First volcano begins as melted rock (magma) which rises from deep inside the earth toward the surface. As the gas-filled magma rises, it melts gaps in the surrounding rock and forms a large chamber. Pressure from the solid rock around it forces the magma up to the surface through the conduit (channel) in a weakened part of the rock. The gas and melted rock blast out an opening called the central vent.The erupted materials gradually pile up around the vent, forming a volcano. A bowl-like crater generally forms at the top of the volcano. The vent lies at the bottom of the crater