Oceanic spreading ridge
An oceanic spreading ridge is the fracture zone along the ocean bottom where molten mantle material comes to the surface, thus creating new crust. This fracture can be seen beneath the ocean as a line of ridges that form as molten rock reaches the ocean bottom and solidifies.

Oceanic trench
An oceanic trench is a linear depression of the sea floor caused by the subduction of one plate under another.

See movie.