Earth's Crust in Motion

1. Earth's Crust in Motion

2. Earthquakes • So…. • What is an Earthquake? • And… • What are some things that can cause them?

3. Stress in the Crust • An earthquake is the shaking that results from the movement of rock beneath Earth's surface. • This is a super powerful force!!! • These forces are examples of stress. • Stress is a force that acts on rock to change its shape or volume.

4. Types of Stress • There are three different kinds of stress that occur in the Earth’s crust… • Shearing • Tension • Compression • All of this stress works over millions of years to change the shape of rock. • So…Any change in the shape of Earth's crust is called deformation.

5. Shearing • Stress that pushes a mass of rock in two opposite directions is called shearing. • Shearing can cause two slabs of rock to slip past each other like the picture below. • What feature in California is an example of this?

6. Tension • Tension is a stress that pulls on the crust, stretching rock so that it becomes thinner in the middle. • Tension occurs where two plates are moving apart. • Think of pulling a Milky Way candy bar apart. • What ocean feature is this an example of?

7. Compression • Compression is a stress force that squeezes rock until it folds or breaks. • One plate pushing against another plate can compress rock easily…. • Almost like Mr. Wise’s strength!!!

8. Kinds of Faults • When enough stress builds up in rock, the rock can break, creating a fault. • A fault is a break in the crust where two slabs of crust slip past each other. • The rocks on both sides of a fault can either move up or down or sideways. • Faults usually occur along plate boundaries • There are three main types of faults: • Strike-slip faults • Normal faults • Reverse faults

9. Strike-Slip Faults   • Shearing creates strike-slip faults. • In a strike-slip fault, the rocks on either side of the fault slip past each other sideways • A strike-slip fault that forms the boundary between two plates is called a transform boundary. • What fault in California is an example of this?

10. Normal Faults   • Tension forces in Earth's crust cause normal faults. • In a normal fault, the fault is at an angle, so one block of rock lies above the fault while the other block lies below the fault. • Tension forces create normal faults where plates diverge, or pull apart. • What ocean feature is an example of this?

11. Normal Faults

12. Reverse Faults   • Compression forces produce reverse faults. • A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction. • What geologic feature is an example created by compression?

13. Reverse Faults

14. Mountain Building • The forces of plate movement can build up Earth's surface. • Over millions of years, fault movement can change a flat plain into a towering mountain range

15. Mountains Formed by Faulting • When normal faults uplift a block of rock, a fault-block mountain forms.

16. Mountains Formed by Folding • Under certain conditions, plate movement can cause crust to fold. • Folds are bends in rock that form when compression shortens and thickens part of Earth's crust. • The collisions of two plates can cause compression and folding of the crust. • Some of the world's largest mountain ranges, such as the Himalayas and the Alps, formed when pieces of the crust folded during the collision of two plates. • Such plate collisions also lead to earthquakes!

17. Mountains Formed by Folding

18. Anticlines and Synclines   • A fold in rock that bends upward into an arch is an anticline. • A fold in rock that bends downward in the middle to form a bowl is a syncline. • Anticlines and synclines are found on many parts of Earth's surface where compression forces have folded the crust.

19. Plateau • The forces that raise mountains can also raise plateaus • Large area of flat land elevated high above sea level • Consists of many different layers • More wide than tall