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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.

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Internal 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.

External Process: Continuous wearing down and rebuilding of the earth’s surface is the result of external process.

Mountains:

• 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.

Mountain Range: 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.

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Types of Mountains:

There are 4 types of mountains, viz. fold mountains, block mountains and volcanic mountains.

#1. Fold Mountains:

The formation of fold mountains

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1. Where an area of sea separates two plates, sediments settle on the sea floor in depressions called geosynclines. These sediments gradually become compressed into sedimentary rock.
2. When the two plates move towards each other again, the layers of sedimentary rock on the sea floor become crumpled and folded.
3. Eventually the sedimentary rock appears above sea level as a range of fold mountains.

Where the rocks are folded upwards, they are called anticlines. Where the rocks are folded downwards, they are called synclines. Severely folded and faulted rocks are called nappes.

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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.

#2. Block Mountains:

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.

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#3. Volcanic Mountains:

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.

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#4. Dome Mountains:

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Dome mountains form when large globs of magma float up from beneath the crust and push up surface rocks, creating a rounded swelling in the crust. Once the magma cools, it creates a large dome of harder rock under the surface, which erosion sometimes reveals.

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What are the 3 basic types of rocks?

Just as any person can be put into one of two main categories of human being, all rocks can be put into one of three fundamentally different types of rocks. They are as follows:

#1. Igneous Rocks

• Igneous rocks are crystalline solids which form directly from the cooling of magma.
• This is an exothermic process (it loses heat) and involves a phase change from the liquid to the solid state.
• The earth is made of igneous rock – at least at the surface where our planet is exposed to the coldness of space.
• Igneous rocks are given names based upon two things:
  • composition (what they are made of) and
  • texture (how big the crystals are)

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The word igneous is derived from the Latin word Ignis which means fire. The rocks formed by the solidification on the cooling of molten magma, are called igneous rocks.

Depending on where the molten magma cools, they are of the following types:

• Intrusive Rocks
• Extrusive Rocks

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When the molten magma cools deep inside the earth’s crust, intrusive igneous rocks are formed. They:

• Cool down slowly
• Form large grains
• Granite is intrusive igneous rock. Grinding stones used to prepare paste / powder of spices and grains are made of granite.

Extrusive Igneous Rocks:

• When the molten magma (lava) comes on the earth’s surface.
• It rapidly cools down and becomes solid.
• Rocks formed in such a manner on the crust are called extrusive igneous rocks.
• They have a very fine grained structure.
• Basalt is an example of extrusive igneous rocks. The Deccan Plateau is made up of basalt rocks.

#2. Sedimentary Rocks

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• These rocks get their name from the Latin word sedimentum which means settle down.
• These rocks are formed by the settling down of sediments.
• Sediments are the smaller particles / fragments that are formed by the breaking down of rocks when they roll down, crack and hit each other.
• These sediments are transported by wind, water etc.
• These sediments; when compressed and hardened; form sedimentary rocks.
• Sandstone is an example of sedimentary rock. It is made up of grains of sand.
• The sedimentary rocks may also contain fossils of plants, animals and other micro – organisms that once lived on them.

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#3. Metamorphic Rocks:

The Greek word ‘metamorphose’ which means change of form, is the root of the word metamorphic. In other words, these are the rocks that are formed when the igneous and sedimentary rocks change their form under the following two circumstances:

• Great heat and
• Great pressure

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The following are the examples of metamorphic rocks:

• Slate: Clay becomes slate after metamorphosis [Texture = Foliated]
• Marble: Limestone becomes marble after metamorphosis [Texture = Non-Foliated]

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#4. What is a Rock Cycle?

The Rock Cycle is a group of changes. Igneous rock can change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock.

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NOTE: This lesson forms a part of the series on Physical Geographic Lectures – Click to read the collection