| A | B |
|---|
| oceanic ridge | a continous elevated zone on the fllor of all the major ocean basins and varying in width from 1,000 to 4,000 kilometers |
| rift valley | a surface feature in the seafloor produced by the desending plate during subduction |
| seafloor spreading | the process by which plate tectonics produce new oceanic lithosphere at ocean ridges |
| subduction zone | a destructive plate margin where oceanic crust is being pushed down into the mantle beneath a second plate |
| trench | a surface feature in the seafloor produced by the descending plate during subduction |
| continental volcanic-are | mountains formed in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent |
| volcanic island-arc | a chain of volcanic islands generally located a few hundred kilometers from a trench |
| magma | a body of molten rock found at depth including any dissolved gasses and crystals |
| lava | magma that reaches Earth's surface |
| hot spot | a concentration of heat in the mantle capable of producing magma |
| seamount | an underwater volcano |
