A volcano is an opening in Earth’s crust through which molten rock and gases erupt from deep below. Most volcanoes look like mountains. Their cone shape is formed as layers of ash and other materials build up around the main vent. This can take thousands of years.

There are many different kinds of volcanoes, but they are all born in the same way — when magma erupts though a weak place in Earth’s crust.
 

Magma usually forms deep below Earth’s surface. Here, it mixes with gases that make the magma lighter and help it to rise. As the magma draws closer to the crust, it collects in a chamber, which is under great pressure from the surrounding rock. Eventually, the magma is forced up through the crust and into a conduit that has been made by the intense heat.

Magma that has erupted from a volcano is called lava. Most lava explodes through the main vent at the top of the volcano. The force is so great that it can shoot the molten material high into the air. Lava can also seep through smaller side vents before flowing down the side of the volcano.

After an eruption, the volcano starts to collapse, and a dishlike hole called a crater forms at the top. Over time, the crater may fill with water, and a lake forms.