天皇海山群
At its southern end ( 26°S) the Tonga Trench is colliding with the Louisville Seamount Chain, a chain of guyots and seamounts on the Pacific Plate roughly parallel to the Hawaiian–Emperor seamount chain in the northern pacific. The Louisville collision zone migrates southward at a rate of because of the difference in the oblique angle between the Louisville Ridge relative the direction of convergence. In the eastern Lau Basin spreading centres are propagating southward at roughly the same rate. The collision zone also offsets the Tonga Trench to the north-west relative to the Kermadec Trench by .