box stable. BE CAREFUL NOT TO SHAKE THE BOX.
2. Use the dropper to dispense a small amount of food coloring under water at the bottom of the water
near the middle of the container. DO NOT USE TOO MUCH FOOD COLORING in any step – you
can always add more if you need it. Carefully remove the dropper.
3. Observe what happens to the colored water for about two minutes. Does the coloring move a lot or
very little? Does it move in a pattern or in random fashion? Does it rise or sink in any predictable
manner? View the box from the TOP and SIDE. Hold a sheet of white paper behind the box to see
what is happening inside the box more clearly.
4. Record observations on the attached Data Sheet. Draw sketches of TOP and SIDE views to show
what happens to the colored water. USE ARROWS to show the direction(s) of movement. Describe
your observations in words in the space provided.
5. Use the spoon to swirl the water in the box to disperse the food coloring. If there is too much color in
the water, change the water before the next trial.
Trial 2 – Central Heat Source
6. Fill one empty cup with hot water from the coffee urn.
7. Carefully slide the cup of hot water beneath the middle of the box as close to the center as possible.
8. Add several drops of food coloring to the bottom of the water in the box directly above the cup of hot
water.
9. Observe the movement of the colored water for about five minutes. If the coloring disperses rapidly,
add more so you can make detailed observations. DO NOT RUSH THROUGH THIS STEP. TAKE
THE TIME TO WATCH THE DEVELOPMENT OF A FULL CYCLE OF MOVEMENT. Does the
coloring move a lot or very little? Does it move in a pattern or in random fashion? Does it rise or
sink in any predictable manner? View the box from the TOP and SIDE.
10. Sketch top and side views and describe your observations. Include arrows in the sketches to show
direction(s) of movement.
11. Use the spoon to swirl the water to disperse the food coloring. If there is too much color in the water,
change the water before the next trial. Save the cup of hot water for the next trial.
Trial 3 – Two Heat Sources
12. Fill the second cup with hot water from the coffee urn. Slide the first cup towards the right side of the
box, close to the supporting cups. Place the second cup beneath the left side of the box, as far from
the first cup as possible.
13. Add several drops of food coloring near the bottom of the box directly above BOTH cups of hot
water. Add a couple of drops of coloring near the middle of the box, as far from the heat sources as
possible.
14. Observe the movement of the colored water about five minutes, long enough to watch at least one
full cycle of movement. Adding more coloring as needed. Does the coloring move a lot or very
little? Does it move in a pattern or in random fashion? Does it rise or sink in any predictable
manner? View the box from the TOP and SIDE.
*DO NOT SKIP THE NEXT STEP.
15.Carefully place the pieces of Styrofoam on the surface of the water. Observe what happens. You need
to be patient with this step. Remember, this is an EXPERIMENT. Sometimes it works and
sometimes it does not! 
16. Sketch top and side views, using arrows to show movement, and describe your observations.
17. Remove the Styrofoam pieces. Use the spoon to swirl the water to disperse the food coloring. If
there is too much color in the water, change the water before the next trial. Save the hot water for the
next trial.
Trial 4 – Your Own Design
18. Design a new set up for the experiment. You might change the locations of heat sources, change the
numbers of heat sources, or change the water temperatures involved.
19. Describe your plan.
20. Predict what will happen.
21. Perform the experiment. Observe for several minutes. Sketch and describe the results.
Clean Up
22. Empty the water from the box into a sink and rinse the inside of the box. Place it back on the stand.
23. Empty the hot water from the cups into a sink. DO NOT NEST THE WET CUPS TOGETHER –
leave them separate so they can dry.
24. Dry any spilled water or food coloring at your station.
25. Place any used paper towels in the trash.
DATA SHEET
TRIAL 1 – Top View
Diagram
TRIAL 1 – Side View
Diagram
Trial 1 – Description of Results
TRIAL 2 – Top View
Diagram
TRIAL 2 – Side View
Diagram
Trial 2 – Description of Results
TRIAL 3 – Top View
Diagram
TRIAL 3 – Side View
Diagram
Trial 3 – Description of Results
TRIAL 4 – Top View
Diagram
TRIAL 4 – Side View
Diagram
Trial 4 – Description of Results
Analysis of Results – Answer in complete sentences.
1. In this activity, you examined potential causes of movement in Earth’s mantle, which in turn cause
plate movement. What variable was tested in the different trials of the lab?
2. Review the results of the different trials. Compare and contrast the movement of the colored water in
Trial 1 (the control) with the results of Trials 2 and 3. Explain why it was important to perform a
control.
3. Describe the patterns of movement of the colored water in Trials 2 and 3 relative to the locations of
the heat sources. How did the addition of heat influence the movement of the colored water? Where
did the colored water rise? Where did it sink?
4. EXPLAIN the movement of the colored water in terms of changes in density. (WHY does heated
water rise and cooler water sink?) Be specific and detailed.
5. In terms of plate movement, what types of plate boundaries are represented by each of the following:
(a) the areas directly above heat sources and (b) the areas away from or between heat sources?
Explain your reasoning.
6. In this model, what part of Earth is represented by each of the following: (a) water in the box,
(b) cup(s) of hot water, and (c) pieces of Styrofoam? Explain your reasoning for each.
7. Suggest a material besides Styrofoam that could be used in the model to represent lithospheric plates.
Explain why it would be a good analogy for the lithosphere.
Conclusion – On a separate piece of paper, write a two-paragraph summary about the cause of plate
movement. In the first paragraph, describe the process of convection and its relationship to temperature
and density. Why does uneven heating make matter move in circular patterns? Relate this to convection
in the asthenosphere and explain how it can cause movement of overlying lithosphere. What tectonic
features form at the surface where underlying convection cells rise and sink? What is the source of heat
in Earth’s interior? READ SECTION 10-2, especially the last three pages, in your textbook. What other
mechanisms influence plate movement? In the second paragraph, describe how well this model illustrates
the driving mechanism of plate tectonics. What are the strengths of this model? What are its limitations?
How would you improve the model? What questions do you still have about plate tectonics?