Microbathymetric maps of the southern East Pacific Rise reveal subtle field relations between volcanic features and provide new insight on seafloor spreading processes. Along one of the shallowest and broadest sections of ridge at 17degrees28'S, lavas have erupted from a fissure system and flooded the axis through a network of lava tubes and lava channels. Along the neighboring ridge segment at 18degrees15'S, the axial area has subsided and formed a broad tectonized trough. A swath of newly accreted crust has since widened that trough; late-stage voicanism consists of small circular pillow mounds. We propose that these contrasting eruptive styles reflect the waxing and waning phases of a common magmatic evolution spanning a few millennia.
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