The study of volcanoes is called volcanology. The word volcano comes from the Ancient Roman god of fire Vulcan.  Throughout the world there are mountains that at times erupt.  These mountains are called volcanoes. 

Volcanoes are formed when rock, so hot that it is a liquid (magma), shoots up through a crack or hole in the ground from the center of the earth. When it cools it forms solid rock. Eventually rock and ash pile up around the hole or crack and form a cone shaped mountain, called a volcano. Some volcanoes are formed under water. In fact, many islands in the Pacific Ocean are the tops of volcanoes.

Volcanoes have played a big role in history. They have caused some of the most deadly disasters wiping out entire towns and killing many people.