Using high-resolution bathymetric data of the Southwest Indian Ridge axial valley floor, 523 seamounts were identified between the Atlantis II fracture zone (57°) and the Rodrigues triple junction (70°). We find that the seamount population has a much larger spatial density (∼ 103 per 103 km2) and shorter characteristic height (∼ 48 m) to the west of 62° than to the east (∼ 8 per 103 km2 and ∼ 105 m, respectively). These densities of seamounts are much lower than those found on the Mid-Atlantic Ridge, suggesting that magma production is attenuated under the Southwest Indian Ridge compared with faster spreading oceanic ridges. We propose that cooler mantle temperatures, which induce lower degrees of partial melting and less magmatic supply to the ridge axis, result in construction of taller and fewer seamounts between 62° and 70°.

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