A volcano is an opening on the surface of the Earth from which magma, associated gases and ash erupt. Volcano has a magma chamber that is a huge bottomless pot of molten rock. The main channel through which magma moves towards the surface is the central vent. A crater sits at the top of a volcano and it is from here that much of the lava, gas, rock fragments and ash are ejected from. Volcanic cones arethe result of eruptions that erupt are mostly small pieces of rocks that build up cone around the vent.