Mid-ocean ridgeAt mid-ocean ridges, plates move apart and magma rises to form new oceanic crust. Seawater circulates through fractured rock, carrying heat and dissolved minerals back to the seabed.The ocean floorContinental shelfContinental slopeAbyssal plainOcean trenchMid-ocean ridgeSeamountVolcanic islandReturn to the coastOcean geology · NOAA