Earth’s Crust in Motion EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Earthquakes Earthquake: The shaking that results from the movement of rock beneath Earth’s surface EQ: How do stress forces affect rock?

Two powerful forces that change rock in the Earth’s crust: Stress Friction

Stress Stress: A force that acts on rock to change its shape or volume EQ: How do stress forces affect rock?

What is Volume? The amount of space an object takes up EQ: How do stress forces affect rock?

Energy is stored in rock until the rock either breaks or changes shape EQ: How do stress forces affect rock?

Shearing Shearing: Stress that pushes a mass of a rock in opposite, horizontal directions EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Tension Tension: Stress that stretches rocks so that it becomes thinner in the middle EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Compression Stress that squeezes rock until it folds or breaks EQ: How do stress forces affect rock?

Figure 2: If shearing continues to tug at the slab of rock in B, what will happen to the rock? The rock will break; the two parts will move in opposite directions EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Deformation Deformation: A change in the volume or shape of Earth’s crust Most changes in the crust occur so slowly that they can not be observed directly EQ: How do stress forces affect rock?

Checkpoint (Page 55): How does deformation change Earth’s surface? It causes it to: Bend Stretch Break Tilt Fold Slide

Guide For Reading: How does stress forces affect rock? The three kinds of forces that affect rock are: Shearing The rocks break and slip apart Tension The rock stretches and becomes thin in the middle Compression The rock squeezes until it folds or breaks These stresses work over millions of years to change the shape and volume of rock

EQ: How do stress forces affect rock? Faults EQ: How do stress forces affect rock? A break in the Earth’s crust where slabs of rock slip past each other Faults occur when enough stress builds up in rock Rocks on both sides of the fault can move up or down, or sideways

EQ: How do stress forces affect rock? Strike-Slip Faults EQ: How do stress forces affect rock? A type of fault where rocks on either side move past each other sideways with little up-or down motion. Shearing causes these types of faults

EQ: How do stress forces affect rock? Normal Faults A type of fault where the hanging wall slides downward Tension forces cause normal faults EQ: How do stress forces affect rock?

Hanging Wall & Footwall Hanging wall: The block of rock that forms the upper half of a fault Footwall: The block of rock that forms the lower half of a fault EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Reverse Faults A type of fault where the hanging wall slides up Compression forces cause reverse faults EQ: How do stress forces affect rock?

Checkpoint (Page 57): What are the three types of fault Checkpoint (Page 57): What are the three types of fault? What force of deformation produce each? Strike-slip faults Produced by shearing Normal faults Produced by tension Reverse faults Produced by compression

Why do faults form and where do they occur? Plate move and they compress, pull or shear the crust so much it breaks Faults occur along plate boundaries

EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Which half of the reverse fault slid up and across to form this mountain, hanging wall or the footwall? Explain. The hanging wall slipped up and across. If the footwall had moved up, the fault would be called a normal fault EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? What is friction? A force that opposes the motion of one surface as it moves across another surface It exists because rocks are not perfectly smooth EQ: How do stress forces affect rock?

Describe what occurs when the friction along a fault line is low. The rocks on both sides of the fault slide by each other without much sticking EQ: How do stress forces affect rock?

Describe what occurs when the friction along a fault line is moderate. The sides of the fault jam together From time to time they jerk free Small earthquakes occur EQ: How do stress forces affect rock?

Describe what occurs when the friction along a fault line is high. Both sides of the fault lock together and do not move The stress increases until it is strong enough to overcome the force of friction Larger and/or more frequent earthquakes will occur EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Fault-Block Mountain EQ: How do stress forces affect rock? A mountain that forms where a normal fault uplifts a block of rock

How does the process of a fault-block mountain begin? EQ: How do stress forces affect rock? How does the process of a fault-block mountain begin? Where two plates move away from each other, tension forces create many normal faults When two of these normal faults form parallel to each other, a block of rock is left lying between them As the hanging wall of each normal fault slips downward, the block in between moves upward When a block of rock lying between two normal faults slides downward, a valley forms

EQ: How do stress forces affect rock? Folds EQ: How do stress forces affect rock? A bend in rock that forms where part of Earth’s crust is compressed

How does the compression of two plates cause an earthquake? The collisions of two plates can cause compression and folding of the crust Such plate collisions also lead to earthquakes, because folding rock can fracture and produce faults EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Anticline Anticline: An upward fold in rock formed by compression of Earth’s crust EQ: How do stress forces affect rock?

EQ: How do stress forces affect rock? Syncline EQ: How do stress forces affect rock? Syncline: A downward fold in rock formed by tension in Earth’s crust

EQ: How do stress forces affect rock? Plateaus A large area of flat land elevated high above sea level EQ: How do stress forces affect rock?

Guide For Reading: How does movement along faults change Earth’s surface? Over millions of years, fault movement can change a flat plain into a towering mountain range Mountain ranges can form from: Fault – block mountain Folding Anticlines & Synclines Plateaus