Glossary of Oceanography Chapter 3

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A single closed-flow circuit of rising warm material and falling cool material.
convection current
An instrument that detects and records Earth movement associated with earthquakes and other disturbances.
An area at which a lithospheric plate is descending into the asthenosphere. The zone is characterized by linear folds (trenches) in the ocean floor and strong deep-focus earthquakes. Also called a Wadati-Benioff zone.
subduction zone
An assemblage of subducting oceanic lithosphere scraped off (obducted) onto the edge of a continent.
The junction between diverging plates at which new ocean floor is being made. Also called spreading zone.
spreading center
The downward movement into the asthenosphere of a lithospheric plate.
Places where crustal plates shear laterally past one another. Crust is neither produced nor destroyed at this type of junction.
transform plate boundary
Canadian geophysicist who proposed the theory of plate tectonics in 1965.
Wilson, John Tuzo (b. 1908)
A plane along which rock masses slide horizontally past one another.
transform fault
An isolated segment of seafloor, island arc, plateau, continental crust, or sediment transported by seafloor spreading to a position adjacent to a larger continental mass. Usually different in composition from the larger mass.
The theory that all of Earth's geological features and history can be explained by processes occurring today and that these processes must have been at work for a very long time.
One of about a dozen rigid segments of the Earth's lithosphere that move independently. The plate consists of continental or oceanic crust and the cool, rigid upper mantle directly below the crust.
A ring-shaped island of coral reefs and coral debris enclosing, or almost enclosing shallow lagoon from which no land protrudes. Atolls often form over sinking, inactive volcanoes.
The hot plastic layer of the upper mantle below the lithosphere, extending some 700 kilometers (430 miles) below the surface. Convection currents within the asthenosphere power plate tectonics.
The zone of seismic and volcanic activity that encircles the Pacific Ocean.
Pacific Ring of Fire
A compressional wave associated with an earthquake and which can move through both liquid and rock.
P wave Primary wave
Movement within a fluid results from differential heating and cooling of the fluid. Convection produces mass transport or mixing of the fluid.
The "fossil," or remnant, magnetic field of a rock.
Name given by Alfred Wegener to the ocean surrounding Pangaea.
Name given by Alfred Wegener to the original "protocontinent." The breakup of Pangaea gave rise to the Atlantic Ocean and to the continents we see today.
A logarithmic measure of earthquake magnitude. A great earthquake measures above 8 on the Richter scale.
Richter scale
German scientist who proposed the theory of continental drift in 1912.
Wegener, Alfred (1880-1930
The theory that the continents move slowly across the surface of the Earth.
continental drift
A transverse wave associated with an earthquake and which cannot move through liquid.
S wave (secondary wave)
The solid masses of the continents, composed primarily of granite.
continental crust
The relatively light crustal rock-composed mainly of oxygen, silicon, and aluminum-that forms the continents. Its density is about 2.7 g/cm3.
The formation of layers in a material, with each deeper layer being denser (weighing more per unit of volume) than the layer above.
density stratification
A region where plates are pushing together and where a mountain range, island arc, and/or trench will eventually form. Often a site of much seismic and volcanic activity.
convergent plate boundary
The ability of an object to float in a fluid by displacement of a volume of fluid equal in mass to the mass of the floating object.
The innermost layer of Earth, composed primarily of iron, with nickel and heavy elements. The inner core is thought to be solid, the outer core liquid. The average density of the outer core is about 11.8 g/cm3, and that of the inner core is about 16 g/cm
The relatively heavy crustal rock that forms the seabed, composed mostly of oxygen, silicon, magnesium, and iron. Its density is about 2.9 g/cm3.
The outermost solid layer of the Earth, composed mostly of granite and basalt. The top of the lithosphere. The crust has a density of 2.7-2.9 g/cm3 and accounts for 0.4% of the Earth's mass.
The transfer of heat through matter by the collision of one atom with another.
The process of determining the age of rocks by observing the ratio of unstable radioactive elements to stable decay products.
radiometric dating
The theory that the Earth's surface features are formed by catastrophic forces such as the biblical flood. Catastrophists believe in a young Earth and a literal interpretation of the biblical account of Creation.
A region where plates are moving apart and where new ocean or rift valley will eventually form. A spreading center forms the junction.
divergent plate boundary
A fracture in a rock mass along which movement has occurred.
The disintegration of unstable forms of elements, which releases subatomic particles and heat.
radioactive decay
A sudden motion of the Earth's crust resulting from waves in the Earth caused by faulting of the rocks or by volcanic activity.
A device that reflects sound off the ocean bottom to sense water depth. Its accuracy is affected by the variability of the speed of sound through water.
echo sounder
The theory that the Earth's lithosphere is fractured into plates, which move relative to each other and are driven by convection currents in the mantle. Most volcanic and seismic activity occurs at plate margins.
plate tectonics
A flat-topped, submerged inactive volcano.
A surface statement of a plume of magma rising from a stationary source of heat in the mantle.
hot spot
The layer of the Earth between the crust and the core, composed of silicates of iron and magnesium. The mantle has an average density of about 4.5 g/cm3 and accounts for about 68% of the Earth's mass.
Molten rock capable of fluid flow. Called lava aboveground.
The brittle, relatively cool outer layer of the Earth, consisting of the oceanic and continental crust and the outermost, rigid layer of mantle.
Balanced support of lighter material in a heavier, displaced supporting matrix. Analogous to buoyancy in a liquid.
isostatic equilibrium
Low-frequency waves generated by the forces that cause earthquakes. Some kinds of seismic waves can pass through the earth. See also P wave and S wave.
seismic waves
A device that measures the amount and direction of residual magnetism in a rock sample.
The outermost solid surface of the Earth beneath ocean floor sediments, composed primarily of basalt.
oceanic crust
The theory that new ocean crust forms at spreading centers, most of which are on the ocean floor, and pushes the continents aside. Power is thought to be provided by convection currents in the Earth's upper mantle.
seafloor spreading

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