An oceanic ridge is an underwater mountain range, usually formed by plate tectonics.
They are geologically active, with new magma constantly emerging onto the ocean floor through a gap called a rift in the earth's crust. In most instances, it accumulates and forms new crust. However, submarine volcanoes might also be formed.
The rocks making up the sea floor are usually younger near the centre of the ridge and the older ones located farther away from the rift. This is evidence that new magma constantly emerges through a rift.
Also, the sea floor is made up of rocks generally much younger than the Earth itself. This suggests that the sea floor is in a constant state of 'renewal'.
List of oceanic ridges
See also