Deck 13: The Ocean Floor

Question 1

Which of the following generally has the lowest surface slope?

A) continental slope
B) beach shoreface
C) continental rise
D) continental shelf

Answer 1

continental shelf

Question 2

The gently sloping submerged surface extending from the shoreline toward the deep ocean is termed the______ .

A) continental slope
B) submarine canyon
C) continental shelf
D) continental rise

Answer 2

continental slope

Question 3

Ocean floor topography can be estimated from space using______ .

A) high resolution measurements of the earth's magnetic field
B) radar pulses that bounce off the ocean surface
C) laser beams that penetrate to the sea floor
D) powerful sound waves that echo to the satellite

Answer 3

radar pulses that bounce off the ocean surface

Question 4

Which one of the following would most likely be covered with thick turbidite layers?

A) upper part of a steep, narrow, submarine canyon
B) ocean floor around a conical- shaped seamount
C) deep- sea fan at the base of a continental slope
D) axial rift zone of an active mid- ocean spreading center

Question 5

Submarine canyons found on the continental slope are believed to have been created ______.

A) by faulting
B) because of a plate plunging into the mantle
C) by rivers during the ice age
D) none of these

Question 6

Which one of the following is not part of the continental margin?

A) continental slope
B) continental rise
C) continental trench
D) continental shelf

Question 7

The first systematic bathymetric measurements came on the voyage of______ .

A) The James Caird
B) The Beagle
C) The Fram
D) HMS Challenger

Question 8

Which ocean has the greatest average depth?

A) Pacific
B) Arctic
C) Indian
D) Atlantic

Question 9

Which ocean is almost entirely within the Southern hemisphere?

A) the Indian Ocean
B) the Atlantic Ocean
C) the Arctic Ocean
D) the Pacific Ocean

Question 10

The best definition of the outer edge of the continental shelf is that point where______ .

A) a rapid steepening of the gradient occurs
B) the water depth reaches 100 fathoms
C) the gradient becomes very gentle
D) it meets an oceanic ridge

Question 11

An echo sounder operates by measuring the time required for a______ .

A) sound pulse travels from a ship to the seafloor and back
B) radar beam to travel from a ship to the seafloor and back
C) light beam to travel from a satellite at a known altitude to the sea bottom and back
D) radar beam to travel from a harbor patrol boat to a fuzz- buster on a speeding yacht

Question 12

The best modern technique for obtaining high resolution bathymetry of the seafloor is______ .

A) seismic reflection profiling
B) sidescan sonar
C) multibeam bathymetry
D) echo sounding

Question 13

It is thought that submarine canyons on the continental slope have been generated by______ .

A) streams when sea level was much lower than it is today
B) streams when sea level was much higher than it is today
C) turbidity currents
D) a submarine glaciations

Question 14

The Ocean is largest.

A) Indian
B) Arctic
C) Pacific
D) Atlantic

Question 15

In the Mississippi River delta in south Louisiana shallow subsurface imaging of the sediments reveal buried channels beneath delta sediments that are less than 10,000 years old that extend offshore past the modern continental shelf. What is a simple explanation for these buried channels?

A) The river must have been bigger in the past, cutting a channel clear to the edge of the shelf below sea level.
B) They represent channels of the Mississippi river delta when sea level was lower, during the ice age.
C) Turbidity currents cut a submarine canyon on the shelf before the delta buried them.
D) They represent giant flood events before the delta was formed and before the river formed.

Question 16

Sailors in the 16^th- 18^th century dreaded "rounding the horn" of South America because of strong winds and heavy seas. Cape Horn is about latitude 55°S at the tip of South America. These sailors were using a passage from the Atlantic to Pacific Ocean that was actually a stormy ocean now often called______ .

A) the Antarctic Ocean
B) the Indian Ocean
C) the Southern Ocean
D) the Australian Ocean

Question 17

Multibeam sonar provides the best modern technique for obtaining seafloor bathymetry, so why has it not been used for the entire ocean?

A) Oceanographers simply have not had time to process all the data.
B) It does not work in deep water.
C) It is too expensive, requiring many ships many years to survey the entire ocean.
D) It does not work where there is ice.

Question 18

Concerning the distribution of land and water, which of the following statements is true?

A) The Northern Hemisphere has much more water surface than the Southern Hemisphere.
B) The Southern Hemisphere has much more water surface than the Northern Hemisphere.
C) The percentage of land and water is about the same in both the Northern and Southern Hemispheres.
D) None of the above is true.

Question 19

______develop where oceanic lithosphere bends downward and sinks into the mantle.

A) Rift valleys on mid- ocean ridges
B) Submarine canyons
C) Deep ocean trenches
D) Abyssal seamounts

Question 20

The oceans cover approximately ______ percent of Earth's surface.

A) 60
B) 40
C) 50
D) 70

Question 21

Consider the diagram below. What type of margin is this?

A) Passive, because the deep sea fans indicate tectonic activity.
B) Passive, because the lack of trenches and subducting oceanic crust indicate tectonic activity.
C) Active, because the deep sea fans indicate tectonic activity.
D) Active, because the lack of trenches and subducting oceanic crust indicate tectonic activity.

Question 22

Which one of the following statements about mid- ocean ridges is false?

A) They are sites for submarine eruptions of basaltic lava.
B) Sediments include thick siliceous ooze deposits and sandy turbidite beds.
C) They are where young lithosphere is added to the edges of spreading, oceanic plates.
D) Terrigenous sediment coverings are very thin or absent.

Question 23

Abyssal plains are very flat because ______.

A) they are not really flat; it is just that there is no data so they are shown as flat
B) basalt volcanoes on the seafloor produce little terrain
C) sediments accumulate to cover the seafloor topography
D) they have flat faults, the form flat, planar topography

Question 24

What is the difference between an active continental margin and a passive continental margin?

A) An active margin receives large amounts of sediment whereas a passive margin is sediment starved.
B) A passive margin is the site of an ancient continental rift, left behind when seafloor spreading moved offshore, whereas an active margin is an active plate boundary.
C) An active margin has earthquakes whereas a passive margin has quiet erupting aka passive. volcanoes.
D) A passive margin is passively carried along by plate tectonics in a transform system, like the San Andreas whereas an active margin is a trench.

Question 25

If Yellowstone were on the ocean floor, it would produce ______.

A) a mid- ocean ridge
B) an island arc
C) a chain of line islands, like Hawaii
D) a trench

Question 26

"Black smokers" are associated with______ .

A) hot water
B) oceanic ridges
C) mineral- rich waters
D) all of these

Question 27

The continental rise is located______ .

A) at the top of the continental slope
B) between an abyssal plain and continental slope
C) at the seaward edge of a deep ocean trench
D) at the top of a mid- ocean ridge

Question 28

Which of the following is associated with ocean ridges?

A) mountainous topography
B) volcanic structures
C) rift zones
D) all of these

Question 29

Where are the deepest parts of the oceans?

A) along the base of the continental slope
B) in the abyssal plain
C) in rift valleys at sea floor spreading center
D) in trenches

Question 30

Ocean ridges form because ______.

A) they are chains of volcanoes, like the Hawaiian Islands, that form along hot spots
B) they are a broad seafloor highland formed by sea floor spreading
C) they are submarine collisional mountain belts, forming submarine mountains that haven't yet risen from the sea floor
D) rocks bulge up in ridges along transform faults associated with the ridge

Question 31

The crests of mid- oceanic ridges______ .

A) are geologically old features
B) lie at depths exceeding 6 kilometers
C) contain active rift zones
D) are heavily mantled with sediment

Question 32

Why are there virtually no sediments at ocean ridges, even when they are close to land?

A) The sediments get deflected from the topographic high of the ridge.
B) The sediments get buried by volcanic rocks, so are not visible.
C) The crust is too young; there hasn't been enough time for sediments to accumulate.
D) No one knows, it is one of the mysteries of geology.

Question 33

Which of the following is not true of deep ocean trenches?

A) They may act as sediment traps.
B) They are geologically very stable.
C) They are sites where plates plunge back into the mantle.
D) They are long and narrow depressions.

Question 34

The______ Ocean has more extensive abyssal plains than the Pacific Ocean because it has fewer trenches to trap sediments moving down the continental slope.

A) Indian
B) Arctic
C) Atlantic
D) none of these

Question 35

Seamounts______.

A) are a special type of oceanic trench
B) form only in the Pacific Ocean basin
C) are volcanoes that form on the ocean floor
D) are submarine canyons found near Australia

Question 36

Earlier we discussed the concept of isostasy, where lower density rocks rise higher than higher density rocks. How is the variation of water depth at spreading centers ridges. controlled by isostasy?

A) Volcanic rocks are lighter than other rocks, and so the abundant volcanic rocks at the ridges are lower density features that produce the seafloor topography.
B) The lithosphere cools as it moves away from the ridge axis by sea floor spreading, and cooler rocks are lower density, so the sea floor gets deeper as the lithosphere gets more dense.
C) Oceanic ridges are sites where the lithosphere is carried into the mantle on one side aka subduction zones., and the volcanoes along these margins produce the ridge by buildup of lower density crust.
D) It has nothing to do with isostasy; the areas are simply high because there are chains of active volcanoes along the ridge crest, producing the topography.

Question 37

The deepest place in the world's oceans is known as the______ .

A) Challenger Deep
B) Maldives Trench
C) Asuncion Hole
D) Aleutians Pit

Question 38

Deep sea trenches are important features for plate tectonic studies because______ .

A) they are sites where the oceanic lithosphere is consumed into the mantle
B) they are sites where oceanic lithosphere is formed
C) they are sites where two plate move past each other horizontally
D) none of the above

Question 39

The seafloor spreading process at ridges produces what type of faults?

A) normal faults
B) oblique- slip faults
C) thrust fault
D) strike- slip faults

Question 40

Subduction of oceanic lithosphere at the trenches sometimes comes pieces of both the continental and oceanic lithosphere to break off and pile up to produce______ .

A) a strike slip fault like the San Andreas
B) a subduction slope
C) subduction erosion
D) an accretionary wedge

Question 41

Why is manganese not mined on the seabed given that there are abundant manganese nodules in some parts of the ocean floor?

A) It is not economical to mine manganese nodules at present- day world prices for manganese and associated metals in nodules.
B) The manganese market is held by a global cartel who prevent the material from being mined.
C) It is impossible to extract the nodules from the seafloor with present- day technology.
D) The manganese is too difficult to extract from the nodules; a new technology is needed.

Question 42

Give the correct type of ocean floor sediment for each phrase.

-Manganese nodule

A) biogenous
B) hydrogenous
C) terrigenous
D) phytogenuous

Question 43

How do atolls form?

A) from turbidity currents
B) from fringing coral reefs around a volcano
C) sediment traps in trenches
D) from black smokers that build up excess minerals

Question 44

Sediments derived primarily from the products of weathering on the continents are called

A) terrigenous sediment
B) biogenous sediment
C) hydrogenous sediment
D) both terrigenous and biogenous sediment

Question 45

Micro- organisms called foraminifera have tiny coiled shells with chambers. In modern oceans the coiling direction of foraminifera shells is correlated to temperature. Using coiling direction from foraminifera fossils is an example of ______.

A) using the fossil as a paleo- depth indicator because water temperature varies with depth
B) using isotopes to fingerprint temperature
C) geomagic; the whole idea is preposterous
D) using the fossil's coiling direction is a proxy for climate because the surface water temperature would be highly correlated to surface temperature

Question 46

African dust from the Sahara desert is observed across the Atlantic as far west as the Caribbean region where it produces a hazy sky condition during the annual dry season. You are a climate scientist and make a prediction that the Sahara was not a desert during glacial periods in the northern hemisphere. How could you test this hypothesis by looking at deep sea sediments from the Atlantic off west Africa?

A) The hypothesis is untestable with deep sea sediment.
B) You could measure the isotopes in the sediment to estimate the sea surface temperatures.
C) You would look at fossils to see if there were organisms that preferred dusty conditions vs. clear water conditions.
D) You could look at the sediments to see if there were biogenic sediments interbedded with sediments with terrigeneous input corresponding to the dry, interglacial intervals.

Question 47

Give the correct type of ocean floor sediment for each phrase.

-Abyssal plain clay

A) biogenous
B) hydrogenous
C) terrigenous
D) phytogenuous

Question 48

Manganese nodules are an example of______.

A) terrigenous sediment
B) biogenous sediment
C) hydrogenous sediment
D) both terrigenous and biogenous sediment

Question 49

Identify what is pictured here:

A) rift valleys
B) hydrogenous flow structures
C) black smokers
D) guyots

Question 50

Radiolarian chert is produced in the deep sea by the accumulation of siliceous radiolarian shells. What kind of sediment is radiolarian chert?

A) terrigenous sediment
B) biogenous sediment
C) hydrogenous sediment
D) both terrigenous and biogenous sediment

Question 51

The 2010 Deepwater Horizon oil spill in the Gulf of Mexico was the largest environmental disaster in North American history. It was brought on in part by new technology allowing development of oil and gas reserves in deep water. Given the scope of the spill, why do companies take a risk of such a disaster given the scope of the litigation following the disaster?

A) The oil and gas industry is poor at assessing risk, and didn't understand the risk.
B) They just assume their lawyers can win any lawsuit, regardless of the disaster.
C) The potential profit is so large from a major oil find that the companies take the risk, try to use all cautions to minimize risk, but sometimes fail.
D) They didn't care about the risk, they just drove forward.

Question 52

Minerals that crystallize directly from seawater are examples of______ .

A) terrigenous sediment
B) biogenous sediment
C) hydrogenous sediment
D) both terrigenous and biogenous sediment

Question 53

Much of the Gulf of Mexico is underlain by thick layers of salt that formed in a small ocean basin like the Red Sea, which formed from sea floor spreading. This salt is a good example of ______ .

A) terrigenous sediment
B) biogenous sediment
C) hydrogenous sediment
D) both terrigenous and biogenous sediment

Question 54

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

A) radar altimeters
B) sidescan sonar
C) echo sounder
D) Doppler radar

Question 55

Give the correct type of ocean floor sediment for each phrase.

-Calcareous ooze

A) biogenous
B) hydrogenous
C) terrigenous
D) phytogenuous

Question 56

Most of our table salt comes from______ .

A) combining the metal sodium and the nonmetal chlorine gas in a chemical reaction vessel to make pure NaCl
B) China
C) salt obtained by evaporating seawater in dry climates
D) salt taken from mines

Question 57

How do calcareous oozes form?

A) The particles are precipitated in the water column below the depth of sunlight penetration and then sink to the bottom.
B) The particles settle out from calcite- rich turbidity currents at depths greater than 15,000 feet.
C) The particles are precipitated by bottom- dwelling organisms.
D) The particles are precipitated in warm surface waters and sink to the bottom.

Question 58

A geologist is studying sediments on land that were originally deep sea sediments. She finds the minerals zircon and garnet in the sediments, which could only come from a continental region. These sediments must be ______.

A) terrigenous sediment
B) biogenous sediment
C) hydrogenous sediment
D) both terrigenous and biogenous sediment

Question 59

In the present day, what is the most valuable non- living commodity obtained from sea floor?

A) oil and gas
B) gas hydrate
C) sand and gravel
D) gold

Question 60

When organisms living in seawater grow shells, the ratio between the isotopes of oxygen ¹⁸O/¹⁶O. trapped in their shell is dependent on the sea temperature. Why might geologists collect these sea shells from deep- sea sediments that are Pleistocene in age and measure their oxygen isotope ratios?

A) They might want to know how cold the water was at the seafloor in the past.
B) The organisms live near the surface, so their oxygen isotope ratios record surface temperature during Earth's great climate fluctuations of the ice age.
C) The organisms live in the photic zone, and so photosynthesis must be the main factor in the oxygen content.
D) They want to know how metabolism of the organism affects the oxygen isotope ratios.

Question 61

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

A) evaporites
B) manganese nodules
C) metal sulfides
D) calcareous ooze

Question 62

The gently sloping submerged surface extending from the shoreline toward the deep ocean is termed the continental_______ .

A) slope
B) shelf
C) plain
D) rise

Question 63

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

A) continental slope
B) continental volcanic arc
C) continental shelf
D) continental rise

Question 64

There are mid- ocean ridges in _______ .

A) the Indian Ocean
B) the Atlantic Ocean
C) the Pacific Ocean
D) all three of these oceans

Question 65

_______ does not accumulate below 4500 meters depth because it is highly soluble in seawater below that depth.

A) Calcium carbonate
B) Sulfur oxide
C) Iron oxide
D) Manganese

Question 66

_______ continental margins occur where oceanic lithosphere is being subducted beneath the edge of a continent.

A) Active
B) Passive
C) Deep sea
D) Turbidity

Question 67

Seafloor hot springs occur mainly in_______ .

A) mid- ocean ridges
B) abyssal plains
C) continental slopes
D) continental shelves

Question 68

Submerged, flat- topped seamounts are known as _______ .

A) guyots
B) oceanic plateaus
C) nodule stacks
D) abyssal mounts

Question 69

Examine the words and/or phrases below and determine the relationship among the majority of words/phrases. Choose the option that does not fit the pattern.

A) volcanic island arc
B) subduction
C) trench
D) rift valley

Question 70

_______ form the deepest parts of the ocean basins.

A) Trenches
B) Submarine canyons
C) Continental shelves
D) Continental slopes

Question 71

The west coast of South America has an_______ continental margin and the east coast of North America has an. continental margins.

A) active; active
B) passive; active
C) passive; passive
D) active; passive

Question 72

Sand, silt, and clays deposited on the ocean floor are described as _______ sediments.

A) terrigenous
B) hydrogenous
C) biogenous
D) phytogenuous

Question 73

Oil and gas resources are most common on the _______ .

A) continental shelf
B) abyssal plains
C) mid- ocean ridge
D) guyots

Question 74

Abyssal plains with sediments covering the seafloor igneous rocks are _______ in the central Pacific basin than in the North Atlantic.

A) less biogenous
B) more economically viable
C) more terrigenous
D) less extensive

Question 75

The lowest point on earth is in the_______ Ocean.

A) Pacific
B) Atlantic
C) Southern
D) Indian

Question 76

The most important economic mineral resource extracted from the seafloor today is_______ .

A) oil and gas
B) sulfides
C) fossil fuels
D) heavy minerals

Question 77

The continental rise lies_______ the continental slope.

A) within
B) just above
C) nowhere near
D) just below

Question 78

Most of the world's landmass is in the_______ hemisphere.

A) Northern
B) Southern
C) Central
D) Eastern

Question 79

Turbidites are_______ sediments.

A) biogenous
B) terrigenous
C) hydrogenous
D) phytogenuous

Question 80

The principal technique for finding ocean depth today is_______ .

A) seismic waves
B) loran
C) radar
D) sonar