What are Volcanoes?

A volcano is a landform, a mountain, where molten rocks erupt through the surface of the planet. The volcano mountain opens downwards to a pool of molten rocks underneath the surface of the earth.


A pressure builds up in the earth’s crust and this is the reason why eruptions occur. Gases and igneous rocks shoot up and splash over or fill the air with lava fragments. The volcano eruption can cause hot ash, lateral blasts and lava flow, mudslides and more.

Formation of Volcanoes:

A volcano mountain is formed by the surface eruption of magma from within the earth’s upper mantle. The magma that erupts to the surface and forms a lava flow that deposits ash. As the volcano continues to erupt, a new layer of lava is added to the surface accumulating to form a mountain.

Different Stages of Volcanoes:

They tend to be conical in shape although there are a variety of forms, depending upon:

  • The nature of the material erupted
  • The type of eruption
  • The amount of change since the eruption

Volcanoes are categorized into three main categories:

  • Active Volcanoes: A volcano will be classified as an active volcano if at the present time it is expected to erupt or is erupting already.
  • Dormant Volcanoes: The classification of volcanoes which is called dormant would be a volcano that is not erupting or predicted to erupt in the near future.
  • Extinct Volcanoes: An extinct volcano is a volcano that no one expects will ever have another eruption.

Reason Behind the Eruption of Volcanoes:

The volcano eruption begins with the formation of magma in the lower section of the earth’s crust. The earth’s crust is made up of massive slabs called plates, which fits together like a jigsaw puzzle. The friction during the movement of plates causes earthquakes and volcanic eruptions.


With pressure, it travels upwards with tremendous force hitting solid rocks and other material and creates a new passage to the earth’s surface. Once the magma reaches the air it is called as lava.

Types of Volcanoes:

These are grouped into four types:

  • Cinder cones
  • Composite volcanoes
  • Shield volcanoes
  • Lava volcanoes

Cinder Cones: These are the simplest type of volcano. They occur when particles and blobs of lava are ejected from a volcanic vent. The lava is blown violently into the air, and the pieces rain down around the vent. Over time, this builds up a circular or oval-shaped cone, with a bowl-shaped crater at the top. Cinder cone volcanoes rarely grow larger than about 1,000 feet above their surroundings.

Composite Volcanoes: Composite volcanoes are some of the Earth’s grandest mountains and they are also called as stratovolcanoes. They are typically symmetrical cones of large dimension built of alternating layers of lava flows, steep-sided, volcanic ash, blocks, bombs and cinders and may rise as much as 8,000 feet above their bases.

Shield Volcanoes: A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They have very gentle slopes and are developed horizontally. Shield volcanoes are built by effusive eruptions, which flow out in all directions. They almost never have violent eruptions, with basic lava simply flowing out.

Lava Domes: Lava domes are the fourth type of volcano that we are going to discuss. Unlike composite and shield volcanoes, lava domes are of significantly smaller stature. They are formed when the lava is too viscous to flow to a great distance. As the lava dome slowly grows, the outer surface cools and hardens as the lava continues to pile within. Eventually, the internal pressure can shatter the outer surface, causing loose fragments to spill down its sides. Generally, such lava domes are found on the flanks of larger composite volcanoes.

Stay tuned with Byju’s to learn more about volcanoes, types of volcanoes and much more.

Practise This Question

What is the principle behind ocean thermal energy?

Statement1: The warm water at surface is used to boil ammonia , which vaporizes and then used to rotate turbine.

Statement 2: The ammonia is vaporized as only then it gains sufficient kinetic energy for power generation.