Catastrophic Events

Part II

Lesson 15: Investigating Plate Movement and Faults

FQ: How does plate movement affect landforms?

Learning Targets:

  • I understand scientists and engineers construct models to help them understand how complex systems behave.
  • I understand lithospheric plates on the surface of the earth slide past one another, collide, and separate at a rate of 2 to 20 cm per year.
  • I understand landforms-mid-ocean ridges, trenches, and mountains-form as a result of plate movement.
  • I understand rock responds to the forces caused by plate movement by either folding (bending) or fracturing (breaking).
  • I understand faults are fractures in the earth’s crust and upper mantle along which measurable movement of rock has occurred.
  • I understand earthquakes occur along faults and are common along plate boundaries.

Student Objectives:

  • Describe what a model is and distinguish models from real objects or events.
  • Use models to simulate the movement of Lithospheric plates as they collide, separate, and slide past one another.
  • Use a globe and a map to find evidence of plate movement and to identify landforms- such as mid-ocean ridges, mountains, and trenches- that result from plate movement.
  • Classify materials as either brittle or ductile.
  • Investigate the effects of applying a force to a model of a fault.

Getting Started:

  1. Look at the wall map called “Earth’s Fractured Surface” with your class. How is this map different from others you have seen? How is it the same?
  2. Review your homework (Student Sheet 14.1) from Lesson 14 with your teacher. You may be asked to plot a volcano data point on the wall map. Describe any patterns you notice in the location of volcanoes and earthquakes.
  3. Look at the plates shown on the map. Describe any relationship you see between the locations of earthquakes and volcanoes on the earth and the boundaries, or outer edges, of plates. What ideas do you have to explain this relationship?
  4. View the CD-ROM, The Theory of Plate Tectonics. How do plates move? How does plate movement cause earthquakes, volcanoes, mountains, and trenches? Discuss your observations with your class.
  5. Discuss what you know about models with your class.
  6. Look at the models you will use in this lesson. Which kind of plate boundary do you think you will model with each one? Discuss with your class why and how models are used in the science classroom.
  7. Pick up one copy of Student Sheet 15.1: Plotting Earthquakes by Depth. You will complete the first section of it for homework. You will finish the questions after you complete Inquiries 15.1 and 15.2.

Inquiry 15.1: Using a Simple Model of Plate Movement

  1. In your group, examine the foam pads. Describe their properties. Consider density, appearance, thickness, weight, and size. Record your group’s ideas in your science notebook.
  2. Predict how you think each pad would respond if you did the following:
  3. Pulled on the pad from opposite ends.
  4. Pushed on the pad at opposite ends toward the center.
  5. Slid two pads past one another.
  6. Collided two pads by pushing them together.

Discuss your predictions with your group.

  1. Test your predictions. Pull on one pad. What happens to its appearance? What happens to its volume and size? In your notebook, draw a picture of what happens to the pad.
  2. Hold one foam pad by its opposite ends, as shown in Figure 15.1. Compress the pad by pushing your hands toward each other. In your notebook, draw a picture of what happens to the pad. Repeat this process with the other type of pad. Now try stacking the pads on top of each other. Compress them. What do you observe? Record your results.
  3. Place two pads of the same thickness side by side on the desk or table. Slide them past one another, as shown in Figure 15.2. Record your observations in your notebook. Now try this with one thick and one thin pad. Did your results change?
  4. Now work over a 10-cm opening between two desks or thick books. Place two thick pads side by side. Make the pads collide (push them together), as shown in Figure 15.3(A). What happens?
  5. Place one thick and one thin pad side by side and make them collide. Again, work over a 10-cm opening between two desks or books if possible, as shown in Figure 15.3(B). With your group, discuss what happens. How does the behavior of the pads differ from their behavior in procedure Step 6? Why do you think this happens? Record your ideas and drawings in your notebook.
  6. If possible, examine a relief globe. Look for evidence of trenches and mountains. Then discuss with your group how you think they formed. (Think about the behavior of your pads and what you learned about plate movement from the CD-ROM.)
  7. Clean up. Prepare your station for the next group.

Reflecting on What You’ve Done:

  1. Answer these questions in your notebook.
  2. How did the pads behave when pulled from opposite ends?
  3. How did the pads behave when compressed?
  4. If oceanic plates are colder, denser, and thinner than continental plates are, which pad do you think represented oceanic plates? Which pad represented continental plates?
  5. How did the density of the pads affect the way they behaved when you made them collide?
  6. When do colliding plates on the earth form mountains?
  7. When do colliding plates on the earth form mountains?
  8. Why would a more dense oceanic plate slide under a less dense continental plate?
  9. Can plates ever move without forming new land? If so, when?
  10. How do you think colliding plates on the earth cause earthquakes?
  1. Read “Colliding, Sliding, and Separating Plates.”

Inquiry 15.2: Using the Moving Plates Model

  1. Set up your Moving Plates Model as shown in Figure 15.4. Make certain the belts on top of the lid are black, with red just about to emerge from the slit in the center.
  2. Have one member of your group hold both knobs. Try to move the knobs in opposite directions at the same time. What happens?
  3. Reset your Moving Plates Model by turning the knobs so that only black belts show on top and red belts are directly below the slit. Very slowly, turn the knobs so that both belts move away from the slit in the center. How are the belts changing on either side of the center slit? What happens to the black belts as they get near the edges of the lid? Discuss your answer with your group.
  4. Flatten out the dough. Make it as think as possible. Place the continent stencil on the top of the flattened dough. Outline each continent-North America, Africa, and South America-in the dough using a sharp toothpick. Remove the dough continents. What observations can you make about their shapes? Look on a map and discuss with your group what landforms exist on these continents and why you think they are there.
  5. Reset the belts again. Place two of the three continents over the center slit. Try different combinations. Which continents seem to fit well together? Why do you think this is so? Discuss these questions with your group.
  6. Place South America and Africa together like puzzle pieces on the black belts and over the center slit, as shown in Figure 15.5. Slowly turn the knobs so that the continents move away from one another. Move the clay models slightly, about 8 cm. This represents movement of the continents over millions of years.
  7. Look at your Catastrophic Events World Map. What patterns do you observe in the shapes of the continents and the shape of the ridge in the center of the Atlantic Ocean? What do you think is responsible for these patterns? How do you think the Atlantic Ocean formed? Discuss your observations with your group.
  8. Place North America and Africa on the outer ends of the belts, as shown in Figure 15.6. Pinch the outer edges of the continents onto the belt to secure them. Now you will go back in geological history. Turn the knobs so that the continents move inward, toward the center slit. What happens as the continents collide?
  9. On your Catastrophic Events World Map, look at North America’s eastern states. What landforms do you notice there? What process do you think might have been responsible for forming the mountain range there (called the Appalachian Mountains)?
  10. Look at the relief globe. Do the following with your group, and discuss the answers to the questions as you work:
  11. Feel the globe. What do you observe? How is it different from other globes you have used?
  12. Where on the earth do you see evidence that plates collided in the past? What evidence do you have that plates may have collided there? (Answer the next question only if you have already completed Inquiry 15.1.) Do you think those plates were continental, oceanic, or both? Why?
  13. Where on the globe do you think plates are separating? Find evidence of this both within continents and under the ocean.
  14. Find Japan and the Japan Trench. Feel these areas on the relief globe. What do you observe about these areas? What do you think is happening to the two plates that meet at this trench?
  15. Find the middle of the Atlantic Ocean, called the Mid-Atlantic Ridge. Feel this ride on the relief globe. What do you observe about this landform? What do you think is happening to the two plates located along the Mid-Atlantic Ridge? Why do you think this ridge is higher than the rest of the ocean floor?
  16. Are there other places on the globe similar to the Japan Trench and the Mid-Atlantic ridge?
  1. Clean up. Remove any dough that may be stuck to the belts of the Moving Plates Model. Roll the dough back into a ball.

Reflecting on What You’ve Done:

  1. Apply what you observed in this inquiry to the earth’s plate boundaries. Answer these questions in your notebook:
  2. How do you think the Moving Plates Model shows what happens on the earth when two plates separate?
  3. What causes the ocean floor to separate and “grow”?
  4. Think about what happened to the black belt as it reached the edges of the model’s lid. What landform is created when the ocean floor sinks back into the earth?
  5. What patterns did you observe in the shapes of Africa and South America? How did the shapes of these continents compare with the shape of the Mid-Atlantic Ridge?
  6. What landform is created when two continental plates collide? Give an example.
  1. Share your observations with the class.
  2. With your class, look at the “Earth’s Fractured Surface” plate boundaries map. Why do you think there are mountains north of India?

Inquiry 15.3: Investigating Faults with Models

Getting Started:

  1. With your class, discuss what happens to rock when plates move.
  2. Predict what would happen if you applied a force to a stick at both ends. Watch as your teacher tests your predictions.
  3. Collect a set of brittle and ductile materials for your group. Observe their properties. Then classify each item as brittle, (breaks when a force is applied to it), ductile (bends, stretches, or flows when a force is applied), or both. Record your group’s classifications in your notebook using either a list or Venn diagram. What other items could you put in these categories? List them.
  4. Discuss your group’s classifications and reasons for choosing each with the class. Answer the following:
  5. Which materials were brittle? Which were ductile? Why did you classify them this way?
  6. How did you apply force to each object? How did each object respond to that force?
  7. Did temperature and pressure affect the behavior of your objects? If so, how?
  8. On the basis of these observations, what do you think are the conditions that affect how an object responds to a force?
  9. The objects that you investigated respond to force; similarly, rocks that make up plates respond to force-the force caused by plate movement. Examine the picture of the rock shown in Figure 15.7. How do you think it became folded? Share your observations with the class.
  10. Apply what you learned about brittle and ductile objects to rock on the earth. Discuss these questions with your class.
  11. In what part of the earth might rocks be more brittle and fracture more easily?
  12. How do you think the ability of the rocks to fracture relates to earthquakes?

Procedure:

  1. Discuss with your group what you already know about faults. What questions do you have about faults? Record your group’s ideas in two lists in your notebook. Title the lists. Share your ideas with the class.
  2. Look at the Fault Laboratory. You will use this model to investigate movement along a fault where blocks of rock slide past one another. What do you think will happen when a force is applied to the blocks? Discuss your hypothesis with the class.
  3. Read “Earthquake and Faults, on pages 182-183.
  4. Review Steps 8 through 15 of the Procedure with your teacher.
  5. Collect one copy of Student Sheet 15.3a for your group. Work with your group to design an experiment that demonstrates how frictional resistance along a fault affects how rock moves during an earthquake. Record the materials and procedure you will use, how you will control all variables except the one you are testing, what you will look for, and what you will measure.
  6. Share your experimental design with the class.
  7. Discuss with the class how you will record your data. If you graph your data, how will you graph it? Use Student Sheet 15.3b as one way of recording and analyzing the data you will collect as you experiment with the blocks. Note that you will conduct trials with no Velcro strips and with one, two, and three strips.
  8. Collect your materials. Use Figure 15.8 to set up your Fault Laboratory. Make sure that your fault Laboratory is assembled correctly by checking each of the following steps:
  9. Carefully place the block with the hole so that the long strip of soft, looped Velcro is facing the “fault.” Use the bolt, washers, and wing nut to fix, or secure, the block with the hole to the plastic box.
  10. Notice how each side of the block has a different number of strips of “hooked” Velcro. For each test, you will rotate the block so there is more booked Velcro (or frictional resistance) between the two blocks.
  11. Slide the solid block (with no hole) in place next to the fixed block. Make certain the soft loop Velcro on both blocks is touching and secure. Use one to two tongue depressors as spacers between the plastic box and the solid, unfixed block only if the blocks are loose. This will push the blocks together.
  12. Make a loop or tightly knot the cord to the hood on the solid, unfixed block.
  13. Thread the cord through the hole opposite the hook.
  14. Use a loop or tightly knot the cord to the spring scale.
  15. Experiment freely with the unfixed block. How does the block move when you pull it? Try putting masking tape across the boundary, or “fault,” where the two blocks meet. Pull on the block again. What happens to the tape that indicates stress is building along the fault? Reset the blocks. Place houses (plastic centimeter cubes) on the blocks along the fault. Pull on the block again.
  16. Remove the tape and houses. Put them aside for now. Collect and analyze data to find out how the amount of frictional resistance along a fault affects the way it ruptures. Follow your plan on Student Sheet 15.3a and Procedure Steps 11 through 15 as you work.
  17. Pull on the spring scale, which will apply a sliding force to the unfixed block. How much force do you have to apply to the block before the fault ruptures (that is, before the block move abruptly)? Record the maximum force in your data table under “0,” since you are not using any hooked Velcro on the blocks, and there is very little frictional resistance along your fault. Conduct three trials.
  18. Now rotate the unfixed block so there is one strip of hooked Velcro along the fault. Repeat Procedure Step 11. Conduct three trials. Record your force data each time under “1” on Table 1 on Student Sheet 15.3b.
  19. Now repeat these procedures with two strips of hooked Velcro, recording data under “2” in Table 1 as you do.
  20. Finally, rotate the block again and test the force using three strips of hooked Velcro. Record your data under “3” in Table 1. Place houses (plastic centimeter cubes) on the blocks. What happens to the houses during an “earthquake”?
  21. Finish Student Sheet 15.3b and the last box on Student Sheet 15.3a.
  22. Clean up.

Reflecting on What You’ve Done: