Volcanism is an important phenomenon and a major topic of Geography in the UPSC syllabus. It is important to read on this topic and also understand the various terminologies and concepts associated with it. In this article, you will get a brief on volcanism for the civil service exam.

Volcanism can be defined as an igneous activity which includes the following :  

  1. Formation of Magma
  2. Upward movement of Magma
  3. Ejection on the surface
  4. Cooling and Solidification

  Magma: Partially molten rock is known as Magma. It is composed of the following :  

  1. Gas in the form of water vapour and carbon dioxide
  2. Pyroclastic matter which is solid
  3. Liquid magma content is commonly known as lava

Upward Movement: As discussed above, gases consist of water vapour and carbon di oxide, which help the magma in its upward movement.  

Ejection on the surface:   Commonly known as eruption, it can be classified into two types :

  1. Fissure eruption
  2. Central eruption

Fissure eruption

In this kind of eruption, magma comes onto the surface through the cracks and hence is not explosive. The ejection is smooth and thus it forms landscapes such as plateaus since the lava spreads to a larger area.

Central eruption  

Unlike in the fissure eruption, here the magma comes out through narrow pipes and hence results in an explosion while ejection onto the surface. This explosive nature results in the formation of mountains which can be called volcanic mountains. All the volcanic islands are actually volcanic mountains.  

Cooling and Solidification: The cooling and Solidification of magma can happen both inside the earth and over the surface of the earth. The examples of intrusive landforms (forming inside the earth) are:  

  1. Batholiths
  2. Laccoliths
  3. Lapoliths
  4. Phacoliths
  5. Sills/Sheets
  6. Dikes

  The examples of extrusive landforms (forming over the surface) are :  

  1. Lava plateau
  2. Volcanic mountain

It may be noted that since the lava flows to a larger area to form plateaus, it consists of a larger consistency of liquid in it while the volcanic mountains are formed due to an explosion. This explosion has a greater carrying force for the solids to eject onto the surface. Thus the mountain landscape formed due to a volcanic explosion, contains more of solids.

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