Some appeared hundreds of thousands of years ago, while others just appeared recently.

But each time, it’s the same phenomenon: magma, a mixture of molten rock and hot gas from the depths of the earth, escapes through a crack in the Earth’s crust. 

On contact with the air, magma cools down and hardens. With each eruption, the rock piles up. A volcano is born!

But why does the Earth’s crust crack?

Because tectonic plates move. 

That’s right, the continents and oceans sit on huge plates which slot together like a jigsaw puzzle.

These tectonic plates are always moving and sliding over and under each other, like on a conveyor belt.

Most volcanoes are found at the junction of two plates.  

For example, the volcanoes of the Pacific “Ring of Fire” formed when 2 plates slid under each other.

Other volcanoes are made when 2 plates move apart. That’s the case of most underwater volcanoes.

Sometimes, magma pushes through the Earth’s crust on its own. 

This causes the birth of many volcanoes in a row, like in Hawaii.

About 50 volcanoes erupt every year. Most are without risk for human populations, and the most dangerous, such as Etna, in Sicily, are closely monitored.