The collision between the 22 degree S salient of the Loyalty Ridge and the southern New Hebrides Arc began some 300,000 years ago. Nevertheless, the ridge probably influences, since 1 to 2 Ma, the subduction at the southern arcuate New Hebrides Trench through its action on the bulge of the downgoing plate. The morphology of the ridge, its deep root and relative buoyancy affect the flexure and the subduction of the downgoing plate in several ways. The proposed effects of this arc-ridge collision may be traced on a regional scale: in front of the collision zone, the southern New Hebrides active volcanic line is weakly developed, the intra-arc troughs are absent, and the Benioff zone is short. On the nearby north Fiji basin, the offset of the southern active spreading ridge could also be a consequence of this collision.