Folds and Folding:
The bend or the wrap of layered rocks is known as a fold. When a crystal rock comes under pressure and stress, it tends into Basins a hundred kilometers across along with normal faulting action. The size of the folds may differ based on the difference in the landscape. Some are too small to see, while others are road-cut size, whereas others are equal to the size of a mountain ridge. Mostly folding and faulting takes place together. The folding of the Zagros Mountains of Iran, the Andes Mountains of South America, and the Appalachians of North America are the best examples of folding. If the folds come into existence as a result of pressure exerted from both sides, are known as narrow folds. The folds of the Alp mountains in Europe are the best examples of Narrow Folds. The crests of such folds are very high, and the troughs are very deep. However, the folds which are resulted from stress or pressure exerted from one side, are known as Open folds, such folds are low and broad. The folds are known as Open folds.
Types of Folds:
Different intensities of compression and the nature of rock structure give rise to different types of folds. Major types of folds are as given below:
These folds are mostly open and upright with a vertical axis. The slides of such folds have identical inclination.
In such folds, one side is long with a gradual slope but the other side is comparatively short and steep.
Such fold is also termed overfold. An Isoclinal is formed when a fold is pushed over on one side so that both the sides of the fold are inclined in the same direction. Moreover, the short and steep side also dips in the same direction as the flatter side.
It is a highly compressed folds that double back on itself with an axial plane which is nearly horizontal. It is also called Nappe.
Perpendicular or Vertical Folds:
A perpendicular or vertical fold is formed when the short and steep side is vertical.
Land-forms Due to Folding:
The process of folding result in different types of landforms as detailed below:
These are dome-like down-warped structure. The basins are identified through the age of the rocks because they contain sedimentary beds. In respect of location, the oldest rocks are found at the flanks and the youngest rocks are located in the center.
These are dome-shaped up-warped rocks which come into existence due to compressional stresses.
A cuesta is a long ridge with a steep escarpment on one side and a gently dipping slope and rock beds on the other.