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In this article, we would discuss the types of volcanoes.

1. The molten material erupting from the Earth’s interior through a pipe or a passageway and accumulating around the pipe like a mound is called a volcano.

2. Volcanoes occur when magma (the molten material beneath the Earth) is brought to the surface in the form of lava or volcanic fragments.

3. The temperature of lava ranges between 800 and 13,000 degree Celsius. It consists of steam and many other gases.

4. There are three types of volcanoes: active, dormant and extinct.

5. Active volcano is one that erupts frequently or has erupted recently.

6. Dormant volcanoes have been known to erupt and show signs of possible eruption in future.

7. Extinct volcanoes are those that have not exploded in historical times. However, one cannot be certain these volcanoes will not erupt in future. Mt. Vesuvius and Mt. Krakatau erupted violently though they were believed to be extinct.

8. Process of vulcanisation:

a. At the base of the Earth’s crust, hot rock remains solid due to the pressure above it.

b. When the pressure is reduced by a crack in the Earth, the heated rock can transform into liquid in small chambers called magma chambers.

c. Zones of weakness, regions of lessened pressure or pre-existing fissures are an ideal escape for magma.

d. Gas pressure within the Earth forces the magma to move. As it moves, the magma melts overlying rocks or pushes them aside.

9. Volcanic features:

Extrusive Features:

a. Lava erupts from an opening called volcanic vent. A saucer-shaped chasm created around the vent is called crater.

b. A volcanic explosion throws out a huge amount of magma along with previously solidified lava. Such explosions create a steep crater, which is formed by the destruction of the central part of the volcano and is known as caldera.

c. Rock and mineral fragments blown out from a volcano are known as pyroclastic material.

d. Smaller particles of lava (4 to 25 mm) are called volcanic lapilli whereas particles smaller than this are called as volcanic ash or dust. These particles are either blown away by the wind or come down with rainfall to get deposited as a sedimentary layer known as tuff.

Intrusive Features:

a. Formed by cooling and solidification inside surface of earth in cracks, joints and fractures of rock.

b. Horizontal manner – Sill: Horizontal intrusions along the lines of bedding planes (surface that separates each successive layer of stratified rock)    

c. Vertical manner – Dyke: Vertical intrusions with horizontal cooling cracks

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