median valley (axial rift, axial trough) The valley which lies along the axis of some oceanic ridges. From observations from submarines and the interpretation of seismic records of earthquakes in the median valley, the inner floor has been found to have scattered volcanoes and black smokers, with normal faults dipping towards the inner floor on each side. These faults raise slices of old floor to the ridge crest, from where it is lowered by further normal faults which dip away from the ridge axis. Median valleys develop on slower-spreading ridges (e.g. Mid-Atlantic and Carlsberg) and are up to 3 km deep.

median valley(axial rift, axial trough) The valley which lies along the axis of some oceanic ridges. Median valleys develop on slower-spreading ridges (e.g. Mid-Atlantic and Carlsberg) and are up to 3 km deep.