Glossary of Oceanography Chapter 4

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Continental margins near an area of lithospheric plate convergence. Also called Pacific-type margin.
active margin
The discovery and study of ocean floor contours.
Flat, cold, sediment-covered ocean floor between the continental rise and the oceanic ridge at a 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 in the Pacific.
abyssal plain
The submerged outer edge of a continent, made of granitic crust. Includes the continental shelf and continental slope. Compare ocean basin.
continental margin
Deep-diving submersible designed like a blimp, which uses gasoline for buoyancy and can reach the bottom of the deepest ocean trenches. From the Greek batheos ("depth") and skaphidion ("a small ship").
The wedge of sediment is forming the gentle transition from the outer (lower) edge of the continental slope to the abyssal plain. Usually associated with passive margins.
continental rise:
The sloping transition between the granite of the continent and the basalt of the seabed. The true edge of a continent.
continental slope
Gradually sloping submerged extension of a continent, composed of granitic rock overlain by sediments. Have features similar to the edge of the nearby continent.
continental shelf
Area of irregular, seismically inactive topography marking the position of once-active transform faults.
fracture zone
The point on the Earth's surface directly above the focus of an earthquake.
A fracture in a rock mass along which movement has occurred.
A flat-topped, submerged inactive volcano.
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).
ice age
Spring of hot, mineral and gas rich seawater found on some oceanic ridges in zones of active seafloor spreading.
hydrothermal vent:
Curving chain of volcanic islands and seamounts almost always found paralleling the concave edge of a trench.
island arc
Young seabed at the active spreading center of an ocean, often unmasked by sediment, bulging above the abyssal plain. The boundary between diverging plates. Often called a mid-ocean ridge, though less than 60% of the length exists at mid-ocean.
oceanic ridge
Deep-ocean floor made of basaltic crust. Compare continental margin.
ocean basin
Circular or elliptical projection from the seafloor, more than 1 kilometer (0.6 mile) in height, with a relatively steep slope of 200 to 250.
A deep, V-shaped valley running roughly perpendicular to the shoreline and cutting across the edge of the continental shelf and slope.
submarine canyon
The abrupt increase in slope at the junction between continental shelf and continental slope.
shelf break
Small sediment-covered inactive volcano or intrusion of molten rocks less than 200 meters (650 feet) high, thought to be associated with seafloor spreading. Abyssal hills punctuate the otherwise flat abyssal plain.
abyssal hill
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.
A plane along which rock masses slide horizontally past one another.
transform fault
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.
turbidity current
Continental margins near an area of lithospheric plate divergence. Also called Atlantic-type margin.
passive margin

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