Rotating Earth with vertical relief highlighted. The land regions are shown in true colour, with vegetation green and desert and rocky areas yellow. The oceans are grey, and the margins of the tectonic plates are prominent. Between Africa and the Americas, the Mid_Atlantic Ridge runs down the Atlantic Ocean, following the shape of the land masses. At this mid_ocean ridge, magma rises from within the Earth磗 mantle, cooling and forming new sea floor. This process pushes the plates either side of it apart, moving the continents they carry. In other locations deep trenches are seen, most prominently in the western Pacific Ocean. These are subduction zones, where dense ocean crust is pushed beneath lighter continental crust, forming deep trenches as the plate descends back into the mantle. These regions are the sites of frequent earthquakes and volcanism due to this process.