Forces in Earths Crust Pages 120 123 Build

Forces in Earth’s Crust Pages 120 -123

Build Background Knowledge Have you ever experienced an earthquake? If so, describe the event. If not, what have you learned from television reports, movies, newspaper and magazine articles, etc. ?

The Big Questions ● How does stress change the Earth’s crust? ● How do faults form?

My Planet Diary page 120 How long do you think it took Mount Everest to form? Hundreds of years? Thousands? Millions? Explain. Forces inside Earth act very slowly, so Mount Everest likely took millions of years to form.

Forces in Earth’s Crust • • • The movement of Earth’s plates creates enormous forces that squeeze or pull the rock in the crust as if it were a candy bar. These forces are examples of stress. Stress is a force that acts on rock to change its shape or volume. Because stress is a force, it adds energy to the rock. The energy is stored in the rock until the rock changes shape or breaks.

Types of Stress Three different kinds of stress can occur in the crust: Tension Compression Shearing

Tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

What type of landform results from tension? Valley

Compression squeezes rock until it folds or breaks.

What type of landform results from compression? Mountain

Shearing pushes a mass of rock in two opposite directions.

How does shearing affect rock in Earth’s crust? Shearing can cause rock to break and slip apart.

Figure 1: Stress in Earth’s Crust page 121 Look at the pair of arrows in the second diagram. These arrows show tension affects rock.

Figure 1: Stress in Earth’s Crust page 121 Draw a pair of arrows on the third diagram to show compression affects rock.

Figure 1: Stress in Earth’s Crust page 121 Draw a pair of arrows on the bottom diagram to show shearing acts on rock.

Assess Your Understanding page 121 I get it! Now I know that stress changes Earth’s crust by changing the ___________. shape and volume of rock

Kinds of Faults pages 122 -123 Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks. There are three main types of faults: Normal Faults Reverse Faults Strike-Slip Faults

Normal Faults • • Tension in Earth’s crust pulls rock apart, causing 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. The block of rock that sits over the fault is called the hanging wall. The rock that lies under the fault is called the footwall.

Normal Faults • When movement occurs along a normal fault, the hanging wall slips downward. • Normal faults occur where plates diverge, or pull apart.

Normal Faults Normal faults occur where plates diverge, or pull apart.

Reverse Faults • • Compression in Earth’s crust pushes rock together, causing reverse faults. A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

Reverse Faults • • The rock forming the hanging wall of a reverse fault slides up and over the footwall. Movement along reverse faults produced part of the northern Rocky Mountains in the western United States and Canada.

Reverse Faults Reverse faults occur where plates are compressed, or pushed together.

Strike-Slip Faults • • In places where plates move past each other, shearing creates strike-slip faults. In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up or down motion.

Strike-Slip Faults • A strike-slip fault that forms the boundary between two plates is called a transform boundary. • The San Andreas fault in California is an example of a strike-slip fault that is a transform boundary.

Strike-Slip Faults Rocks on either side of a strike-slip fault slip past each other.

Faults http: //www. youtube. com/watch? v=x Fi 8 p. VLp. Jj. E

Forces in Earth’s Crust Review Textbook: Page 122 Figure 2: Faults Normal Fault: In a normal fault, the hanging wall __________ relative to the footwall. slips down

Forces in Earth’s Crust Review Textbook: Page 122 Figure 2: Faults Reverse Fault: In a reverse fault, the hanging wall moves _____ relative to the footwall. up

Forces in Earth’s Crust Review Textbook: Page 123 Apply It! The low angle of a thrust fault allows rock in the hanging wall to be pushed great distances. For example, over millions of years, rock along the Lewis thrust fault in Glacier National Park has moved 80 kilometers. 1. Identify: Based on the arrows showing fault movements in the diagram, a thrust fault is a type of (normal fault, reverse fault). reverse fault

Forces in Earth’s Crust Review Textbook: Page 123 Apply It! 2. Challenge: Why might the type of rock in the hanging wall of the Lewis thrust fault be different from the type of rock in the footwall? Because the hanging wall now sits above rock that might be different from the original rock 80 km away.

Forces in Earth’s Crust Review Textbook: Page 123 1 a. Review When enough stress builds up in brittle rock, the rock breaks, causing a _____ to form. fault b. Infer: A geologist sees a fault along which blocks of rock in the footwall have moved higher relative to blocks of rock in the hanging wall. What type of fault is this? a normal fault

Forces in Earth’s Crust Review Textbook: Page 123 Got it? I get it! Now I know that faults form when______. enough stress builds up in rock to break it

Forces in Earth’s Crust Review Understanding Main Ideas Diagram A a. Type of fault: reverse b. Stress force: compression c. Movement along fault: vertical

Forces in Earth’s Crust Review Understanding Main Ideas Diagram B a. Type of fault: normal b. Stress force: tension c. Movement along fault: vertical

Forces in Earth’s Crust Review Understanding Main Ideas Diagram C a. Type of fault: strike-slip b. Stress force: shearing c. Movement along fault: horizontal

Forces in Earth’s Crust Review Evidence of Movement Along Faults Fault 1: strike-slip road shows horizontal movement; not vertical Fault 2: reverse fault dry riverbed Fault 3: normal fault waterfall

The Big Question ● How does plate movement create new landforms?

Changing Earth’s Surface Over millions of years, the forces of plate movement can change a flat plain into ____ such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus.

Anticline An _____ is a fold in rock that bends ____ into an arch. Anticlines are found in places where compression forces have folded the crust.

Syncline A ______ is a fold in rock that bends ____ to form a valley. Synclines are also found in places where compression forces have folded the crust.

Figure 4 page 125 ● Label the anticline and the syncline. ● Draw arrows to show the direction in which forces act to compress the crust.

Folded Mountains The collision of two plates can cause _____ and ____ of the crust over a wide area.

World’s Largest Mountain Ranges created from the folding of Earth’s crust: Himalayas in Asia and the Alps in Europe

Fault-block Mountains ● Fault-block mountains form when _____ in Earth’s crust causes faulting. ● The hanging wall of _____ normal faults slip downward due to tension. ● e block between now stands above the surrounding _____.

Fault-block Mountains The Great Basin region contains many mountains separated by broad valleys, or basins.

Figure 5: Tension and Normal Faults page 126 Label the hanging wall and the two footwalls in diagram A. a. footwall b. hanging wall c. _____

Figure 5: Tension and Normal Faults page 126 In diagram B, draw the new position of the hanging wall after movement occurs.

Figure 5: Tension and Normal Faults page 126 Describe what happens. ____ causes the footwalls to move outward. The hanging wall then slips down along the faults, forming the ______.

Plateaus A _____ is a large area of flat land that is elevated high above sea level. The same forces that raise mountains can also uplift, or raise, plateaus.

Forces in Earth’s Crust Review Textbook: Page 127 Assess Your Understanding 2 a. Normal faults often occur when two plates (come together, pull apart). _______ b. Look at the diagram that accompanies the photograph in Figure 5. Does the block of rock in the middle move up as a result of movement along the normal faults? Explain. _______, the middle block does not move up. Rather, the two blocks forming the hanging walls move _____.

Forces in Earth’s Crust Review Textbook: Page 127 Got It? I get it! Now I know that plate movements create new features by____________. Acting over _____ of years to change flat plains into anticlines, synclines, folded mountains, fault-block mountains, valleys, and plateaus.