Unit 4: Plate Tectonics The Crust Under Stress & Mountain Building Notes

Stress: Compression & Tension Stress is the amount of force that is put on a material. All things can undergo a certain amount of stress until it breaks. Elastic rebound: The sudden return of elastically deformed rock to its un deformed shape. The crust of the Earth can also withstand a certain amount of stress. When too much stress occurs on the Earth’s crust it suddenly breaks.

When rock changes its shape due to stress it is called deformation. Deformation can occur when plates collide and are squeezed together. This is called compression. Tension occurs when rock layers of a plate are pulled away from each other.

Folding (Compression) Folding of rock layers can occur when rock layers are compressed. Depending how the layers are deformed, anticlines, synclines and monoclines can form. These folds can be extremely large like those at the Delaware Water Gap. Others are measured in just centimeters (small).

Faulting (Tension) Faulting occurs when enough stress causes rock layers to break.

There are 3 kinds of faulting:

Normal faults: occurs when tension causes the footwall to move up, or the hanging wall moves down

Reverse Faults: occurs when compression causes the hanging wall to move up, or the footwall to move down.

Strike-Slip Faults: occur when rock layers slide (shear) horizontally along each other’s edge.

Mountain Building When large areas of a plate undergo compression or tension, it results in the formation of mountains.

There are 3 common types of mountain formations: Folded Mountains: form when the areas along the edge of a continental plate are compressed and forced upward. They form along convergent boundaries.

Fault Block Mountains: form along the edges of plates that are undergoing tension due to diverging plates. As these areas diverge, rock layers break forming mountains with sharp jagged peaks. Volcanic Mountains: form when molten rock erupts along a convergent boundary.