Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Mountains can form as rocks move along faults. CONTENT FRAME Add information about fault-block mountains to your content frame. In the southwestern United States and northwestern Mexico, hundreds of mountain ranges line up in rows. The ranges, as well as the valleys between them, formed along nearly parallel normal faults. Mountains that form as blocks of rock move up or down along normal faults are called fault-block mountains. How can the movement of rocks along faults lead to the formation of mountains? Fault-block mountains form as the lithosphere is stretched and pulled apart by forces within Earth. The rocks of the crust are cool and rigid. As the lithosphere begins to stretch, the crust breaks into large blocks. As stretching continues, the blocks of rock move along the faults that separate them. The illustrations on page 259 show how this process forms fault-block mountains. Fault-Block Mountains How do fault-block mountains form? Fault-block mountains form along normal faults as blocks of continental crust are pulled apart. In this activity, you will use wooden blocks to demonstrate the processes that form fault-block mountains. PROCEDURE 1 Use the triangular blocks to demonstrate how movements along normal faults form two mountains separated by a valley. Start with the blocks arranged as shown. Move the outer blocks apart to form two mountains separated by a valley. Draw a diagram of your results. 2 Use the rectangular blocks to demonstrate how a row of tilted fault-block mountains forms along normal faults. (Hint: You can tilt the blocks as they move.) Draw a diagram of your results. WHAT DO YOU THINK? • How do your diagrams show that fault-block mountains form as the crust is being stretched? • Along which type of plate boundary would fault-block mountains be most likely to form—divergent, convergent, or transform? Explain. CHALLENGE Why do fault-block mountains not form at strike-slip faults? 258 Unit 2: The Changing Earth SKILL FOCUS Modeling MATERIALS • 3 triangular blocks • 3 rectangular blocks TIME 15 minutes