Mountain Building

What are mountains: The highlands, which rise up to several hundred meters or more above the surrounding terrain. Large mountain systems generally show evidence of enormous forces, which have folded, faulted, and deformed large sections of the earth’s crust.

(1). Orogenic Movement: The crustal movement, which results in the formation of the mountain system, are called the ”orogenic movements”. During these movements extensive folding and faulting of sedimentary strata take place.

(2). Epeirogenic Movements: The sedimentary rocks, which were originally deposited in the ancient sea, are now present on the land surface, several hundred meters above sea level. Although these rocks have been uplifted to hundreds of meters, the individual rock layers are still in a horizontal position. Such vertical movements by which continental blocks are raised or lowered slowly and continuously are called the ”epeirogenic movements”. In such cases, generally folding of strata does not take place.

The theory of isostatic balance can account for some uplifting. The earth’s crust is believed to be floating on the partially molten asthenosphere. As erosion removes the tops of mountains, the mountains themselves will rise up. The processes of uplifting and erosion will continue till the root of the mountain has reached the same height as the surrounding land. Similarly, if weight is added to the crust, as by the accumulation of sediments on the ocean basins, it will respond by subsiding.

Types of Mountains:

There are five main types of mountains; (i) volcanic mountains, (ii) relict mountains, (iii) fault-block mountains, (iv) up-warpring mountains, and (v) fold mountains. Since fold mountains represent the wold’s major mountains systems, the process of mountain building is usually described in terms of their formation.

(1). Volcanic Mountains: 

The volcanic mountains are formed due to the accumulation of lavas and pyroclastic materials. Many of the mountain peaks in the western Andes of South America are of volcanic origin.

(2). Relict Mountains/Residual Mountains:

The relict mountains are also called the ”erosional mountains”. They are formed due to differential erosion of the rock masses. Plateaus are examples of relict mountains. ”Plateaus” may be defined as flat-topped areas that rise to a height of over 300 meters above their surrounding terrain.

(3). Fault Block Mountains: 

These mountains are commonly called ”block mountains”. They are bounded by high-angle normal faults. They are usually associated with rift valleys. The block mountains, found in the Basin and Range Province of south-western United States, are notable examples of this class.

(4). Upwarped Mountains: 

These mountains are also called ”domed mountains”. They are formed by the intrusion of an igneous body (magma), such as a batholith or laccolith. When the igneous body is intruded, up-warping of the overlying strata may occur thereby forming a mountain.

(5). Fold Mountains: 

The largest and most complex mountain systems of the world belong to this category. In the fold mountains, folding is always dominant but faulting and igneous activity are also present in varying degrees. The Himalayas, Alps, Urals, Rockies are examples of this type of mountain.