 On shield volcanoes forming from level seafloor without neighboring vents, flank rifting occurs more evenly distributed around the vent.However, where the flanks of a volcano may be supported on one side by the presence of a pre-existing feature, or burdened with various planes of weakness, rift zone formation promulgates according to down-slope pull of gravity.The infill of magmas in the form of dykes helps to define the shape of a volcano.