Orogeny: Types of Mountains and Mountain Building

Orogeny is primarily the mechanism by which mountains are built on continents due to the large structural deformation of the Earth’s lithosphere caused by Plate Tectonics.  Orogenesis involves the following:

• Structural deformation of the rocks
• Faulting of rocks
• Folding of rocks
• Igneous Processes
• Metamorphism
• Glaciation
• Erosion
• Sedimentation

Mountains are born and have a finite life span. Young mountains are high, steep, and growing upward. Middle-aged mountains are cut by erosion. Old mountains are deeply eroded and often buried.

We have to note here that the constructive processes, like deformation, folding, faulting, igneous processes and sedimentation build mountains up. On the contrary, the destructive processes like erosion and glaciation, tear them back down again.

Causes of Mountain Building

There are three primary causes of mountain building as follows, which have already studied:

• Convergence at convergent plate boundaries.
• Continental Collisions
• Continent Rifting

Forms of Mountains

A mountain may have several forms. Important among them are: i) mountain ridge, ii) mountain range, iii) mountain chain, iv) mountain system, v) mountain group, and vi) cordillera.

Mountain Ridge

It is a linear, steep-sided high hill, or spur. The slope of one side of a ridge is steep, while the other side is of moderate slope. A ridge, however, may have symmetrical slopes on both sides. The Shimla Ridge is a good example of mountain ridge.

Mountain Range

A mountain range is a linear system of mountains and hills having several ridges, peaks, summits and valleys.

Mountain Chain

A mountain chain consists of several parallel long and narrow mountains of different periods.

Mountain System

A mountain system consists of different mountain ranges of the same period. In a mountain system, different mountain ranges are separated by valleys.

Mountain Group

A mountain group consists of several unsystematic patterns of different mountain systems

Cordillera

It is a Spanish term referring to a system or major group of mountains. A cordillera consists of several mountain groups and systems. In other words, cordillera is a community of mountains having different ridges, ranges, mountain chains and mountain systems. It usually refers to an orogenic belt at a continental scale, e.g., the Western Cordillera of the U.S.A., which includes all the ranges between the Pacific and the Great Plains.

Types of the Mountains

No two mountains are the same. They, however, can be classified on the basis of their most dominant characteristics into: i) folded mountains, ii) volcanic mountains, iii) fault-block mountains, and iv) upwarped (dome) mountains.

Folded Mountains

Folded mountains comprise the largest and most complex mountain systems. Although folding is the dominant characteristic, faulting and igneous activity are always present in varying degrees in folded mountains. The Alps, Himalayas, Rockies, Andes, Appalachians, Tien Shan, Caucasus, Elburz, Hindukush, etc., are all of this type. The folded mountains present the world’s major mountain systems. They are the youngest mountains in the world.

Volcanic Mountains

Volcanic mountains are formed from the extrusion of Java and pyroclastic materials, which if continued long enough, produces gigantic volcanic piles. The Kilimanjaro (Africa), Cotopaxi (Andes), Mt. Rainier, Hood and Shasta (U.S.A.),  are some of the examples of volcanic mountains.

Fault Block Mountains

Fault-block Mountains are bounded by high angle normal faults. Some of them are associated with rift valleys such as those in East Africa, while others appear to be formed by vertical uplifting. A notable example of fault-block mountain is found in the Basin and Range Province of the southwestern USA. The Salt Range of Pakistan, and Siena-Nevada of California (U.S.A.) are also the typical examples of fault-block mountains.

Upwarped (Domed) Mountains

Upwarped or domed mountains are formed by magmatic intrusions and upwarping of the crystal surface. The lava domes, batholithic domes, laccolithic domes, salt domes, etc., are the examples of Dome Mountains. The Black Hills of South Dakota, and the Adirondack mountains of New York may be cited as the examples of upwarped (domes) mountains.

Different Stages of Orogeny

Mountains can also be divided on the basis of their making i.e. Orogeny during different geological periods.

Pre-Cambrian Orogeny

This was the first ever Orogeny on earth and represents the oldest mountains of the earth. The examples are Laurasian of North America, Elogoman etc.

Caledonian or Mid Paleozoic Orogeny

It occurred during Silurian and Devonian periods. The example are Aravallis of India, Brazilian Highlands in America, Scotland of Europe etc.

Harcynian or Late Paleozoic Orogeny

This occurred in the Permian period. Example are Appalachian of North America, Black Forest of Europe etc.

Alpine Orogeny

This took place in Tertiary period and represents the youngest and newest mountain ranges of Earth. The examples are Himalaya, Rocky, Andes, Apennines, Alps etc.