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Fissure densities and widths have been mapped along the axial zone of the superfast spreading southern East Pacific Rise (EPR) at 17_150–400S with the near-bottom DSL-120 and Argo II imaging systems. We observe that the youngest lava flows (on a relative age scale) are sparsely fissured and that there is a cumulative increase in fissure abundance with time that produces a strong positive correlation between fissure density and relative age of lava flows. Average fissure widths were used to estimate fissure depths. In the 17_150–400S area, calculated fissure depths are estimated to extend below the seismic layer 2A/2B boundary, and fissures are widest/deepest where lava flows are youngest. We interpret these wide fissures in relatively young flows to be eruptive fissures. Relatively young lava flows combined with high average fissure widths south of 17_250S suggest that there may have been recent dike propagation along the ridge crest in this area. In comparison to the northern EPR at 9_–10_N the density of fissuring on the southern EPR is significantly higher, due in part to the higher occurrence of relatively older, more areally restricted pillow lava flows.