Stress in the Crust
The movement of Earth's plates creates powerful forces that squeezes or pull the rocks in the crust. These forces are examples of stress, a force that acts on rock to change its shape or volume. Because stress is a force, it adds energy to the rock. The energy is stored in the rock until the rock either breaks or change shape. When the rocks break, an earthquake forms.
Types of Stress
Shearing, tension, and compression are the three types of stress that happens in Earth. These three types of stress forces work over millions of years so they can change the shape and the volume of earth because of these forces, some rocks tend to become weak and break other rocks bend slowly and get hot from the heat of the sun.
Shearing is stress that pushes a mass of rock into two different directions. Shearing occurs at transform boundaries because that's where the rocks go past each other. Shearing can cause rock to break and slip apart or to change it's shape. Just like two scissor blades going back and forth past each other. The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle. Tension occurs at divergent boundaries because that's where the rocks move away from each other. Tension occurs where two plates are moving apart. Just like stretching out a piece of bubble gum. The last stress force is called compression, it squeezes rock until it either folds or breaks. Compression occurs at convergent boundaries because the two rocks are squeezing together. Just like if you were squeezing a lemon. The two sides of the lemon are being pushes together to get the juice out. Any changes in the shape or volume of earth's crust is called deformation. Some of the changes happen so slowly, they can't be seen. If you sped up time though, you could see every bend, tilt, or fold in the crust. This slow movement is how deformation happens. |