Inside a Volcano

Deep under the ground, it is hot enough to melt rock. This melted rock is called magma. Magma collects in a big space called a magma chamber. Magma is lighter than the hard rock around it, so it slowly pushes up.

It rises up a long, thin pipe. Gases in the magma push harder and harder, like the fizz in a shaken soda bottle. When the push gets too strong, the volcano erupts. Magma bursts out of an opening called a vent. The vent sits in a bowl-shaped hole at the top, called the crater. Once magma reaches the air, it has a new name: lava.

Sometimes lava oozes gently down the sides. Other times, huge clouds of ash blast high into the sky. When the lava and ash cool, they harden into new rock. After many eruptions, layer upon layer of rock builds up. That is how a volcano can grow into a tall mountain.