oceanic ridge

For more information on oceanic ridge, visit Britannica.com.

An underwater mountain range developed at a section of oceanic crust where magma rises up through a cracking and widening ridge. Some magma cools below the crust, some of it forces into fractures, and much flows out to form new crust, which is then pushed away from the ridge. As new crust is created by the extrusion of lava each side of the ridge, it takes up the prevailing magnetic polarity of the earth, which reverses from time to time. As a result, symmetrical bands of crust, with alternating polarity, develop on either side of the ridge. These magnetic patterns are used to calculate the rate of the sea-floor spreading resulting from the lava flow. The term mid-oceanic ridge properly refers to the ridge at the centre of the Atlantic Ocean, which comes to the surface at points such as Tristan da Cunha and Ascension Island. Other ridges, such as the Pacific-Antarctic ridge, are not truly at the centre of the ocean. See also plate tectonics.