What Causes Volcano?

Volcano's are caused by the friction of the earths plates moving and crashing into each other. This collision is refereed to as plate tectonics. The Earths surface is actual a series of plates that are continually growing and moving. When the plates contact with an opposing plate the forces of the immovable object and the impregnable force exists. Since something has to give the plate with the stronger or larger and more able capacity forces the weaker plate underneath. The results are major friction, power and force. This force and power is accumulated in areas know as volcano's and when the cavities and forces reach a point that it is no longer containable the eruptions are seen in the form of a volcanic eruption. This eruption reduces the built-up stress, heat and pressure generated by the collision of the earths plates.

The lava from them harded in the earth and theen  ie pushed back up through the lava

Magma adds pressure tothe surface