Science Articles

The How and Why of Volcanoes

Of all the natural disasters in the world, volcanoes are the ones that hold the most fascination for children and young teens. In fact, the most popular project made by kids in middle school is that of a sizzling, burning and overflowing volcano, using various chemicals and concoctions. But do you know how a volcano is formed?


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Of all the natural disasters in the world, volcanoes are the ones that hold the most fascination for children and young teens. In fact, the most popular project made by kids in middle school is that of a sizzling, burning and overflowing volcano, using various chemicals and concoctions. But do you know how a volcano is formed?

The formation of a volcano is a very interesting topic that not many know much about. So let us understand how a volcano is formed-

How a Volcano is Formed –

The reason volcanoes are formed is because the temperature under the surface of the earth becomes hotter and hotter the deeper down you go. At a depth of about 32 kilometres, it is hot enough to melt most rocks.
When rock melts, it expands and increases in volume, thus needing a lot more space. In some areas of the world, mountains are being uplifted. The pressure is not so great under these rising mountain ranges, and so a reservoir of melted rock known as ‘magma’ forms underneath them.

This molten rock rises along cracks formed up the uplift. When the pressure in the reservoir becomes greater than the roof of rock over it, it bursts out as a volcano.

During the eruption, hot gaseous liquid or solid material is actually blown out. The material piles up around the opening and a cone-shaped mound is formed. The cone is the result of a volcano. This erupting cone is now a volcano.

In February, 1943, in the middle of a cornfield in Mexico, people saw a rare and amazing thing take place. A volcano was being born. In three months it had formed a cone about 1000 feet high!

How do volcanoes erupt?

In the centre of a volcano is a mass of molten rock, which when it reaches the surface is known as lava. Its temperature can be as high as 1200 degrees. Lava can be as runny as water or so thick that it scarcely moves at all. When the pressure in the centre of volcano becomes too great, it simply erupts.

When a volcano erupts it hurls out masses of dust and rock, ash, steam, and sulphurous gases. Lava may escape from the crater in the centre or find its way out through vents in the sides of the volcano, solidifying as it cools in the air. A major volcanic eruption can hurl boulders high into the air. These boulders, called volcanic bombs, can be very large in size.

Pompeii and Herculaneum were both Roman towns that were buried under volcanic debris when Mount Vesuvius erupted in AD79. Many people perished while trying to escape and the two towns are still being excavated today.
Active, Dormant and Extinct Volcanoes-

Active volcanoes are those that have erupted at least once in the past 10,000 years. Some active volcanoes erupt at regular intervals of time, while some may erupt just once in a couple of centuries. Active volcanoes can be classified into two types-

• Erupting
• Dormant

Erupting- An erupting active volcano is that which is undergoing an eruption just then.
Dormant- A dormant volcano is that which is not erupting at present, but which may erupt anytime in the future.
Scientists have found a way to predict the eruption of active volcanoes, thus allowing timely evacuation of nearby residents and saving precious lives.

• Extinct Volcano-
An extinct volcano is that which has not erupted in the last 10,000 years and may not erupt in the future.