| Abstract | Deep-towed DSL-120 bathymetric data are used to investigate the pattern of lava dome formation along
a superfast spreading portion of the southern East Pacific Rise (EPR), including the overlapping limbs of a
giant (120 120 km) propagator near 29 S. Along the 670 km of the axis surveyed, 1172 small domes
were identified using a closed contour algorithm. Their abundance, defined by spatial density, is well
correlated with the along-axis relief of the ridge crest. Where the western and eastern limbs plunge toward
the overlap zone, densities are high (3–6 km 2); however, where the axial depth profile is shallow and
flat, densities are comparably low (0.4 km 2). Volcanic domes within the low abundance areas are
characterized by lower ratios of height to basal radius (0.15 versus 0.22), smaller maximum heights
(18 versus 40 m), and a larger relative percentage of small versus large mounds. The zone of high dome
abundance encompasses the overlapping limbs of the rift and extends more than 100 km to the north and
south beyond the overlap zone. Domes form dominantly during low effusion rate, point-source eruptions,
which suggests that discontinuous melt lenses underlie the ridge axis proximal to the overlapper.
Conversely, fissure-fed sheet flows dominate along the more distal segments, implying the presence of a
more continuous axial magma lens. Throughout the survey area, dome abundance increases systematically
near second-order segment boundaries. Within the high abundance zone, some third-order offsets also
correlate with increased dome production, but local peaks in abundance are not tied exclusively to higherorder
ridge offsets. Where dome abundance is low, domes are clustered tightly near second-order offsets
and there is no increase in dome abundance near third-order segment boundaries.
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