Forces in Earth’s Crust Section 1 Forces in Earth’s Crust

Types of Stress Stress is a force that acts on rock to change its shape or volume. A rock’s volume is the amount of space that the rock takes up. Stress adds energy to the rock 3 Different kinds of stress in the crust: Tension Compression Shearing

Tension Tension pulls the crust stretching the rock so that it becomes thinner in the middle. Think of when we pulled apart the Milky Way Bar. Tension occurs when 2 plates pull apart.

Compression Compression squeezes rock until it folds or breaks One plate pushes against another.

Shearing Shearing is a type of stress that pushes mass of rock in two opposite directions Shearing causes rock to break or slip apart or change its shape

Kinds of Faults A 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 curst breaks. There are 3 main types of faults: Normal Faults Reverse Faults Strike-Slip Fault

Normal Fault Tension in Earth’s crust pulls rock apart In a normal fault, the fault is at an angle, so one block of rock lies about the fault while the other block lies below. The block of rock that lies above is called the hanging wall. The block of rock that lies below is called the footwall. In a normal fault, the hanging wall slips downward.

Normal Fault

Reverse Fault In reverse faults, the rock of the crust is pushed together. The rock forming the hanging wall of a reverse fault slides up and over the footwall. Part of the Rock Mountains were produced due to reverse faults.

Reverse Fault

Strike-Slip Fault In places where plates move past each other, shearing create strike-slip faults. In a strike-slip fault, the rocks on either side of the fault slip past each other sideways. A strike-slip fault between plate boundaries is called a transform fault.

Strike-slip Fault

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

Anticlines and Synclines Anticline is a fold that bends upward into an arch. Syncline is a fold that bends downward to form a valley. This is produced when two plates have compression (come together).

Fault-Block Mountain When 2 normal faults cut through a block of rock, a fault-block mountain is formed. As the two faults are pulled apart, land is left in the middle. The hanging wall of each fault goes down and the block in between move up, creating a mountain.

Plateau Plateaus are large areas of flat land that elevated high above sea level. Some plateaus form when forces in Earth’s crust push up a large, flat block of rock. Plateaus consist of many flat layers that are wide.