The lithospheric plates move relative to each other. They are created at mid-oceanic
ridges and destroyed at subduction zones.
A mid-ocean ridge 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 is entropic
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
emerge 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.
