All volcanoes are formed by the accumulation of magma. Magma can erupt through one or more volcanic vents, which can be a single opening, a cluster of openings, or a long crack, called a fissure vent. It forms deep within the earth, generally within the upper part of the mantle.High temperatures and pressures are needed to form magma. The solid mantle or crustal rock must be melted.Once tiny droplets of magma are formed, they begin to rise because the magma is less dense than the solid rock surrounding it.As the individual magma droplets rise, they join to form ever-larger blobs and move toward the surface. The larger the rising blob of magma, the easier it moves.With each eruption, whether explosive or nonexplosive, the material erupted adds another layer to the growing volcano. After many eruptions, the volcanic materials pile up around the vent or vents. These piles form a topographic feature, such as a hill, mountain, plateau, or crater, that we recognize as a volcano.