A volcano is molten magma from the upper mantle
or crust that has reached the surface. The liquid rock is referred to
as lava when it refers to volcanoes. Lava will cool down and become a
fine grained igneous rock (volcanic) and magma when cooled with be a
large grained igneous rock (plutonic).
Volcanoes have different styles of eruption.
They can be violent or they can be quiet. Violent eruptions are
usually charged with "bottled" up gases. Just like a can of
carbonated soda that you shake and then quickly open. Ash and volcanic
bombs rain down after a violent eruption.
Volcanoes are also classified by the general
shape and the type of rocks. There are many different type of
classifications that vulcanologists use depending on the depth of your
research. Basically there are three types of volcanoes based on
composition including composite, shield, and cinder.