<P> A mid-ocean ridge ( MOR ) is an underwater mountain system formed by plate tectonics . It consists of various mountains linked in chains , typically having a valley known as a rift running along its spine . This type of oceanic mountain ridge is characteristic of what is known as an ' oceanic spreading center ' , which is responsible for seafloor spreading . The production of new seafloor results from mantle upwelling in response to plate spreading ; this isentropic upwelling solid mantle material eventually exceeds the solidus and melts . The buoyant melt rises as magma at a linear weakness in the oceanic crust , and emerges as lava , creating new crust upon cooling . A mid-ocean ridge demarcates the boundary between two tectonic plates , and consequently is termed a divergent plate boundary . </P>
mid-ocean ridges form at which type of boundary
divergent plate boundary