What causes a volcanic eruption to occur?

Since the magma is always building up pressure and the earth is always spinning, it sometimes causes a crack in the earth. The two sides of the crack may shift. This is called plate tectonics, known to be the cause of volcanic eruptions. The magma will burst through the crack. When magma comes out or erupts, it is called lava. If this crack is in the ocean, an island can be created. After it erupts numerous times, a cone is created. When there is an eruption in a volcano, the place where pressure builds up and where the magma is is called the magma chamber.