I. Types and Effects of Stress

A. Stresses occur in the crust working over millions of years to change shape and volume of rock.

            B. Types of Stress

                        1. Shearing:

a) force that pushes rock in 2 opposite directions

b) causes masses of rock to break, slip, or change shape

                        2. Tension:

                                    a) force that pulls on crust in opposite direction

                                    b) causes crust to stretch and become thin in middle

                        3. Compression:

                                    a) force that pushes rock in together

                                    b) causes crust to rise

            C. Stress causes deformation (any change in the volume or shape of Earth’s crust.)


II. Types and Effects of Faults

            A. A fault is a break in the Earths crust where slabs of crust slip past each other.

B. Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks.

C. Types of Faults

            1. Strike-Slip Fault

                        a) found along transform plate boundaries.

                        b) caused by shearing force

                        c) example: San Andreas Fault in CA.

            2. Normal Fault

a) caused by tension force

b) the fault is at an angle so one block lies above the fault (hanging wall) while the other lies below the fault (footwall).

c) movement will cause the hanging wall to slip downward

d) example: Rio Grande rift valley in New Mexico (diverging crust)

                        3. Reverse Fault

                                    a) caused by compression forces

b) fault is at an angle, so the hanging wall slides over the top of the footwall.

c) movement will cause the hanging wall to move upward

d) example: Mountains in Glacier National Park



D. Friction along faults

                        1. Low friction: Rocks slide by each other without much sticking

2. Moderate friction: Sides of the fault jam together, but eventually break free producing small earthquakes.

3. High friction: Rocks lock together and do not move. Stress continues to increase until it is strong enough to overcome the friction force.

III. Mountain Building

            A. It takes millions of years to build mountains

            B. Fault-Block Mountain

                        1. Caused by tension forces at diverging plates at normal faults.

                        2. The hanging walls slip downward, the footwall moves upward.

            C. Mountains formed by Folding

1. Folds are bends in rock that form when compression shortens and thickens part of Earth’s crust.

D. Anticlines and Synclines are found on Earth’s surface where compression forces have folded the crust.

                        1. Anticline: A fold in rock that bends upward into an arch

                        2. Syncline: A fold in rock that bends downward to form a bowl

            D. Plateaus: a large area of flat land elevated high above sea level.