Oceanography Chapter 4

Front 1

Abyssal Hill

Back 1

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

Front 2

Abyssal Plain

Back 2

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

Front 3

Active Margin

Back 3

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

Front 4

Bathymetry

Back 4

the discovery and study of ocean floor contours.

Front 5

Continental Margin

Back 5

Submerged outer edge of the continent.

Front 6

Continental Rise

Back 6

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

Front 7

Continental Shelf

Back 7

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

Front 8

Continental Slope

Back 8

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

Front 9

Fracture Zone

Back 9

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

Front 10

Guyot

Back 10

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

Front 11

Hydrothermal Vent

Back 11

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

Front 12

Ice Age

Back 12

Period of widespread glaciation.

Front 13

Island Arc

Back 13

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

Front 14

Ocean Basin

Back 14

The deep sea floor beyond the continental margin.

Front 15

Oceanic Ridge

Back 15

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

Front 16

Passive Margin

Back 16

Continental margins facing the edges of diverging plates.

Front 17

Seamount

Back 17

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

Front 18

Shelf Break

Back 18

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

Front 19

Submarine Canyon

Back 19

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

Front 20

Transform Fault

Back 20

Fractures along which plates slide horizontally.

Front 21

Trench

Back 21

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

Front 22

Turbidity Current

Back 22

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.

Front 23

Fault

Back 23

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

Front 24

Why is Earth so hard to map compared to jupiter?

Back 24

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

Front 25

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

Back 25

Rope and stone, later winch and weight.

Front 26

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

Back 26

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.

Front 27

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

Back 27

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

Front 28

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

Back 28

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.

Front 29

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

Back 29

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.

Front 30

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

Back 30

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

Front 31

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?

Back 31

The continental margins and the ocean basin.

Front 32

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

Back 32

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

Front 33

What are the features of continental margins?

Back 33

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

Front 34

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

Back 34

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.

Front 35

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

Back 35

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.

Front 36

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

Back 36

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.

Front 37

What are submarine canyons?

Back 37

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

Front 38

Where are submarine canyons found?

Back 38

They are found at 90 degree angles to the shoreline.

Front 39

How are submarine canyons thought to have been formed?

Back 39

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.

Front 40

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

Back 40

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.

Front 41

What are typical features of deep-ocean basins?

Back 41

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

Front 42

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

Back 42

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

Front 43

What are fracture zones? What causes these lateral breaks?

Back 43

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.

Front 44

What are abyssal plains? What is unique about them?

Back 44

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.

Front 45

Why are abyssal plains relatively rare in the Pacific?

Back 45

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.

Front 46

How do guyots form?

Back 46

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.

Front 47

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

Back 47

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

Front 48

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

Back 48

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.

Front 49

Why are trenches and island arcs curved?

Back 49

Trenches are curved because the curvature of the Earth.

Front 50

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?

Back 50

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

Front 51

Where is the true edge of the continent located?

Back 51

The bottom of the continental slope

Front 52

Where are ridges widest?

Back 52

Where they are most active at rapid spreading centers.

Front 53

What is the difference from slow spreading vs. fast?

Back 53

slow spreading creates ridges with a steeper profile.

Front 54

How are hydrothermal vents thought to circulate water?

Back 54

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.

Front 55

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

Back 55

gas and mineral rich, very hot, acidic