Plastic Deformation
Charlene Estrada
Solid rock exposed to stress can undergo folding, stretching, compression, and bending when there is sufficiently high temperature and pressure with depth. This is called plastic deformation.
First, we will explore the two main types of stress. Confining pressure is stress that is applied equally in all directions. Differential stress is stress that is applied unevenly.
Photo: G. Shuttleworth
In plastic deformation, stretching and bending do not just occur on the scale of individual rocks! You can see folds in the rock layers themselves! This is something that you might have even seen driving around on road trips across America! There are two main types of folds that you learned about already in the video several slides ago: Anticlines and Synclines.
Anticlines tend to arch upward, and Synclines arch downward. This isn’t all there is to them, however!
The OLDEST beds are found at the core of an anticline. The YOUNGEST beds are found at the core of a syncline.
Another way to remember: ANTICLINE has an “A” or arch shape. Syncline has a Smile shape.
