天皇海山群
Over the next decade it was discovered that Late Cretaceous and Eocene volcanism had occurred close to Caroline Island, as well thousands of kilometres to the north, which disproved the single hotspot model for the formation of the Line Islands, and instead suggested the chain was made by a more complex series of volcanic events than the Hawaiian–Emperor seamount chain. During the 1980s, scientists put forward new theories to explain the evolution of the chain, including a transform fracture zone theory (since refuted by paleomagnetic data), and a multiple hotspot model which is still being discussed as of 2020. A combination of hotspot-transform fracture zone phenomena is also possible.