Oceanography Chapter 4

Front 1

Abyssal Hill

Back 1

Small sediment-covered inactive volcano or intrusion of molten rock less than 200 meters (650 feet) high, thought to be associated with seafloor spreading. Abyssal hills punctuate the otherwise flat Abyssal plain.

Front 2

Abyssal Plain

Back 2

Flat, cold, sediment-covered ocean floor between the continental rise and the oceanic ridge at the depth of 3,700 to 5,500 meters (12,000 to 18,000 feet). Abyssal plains are more extensive in the Atlantic and Indian oceans than the Pacific.

Front 3

Active Margin

Back 3

The continental margin near an area of lithospheric plate convergence; also called Pacific-type margin.

Front 4

Bathymetry

Back 4

The discovery and study of submerged contours.

Front 5

Continental Margin

Back 5

The submerged outer edge of a continent, made of granitic crust; includes the continental shelf and continental slope. Compare ocean basin.

Front 6

Continental Rise

Back 6

The wedge of sediment forming the gentle transition from the outer (lower) edge of the continental slope to the abyssal plain; usually associated with passive margins.

Front 7

Continental Shelf

Back 7

The gradually sloping submerged extension of a continent, composed of granitic rock overlain by sediments; has features similar to the edge of the nearby continent.

Front 8

Continental Slope

Back 8

The sloping transition between the granite of the continent and the basalt of the seabed; the true edge of the continent.

Front 9

Deep Scattering Layer (DSL)

Back 9

A relatively dense aggregation of fishes, squid, and other mesopelagic organisms capable of reflecting a sonar pulse that resembles a flat bottom in the ocean. Its position varies with the time of day.

Front 10

Deposition

Back 10

Accumulation, usually of sediments.

Front 11

Earthquake

Back 11

A sudden motion of Earth's crust resulting from waves in Earth caused by faulting of the rocks or by volcanic activity.

Front 12

Fracture Zone

Back 12

Area of irregular, seismically inactive topography marking the position of a once-active transform fault.

Front 13

Guyot

Back 13

A flat-topped, submerged inactive volcano.

Front 14

Hydrothermal Vent

Back 14

A spring of hot, mineral and gas rich seawater found on some oceanic ridges in zones of active seafloor spreading.

Front 15

Ice Age

Back 15

One of several periods (lasting several thousand years each) of low temperature during the last million years. Glaciers and polar ice were derived from ocean water, lowering sea level at least 100 meters (328 feet).

Front 16

Ice Cap

Back 16

Permanent cover of ice; formally limited to ice atop land, but informally applied also to floating ice in the Arctic ocean.

Front 17

Iceberg

Back 17

A large mass of ice floating in the ocean that was formed on or adjacent to land. Tabular icebergs are tablelike or flat; pinnacled icebergs are castellated, or jagged. Southern icebergs are often tabular; northern icebergs are often pinnacled.

Front 18

Island Arc

Back 18

Curving chain of volcanic islands and seamounts almost always found paralleling the concave edge of a trench.

Front 19

Ocean Basin

Back 19

Deep-ocean floor made of basaltic crust. Compare continental margin.

Front 20

Oceanic Ridge

Back 20

Young seabed at the active spreading center of an ocean, often unmasked by sediment, bulging above the abyssal plain. The boundary between deverging plates. Often called a mid-ocean ridge, though less than 60% of the length exists at mid-ocean.

Front 21

Orbital inclination

Back 21

The 23*27' "tilt" of Earth's rotational axis relative to the plane of its orbit around the sun.

Front 22

Passive Margin

Back 22

The continental margin near an area of lithospheric plate divergence; also called Atlantic-type margin.

Front 23

Sea Level

Back 23

The height of the ocean surface. (mean sea level)

Front 24

Seamount

Back 24

A circular or elliptical projection from the seafloor, more than 1 kilometer (0.8 mile) in height, with a relatively steep slope of 20* to 25*.

Front 25

Shelf Break

Back 25

The abrupt increase in slope at the junction between continental shelf and continental slope.

Front 26

Submarine Canyon

Back 26

A deep, V-shaped valley running roughly perpendicular to the shoreline and cutting across the edge of the continental shelf and slope.

Front 27

Telepresence

Back 27

The extension of a person's senses by remote sensors and manipulators.

Front 28

Transform Fault

Back 28

A plane along which rock masses slide horizontally past one another.

Front 29

Trench

Back 29

An arc-shaped depression in the deep-ocean floor with very steep sides and a flat sediment-filled bottom coinciding with a subduction zone. Most trenches occur in the Pacific.

Front 30

Turbidity Current

Back 30

An underwater "avalanche" of abrasive sediments thought responsible for the deep sculpturing of submarine canyons and a means of transport for sediments accumulating on abyssal plains.

Front 31

Turbulence

Back 31

Chaotic fluid flow