1. Movement of the Earth’s Crust
Essential Questions
Describe how the Earth’s crust is deformed.
How does the formation of mountains, valleys, plateaus, and domes relate to stress?
How do faulting and folding change the appearance of the Earth’s surface?
Define isostasy and explain its effect on the movement of the Earth’s crust.

2. How Does Earth’s Surface Change?
Stress pushes and pulls on the Earth’s crust.
The rocks slowly change shape and volume
They move up or down or sideways
The breaking, folding or tilting of rocks is called deformation.
3 types of stress – compression, tension and shearing.

4. What is Compression?
Squeezes the rocks of the crust. Moves particles closer making rocks more dense.
Rocks are pushed both higher up and deeper down.

5. What is Tension?
Pulls on rocks of crust causing them to stretch out over a larger area.
Becomes thinner in the middle
Volume increases while density decreases

6. What is Shearing Pushes rocks of crust in 2 opposite directions.
Causes rocks to twist or tear.
Not compressed or stretched, just bent or broken apart

7. What are the results of compression, tension and shearing?
Change a rock’s volume, shape or both
Can cause rocks to fracture, or crack
Fractures along numerous flat surfaces which show no displacement are called joints. They are generally parallel to each other.
If rocks have joints that form in more than one direction they may break into blocks.

8. What is Faulting
A break or crack along which rocks move is called a fault.
Rocks on one side of a fault slide past the rocks on the other side.
Movement can be up, down or sideways.
Earthquakes often occur along faults

9. What are the two blocks of rocks that make up a fault?
Hanging wall – block of rock above the fault
Foot wall – block of rock below the fault

10. What are the types of faults?
Normal fault – tension acts on a fault and the hanging wall moves down relative to the foot wall

11. Reverse Faults
Reverse fault – compression acts on a fault and the hanging wall moves up relative to the foot wall.

12. Thrust Faults
Thrust fault – special type of reverse fault where the hanging wall slides over the foot wall. The movements are almost horizontal where normal and regular reverse faults are mostly vertical. Thrust faults often cause older rocks to be above younger rocks.

14. Lateral fault – shearing causes blocks of rock to slide horizontally past each other

15. What are faulted Mountains and Valleys?
Fault-block mountains – caused by blocks of rock uplifted by normal faults
Ex. Cordilleran mountain region of North America. Extends from central Mexico to Oregon, and Idaho. Includes western Utah, Nevada and eastern California

17. Rift valleys – formed when the block of land between 2 normal faults slides downward.
Ex. Death Valley in California

19. What is folding? Fold – a bend in a rock.
Anticline – upward fold in a rock
Syncline – downward fold in a rock
Folds vary in sizes
Ex. Of folded mountains – Appalachian mountains extend from Alabama to Canada

20. Why do some rocks fold and some fault?
Temperature is one factor – hotter more likely to fold
Pressure – greater pressure, more likely to fold
Rock type
brittle – break when stress is applied
ductile – bend under stress
Application of stress
if applied gradually the rocks will usually fold
if applied suddenly the rock will usually fault

21. What are plateaus?
Large area of flat land raised high above sea level, wider than it is tall, surrounded by steep cliffs
Rock layers in a plateau remain flat
Formed by:
a slow flat-topped fold, Ex. The Appalachian plateau which lies west of the Appalachian mountain.
Vertical faulting, Ex. Colorado Plateau which lies west of the Rocky Mountains
Series of molten rock flows, Ex. Columbia Plateau, in Oregon, Washington and Idaho
Rivers often carve a plateau into many smaller plateaus. Ex. Colorado river carving the Colorado Plateau forms the Grand Canyon

23. What are Domes?
Uplifted area created by rising magma. Magma pushed upward but does not reach the Earth’s surface. Stress causes the rock layers to fold upward. Eventually magma cools and forms hardened rock.
When domes wear away they form many separate peaks called dome mountains. Ex. Black Hills of South Dakota and Wyoming

25. What is Isostasy?
The balance of the downward force of the crust and the upward force of the mantle
The more material that is added to an area of crust, the lower the crust floats on the mantle. The less material on the crust, the higher the crust will float on the mantle
Examples of changes
melting glaciers removing weight from the crust – end up floating higher
added mud and sand from river discharge causes crust to float lower.

26. Isostasy

27. Credits http://www.eos.ubc.ca/~ehearn/research2.html