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55 Cards in this Set

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Abyssal Hill

Small, sediment covered extinct volcanoes or intrusions of once molten rock.

Abyssal Plain

flat, featureless expanses of sediment covered ocean floor found on the periphery of all oceans.

Active Margin

Continental margins near the edges of converging plates or transform faults.


the discovery and study of ocean floor contours.

Continental Margin

Submerged outer edge of the continent.

Continental Rise

Apron of accumulated sediment located at the base of the continental slope.

Continental Shelf

The shallow submerged extension of a continent underlaid by granitic crust.

Continental Slope

The transition between the gently descending continental shelf and the deep-ocean floor.

Fracture Zone

Transform faults are the active part. Seabed grows the same direction.


Flat-topped seamounts that were once tall enough to approach or penetrate the surface.

Hydrothermal Vent

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

Ice Age

Period of widespread glaciation.

Island Arc

Curving chains of volcanic islands and seamounts. Found parallel to trenches.

Ocean Basin

The deep sea floor beyond the continental margin.

Oceanic Ridge

A mountainous chain of young basaltic rock at the active spreading center of an ocean.

Passive Margin

Continental margins facing the edges of diverging plates.


Volcanic projections that do not rise above the sea-level. Steep slopes, circular or eliptical, over 1 km high.

Shelf Break

Marks the abrupt transition from continental shelf to the continental slope.

Submarine Canyon

Cut into the continental shelf and slope, often terminating on the deep-sea floor in a fan-shaped wedge of sediment.

Transform Fault

Fractures along which plates slide horizontally.


An arc-shaped depression in the deep-ocean floor.

Turbidity Current

An underwater 'avalanche' of abrasive sediments thought responsible for the deep sculpturing of submarine canyons and a means of transport for sediments accumulating an abyssal plain.


A fracture in the lithospheric plate along which movement has occurred.

Why is Earth so hard to map compared to jupiter?

Clouds and oceans cover the earth's surface than those of other planets.

What was the first method of measuring the depth of the ocean?

Rope and stone, later winch and weight.

How was Bathymetry accomplished in years past? How do scientists do it now?

Bathymetry from 85 B.C. to 1914 was done by putting a weight on the end of a rope and waiting until it hit the bottom. After 1914 new devices, echo sounders were invented that use single or multi beams that bounce sound off of the seabed and listen for a response. 1985, satellites began measuring the variation in the sea's height to figure out the depths.

Echo sounders bounce sound off of the seabed to measure the depth. How does this work?

The echo sounder sends out a pulse and times how long it takes to get back to the device.

Satellites orbit in space. How can a satellite conduct oceanographic research?

Satellites measure the distance between them and the ocean. The differences in these distances tell us about the variations in the depth of the ocean.

Why does the surface of the ocean 'bunch' up over submerged mountains and ridges?

The bumps are caused by how close a large underwater body is to the mass of water. It will pull more water towards it making a bulge at the surface detectable by satellite.

How would you characterize the general shape of an ocean basin?

I would say it's lots of mountains put into one big bathtub with canyons and trenches and gorges, etc....

If you could walk down into the seabed, the transition from granite to basalt would mark the solid edge of the continent and would divide ocean floors into two major provinces. What are they?

The continental margins and the ocean basin.

How does a continental margin differ from a deep-ocean basin?

The continental margin is the submerged edge of the continent whereas an ocean basin is beyond the continental margin.

What are the features of continental margins?

The continental margins have a shelf, slope, rise submarine canyons, as well deep sea fans.

How is an active tectonic margin different from a passive tectonic margin?

The main difference is that the active martin is very close to a plate boundary, therefore having earthquake activity and volcanism. It also has a shorter shelf, steeper slope, and the possibility of the subducted plate (usually) donating some sediment. The passive margin is on the trailing off the edge of a continent with no boundaries.

How do the widths of continental shelves differ between active margins and passive margins?

The passive margins have a wider slope since they are further, and older, away from the mid-atlantic ridge due to when Pangaea split apart. Active margins have short shelves because they have plate on plate collision occurring.

How has sea-level varied with time? Is sea level unusually high or low at present?

The sea level about 18,000 ya was 125m lower due to icebergs. When those icebergs melted it covered the lower leveled areas of the continents (continental shelf). It is a high sea level as we exit our last glacial period.

What are submarine canyons?

Submarine canyons are canyons cut into the continental shelf and ending at the deep ocean basin.

Where are submarine canyons found?

They are found at 90 degree angles to the shoreline.

How are submarine canyons thought to have been formed?

The canyons are created by an earthquake (that may cause large debris to gouge the crust) that triggers sediment to mix with water. This denser mixture flows to the ocean basin carving a path as it goes.

Where would you look for a continental rise? What forms a continental rise?

I would look at the bottom of a continental slope. These rises form because parties sink down off of the shelf break, but mostly they form at the end of submarine canyons by turbidity currents.

What are typical features of deep-ocean basins?

Near the 'center' are spreading centers, hydrothermal vents, abyssal hills, guyots, abyssal plains, trenches, and seamounts and island arcs being the furthest from the spreading.W

What is the extent of the mid-ocean ride system? Are mid-ocean ridges always literally in mid-ocean?

The mid-ocean ridge system winds its way through the oceans (usually not centered) to the length of 1.5 times the globes circumference.

What are fracture zones? What causes these lateral breaks?

Fracture zones are where the Earth's crust splits to allow the plates to move such as at transform boundaries. These lateral breaks are caused by the uneven expansion of the seafloor and the spherical shape of the Earth.

What are abyssal plains? What is unique about them?

Abyssal plains are very flat expanses of ocean floor between the ridges and the continental margins. The unique characteristic is that they hold over 1,000 meters of sediment that covers the contouring of old ridges, volcanoes, etc... Their depth also only varies by 2 meters.

Why are abyssal plains relatively rare in the Pacific?

They are rare because they need sediment deposits to form and all the sediment they would usually get, gets carried to the bottom of the trenches.

How do guyots form?

Guyots form from volcanic activity near the spreading center. They however sometimes reach the surface of the sea, just high enough to be worn down by waves and currents to achieve a flat top look.

How were lines of guyots and seamounts important in deciphering plate tectonics?

The lines of seamounts and guyots proved that the seafloor was spreading and they even showed from which direction.

How are the ocean's trenches formed? How are earthquakes related to their formation?

Trenches are formed when one tectonic plate subducts and forms a v-shaped depression where the plates meet. Earthquakes are caused by the subducting plate lurching which can suggest a trench is off the coast.

Why are trenches and island arcs curved?

Trenches are curved because the curvature of the Earth.

Is the descent to the bottom steeper on the convex side of the arc or on the concave side? Why do you think most of the trenches are in the Western Pacific?

It is steeper on the convex side of the arc. The trenches are mostly in the pacific because the most plate subduction occurs here.

Where is the true edge of the continent located?

The bottom of the continental slope

Where are ridges widest?

Where they are most active at rapid spreading centers.

What is the difference from slow spreading vs. fast?

slow spreading creates ridges with a steeper profile.

How are hydrothermal vents thought to circulate water?

1) water descends through fissures and cracks in the ridge floor, 2) water comes into contact with hot rocks associated with seafloor spreading, 3) water dissolves minerals and gases and escapes upwards by convection.

What are the properties of water that comes out of a hydrothermal vent?

gas and mineral rich, very hot, acidic