Mountains of fire
A volcano is a special kind of mountain that actually builds itself! It
is made of red-hot rock that pours up out of the earth amid earthquakes,
explosions, and towering clouds of smoke and ash.
Scientists think that far down in the earth, where it is fiercely hot,
there are “pockets” of melted rock. It is thought that 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!
There are different kinds of volcanoes that erupt
tunnel
Mount Hekla, Iceland
hot lava
cooled lava
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 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
San Pedro volcano, Guatemala
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.
