ocean floor![click to hear](/images/speaker.jpg)
Part of the Earth’s surface beneath the seas and the oceans; its topography is highly variable.
continental margin ![click to hear](/images/speaker.jpg)
Underwater extension of the continent; it comprises the continental shelf, the continental slope and the continental rise.
continental shelf ![click to hear](/images/speaker.jpg)
Section of the continental margin extending from the coast of the continent to the continental rise; its depth is no more than 660 feet.
guyot ![click to hear](/images/speaker.jpg)
Ancient volcano whose summit has been cut off by erosion and then submerged.
magma ![click to hear](/images/speaker.jpg)
Molten rock and gas under very high pressure that can reach extremely high temperatures.
seamount ![click to hear](/images/speaker.jpg)
Isolated mountain of volcanic origin featuring a pointed summit.
trench ![click to hear](/images/speaker.jpg)
Extremely deep elongated depression bordering a continent or island arc; it occurs when one tectonic plate moves under another.
volcanic island ![click to hear](/images/speaker.jpg)
Volcano whose summit rises above sea level.
island arc ![click to hear](/images/speaker.jpg)
String of volcanic islands formed when two tectonic plates meet.
abyssal hill ![click to hear](/images/speaker.jpg)
Rounded underwater rise of low elevation.
sea level ![click to hear](/images/speaker.jpg)
Mean water level observed for a given duration (day, month, year); it is used as a reference to define coastal features and calculate the elevation of topographical elements.
mid-ocean ridge ![click to hear](/images/speaker.jpg)
Group of underwater mountain chains criss-crossing the oceans; it is formed by an outpouring of magma.
continent ![click to hear](/images/speaker.jpg)
A collective term for the vast landmasses and their submerged margins.
submarine canyon ![click to hear](/images/speaker.jpg)
Deep valley that is frequently the extension of a river; it ends in a sediment buildup.
continental slope ![click to hear](/images/speaker.jpg)
Slope of a few degrees that extends from the continental shelf; it is 660 to 6,600 feet deep.
continental rise ![click to hear](/images/speaker.jpg)
Gently sloping section of the continental margin; it connects the continental slope to the abyssal plain.
abyssal plain ![click to hear](/images/speaker.jpg)
Zone located at a depth of 6,600 to 20,000 feet; it covers most of the ocean floor.