The formation of volcanoes is Magma under Earth's crust was inserted to the compression pressure cracks to the surface world. The force of the eruption or explosion caused by a volcanic eruption on the volcano's magma is steam, dust, debris and gases. It will be ejected from the crater. (If the magma is rising from the Earth's surface is called lava ).Volcano are located around the Pacific Plate, in a region called at the Ring of Fire. In the Atlantic Ocean. Indonesia is area volcanoes most erupt because Indonesia near plate boundaries.