Volcanoes for Kids - What is a Volcano - Types of volcanoes - How volcanoes erupt

Volcanoes are a special kind of mountains that actually build themselves!
Volcanoes are made of red-hot rocks that pour up out of the earth followed by earthquakes, explosions, and towering clouds of smoke and ash.

Far down in the earth, where it is fiercely hot, there are “pockets” of melted rock. The pressure of gas pushes this melted rock, called magma, up out of the ground.
When magma comes out of the ground it is called lava. It may be as thick as syrup or as thin as watery soup, but it cools into a black, gritty rock.
It is this rock that builds the volcano. As the lava pours out of the earth, it piles up into the shape of a cone or dome, with a tunnel running down its middle. The more lava that comes out, the higher and wider the volcano gets.
After a volcano has built itself, it may sit quietly for hundreds or even thousands of years.
Then, suddenly, the volcano becomes active.
The ground begins to shake.
Rumbling noises come from deep inside the earth.
From the top of the volcano, clouds of dark smoke twist up into the sky.
The rumblings become a loud, steady, rushing roar. Magma or hot gas comes surging up through the tunnel. It may burst out of the top of the volcano or flow out of cracks in the side.
The volcano has erupted!


"Rinjani 1994" by Oliver Spalt (talk · contribs), http://www.artweise.de - Own work. Licensed under CC BY 2.0 via Wikimedia Commons.

Types of volcanoes - how volcanoes erupt?

There are different kinds of volcanoes that erupt in different ways.
One kind shoots a stream of glowing lava high into the air, like a giant, fiery fountain.
Another kind shoots out solid chunks of red-hot rock and cinders.
Some volcanoes pour rivers of lava through cracks in their sides.
Some send clouds of glowing, super-hot steam and gas rushing down the mountainside.
And some volcanoes blow themselves to pieces when they erupt!

There are several thousand volcanoes in the world. 
Many of them do not seem able to erupt any more, and are called “dead” volcanoes.
But some volcanoes that have been “dead” for hundreds of years have suddenly become active and had terrible eruptions.
And active volcanoes are liable to erupt at any time.
Volcanoes have killed many people and destroyed whole cities.

But volcanoes have done good things, too.
The ash that comes from volcanoes becomes some of the richest, most fertile soil in the world. And scientists think that, billions of years ago, much of the earth's first air and water came from gas and steam spouted from volcanoes.