W.R. Dickinson, as part of his wide study of the geological history of the Pacific islands, has linked the unique case of the deeply submerged Lapita site of Mulifanua in western Upolu (Samoa) to the slow subsidence of Upolu island. Recent archaeological research on the neighbouring small island of Manono has yielded new and detailed data on this geological process. A series of new dates has allowed us to define the speed of the subsidence and demonstrate the massive environmental changes to which the local population has had to adapt over the past 2000 years.