Volcanoes are found along constructive and destructive plate boundaries. When two plates move apart, constructive, the cracks in the crust allow liquid rock, called magma, to rise from the mantle, through the earth’s crust, to the surface.
When this molten rock reaches the surface it is called a volcanic eruption. Magma at the surface is called lava and it cools and solidifies into solid rock. This process can repeat itself over many years forming a cone-shaped mountain or volcano.
Destructive plate boundaries involve two plates moving towards each other. The heavier plate is forced down below the lighter plate into the mantle, where it melts. The molten rock rises up to the surface through cracks in the rocks creating a volcanic eruption. These eruptions are usually very explosive because they are mixed with gases.