GS 1, TLP-UPSC Mains Answer Writing, World Geography
With the help of suitable examples, explain the formation of fault-block mountains. How are they different from vault or dome Mountains? Discuss.
उपयुक्त उदाहरणों की सहायता से भ्रंश-खंड पर्वतों के बनने की व्याख्या कीजिए। वे वॉल्ट या गुम्बद पर्वतों से किस प्रकार भिन्न हैं? चर्चा करें।
Approach-
In this question candidates need to write about formation of fault mountains along with examples.In second part discuss about how they are different from dome mountains.
Introduction –
A mountain can be defined as the natural elevation on the earth’s surface. It may be broad at the base and narrow at the top. There are four types of mountains classified on the basis of formation and nature. They are Fold Mountains, Block Mountains, Volcanic Mountains, and Dome Mountains.
Body –
The Block Mountains are formed due to faults in the crust, which are planes where rocks have moved past each other, generating “block mountains”.
- A mountain can be formed when the rocks on one side of a fault rise relative to the other. Block mountains, or horsts, are raised blocks.
- Block Mountains are formed as the result of damage caused by the tensile and compressive forces caused by endogenous forces from the Earth’s interior, also known as fault-block mountains.
- The Block mountains represent an upright portion of the land between two faults or on either side of a valley or canyon gap.
Formation of Block Mountains-
- Block mountains are formed due to the upward movement of the middle block between two normal faults. The up-thrown block is also called a horst. The submitter area of such a block mountain is of the flat surface but the side slopes are very steep.
- Block mountains may be formed when the side blocks of two faults move downward whereas the middle block remains stable at its place.
- It is apparent that the middle block projects above the surrounding surface because of the downward movement of side blocks.
- Such block mountains are generally formed in high plateaux or broad domes.
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- Thus, the side blocks become horsts and block mountains. Such mountains are associated with the formation of rift valleys.
- When a fault block is raised or tilted, block mountains can result. Higher blocks are called horsts and troughs are called grabens.
- A spreading part of the surface causes tensional forces.
- When the tensional forces are strong enough to cause a plate to split apart, it does so much that a center block drops down relative to its flanking blocks.
- Block mountains may be found in India’s central-western region, such as the Satpura and Vindhya mountains.
There are two basic types of block mountains:
- Tilted block mountains have one steep side contrasted by a gentle slope on the other side.
- Lifted block mountains have a flat top and extremely steep slopes.
Examples of block mountains –
- A Sierra Nevada Range, where delamination created a block 650 km long and 80 km wide that consists of many individual portions tipped gently west, with east-facing slips rising abruptly to produce the highest mountain front in the continental United States.
- Block mountains include the Great African Rift Valley (valley floor is graben), the Rhine Valley (graben) in Germany, the Vosges mountain range in France, the Sierra Nevada in the United States, and the Harz mountains in Germany.
- Block mountains are also called fault-block mountains since they are formed due to faulting as a result of tensile and compression.
Dome mountains –
- A mountain range resulting from dissection of a structural dome
- A structural dome is generated when a region of flat-lying sedimentary strata is bent or bowed upward, forming a dome mountain.
- When magma cools, it forms a huge dome of harder rock beneath the surface, which erosion occasionally exposes.
- The top of the dome gets eroded by wind and rain since it is higher than its surroundings. As a result, a circular mountain range emerges.
- Dome Mountains ranges are made up of numerous individual peaks formed by worn-away domes.
| Fault block mountains .
They have continental type of crust
They have found in western united states .
In uplift mechanism they have uplift forces
Block mountains may be formed when the middle block between two normal faults moves downward.
Examples -Sierra newada mountains . In India they are found in south western region such as Satpura and vindya mountains . |
Vault or dome mountains .
They have crustal and igneous rock inland .
They found in isolated structures in in flat lying sedimentary rocks .
In uplift mechanism they have igneous intrusion
Dome mountains arise when enormous globs of magma float up from beneath the crust and push up top rocks, causing the crust to bulge in a rounded shape.
Examples -The Weald in Southeast England and The Black Hills of South Dakota are typical examples of Dome Mountains. |
Conclusion–
When a fault block is raised or tilted, block mountains are formed. Higher blocks are called horsts and troughs are called grabens. A spreading apart of the surface causes tensional forces. When the tensional forces are strong enough to cause a plate to split apart, it does so much that a center block drops down relative to its flanking blocks.
