Tectonics Model

Introduction

This model will allow for the rapid demonstration of geological processes that shape the Earth! Easily demonstrate the concepts of folds, faults, rifts and compression.

Concepts

• Tectonics
• Faults
• Rifts
• Folds
• Compression
• Earth forces

Materials

Safety Precautions

Wash hands thoroughly with soap and water before leaving the classroom. Follow all laboratory safety guidelines.

Procedure

Part I. Compression—Fold and Reverse Fault Formation

1. Obtain the tectonics container, the long push handle, L-shaped plastic plate, square plate, one short push handle, four washers, two weld nuts, a bag of green and a bag of yellow sand.
2. Place two washers over the shaft of a weld nut. Place the square plate over the weld nut shaft (see Figure 1).
   {12618_Procedure_Figure_1}
3. Assemble a sand tamper by screwing the short push handle into the square plate (see Figure 1).
4. Place the large plastic plate into the tectonics container (see Figure 2).
   {12618_Procedure_Figure_2}
5. Place two washers over the shaft of a weld nut. Place the shaft of the weld nut into the hole on the inside of the L-shaped plate. Push the long push handle through the hole on the side of the tectonics container and screw the handle into the weld nut (see Figure 3).
   {12618_Procedure_Figure_3}
6. Slide the L-shaped plastic plate until it is approximately 4" from the far edge of the tectonics container. Place a piece of tape over the hole at the opposite end of the container.
7. Place a ¼" to ½" layer of yellow sand in the bottom of the tectonics container. Pat the layer flat with the tamper (see Figure 4).
   {12618_Procedure_Figure_4}
8. Place a ¼" to ½" green layer of sand on top of the yellow layer of sand. Pat the sand flat with the tamper once again.
9. Repeat steps 7 and 8 two more times. There should be a total of 6 layers (3 yellow, 3 green) in the tectonics container.
10. Have students draw the layers of sand seen in the tectonics model on the Tectonics Worksheet.
11. Slowly push the handle of the large plastic plate to start the compression of the sand layers (see Figure 5).
    {12618_Procedure_Figure_5}
12. Once the plate has been pushed approximately 1½" have the students draw the resulting configuration of the sand on the Tectonics Worksheet (see Figure 6).
    {12618_Procedure_Figure_6}
13. Push the large plastic plate an additional 1½". Have students draw the resulting configuration of the sand on the Tectonics Worksheet (see Figure 7).
    {12618_Procedure_Figure_7}
14. Have the students answer the questions for Part I of the Tectonics Worksheet.
15. Save the resulting model for Part II.

Part II. Erosion and Peneplain Formation

1. Using a teaspoon, create a cut through the sand as shown in Figure 8. This cut represents erosion from a river or stream channel. Have students draw the resulting channel in the Tectonics Worksheet.
   {12618_Procedure_Figure_8}
2. Using the teaspoon, carefully remove sand evenly from across the model until the level of the sand is once again flat (see Figure 9). This current model of the sand represents a peneplain (see the Discussion section for further information). Have students observe and draw the peneplain in the Tectonics Worksheet.
   {12618_Procedure_Figure_9}
3. Have the students answer the questions for Part II on the Tectonics Worksheet.
4. Empty the sand from the tectonics container. Rinse with water, if desired.

Part III. Divergence and Rift Valley Formation

1. Obtain two L-shaped plates, the assembled tamper, two long push handles, the empty tectonics container, a bag of green and a bag yellow sand.
2. Assemble the L-shaped plates using the long push rods as described in step 5 of Part I.
3. Place both of the L-shaped plates in the tectonics container (see Figure 10).
   {12618_Procedure_Figure_10}
4. Push the L-shaped plates together so they touch (see Figure 11).
   {12618_Procedure_Figure_11}
5. Place a ¼" to ½" layer of yellow sand in the bottom of the tectonics container. Pat the layer flat with the tamper.
6. Place a ¼" to ½" green layer of sand on top of the yellow layer of sand. Pat the sand flat with the tamper once again.
7. Repeat steps 6 and 7 two more times. There should be a total of 6 layers of sand (3 yellow, 3 green).
8. Have students draw the layers of sand seen in the tectonics model on the Tectonics Worksheet.
9. Slowly start to pull the two L-shaped plates away from each other. Stop moving the plates every inch or so and have students observe and draw the formation of the resulting rift valley (see Figure 12).
   {12618_Procedure_Figure_12}
10. Continue pulling the L-shaped plates until they come in contact with the outer walls of the tectonic container. Have students sketch the final appearance of the rift valley on the Tectonics Worksheet (see Figure 13).
    {12618_Procedure_Figure_13}
11. Have students answer the questions for Part III on the Tectonics Worksheet.

Student Worksheet PDF

12618_Student1.pdf

Teacher Tips

• This kit contains enough sand to perform each demonstration as written in this kit once.
• As an extension you may wish to fill-in the rift valley formed in Part III further discuss the topic of sedimentation.
• Have students locate a picture of a cross section of a mountain range. Have them examine and label the topics covered in this activity.
• Plate tectonics is further discussed in the Pangea Student Activity Kit (Catalog No. AP7170) and Sea Floor Spreading Student Activity Kit (Catalog No. AP7171) available from Flinn Scientific.
• A kit containing the materials and instruction for making permanent tectonic models is available from Flinn Scientifc (Catalog No. AP7191).

Answers to Questions

Part I.

1. Define compression. At what type of boundaries does compression occur?

   Compression occurs when two plates come in contact with one another. The crust of the two moving plates usually begins to crack and buckle (fault). Compression occurs at convergent boundaries.

2. Using your observations from Part I, briefly explain how mountains may form.

   As two plates push upon one another, compression and folds occur. These folded regions build upwards creating mountains.

3. Label possible weak points or areas on your final drawing for Part I. What are these weak points called?

   Drawings will vary. The weak points are called reverse faults.

Part II.

1. List two major factors that cause erosion.

   Wind and water.

2. How can erosion in one area lead to sedimentation in a different location?

   Wind and/or water may pick up sand and other particulates from one location and carry and deposit them in another area.

3. Define the term peneplain. Label the peneplain in your final drawing for Part II.

   A peneplain is a nearly flat, almost featureless plain of land that is produced by an extended period of erosion.

Part III.

1. Based on your observations for Part III, describe what happens as continental plates diverge.

   As continental plates diverge, the center of the divergence or valley will break apart. This valley may break apart in a steplike manner.

2. List an example of where the type of movement seen in Part III (divergence) occurs.

   Sea floor spreading or rift valleys.

3. Label possible weak points in your final drawing for Part III. How is the formation of these weak points different from those seen in Part I?

   Drawings will vary. The faults seen in Part I were reverse faults. The faults seen in Part III were formed by divergence and can be classified as normal faults.

Discussion

The Earth is a constantly changing planet consisting of an extremely hot core. The heat in the interior of the Earth leads to convection that shifts and moves the rocky plates making up the Earth’s crust. The interaction of these plates produces enough force to create ocean basins, build mountains, and create earthquakes and volcanoes. The theory of moving landmasses or plate tectonics was first coined by the German meteorologist Alfred Wegener (1880–1930).

When crustal plates move, three things can occur—convergence, divergence or conservative movement. Convergence occurs when plates move toward one another. When two convergent plates come in contact or collide, compression occurs. The Earth’s crust becomes compressed between the two moving plates and the crust begins to crack and buckle (known as a fault). Since both of the plates involved in a collision are very dense, they usually collide and crumple (or fold) to form mountains. Because the buckling of the crust is thrust upward, the crack that forms along the broken area of crust is known as a reverse fault. If an oceanic plate converges upon a less dense continental plate, the denser oceanic plate sinks and forms a zone of subduction. This is a common location for volcano formation. Earthquakes are also very common at convergent boundaries.

Divergence occurs when plates move away from one another. An example of a divergent boundary is sea floor spreading. Sea floor spreading occurs when the molten material in the mantle rises to the surface of a mid-ocean ridge. The molten material flows sideways, carrying the sea floor away from the ridge as it cools. As this new cooling sea floor contracts and becomes denser it sinks and forms a ridge. The valleys that form in the middle of a mid-ocean ridge are also known as rift valleys.

Conservative movement occurs when two plates slide past one another. The plates may move in opposite directions or they may move in the same direction at different rates. The edges of the plates may catch for a period of time and then suddenly slip and move. When two plates rapidly move past one another earthquakes commonly occur.

Erosion and sedimentation also cause changes that affect the physical makeup of the Earth’s surface. Erosion is typically caused by wind and water and is responsible for the gradual decline in mountain ranges. Sedimentation—the settling or layering of particles or other suspended material—leads to the filling in of water basins. In Part II of this demonstration a peneplain is formed. A peneplain is a nearly flat, almost featureless plain that is produced by a long period of erosion. Over the course of geologic time, a peneplain reduces the land so that essentially no more erosion can occur.