Deck 10: Seafloor and Continental Margins

Question 1

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

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

Answer 1

B

Question 2

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

Answer 2

A

Question 3

Which of these numbers is closest to an oceanic trench?

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

Answer 3

D

Question 4

Rock units beneath the seafloor can be imaged with sound waves using a method called:

A) seismic-reflection profiling
B) magnetic profiling
C) bounce profiling
D) physical profiling

Question 5

Which of these numbers is near a continental shelf?

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

Question 6

What is the source of energy for giant worm tubes and clams that live at hydrothermal vents?

A) Bacteria that break down H2S
B) Plants that grow on the seafloor
C) Sunlight

Question 7

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

Question 8

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

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

Question 9

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 10

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 11

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

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

What method produces images of the materials beneath the seafloor using sound waves?

A) Seismic-reflection profiling
B) Ocean drilling
C) Satellites
D) Submersibles

Question 14

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 15

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

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

Question 16

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 17

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

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

Question 18

Which creatures belong to the community of organisms that live at hydrothermal vents?

A) Giant clams
B) Red worm tubes
C) White crabs
D) All of these creatures belong to the community of organisms that live at hydrothermal vents.

Question 19

What information can be determined directly by analyzing drill cores?

A) The type of sediment on the seafloor
B) The rate of sediment deposition
C) The type of rock on the seafloor
D) All of these

Question 20

The source of heat for the water emitted by black smokers at the mid-ocean ridges comes from:

A) magma
B) friction
C) radioactive decay
D) an unknown source

Question 21

Oceanic plateaus form from basaltic volcanism originating from:

A) hot spots
B) mid-ocean ridges
C) trenches

Question 22

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 23

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 24

What do the island chains of Hawaii, Tahiti, and Tristan da Cunha have in common?

A) They formed from hot spots.
B) They are part of island arcs.
C) They are part of an oceanic plateau.

Question 25

Hot spots form linear island chains because:

A) the plate moves relative to the underlying hot spot
B) they are aligned with trenches formed by subduction
C) they occur along the mid-oceanic ridges

Question 26

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 27

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 28

The area behind an island arc that develops a spreading center is a an):

A) back-arc basin
B) trench
C) abyssal plain
D) passive margin

Question 29

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 30

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 31

Which area shown on the map has the shallowest seafloor depth?

A) P) passive continental margin
B) R) oceanic ridge
C) T) trench

Question 32

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 33

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 34

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 35

What rock type forms oceanic plateaus?

A) basalt
B) granite
C) rhyolite

Question 36

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 37

Which area shown on the map has the greatest seafloor depth?

A) T) trench
B) P) passive margin
C) R) oceanic ridges

Question 38

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 39

On the map shown, R has the youngest oceanic crust because:

A) it is at a spreading center
B) it is at a passive margin
C) it is at a trench

Question 40

The red dots that coincide with volcanically active island chains shown on the map are called:

A) hot spots
B) mid-ocean ridges
C) abyssal plains
D) island arcs

Question 41

The Sea of Japan formed as a deep basin between Asia and Japan because:

A) of back-arc seafloor spreading
B) of trench subduction
C) it is part of a continental platform

Question 42

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 43

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 44

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 45

Which of the following letters marks the Red Sea?

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

Question 46

Which of these numbered features is an atoll?

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

Question 47

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

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

Question 48

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 49

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 50

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 51

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 52

Which of the following seas) 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 53

Which sea was a lake prior to being flooded by the ocean at the end of the Ice Age?

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

Question 54

Which of the following letters marks the Sea of Japan?

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

Question 55

Which of the following letters marks the Persian Gulf?

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

Question 56

Submerged ridges in the Philippine Sea were formed by a:

A) back-arc basin
B) trench
C) hot spot

Question 57

Subduction zones in the open ocean produce a an):

A) island arc
B) abyssal plain
C) mid-ocean ridge

Question 58

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 59

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 60

Island arcs form in association with what type of tectonic setting?

A) ocean-ocean convergent
B) ocean-continent convergent
C) transform
D) continental rift

Question 61

Which of these numbered features is on the continental shelf?

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

Question 62

Which conditions promote the growth of coral reefs?

A) shallow water
B) warm water
C) clear water
D) all of these conditions promote the growth of coral reefs

Question 63

Which of these numbered features is on the continental slope?

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

Question 64

Which of these numbered features has the thinnest sediment?

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

Question 65

Why did the Great Barrier Reef in Australia grow upward, forming the largest organic structure on Earth?

A) Sea level rose.
B) Sea level fell.
C) Elevation of the seafloor rose.

Question 66

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 67

What process thins the continental crust before it meets the oceanic crust at the continental slope?

A) normal faulting
B) subduction
C) river erosion
D) sediment deposition

Question 68

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 69

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 70

Salt is less dense and weaker than other types of rocks so it flows upward to form:

A) domes
B) folds
C) basins
D) faults

Question 71

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 72

Salt is a weak rock that can flow and therefore it forms:

A) domes
B) slip plane fold thrust faults
C) salt glaciers
D) all of these

Question 73

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 74

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 75

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 76

Submarine canyons in the continental slope are eroded by:

A) turbidity currents
B) rivers
C) glaciers

Question 77

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 78

Which of the following locations contains modern coral reefs?

A) Bahamas
B) Philippines
C) Polynesia
D) All of these locations are contain modern coral reefs

Question 79

The abrupt change from thinned, faulted continental crust to oceanic crust occurs at the:

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

Question 80

What are the characteristics of natural salt NaCl) deposits?

A) Deposited in layers
B) Very soluble in water
C) Can flow to form domes
D) All of these are characteristics of natural salt deposits