Deforming the Earth’s Crust Key Concept: Tectonic plate motions deform Earth’s Crust. Deformation causes rock layers to bend and break and causes mountains to form.

Deformation Stress is the amount of force per unit area on any given material. When plates move, rocks layers on Earth receive stress. Rocks react differently with stress, sometimes they bend other times they break.

Deformation continued Deformation is the process in which rocks change shape in response to stress.

Folding Bending rock due to stress is called folding Scientists assume that all rock layers started horizontally

Anticlines An anticline is a fold which the oldest rock layers are in the center of the fold. Many times the rocks fold in the center and form an arch.

Syncline A syncline is a fold which the youngest rock layers are in the center of the fold. Many times the rocks fold in the center and form a “U” Shape.

Shapes and Folds Folds do not always have symmetrical bends (look the same on both sides). Sometimes Asymmetrical bends occur (look different) Folds may also be turned on their side, called a recumbent fold.

Faulting When a rock has so much stress that it can no longer bend or stretch it will break. The surface along the break is called a fault. The broken crust at the fault are called fault blocks. Faults are sometimes vertical.

Faulting cont. Sometimes a fault block is not vertical. The fault will contain two different fault blocks. A foot wall and a hanging wall.

Normal Faults In a normal fault, the two plates move away from each other. Tension is a force that pulls apart. The hanging wall slides on the footwall. Example is a mid ocean ridge.

Reverse Fault In a reverse fault the hanging wall moves up on the foot wall. Compression is the stress that pushes the plates together. Occurs in a Subduction zone.

Strike-Slip Fault Along a Strike-Slip fault, two faults move horizontally past each other. Occur at transform boundaries.

Plate Tectonics and Mountain Building When giant plates moved around, their edges grind and cause stress. Over long periods of time, this process may crumple and push up the margin of the plates. When this happens mountain building may occur. Three types of mountains are: Folded, Fault-Block and Volcanic. Continental-Continental Collision Normal Fault Strike-Slip Fault Reverse Fault

Folded Mountains When rocks are squeezed together and pushed upward, folded mountains form. This occurs at convergent boundaries. The Appalachian Mountains are an example of folded mountains.

Fault-Block When tension on the earth’s crust causes it to break into many faults Fault-Block mountains form. The layers of the crust break and drop in elevation compared to surrounding layers. The Tetons are an example.

Volcanic Mountains Occur when molten rock erupt onto the Earth’s surface. Most volcanic mountains occur around convergent boundaries. Occur on land and in the sea. Mt. Shasta is an example.