Layers of rock can wrinkle or contort into a series of wave-like curves that geologists call folds. Not all folds look the same—some look like an arch, some like a tough, and some have other shapes. This animation examines how two types of folds are formed. View 1 illustrates the formation of a flexural-slip fold, and View 2 shows the formation of a passive-flow fold.

by Stephen Marshak

>>see: p.259