africa african plate amazon river americas arctic ocean ascension island asthenosphere atlantic ocean atlantis massif aulacogen azores bathymetry beerenberg bermuda bouvet island bouvet triple junction canada central indian ridge charles wyville thomson chile rise continental drift earthquake east pacific rise equator eurasian plate explorer ridge fundy basin gakkel ridge geological society of america gorda ridge gough island graben greenland iceland jan mayen juan de fuca ridge kula-farallon ridge lava lithosphere magma marie tharp matthew fontaine maury maurice ewing mid-ocean ridge mississippi river new brunswick niger river north american plate nova scotia oceanic crust pacific-antarctic ridge pacific-farallon ridge pacific-kula ridge pangaea phoenix ridge pico island romanche trench saint peter and paul rocks seafloor spreading seismology south american plate southeast indian ridge southwest indian ridge tectonics transatlantic telegraph cable triassic triple junction tristan da cunha university of oklahoma