Stress The surface of the earth is divided into 13 major tectonic plates. These plates interact with each other constantly.
Stress The movement of tectonic plates create stress ( a force that acts on a rock changing its shape and/or volume.
3 Types of Stress The rocks reaction to stress is called strain. The types of stress are: –Shearing –Tension –Compression
Shearing: rocks break and slip past each other horizontally as they are pushed in opposite directions. Tension: pulling of rock causes it to become thinner in the middle (think of stretching bubble gum after you chew it!) Compression: rock is squeezed then folds or breaks. (Pushing two things together) Types of Stress
Faults/Fractures Breaks in rocks create fractures. A fracture in which there is movement along the line of the break is called a fault.
Normal Fault (Divergent boundary) Created by tension in which the hanging wall moves downward relative to the footwall. (Notice the way arrows are pointing)
Reverse Fault ( Convergent boundary ) Created by compression in which the hanging wall slides up over the footwall. (Notice the way arrows are pointing) These blocks are called Fault Blocks! The position of a Fault Block determines whether it is a hanging wall or a footwall
Strik-slip Fault (Transform boundary ) Created by shearing in which the boundaries slide horizontally past each other.
Monocline Fold One side is vertically lifted higher than the other side of the rock.
Folding Causes Mountains Folded (when rock layers are squeezed together and pushed upward) Fault-block (faulting causes large blocks to crust to drop down relative to other blocks. Volcanic (molten rock erupts onto Earth’s surface)