1. Deforming Earth's Crust
Section 3
Chapter 6

2. Key Concept
Tectonic plate motions deform Earth’s crust. Deformation causes rock layers to bend and break and causes mountains to form.

3. Deformation
Rocks react differently depending on the amount of stress put on them.
The process by which the shape of a rock changes in response to stress is called deformation.
Rock layers bend when stress is placed on them.
When enough stress is placed on them they break.

5. Folding
The bending of rock layers in response to stress in the earth’s crust is called folding.
All folds have a hinge and 2 limbs. Limbs are the sloping sides of a fold. A hinge is the bend where the two limbs meet.

6. Anticlines and Synclines
The two most common types of folds are anticlines and synclines.

7. Anticline Folds
In an anticline fold, the oldest rock layers are in the center of the fold. The rock limbs slope down from the center to form an arch.

8. Syncline Folds
In a syncline fold, the youngest rocks are in the center of the fold. The limbs slope up from the center to form a trough.

9. Coming up… Shapes of Folds
Symmetrical
Asymmetrical
Overturned
Recumbent

10. Symmetrical Fold
Symmetrical folds are even and balanced.

11. Asymmetrical Fold
In an asymmetrical fold, one limb may dib more steeply than the other limb does.

12. Overturned Fold
An overturned fold is one in which one limb is tilted beyond 90 degrees.

13. Recumbent Fold
Rock layers which are bent so much that a fold appears to be lying on its side are called recumbent folds.

14. Faulting
When rock is placed under so much stress that it can no longer stretch or bend, it may break. The place that rocks break and slide past each other is called a fault.
The blocks of crust on either side of a fault are called fault blocks.

15. When a fault is not vertical (straight up and down) there are 2 kinds of fault blocks—the hanging wall and the foot wall.

16. Types of Faults
Normal Faults
Reverse Faults
Strike-Slip Faults

17. Normal Faults
Along a NORMAL FAULT, the hanging wall moves DOWN relative to the footwall.
Usually form where tectonic plate motions cause tension. Tension is stress that pulls rocks apart.

18. Reverse Faults
In a REVERSE FAULT, the hanging wall moves UP relative to the footwall.
Caused when tectonic plate motion causes compression.
Compression is stress that pushes rocks together.
Common in subduction zones.

19. Strike-Slip Faults
The 2 fault blocks move past each other horizontally.
Usually form where tectonic plate motions cause shear stress parallel to Earth’s surface.
Shear stress pushes different parts of the rock in different directions.
Common in transform boundaries.

20. Recognizing Faults
Some faults are only a few meters long, while other are several hundred meters.
Faults cause rock layers to become offset.
Also grooves, striations, or polished surfaces called slickenslides show where rocks have moved.
Fault offset is obvious along faults that break surface for many kilometers.
Streams may change direction at a fault.
A scarp is a row of cliffs formed by faulting.

21. Scarps

22. Plate Tectonics and Mountain Building
Edges of tectonic plates grind against each other.
Causes stress in Earth’s crust because the plates have a great deal of mass.
This process may crumple and push up the margins of the plates.
Causes mountains to form.

23. Types of Mountain Formation
Folded Mountains
Fault-Block Mountains
Volcanic Mountains

24. Folded Mountains
Occur when rock layers are squeezed together and pushed upward
Occur at convergent boundaries where continents have collided.
Himalaya Mountains
are FOLDED MOUNTAINS

25. Fault-Block Mountains
Occur when tension in the crust causes the crust to break into a large number of normal faults.
Large blocks of crust drop down relative to other blocks.
Grand Teton Range, Wyoming

26. Volcanic Mountains Occur when molten rock erupts onto Earth’s surface.
Located at convergent boundaries when hot mantle rocks rise beneath the plate.
Molten rock rises to the surface and erupts.
Form on land and the ocean floor.
Sometimes become islands.
Most active volcanic mountains have formed around the tectonically active rim of the Pacific Ocean.

27. Ring of Fire

28. Summary
Deformation structures, such as faults and folds, form as a result of stress in the lithosphere. This stress is caused by tectonic plate motion.
Folding occurs when rock layers bend because of stress.
Faulting occurs when rock layers break because of stress and then move on either side of the break.
Three major fault types are normal faults, reverse faults, and strike-slip faults.
Mountain building is caused by the movement of tectonic plates. Folded mountains and volcanic mountains form at convergent boundaries. Fault-block mountains form at divergent boundaries.