Volcanoes are openings in the Earth's crust.
When they erupt they let out gas, ash and melted rock.
There are different kinds of volcanoes
They are usually found where tectonic plates meet.
When a volcano erupts
An exploding volcano throws lava, gas and ash into the air. The liquid magma, which is melted rock, starts its journey upwards through the volcano from a magma chamber, or lake, deep inside the earth.
Magma is hot fluid melted rock below the earth's crust.
Magma reaches the surface through the vertical main pipe of a volcano. It is forced up by pressure from deep inside the earth. When it comes out of the earth's surface it is called lava.
The lava pours out of the hole or vent, at the surface of the volcano. A vent can be at the top or sides of a volcano.
Different kinds of volcano
A cone volcano is made up of layers of hardened lava and ash, built up each time the volcano erupts.
Cone volcanoes are triangle-shaped and most have one crater at the top.
A crater volcano is formed when a cone volcano collapses into the magma chamber, forming a caldera. When the volcano next erupts a new cone is formed, in the middle of the caldera. Sometimes, the caldera fills with water, forming a caldera lake.
Another kind of volcano is a shield volcano, which is built almost entirely of fluid lava flows. Flow after flow pours out of the volcano's vent or vents in all directions, to build a broad, gently sloping cone.
From the side the volcano looks like a warrior's shield, which is how it got the name.
Other interesting facts
There are volcanoes under the ocean and under the icecaps.
They can also form in hotspots on Earth. Hawaii is an example of a hotspot.