FORCES IN EARTH’S CRUST

1. FORCES IN EARTH’S CRUST Chapter 2 Section 1 Grade 7 Science

2. Your task: Show your understanding of forces in Earth’s crust using various forms of graphic organizers. • READ pages 44-50 in textbook and then view the entire PowerPoint presentation. • Complete the Vocab Chart for types of stress. Use information from the slides & textbook. (ISN pg 81) • Fill in the Venn Diagram comparing Folding & Faulting. You should include AT LEAST 3 similarities and differences- be specific! (ISN pg 83) • Compile all of the CH 2 Sec 1 material in an original acrostic using the word “STRESS”. For each letter, write a descriptive sentence. Add at least 1 colored drawing that shows an important fact about stress. (ISN pg 80)

3. FORCES IN EARTH’S CRUST Key Concepts of CH 2 Section 1 • How does stress in the crust change Earth’s surface? • Where are faults usually found, and why do they form? • What land features result from the forces of plate movement?

4. What does stress look like? • A teacher under stress! • Earth’s crust under stress!

5. What is stress? • Stress is a force • Stress acts on rock to change its shape or volume • Deformation of rock occurs (“de”- undo “form”- shape/appearance) • Examples of stress are TENSION, COMPRESSION, and SHEARING • Stress adds energy to the rock • Energy is released when rock changes shape or breaks (ex. Such as during an earthquake!)

6. Diagram of Stress in Earth’s Crust

7. Comparing Types of Stress

8. - Forces in Earth’s Crust TENSION • The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

9. - Forces in Earth’s Crust COMPRESSION • The stress force called compression squeezes rock until it folds or breaks.

10. - Forces in Earth’s Crust SHEARING • Stress that pushes a mass of rock in two opposite directions is called shearing.

11. Where does stress come from? • The movement of Earth’s plates creates enormous stress that squeezes or pulls rock in the crust. • Since plates move slowly, changes in Earth’s crust also occur slowly. • Over millions of years, stress will cause crust to bend, stretch, break, tilt, fold, & slide.

12. Folding & Faulting • Folding occurs as rocks bendslowly, like road tar softened by the sun. • Folding is caused mainly by compression. • Folds are bends in rock that form when compression shortens and thickens the crust. • Faulting occurs when rocks break • Faulting is caused by extreme stress- tension, compression, or shearing. • Faults are breaks in the crust where rock surfaces slip past each other.

13. How folding changes Earth’s surface • Folding of rock is caused by compression forces as one plate pushes against another plate squish! • Compression makes parts of crust shorter and thicker. • Folds can bend upward like an arch (anticline), or downward like a valley (syncline). • Compression can form folded mountains in the middle of a continent (like Appalachians) or at the edges of a convergent boundary (like Himalayas and Alps)

14. Folded Mountains- in the middle of a continental plate Appalachian Mountain Range, USA

15. Folded Mountains- at convergent plate boundary Himalayas Mountain Range, Nepal

16. How faulting changes Earth’s surface • When enough stress builds up in rock, it breaks, creating a fault. • Rocks on either side of a fault move up, down, or sideways • Most faults occur along plate boundaries, but can be found anywhere stress builds up in the crust (ex. There are small faults in central Oklahoma, this is why they had EQ activity recently!) • Three kinds of faults: normal, reverse, strike-slip- each differs in the direction rock moves on either side of fault • Movement along a fault usually results in seismic activity…. earthquakes!!!

17. Comparing FAULTS