Folded mountains, or fold mountains, form when two tectonic plates within the Earth's crust push against each other, generating pressure sufficient for creating large mounds. Fold mountains exist primarily in mountain ranges, and develop over many years. The process of mountain creation begins as two tectonic plates move apart from each other, then gradually move inwards again, forcing deposits of sedimentary rock upwards.
Fold mountains take place through the process of orogeny, which takes place over millions of years. The accumulation of sedimentary rock in the orogenic process results in the uneven distribution of rock, which in turn creates jagged and uneven mountain surfaces. Fold mountains generally form in mountain ranges, and include some of the highest and most dramatic mountains in the world. These mountains comprise most of the mountains on Earth. This group contains the Andes, Himalayan and Appalachian mountain ranges. Fold mountains, like other types of mountains, never stop growing. They continue accruing sedimentary rock, growing taller and wider over time. Some, however, face constant erosion, which slows or reverses their growth. These mountains form on land and in the ocean. Most grow upwards and are classified as anticlines, while others grow in inverted patterns called synclines. Fold mountains forming on the ocean floor can reach tremendous heights, growing tall enough to rise above the water surface.