The seafloor is not completely flat. Immense mountain ranges called oceanic ridges stretch for almost 70,000 km across the abyssal plains! With altitudes of between 1,000 and 3,000 m, these underwater mountains are sharply defined along their entire length by a rift valley, a central plain of subsidence, which forms as the oceanic plates spread apart. Where lithospheric plates meet, gigantic oceanic depressions called trenches reach depths comparable to the altitude of the highest peaks on the continents.
The seafloor is not completely flat. Immense mountain ranges called oceanic ridges stretch for almost 70,000 km across the abyssal plains! With altitudes of between 1,000 and 3,000 m, these underwater mountains are sharply defined along their entire length by a rift valley, a central plain of subsidence, which forms as the oceanic plates spread apart. Where lithospheric plates meet, gigantic oceanic depressions called trenches reach depths comparable to the altitude of the highest peaks on the continents.