Bathymetric and seismic data show that the southernmost segment of the EastScotia Ridge (segment E9) is anomalous in its curved plan form, and in the presence of a large axial volcanic ridge (AVR). Spreading commenced only within the past 1 million years on this segment, which appears to have propagated both northward and southward. The presence of a caldera at the summit of the AVR indicates that a shallow magma chamber of limited extent existed recently beneath the ridge. Eruption from this magma chamber, probably within the past 0.1 million years, may have led to the formation of the AVR itself. Careful examination of seismic reflection profiles suggests that small pockets of magma may still exist beneath the AVR. Magmatism on segment E9 may be enhanced as a result of the flow of shallow mantlearound the southern end of the subducting slab beneath the South Sandwich Arc in a manner similar to that proposed for the northern end. This mantle probably carries a slightly enriched ‘hotspot’ signature, and is affected by volatiles released from the edge of the slab, both tending to increase the supply of magma to the back-arc spreading centre.