Volcanos are a good example of nature and her unpredictable powers, and man's inferiority to her. The earth is made up of plates which are in a constant state of motion. Usually volcanos develop on the boundaries of these plates. The plates have two types of movement, convergent and divergent.
Convergent movement is when the plates come together and divergent movement is when they separate.
A hot spot refers to an area on a plate that has been heated internally, from the mantle. A volcano can form in any one of these situations. It is not even uncommon for the majority of our volcanos to begin on the ocean floor. Basically the earth is made up of various layers. The molten iron core and surface crust have sandwiched between them a layer referred to as the mantle.