Earthquake in Southeast Indian Ridge Indian Ocean Today |

The Southeast Indian Ridge (SEIR) is the spreading centre closest to the Kerguelen and Amsterdam–Saint-Paul hotspots. The SEIR has an intermediate full spreading rate of 65 mm/a (2.6 in/year), and, because Antarctica is virtually stationary, this results in a northward ridge migration of half that rate. Spreading rates along the SEIR varies from 69 mm/a (2.7 in/year) near 88°E to 75 mm/a (3.0 in/year) near 120°E.

During the past few million years hotspot activity has produced a 150 km × 200 km (93 mi × 124 mi) plateau straddling on the SEIR. This Amsterdam–St. Paul Plateau while formed in the last 10 million years, started this formation beneath the Australian Plate so the plateau is now built on the components of two tectonic plates (see Kumar et al. for diagram of this complex process). For several reasons, including that the composition at and near Amsterdam and Saint Paul Island is distinct from other Kerguelen hotspot material, this has suggested to many that the Amsterdam–St. Paul hotspot (ASP) is separate from the Kerguelen hotspot. The ASP Plateau covers an area of 30,000 km² (12,000 sq mi) and rises 500 m (1,600 ft) above the surrounding seafloor.^[3]

Both Amsterdam and St. Paul are located on the Antarctic Plate side within 40 km (25 mi) of the SEIR. North-east of the ASP Plateau a string of submarine volcanoes, the Chain of the Dead Poets, 1–3 km (0.62–1.86 mi)-high and 40 km (25 mi)-wide, mark the track of the ASP hotspot across the Australian Plate. This track leads to the intersection of the Broken Ridge and Ninety East Ridge west of Australia. The ASP hotspot ceased to produce these volcanoes some 10 to 5 million years ago when the SEIR started to interact with it and the hotspot started to build the shallow plateau. There is an active submarine volcano, the 1,100 m (3,600 ft)-high Boomerang Seamount, 18 km (11 mi) north of Amsterdam Island near the SEIR. Analyses of the isotope composition of basalts recovered from its caldera support that the ASP hotspot contributed to the formation of the southern Ninety East Ridge.

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