Why do volcanoes erupt?
A volcano is a mountain with a secret: inside, it is full of fire. Every now and then, that fire bursts out of the top with a great roar, and we call it an eruption. Why does it happen?
It is very hot inside the Earth
The Earth is made of layers. The outermost is the crust, where we live, and beneath it lies another called the mantle, where it is so hot that some rocks melt. Melted rock mixed with gases is called magma.
The magma rises
Magma is lighter than the solid rock around it, so it tends to rise, just like an air bubble in water. It gathers in a big pocket under the volcano, the magma chamber, and the gases dissolved in it create more and more pressure.
The eruption
When the pressure gets too high, the magma looks for a way out through cracks and through the crater. It is like shaking a bottle of soda and opening it: the gas pushes the liquid out. Once it reaches the surface, magma is called lava and it can be hotter than a thousand degrees. The volcano also throws out ash, gases and rocks.
The parts of a volcano
A volcano has a pipe through which magma rises, a crater at the top where it comes out and slopes down which the lava flows. With every eruption new layers are deposited and the volcano slowly grows.
Helpful volcanoes
Although they deserve respect, volcanoes are also useful: their ash fertilizes the soil, their heat is used as geothermal energy and they have created whole islands, such as the Canary Islands or Hawaii.
How they are watched
Volcanologists, the scientists who study volcanoes, measure tremors, temperature and gases to know when an eruption may happen and to warn people in time.
Experiment: your own volcano
With an adult to help, put baking soda in a small cup inside a tray, add a few drops of red food coloring and pour in vinegar. The reaction makes gas bubbles that overflow the cup, like a small eruption.
