Mid-ocean ridges - Credo Reference

Definition: mid–ocean ridge from Merriam-Webster's Collegiate(R) Dictionary

(1961) : an elevated region with a central valley on an ocean floor at the boundary between two diverging tectonic plates where new crust forms from upwelling magma

Image from: The size of the plates is not constant. The... in Guide to the Oceans

Summary Article: mid-ocean ridge

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

Long submarine mountain range that winds along the middle of the ocean floor. The mid-ocean ridge system is essentially a segmented, linear shield volcano. There are a number of major ridges, including the Mid-Atlantic Ridge, which runs down the centre of the Atlantic; the East Pacific Rise in the southeast Pacific; and the Southeast Indian Ridge. These ridges are now known to be spreading centres, or divergent margins, where two plates of oceanic lithosphere are moving away from one another (see plate tectonics). Ocean ridges can rise thousands of metres above the surrounding seabed, and extend for up to 60,000 km/37,000 mi in length.

Ocean ridges usually have a rift valley along their crests, indicating where the flanks are being pulled apart by the growth of the plates of the lithosphere beneath. The crests are generally free of sediment; increasing depths of sediment are found with increasing distance down the flanks.