External Structure of the Earth

External Structure of the Earth

 The diversified outward appearance of the earth is known as the external structure of the earth. Some principal and important examples are described below.

Main Landforms of the Earth

Earth's topography is made up of many different types of landforms. While the planet is covered primarily with water, the three major types of landforms are mountains, plains and plateaus. These can be formed by a variety of natural forces, including erosion from water and wind, plate movement, folding and faulting, and volcanic activity.


While most mountains are created due to the slow and gigantic movement of the earth's tectonic plates, some are formed as a result of erosion and volcanic activities. Mountains are characterized by a higher elevation as compared to the surrounding areas. They are higher than 600 metres, and taller and steeper than the hills. The world's tallest mountains The Himalayas are located in Asia and the largest range of mountains is present in the Atlantic ocean. You will be surprised to know that some of the highest mountain peaks are located deep in the oceans. There are some mountain which is not a part of a mountain range but exists in isolation such as Mount Kilimanjaro in East Africa.

Mountains : Types and their Formation

An elevated landform is identified as a mountain if it has a summit and there are slopes on its sides. They are basically made up of earth and rock materials. Regarding mountain formation, the outermost layer of the earth or the earth's crust is composed of six tectonic plates. When two plates move or collide with each other, vast land areas are uplifted, resulting in the formation of mountains. Depending upon the geological processes responsible for uplift of mountains and landform characteristics. There are four major types of mountains.

Fold mountains

Fold mountains : Fold mountains  are the most common type of mountains. They are formed due to collision of two plates, causing fold that descends on both folding of the earth's crust. The sides is called Anticline, whereas, the fold that ascends from a common low point (on both sides) is called Syncline (fig. 4.13). Examples of fold mountains are the Himalayas located in Asia, Rocky mountains located in North America, and the Alps located in Europe.

Volcanic mountains : Volcanic mountains are created due to volcanic eruptions. When this lava erupts and piles up on the surface of the earth, it cools and solidifies to form a volcanic mountain. In many instances, the volcanic materials erupt to great heights due to pressure from under the earth’s crust (fig. 4.14).

Volcanic Mountains

Examples of volcanic mountains are the Mount Fujiyama in Japan, Mount Vesuvius in Italy and Mount Pinatubo in Philippines.

Fault-block mountains: Due to tectonic movement in the earth's surface contraction and expansion of rocks takes place. This movement creates cracks in the earth's surface which leads to displacement of the earth’s surface. It is called Fault.

Fault - block mountains

Fault mountains or fault-block mountains are created when blocks of rock materials slide along faults in the earth's crust.

There are two types of block mountains, viz., the lifted and tilted. In the former type, the mountain has two steep sides, whereas, the tilted type has one steep side and a gentle sloping side (fig. 4.15). Examples of fault-block mountains are the Vindhya mountains and Satpuras mountain in India, Salt mountain in Pakistan and Black forest of Germany.

Dome/Laccolith mountains : Dome mountains are built when the hot magma rises from the mantle and uplifts the overlying sedimentary layer of the earth's crust. In the process, the magma is not actually erupted, but it cools down and hardens, thereby forming the core of the mountain. As their appearance resembles a dome shape, they are called Dome Mountains or Laccolith Mountains (fig. 4.16).

Laccolith mountains

These do not have any summit. Example of dome mountain is the Henry mountain in USA.


Plateaus are formed by various geologic activities, such as immense lava flows, uplifting due to tectonic plate collisions, and sediment plateaus formed from eroded material from mountains. Plateaus are lower than mountains but higher than plains with steep slopes and extensive undulating surface is known as plateau (fig. 4.17). The height of the plateau varies from few hundred metres to few thousand metres. The height of the highest plateaus of the world varies from 4270-5190 metres.


On the basis of the location, plateaus can be classified into three categories :

1. Intermontane plateau

2. Piedmont plateau

3. Continental plateau

1. Intermontane plateau : This type of plateau is surrounded by mountains. The Tibetan plateau is an intermontane plateau where The Kunlun mountain is in the north, The Himalayas in the south and it the east and west there are mountains, Bolivia in South America, Mexico in Latin America, and Mongolia and Tarim in Asia is this type of plateau (fig. 4.18).

Intermontane Plateau

l. Piedmont plateau : When high mountains are eroded and the sediments are deposited at the foothills and creates plateau is known as piedmont plateau. Colorado in North America and Patagonia in South America are the piedmont plateaus.

3. Continental plateau : Extensive highland surrounded by sea and lowlands is called Continental Plateau. These type of plateaus have no link with the mountain. Examples are Spain, Australia, Saudi Arabia, Greenland and India.


Extended lands with gentle slope a bit high from the sea level is called plain land. The plains are formed by the erosional and depositional work of different land forming agents like river, glacier and wind. Gently sloping and undulating land is suitable for agriculture, settlement and road construction. On the basis of origin the plains are classified into two categories : Erosional and depositional plains.

Erosional plains : This type of plains are formed for erosion by river, wind and glacier. The upper rocks are eroded gradually and the lands with steep slope are transformed into plains. The plains at the foothills of Appalachian mountains and the plains of Finland and Siberia are these type of plains. The Barind and the Madhupur Tract of Bangladesh are examples of erosional plains.

Depositional plains: Natural processes of river, wind and glacier transport the sand dust and sediment, from one place and deposit in a lowland forming a depositional plain. Formation of depositional plains are found from the mountainous region to the sea coast. River can form valley such as the valley of Nepal. It can form alluvial fan at the foothills of the mountains by deposition. In the middle course of a river, where velocity of the river is reduceds it overflows the banks causing flood during rainy season and the sediments are deposited gradually on both sides of the river forming a plain land which is known as flood plain. Flood plains of Dhaleswari and Jamuna

are of these type. A plain land formed at the mouth of the river through deposition is known as Delta. Ganges delta is located in the southern part of Bangladesh.

Plains are also formed in the coastal areas by the activity of ocean current. These are known as coastal plains. Coastal plain of Bangladesh stretches from Feni river to Teknaf. Plains are also formed by the deposition of glacial moraines in the cold regions of the world. The Prairie of Canada are formed from the glacial deposits.

Learn more about - 

👉👉 Life Cycle of a River

👉👉 Internal Structure of the Earth

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