SOURCE: 8TH NCERT
· Landform is a natural feature of the earth’s surface.
· The surface of the earth varies from one place to another.
· The main landforms are; mountains, plateau and plains.
· There are two processes which lead to formation of different landforms.
· These processes are; internal process and external process.
· The earth beneath your feet is continuously moving.
· The movement of earth’s surface results in internal process.
· The internal process results in a portion of the earth’s surface getting elevated or getting sunk.
· Continuous wearing down and rebuilding of the earth’s surface is the result of external process.
· Removal of materials is called erosion. Erosion results in lowering of the earth’s surface.
· Erosion is carried out by various agents; like wind and water.
· Deposition of materials results in rebuild of the earth’s surface. It also results in the surface getting elevated.
· Wind and water are the main agents of deposition.
· A mountain is the natural elevation of the earth’s surface.
· A mountain may be narrow at top and broad at the base.
· The elevation of mountain is considerably more than that of surrounding area.
· We know that temperature reduces with increase in altitude.
· Due to this, very high mountains are usually covered with snow.
· Permanently frozen rivers of ice are called glaciers.
· Glaciers are found in some of the very high mountains.
· When mountains are arranged in a line, then it is called a mountain range.
· Some of the mountain systems contain ranges spread over hundreds of kilometers.
Types of Mountains :
There are three types of mountains, viz. fold mountains, block mountains and volcanic mountains.
· Fold mountains are created through a process called orogeny. An orogenic event takes millions of years to create a fold mountain,
· When a tectonic plate gets pressure from two sides, it gets folded. Some of its portion becomes elevated and forms the mountains.
· The depressions form the valleys. The Himalayas,
· The Andes and the Alps are examples of Fold Mountain. They are the young mountains of the world and hence they have some of the highest peaks of the world.
· Highest peaks are found in folded mountains
· Folded mountains are the youngest on the surface of the earth
· fold mountains in India: Himalaya- young fold mountain
· When large areas are broken and displaced vertically, Block Mountains are formed.
· In this case, the uplifted blocks are called horsts.
· On the other hand, the lowered blocks are called graben.
· Examples of Block Mountains are; the Rhine Valley and the Vosges mountain in Europe.
· A mountain formed due to volcanic activity is called Volcanic Mountain.
· Examples of Volcanic Mountains are; Mt. Kilimanjaro and Mt. Fujiyama.
· Andaman and Nicobar islands in India are the tip of the volcanic mountains which rise from the ocean floor