Forces in Earths Crust Chapter 6 Section 1

Forces in Earth’s Crust Chapter 6 Section 1

Stress Movement of the Earth’s plates creates enormous force These forces are examples of stress, a force that acts on rock to change its shape or volume Because stress is a force, it adds energy to the rock Energy is stored in the rock until it changes shape or breaks

Types of Stress Three Types of Stress that occur at the crust are Tension, Compression, and Shearing These forces cause some rocks to become brittle and snap or bend slowly These changes occur slowly If you speed up time so a billion years passed by in minutes, you could see the crust bend, stretch, break, tilt, fold, and slide

Tension Stress force pulls on the crust, stretching rock so that it becomes thinner in the middle The effect of tension on rock is like pulling apart a piece of bubble gum Tension occurs when two plates are moving apart-----divergent boundaries

Compression Stress force that squeezes rock until it folds or breaks One plate pushing against another can compress rock May look like a giant trash compactor

Shearing Stress force that pushes a mass of rock in two opposite directions Can cause rock to break and slip apart or to change its shape

Kinds of Faults When enough stress builds up in rock, the rock breaks, creating a fault----3 main types Recall: Fault is a break in the rock of the crust where rock surfaces slip past each other Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks

Normal Fault Tension in Earth’s crust pull rock apart causing normal faults In a normal fault, the fault is at an angle One block of rock lies above the fault called the hanging wall One block of rock lies below the fault called the footwall

Normal Fault When movement occurs along a normal fault, the hanging wall slips downward Normal faults occur where plates diverge, or pull apart Ex) Rio Grande rift valley

Normal Fault

Reverse Fault In places where rock experiences compression, reverse faults occur A reverse fault has the same structure as a normal fault, but the blocks move in opposite direction The hanging wall slides up and over the footwall EX) Northern Rocky Mountains

Reverse Faults

Strike-Slip Fault Shearing creates strike-slip faults In a SSF, the rocks on either side of the fault slip past each other sideways There is little up or down motion Formed at a transform boundary 2 Types: Right Lateral and Left Lateral Ex) San Andreas Fault

Strike-Slip Fault