Fault Block Mountains

Materials / Preparation

• Mountains Formed by Faults Photos
• 5 or 6 hardback books approximately the same size (textbooks work well for this). This works best if the books are identical and have horizontal bands (lines) on the binding.
• Students will use page 9 of their Mountain Building Journals.

Grouping

Groups of four

Teacher tips

Background information: Fault-block mountains are formed by the sinking or rising of huge blocks of the earth's surface relative to the neighboring blocks. The Basin and Range region of Nevada, Arizona, New Mexico, and Utah is one of the most extensive regions of fault-block mountains.

Students often have difficulty in visualizing how normal faults (fault block movement) contribute to the formation of mountains. This demonstration will help the students understand how faulting can create mountains.

We have provided Mountains Formed by Faults Photos for the teacher.

Procedures

1. Introduce this activity with a question to the students: What happens when the earth's crust is pulled apart? Do you think this could make mountains?
2. Demonstrate the following to the students (See Mountains Formed by Faults Photos )
   a. Hold 5 or 6 hardbound textbooks upright on a desk (binding vertical). Tell the students that the books represent the Earth’s crust and the spaces in between them represent faults in the crust. If there are horizontal lines on the book bindings tell students that these represent sedimentary layers.
   b. Have a student measure the width of the books horizontally. Place a ruler across the top of the books and measure the width beginning with the first book on the left and ending with the last book on the right.
   c. Move one hand so that the books tilt to one side at a 30-45 degree angle. Once again have the student measure the horizontal width using the same technique as above.
   d. Explain to the students that this models stretching of the crust. Gravity actually did all the work as the books slid and tilted, but the “crust” was essentially pulled apart ("tension"). Point out that as tension was applied to the books, the surface stretched and two changes occurred
   1. the “crust” increased in surface area as it stretched to fill in the space
   2. the “crust” changed shape as the tilted blocks (books) now exhibit high peaks and low valleys in place of its formerly flat surface.
   e. Have students look at the model from the top. They should see that the mountains are long and range-like (see Mountains Formed by Faults Photos).
3. Ask students to recall what caused compression of the Earth's crust (plates moving toward one another at convergent plate boundaries). Now ask students what might cause this stretching to take place? (plates moving away from one another – at divergent plate boundaries).
4. Students should make a before and after drawing of this demonstration, labeling the valleys and mountains, on page 9 in their journals. See extension for optional exploration into fault types.
5. Review and Reflection: Have students answer the questions on page 9 of their journals.

Extension: Paper Model Faults

The optional paper model fault activity is a lot of fun for students and enhances their understanding of fault block motion. We have had great success with it in our classrooms, but made it optional as some younger students may have trouble with the cutting and folding. Take a look at the activity and assess for yourself. The most relevant model to mountain building is the model of the horst. However, if time permits, construction of all the models will provide students with better insight into which faults are more likely to be involved in mountain-building processes.

• For this paper-model activity, each team of four students will need:
• Copies of the Seven Paper Models that Describe Faulting in the Earth. Each team will need one copy of the normal fault, reverse fault, strike-slip fault, and horst models (make a few extra as mistakes will be made). A teacher guide is included at this site with background information on faulting.
• Scissors
• Glue
• Colored pencils (optional)
• Tip: Teachers should consider making several versions of each model themselves to help show the class where the folds are. If possible, make one model for each step. Not only will teachers learn exactly how the models are folded so they can help the kids quickly and easily, but also the kids will really appreciate seeing the steps visually. Bring out the model steps one at a time so you don't spoil the surprise.
• If you have limited time, start this activity in class and have the students finish their models as homework. The students will end up with 3-D models of the 7 faults.
• Exploration into Fault Types
1. Remind students of how the tilting happened by movement along the faults (boundaries between the book covers). The following paper models show faults in more detail. The reason that normal faults cause mountains is because of "relative motion" – even though students might say that a block slides downward in a normal fault, if they were standing on that block it would look like the other block was going up. It all depends on your point of view!
2. Faults are cracks in the crust where sliding occurs. We classify faults based on the direction of relative motion into normal faults, reverse faults, and strike-slip faults. These paper models of faults show how that relative motion occurs.
3. Divide the class into groups of 4 and give each group a set of models and instructions for construction. Each group will work as a team to construct the set of paper models. (option: models can be colored before construction begins) Focus on 4 models: normal fault, strike-slip fault, reverse fault, and horst. If time permits, you can pass out the 3 remaining models, but they are less important for demonstrating mountain building.
4. Once all the models are completed, each group will have a set of fault models to use to complete the entries in on pages 10-12 in their Mountain Building Journals. Notice how each model always has TWO arrows (one on each side of the fault) to indicate the direction of relative motion. One of the arrows always points up in normal and reverse faults. That block with the upward arrow is the side that will form the mountain.

Resources used

Seven Paper Models that Describe Faulting in the Earth
http://www.teachingboxes.org/catalog.jsp?id=EARTHQUAKE-000-000-010-397

Mountains Formed by Faults Photos
http://www.teachingboxes.org/mountainBuilding/lessons/faultImages/index.html

Mountain Building Journal
http://www.teachingboxes.org/mountainBuilding/journal/MBJournal.pdf

Mountain Building Journal: Teacher's Guide
http://www.teachingboxes.org/mountainBuilding/lessons/journal/MBJournal_teacherGuide.pdf