Deck 10: The Seafloor and Continental Margins

Question 1

Which of the numbered features on this figure is a continental shelf?

A)1
B)2
C)3
D)4

Answer 1

A

Question 2

What is the ultimate source of food for animals living around deep-sea hydrothermal vents?

A)sunlight and photosynthesis
B)the decay of creatures that float on the ocean surface and settle to the bottom
C)nuclear energy from the heated uranium-rich rocks
D)bacteria that break down hydrogen sulfide

Answer 2

D

Question 3

Which of the following is associated with mid-ocean ridges?

A)a great thickness of oceanic sediment trapped within the central rift
B)very smooth topography as a result of the sedimentary cover
C)melting of the entire thickness of the asthenosphere to produce magma
D)compression that buckles the crust forming the ridge
E)none of these

Answer 3

E

Question 4

Which of these numbers is closest to an oceanic trench?

A)1
B)2
C)3
D)4
E)none of these

Question 5

This figure shows ages of seafloor.Which of the numbered sites is on the oldest seafloor,based on its position?

A)1
B)2
C)3
D)4

Question 6

Which of these numbers has the thinnest sequence of marine sediments?

A)1
B)2
C)3
D)4
E)none of these

Question 7

Which of the numbered features on this figure is a continental slope?

A)1
B)2
C)3
D)4

Question 8

What feature is on the seafloor near Monterey,California?

A)an active subduction zone that causes earthquakes
B)an active mid-ocean ridge that has opened up a rift on the continental margin
C)a large submarine canyon and a number of smaller ones
D)a circular scar interpreted to represent a huge impact crater
E)none of these

Question 9

This figure shows ages of seafloor.Which of the numbered sites is on the shallowest seafloor,based on its position?

A)1
B)2
C)3
D)4

Question 10

This figure shows ages of seafloor.Which pair of numbers likely has crust of similar age?

A)1 and 2
B)1 and 3
C)2 and 3
D)2 and 4
E)3 and 4

Question 11

What occurs near black smokers?

A)circular features (called chimneys)form,composed of sulfide and sulfate minerals
B)heated fresh water is derived from the land
C)organic-rich shale burns in the subsurface
D)coal-rich layers burn in the subsurface
E)none of these

Question 12

Which of these numbers is on the abyssal plane?

A)1
B)2
C)3
D)4
E)none of these

Question 13

This figure shows ages of seafloor.Which of the numbered sites is on the deepest seafloor,based on its position?

A)1
B)2
C)3
D)4

Question 14

What features are NOT recognized on the seafloor near Monterey,California?

A)a canyon partly cut into hard granite
B)faults that cut across the seafloor
C)a broad continental shelf
D)a continental slope
E)all of these features are recognized on the seafloor

Question 15

Which of these numbers is near a site with active seafloor spreading?

A)1
B)2
C)3
D)4
E)none of these

Question 16

Which of these numbers is near a continental shelf?

A)1
B)2
C)3
D)4
E)none of these

Question 17

This figure shows ages of seafloor.Which of the numbered sites is on the youngest seafloor,based on its position?

A)1
B)2
C)3
D)4

Question 18

Which of the following is associated with a fast-spreading ridge?

A)rates of about 10 centimeters per year or more
B)a broad ridge because the rocks remain hotter farther from the center of spreading
C)less of a deep central rift than in a slow spreading ridge
D)all of these

Question 19

Which of the following is NOT a way in which we map and investigate the seafloor?

A)bouncing sound waves from a ship off the bottom
B)drilling holes into the seafloor from ships
C)using satellites to observe the sea surface
D)conducting seismic surveys to investigate rock layers
E)we use all of these techniques

Question 20

Which of the following CANNOT be observed on a seismic-reflection profile?

A)orientation of rock layers
B)shape of the seafloor
C)folds
D)faults
E)all of these can be observed

Question 21

The deepest parts of the seafloor are:

A)mid-ocean ridges
B)abyssal plain
C)seamounts
D)oceanic trenches
E)continental shelves

Question 22

Most oceanic plateaus are:

A)small pieces rifted apart from continents
B)places where the seafloor has been buckled upward by convergence
C)constructed by volcanic eruptions probably over mantle plumes
D)large fan-shaped mounds deposited by turbidity currents

Question 23

What setting has the thinnest cover of sediment in the oceans?

A)mid-ocean ridges
B)abyssal plain
C)oceanic trenches
D)continental shelves and slopes along passive margins

Question 24

Island arcs are curved because:

A)the shapes of the continents were arcuate as they rifted apart
B)the shape of the mid-ocean ridge matches the shape of the continents
C)Earth is a sphere,not a flat plane
D)most terranes added to the continental margin are circular

Question 25

Which of the following is associated with a typical island arc?

A)oceanic trench
B)subduction
C)melting in the mantle
D)ocean-ocean convergence
E)all of these

Question 26

Which of the following parts of the seafloor are the shallowest?

A)mid-ocean ridges
B)abyssal plain
C)oceanic trenches
D)continental shelves

Question 27

Which of the following seas was formed when spreading and transform faulting sliced off a sliver of the continent?

A)Sea of Japan
B)Bering Sea
C)Philippine Sea
D)Gulf of California

Question 28

Why does the elevation of the seafloor decrease from the mid-ocean ridge to the abyssal plain?

A)The oceanic lithosphere cools and becomes denser.
B)The weight of sediments depresses the oceanic crust.
C)The oceanic plate is flexed downward near a subduction zone.
D)Slab rollback pulls the oceanic lithosphere deeper.

Question 29

Which of the following is the presently occurring near the Sea of Japan?

A)oceanic crust in the sea of Japan is being generated by back-arc spreading
B)Japan is moving closer to Asia over time
C)Volcanoes in Japan are related to subduction of oceanic crust that forms in the Sea of Japan
D)all of these

Question 30

On a map showing the age of the seafloor,why are the patterns symmetrical in the Atlantic Ocean but not the Pacific Ocean?

A)Spreading along the Atlantic ridge added seafloor to plates on both sides,while subduction has consumed large areas of old oceanic crust in the Pacific.
B)Subduction occurred at the same rate along the eastern and western sides of the Atlantic,but not in the Pacific.
C)Subduction has consumed large areas of old oceanic crust in the Atlantic,more than in the Pacific.
D)Spreading in the Atlantic has been faster than sea-floor spreading in the Pacific

Question 31

Which of the following is the present plate-tectonic setting of oceanic crust in the Bering Sea?

A)it contains a mid-ocean ridge
B)it is being generated by back-arc spreading
C)it does not contain any currently active plate boundaries
D)it was formed by thinning of continental crust

Question 32

If you drilled into an oceanic plateau,what would you most likely find?

A)a thin layer of oceanic sediment over continental crust
B)andesitic volcanoes buried by turbidity currents
C)a normal thickness of oceanic crust overlain by andesitic volcanoes
D)large amounts of basalt derived from melting in the mantle

Question 33

Most oceanic islands and seamounts are:

A)small pieces rifted apart from continents
B)places where the seafloor has been buckled upward by convergence
C)constructed by volcanic eruptions that first occur under water
D)large fan-shaped mounds deposited by turbidity currents

Question 34

This figure shows a northwest-southeast line of islands and seamounts near Hawaii.If location 3 has the oldest rocks and Hawaii (1)has the youngest rocks,which way is the plate moving with respect to the hot spot?

A)northwest
B)southeast
C)northwest and southeast
D)it is not moving in a consistent direction

Question 35

In the Atlantic Ocean,where is the oldest oceanic crust?

A)mid-ocean ridges
B)abyssal plain next to the continents
C)oceanic trenches
D)seamounts
E)continental shelves close to the shoreline

Question 36

Which parts of the seafloor have the youngest oceanic crust?

A)mid-ocean ridges
B)abyssal plain
C)oceanic trenches
D)continental shelves along passive margins

Question 37

If you wanted to locate hot spots on Earth,which of the following would NOT be good place to look?

A)the volcanically active end of a linear island chain
B)clusters of volcanically active islands
C)Hawaii and the Galapagos
D)all of these would be good places

Question 38

What processes can occur in front of or behind some island arcs?

A)trench rollback or back-arc rifting
B)fold and thrust belts in the mountains,and formation of a continental plateau
C)formation of an oceanic plateau related to subduction
D)all of these

Question 39

Which of the following is an island arc?

A)Hawaiian Islands
B)Iceland
C)the East African Rift
D)Aleutian Islands
E)none of these

Question 40

In what setting does the thickest sediment accumulate in the oceans?

A)mid-ocean ridges in any location in the ocean
B)abyssal plain in the middle of the ocean
C)oceanic trenches in the middle of the ocean
D)continental shelves and slopes along passive margins

Question 41

Which of the following seas was formed by loading of thrust sheets of the Zagros Mountains?

A)North Sea
B)Red Sea
C)Persian Gulf
D)Baltic Sea
E)all of these

Question 42

Which of the following is a consistent feature of reefs and atolls?

A)volcanic islands
B)passive continental margins
C)divergent plate boundaries
D)carbonate rocks and accumulations

Question 43

Which of the following sea(s)was formed when subduction jumped or shifted outward from the continent?

A)North Sea
B)Bering Sea
C)Philippine Sea
D)Gulf of California
E)all of these

Question 44

Which of the following is associated with a continental slope?

A)submarine canyons
B)turbidity currents
C)submarine landslides
D)all of these

Question 45

Which of these numbered features is an atoll?

A)1
B)2
C)3
D)all of these
E)none of these

Question 46

If you were looking for graded beds,where would be a good place to look?

A)in a warm and shallow lagoon
B)in the center of an atoll
C)just offshore of a sediment-poor beach
D)in a submarine fan
E)none of these

Question 47

Which of these numbered features is on the continental shelf?

A)1
B)2
C)3
D)4
E)none of these

Question 48

Which of the following letters marks the Red Sea?

A)A
B)B
C)C
D)D
E)E

Question 49

Which of the following are associated with turbidity currents?

A)a dense slurry of water and sediment that moves downhill
B)submarine canyons
C)submarine fans
D)graded beds
E)all of these

Question 50

Which of these numbered features is on the continental slope?

A)1
B)2
C)3
D)4
E)none of these

Question 51

Which of the following letters marks the Persian Gulf?

A)A
B)B
C)C
D)D
E)E

Question 52

Which of the following letters marks the Bering Sea and Aleutian Islands off Alaska?

A)A
B)B
C)C
D)D
E)E

Question 53

Which sea is shallow because it is underlain by continental crust?

A)Mediterranean Sea
B)Red Sea
C)Black Sea
D)Persian Gulf

Question 54

Which of these numbered features has the thinnest sediment?

A)1
B)2
C)3
D)4
E)none of these

Question 55

Which of the following letters marks the Sea of Japan?

A)A
B)B
C)C
D)D
E)E

Question 56

Which of the following seas currently has back-arc spreading?

A)Sea of Japan
B)Baltic Sea
C)Bering Sea
D)Gulf of California
E)all of these

Question 57

What is a popular model for the formation of an atoll?

A)a moderate-sized meteoroid forms a circular crater on the seafloor
B)a volcanic eruption forms a large circular caldera
C)a volcanic island forms and subsides
D)a barrier reef becomes buried by volcanic eruptions

Question 58

Which of the following places would NOT be a good place to visit a reef?

A)shallow seas that are relatively free of suspended sediment
B)the area offshore of northeastern Australia
C)the Caribbean
D)islands in the southwestern Pacific Ocean
E)shallow,clear waters off Iceland

Question 59

Which of these numbered features is over continental crust that has been the most thinned by rifting?

A)1
B)2
C)3
D)4
E)none of these

Question 60

Which of the following seas was formed by rifting or seafloor spreading?

A)North Sea
B)Red Sea
C)Persian Gulf
D)Baltic Sea

Question 61

Which of the following features are NOT associated with salt structures along the Gulf Coast of the United States?

A)a layer of salt deposited during continental rifting
B)folding and doming of layers above rising masses of salt
C)puzzling bumps and pits on the seafloor
D)a steep slope or escarpment marking the front of a large mass of salt
E)all of these are present in this region

Question 62

What causes the seafloor to deepen across a typical continental slope?

A)thinning of continental crust because of normal faults
B)a transition from continental crust to oceanic crust
C)down flexing of oceanic crust because of subduction
D)deposition of sediment from turbidity currents
E)a and b only

Question 63

Which of the following features is NOT present near the present-day Caribbean?

A)a subduction zone
B)an island arc
C)a long transform fault
D)reefs
E)all of these are present

Question 64

Which part of the Atlantic Ocean was the most recently formed?

A)North Atlantic
B)Central Atlantic
C)South Atlantic
D)Pacific Ocean

Question 65

These globes show the position of the continents and ocean basins at various times in the past.Which of these represents the youngest time?

A)1
B)2
C)3
D)4

Question 66

Which two continents rifted apart to form the central Atlantic Ocean?

A)India and Australia
B)South America and Antarctica
C)Europe and Asia
D)North America and Africa
E)none of these

Question 67

How do most salt deposits form?

A)dense slurries of sediment and water along continental slopes
B)rapid deposition offshore of deltas,like in the Gulf of Mexico
C)evaporation of water,such as in restricted seaways
D)conversion of limestone to dolostone

Question 68

How did the Gulf of Mexico form?

A)loading of thrust sheets of the Appalachian and Ouachita Mountains
B)a large meteoroid impact that formed a crater the same size as the present-day gulf
C)back-arc spreading behind the Lesser Antilles arc
D)Mesozoic (Jurassic)continental rifting and seafloor spreading

Question 69

What is the origin of the volcanoes in the Lesser Antilles and Central America?

A)two hot spots on either side of the Caribbean plate
B)subduction of oceanic crust beneath the Caribbean plate
C)magma leaking up along transform faults
D)rapid spreading along the Mid-Atlantic Ridge

Question 70

This map shows plate boundaries in the Caribbean region.Which number is in the Gulf of Mexico?

A)1
B)2
C)3
D)4
E)5

Question 71

How did the South Atlantic Ocean Form?

A)Asia rifted apart from Europe
B)Africa and North America collided to form the Appalachian Mountains
C)a piece of California started moving northward up the west coast
D)South America rifted apart from Africa
E)none of these

Question 72

What type of feature is interpreted to cause some parts of the Caribbean to be shallower than expected?

A)seafloor spreading along the Mid-Atlantic Ridge
B)an impact crater that formed at about the time that the dinosaurs died
C)an oceanic plateau that may have originated in the Pacific
D)a currently active hot spot that is not associated with volcanoes

Question 73

Approximately when did the central Atlantic Ocean form?

A)four billion years go
B)two billion years ago
C)two hundred million years ago
D)twenty million years ago
E)two thousand years ago

Question 74

This map shows plate boundaries in the Caribbean region.Which number is closest to a transform boundary?

A)1
B)2
C)3
D)4
E)5

Question 75

Once salt deposits are formed,they can:

A)flow upward because they are less dense than normal rocks
B)slip and flow,allowing overlying rocks to fold and fault
C)flow down hillslopes,forming a salt glacier
D)form a steep slope or escarpment on the seafloor
E)all of these

Question 76

This map shows plate boundaries in the Caribbean region.Which number is closest to a subduction zone that has formed an island arc?

A)1
B)2
C)3
D)4
E)5

Question 77

What has happened to the Pacific Ocean in the last 200 million years?

A)it has become deeper as the rate of seafloor spreading increased
B)it became wider because of seafloor spreading
C)it became smaller as the Atlantic Ocean opened
D)it remained unchanged in size
E)none of these

Question 78

These globes show the position of the continents and ocean basins at various times in the past.Which of these represents the oldest time?

A)1
B)2
C)3
D)4

Question 79

These globes show the position of the continents and ocean basins at various times in the past.What is the correct order of these globes,from oldest to youngest?

A)1,2,3,4
B)1,4,3,2
C)4,3,2,1
D)4,3,1,2
E)4,1,3,2

Question 80

What is currently the dominant type of motion along the northern boundary of the Caribbean plate?

A)subduction of the Caribbean plate beneath Cuba
B)subduction of the Gulf of Mexico beneath the Caribbean plate
C)subduction of the Caribbean plate beneath the volcanoes of Central America
D)seafloor spreading that is moving North America farther from South America
E)a long transform fault moving the Caribbean plate eastward relative to North America