A volcano is a hole in the earth's crust through which hot, liquid rock pours out from inside the planet. As the rock cools down, it makes hills and mountains. Most volcanoes are found on the edges of the earth's plates. From time to time an active volcano erupts, or explodes. A volcano that has not erupted for many years is said to be extinct.
Mountain of lava
Below a volcano is a chamber, or pool, of red hot, liquid rock called magma. As pressure increases in the chamber, the magma is forced up to the surface through a central vent, or pipe. it erupts from the crater. On the surface, magma is called lava.