1. Mountain Building Lesson 4.7 How are mountains formed? Lesson 4.7

2. Stressed Out The movement of tectonic plates places stress on rocks Deformation- processes by which rock changes shape under stress – Rocks can bend under stress, but if the stress is too large or happens quickly, it can break – When rock bends, folds forms – When rocks break, faults form

3. Types of Folds Folding occurs when rock layers bend under stress – Will appear bent or buckled Scientists assume rocks start out as horizontal layers deposited in top of each other – When they see a fold, they know deformation has occurred – Two common types of folds Synclines Anticlines

4. Types of Folds Syncline- look like rocks layers that are arched upwards, like a bowl Anticlines-Layers are high in the middle and are arched downward. – Often, both types will be visible in the same rock layers.

5. Types of Faults The crack that forms when large blocks of rocks break and move past each other is called a fault. – Fault blocks: blocks on either side of fault – The sudden movement of fault blocks can cause earthquakes There are 3 main kinds of faults – Classified bases on the way the faults blocks move Strike-slip faults Normal faults Reverse faults

6. Strike-Slip Fault Fault blocks move past each other horizontally. – Shear stress causes rocks to be pushed in parallel but opposite directions Release of energy can cause earthquakes – Are common along transform boundaries San Andreas fault system in California is an example of a strike-slip fault

7. San Andreas Fault

8. Normal Fault Hanging wall moves down relative to the footwall – Called normal because they move in a way you would normally expect as a result of gravity – From when rock is under tension A stress that stretches or pulls rock apart Common along divergent boundaries – Basin and Range area in the US is an example of a location with normal faults.

9. Basin and Range Area

10. Reverse Fault Hanging wall moves up relative to the footwall – Reverse of what you would expect as a result of gravity – Form from the result of compression Stress that squeezes or pushes rock together Common along convergent boundaries – San Gabriel Mountains are an example is the US

11. San Gabriel Mountains

12. Types of Mountains Mountain can form from folding, volcanism, and faulting – Uplift, a process that can cause land to rise can also contribute to mountain building – Tectonic plates are always in motion, some mountain are constantly being uplifted 3 types – Folded Mountains – Volcanic Mountains – Fault-Block Mountains

13. Folded Mountains Layers are squeezed together and pushed upwards Form at convergent boundaries Examples: – Appalachian Mountains – Pyrenees

14. Volcanic Mountains Form when melted rocks erupts onto Earth’s Surface – Many located at convergent boundaries – Volcanoes on the ocean floor can grow so tall that they rise above the surface of the ocean, forming islands – Ex: Mt. Griggs

15. Fault-Block Mountains Form when tensions makes the lithosphere break into many normal faults – Pieces of the lithosphere drop down – Example: Teton Mountains and Sierra Nevada