Folds and Faults
When rocks bend without breaking, they create folds—wave-like formations in rock layers. Anticlines fold upward like an arch, while synclines fold downward like a bowl. Some folds enter the earth at an angle (plunging folds), while others remain horizontal non−plungingfolds.
Faults occur when rocks break under stress, typically in colder, near-surface conditions. They have two sides: the hanging wall (upper side) and footwall (lower side). Different stresses create different fault types: normal faults result from tension with the hanging wall moving down, while reverse faults come from compression with the hanging wall moving up. Strike-slip faults like the San Andreas slide horizontally past each other.
Joints are fractures where rocks crack but don't move significantly. Compression typically creates regular joints, while columnar jointing forms from cooling and shrinking (think Giant's Causeway), and exfoliation jointing happens when pressure is released from deep rocks.
Remember This: The type of fault tells you about the stress that formed it—normal faults indicate pulling apart, reverse faults show compression, and strike-slip faults result from shearing forces.