Deck 13: Divergent Boundaries

Question 1

What is the definition of subduction erosion?

A)Sediments from the ocean floor are scraped off a subducting tectonic plate and adhere to the overriding plate.
B)Diverging tectonic plates will cause rocks to slide downward along normal faults.
C)Glaciers extending off the continent will scour deep grooves in continental shelves.
D)Sediment and rock are scraped off the bottom of an overriding plate and transported into the mantle by a descending plate.

Answer 1

D

Question 2

A(n)________ forms when sediments from the ocean floor and pieces of oceanic crust are scraped from a subducting oceanic plate and adhere to an overriding tectonic plate.

A)accretionary wedge
B)deep-sea fan
C)active tectonic margin
D)submarine canyon

Answer 2

A

Question 3

Which of the following scenarios would likely result in the development of a passive continental margin?

A)Two tectonic plates colliding, creating a submarine trench
B)Continental blocks rifting apart and becoming separated by seafloor spreading
C)Two tectonic plates sliding past each other, rotating part of the crust
D)A mantle plume creating a chain of volcanic islands across the seafloor

Answer 3

B

Question 4

What are the two types of continental margins?

A)Transform and divergent
B)Trenches and rifts
C)Continental shelves and slopes
D)Passive and active

Question 5

Which of the following is associated with a passive continental margin?

A)Divergent boundaries
B)Convergent boundaries
C)Transform boundaries
D)No tectonic boundaries nearby

Question 6

How do researchers today routinely determine the depth of the water to the seafloor?

A)Ship-mounted gravimeters
B)A weighted roped or cable
C)High-resolution multibeam instruments
D)Laser reflector systems linked to satellites

Question 7

Which ship was involved in the first global, comprehensive study of the Earth's oceans starting in 1872?

A)U)S.S.Cyclops
B)H)M.S.Challenger
C)R)M.S.Titanic
D)The Glomar Explorer

Question 8

The continental shelf is composed of which material(s)?

A)Granitic crust covered with sedimentary rocks
B)Basaltic crust
C)Clay sediments and sands
D)Ophiolites

Question 9

What is the definition of a turbidity current?

A)Subsidence of the seafloor
B)Fast-moving water created by density differences
C)Submarine landslide
D)Focused jet of water blasting across the shelf from a surface stream

Question 10

Which part of a passive continental margin is built up by repeated deposition from turbidity currents?

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

Question 11

Submarine canyons found cutting into the continental shelf and slope are believed to have been created ________.

A)by subduction
B)by icebergs
C)by rivers during the ice age
D)by tectonic rifting

Question 12

The measurement of ocean depth and the topography of the ocean floor are known as ________.

A)geophysics
B)seismic tomography
C)topographic surveying
D)bathymetry

Question 13

Which of the following is associated with an active continental margin?

A)Divergent boundaries
B)Convergent boundaries
C)Transform boundaries
D)No tectonic boundaries nearby

Question 14

Which of the following will mark the furthest extent of a continent?

A)The shoreline
B)Tidal flats exposed during low tide
C)The crest of the continental slope
D)The lowest part of the continental slope

Question 15

What is the speed of sound waves in water?

A)1,500 m/sec
B)5,000 m/sec
C)3,200 m/sec
D)10,994 m/sec

Question 16

What tool is often used to measure the topography of the seafloor today?

A)High-resolution multibeam instruments
B)Sonar
C)Echo sounders
D)Radar altimeters

Question 17

Which of the following groups contains all three major topographic provinces oceanographers use to define the seafloor?

A)Continental margins, mid-ocean ridges, and deep-ocean basins
B)Mid-ocean ridges, continental shelves, and divergent boundaries
C)Submarine trenches, mid-ocean ridges, and turbidity currents
D)Deep-ocean basins, active margins, and passive margins

Question 18

Which region is surrounded by an active continental margin?

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

Question 19

Although many areas of the continental shelves are relatively featureless, there are some locations on the shelves that have received extensive glacial deposits and significant dissection by streams.How would this have been possible?

A)Glaciers and streams were powerful enough to shape the shelf underwater.
B)The shelves were once above sea level but have since dropped below sea level due to tectonic activity.
C)The sea level dropped during the last glacial episode because water was stored in large ice sheets, exposing the shelves.
D)As the continents collided in the past, the shelves were lifted above sea level and became exposed to the elements.

Question 20

The Challenger Deep has previously been measured to have a depth of 10,994 meters.You have been sent to the part of the Pacific Ocean to verify this depth with an echo sounder.Assuming that Depth = 1/2 (1,500 m/sec*echo travel time), approximately how many seconds should it take for the sound wave to leave your ship, strike the bottom of the Challenger Deep, and return if the depth is correct?

A)10.5 seconds
B)14.66 seconds
C)17.39 seconds
D)22.67 seconds

Question 21

Which of the following is not a method of obtaining samples and observations of the oceanic ridge system?

A)Finding segments of ocean floor that have been thrust up onto the continent
B)Visual inspections using submersible equipment
C)Deep sea core samples
D)Side-scan sonar

Question 22

Which of the following is not an example of a continental rift?

A)East Africa
B)Rhine Valley, Europe
C)Lake Baikal, Siberia
D)Appalachia, United States

Question 23

Which of the following choices represents a rate of seafloor spreading commonly associated with a ridge such as the Mid-Atlantic Ridge?

A)1-5 mm/yr
B)1-5 cm/yr
C)1-5 m/yr
D)1-5 km/yr

Question 24

________ accounts for greater ocean depths moving away from the oceanic ridge toward the deep ocean basin.

A)Mantle plume
B)Convection
C)Thermal contraction
D)Gravity

Question 25

Thermal springs known as ________ are often associated with oceanic ridges, where hot water containing dissolved minerals gushes from the seafloor.

A)hot springs
B)geysers
C)black smokers
D)ophiolites

Question 26

Approximately what percentage of the Earth's surface consists of deep-ocean basins?

A)10%
B)30%
C)47%
D)49%

Question 27

What rock would you expect to find associated with a mid-ocean ridge?

A)Sandstone
B)Granite
C)Limestone
D)Basalt

Question 28

The oceanic crust is composed almost entirely of ________ rocks that are underlain by ________ rocks, which makes up the lithospheric mantle.

A)felsic; sediments
B)intermediate; felsic
C)sedimentary; mafic
D)mafic; ultramafic

Question 29

Volcanic islands such as the Hawaiian islands form as a result of ________.

A)subduction
B)rifting
C)mantle plumes
D)batholith emplacement

Question 30

What is the average thickness of the oceanic crust?

A)0 km
B)3 km
C)7 km
D)20 km

Question 31

Volcanic island arcs are found near which features on the seafloor?

A)Abyssal plains
B)Coral atolls
C)Deep-ocean trenches
D)Rift zones

Question 32

Where do rift valleys form along the oceanic ridge system?

A)Along the flanks of the continent where the slope levels out to meet the seafloor
B)Along the axis of some ridge segments where the rift is down-faulted
C)Transecting the ridge where transform boundaries exist
D)Where the seafloor plunges back into the mantle as the plate is consumed

Question 33

How do deep-ocean trenches form?

A)Magma from a partially melting tectonic plate makes its way through the crust.
B)Subducting lithosphere descends into the mantle.
C)Two tectonic plates diverge and create a rift valley.
D)Sediments from a turbidity current settle out in a deep ocean basin.

Question 34

What is the source of flood basalts associated with oceanic plateaus?

A)Decompression melting associated with seafloor spreading
B)Partial melting associated with subduction
C)Impact heating from a meteorite strike
D)The melting of the head of a mantle plume

Question 35

Which of the following materials or features are not found at mid-ocean ridges?

A)Basaltic lava eruptions emitted along the ridge
B)Stands higher above the surrounding seafloor
C)Deep submarine trenches
D)Thin layers of sediments

Question 36

A(n)________ is a sequence of layers composing the oceanic crust that includes sheeted dikes, basalts, and gabbro.

A)passive margin
B)ophiolite complex
C)lithospheric sheeting
D)flood basalts

Question 37

Which of the following is an example of a mid-ocean ridge?

A)Puerto-Rico Trench
B)Challenger Deep
C)Mid-Indian Ridge
D)East Pacific Rise

Question 38

Where is the deepest place on Earth?

A)Peru-Chile Trench
B)Challenger Deep
C)Kuril Trench
D)Mid-Continent Rift

Question 39

Along which tectonic boundary are deep-ocean trenches found?

A)Convergent
B)Divergent
C)Transform

Question 40

What generates the magma necessary for seafloor spreading?

A)Decompression melting
B)Partial melting
C)Mantle plumes
D)Subduction

Question 41

A ________ forms when a rising mantle plume causes the overlying crust to dome and separate into three rifts.

A)triple junction
B)complex rift
C)submarine canyon system
D)divergent boundary

Question 42

Continental shelves on active margins are larger and broader than those on passive margins.

Question 43

Oceanic ridges form as a result of compressional stress.

Question 44

What is the name of the supercontinent that preceded Pangaea?

A)Amasia
B)Rodinia
C)Challenger
D)Africana

Question 45

The Challenger Deep of the Mariana Trench is named for the H.M.S Challenger, the ship that first measured it.

Question 46

Which of the following locations displays a triple junction that resulted from a rising mantle plume?

A)Eastern Africa/Arabian Peninsula
B)East Pacific Rise
C)Japan/East Asia
D)Mid-Atlantic Ridge

Question 47

Why do mantle plumes tend to concentrate beneath supercontinents such as Pangaea?

A)Concentrations of radioactive materials build up as continents assemble.
B)Partial melting from subduction concentrates large volumes of magma.
C)A large landmass acts as an insulating blanket to trap heat in the mantle.
D)Friction from converging landmasses heats up the mantle.

Question 48

What happened when the spreading center that generated the Farallon plate collided with the North American plate?

A)A mantle plume formed.
B)A divergent plate boundary was created.
C)The spreading center subducted, resulting in the Yellowstone Hot Spot.
D)A transform boundary was created.

Question 49

Which of the following locations is an example of forced subduction?

A)Mariana Trench
B)Peru-Chile Trench
C)East African Rift
D)Mid-Atlantic Rift

Question 50

Which of the following is a failed rift that formed in North America over one billion years ago?

A)A Mid-Continent Rift
B)East African Rift
C)Chile Rise
D)Kuril Trench

Question 51

Oceanic plateaus form from turbidity currents that flow down the continental slope.

Question 52

Continental shelves are valuable locations that support important fishing grounds.

Question 53

Which process, common near black smokers, will use hot water circulating through the crust to alter olivine and pyroxene into chlorite and serpentine?

A)Hydrothermal metamorphism
B)Decompression melting
C)Partial melting
D)Thermal contraction

Question 54

Which of the following is not a possible mechanism contributing to continental rifting?

A)Changes in gravitational attraction of the moon
B)Concentration of mantle plume heat beneath a continent
C)Tensional stress
D)Upwelling from shallow levels in the asthenosphere

Question 55

Because massive submarine structures such as seamounts and ridges exert stronger than average gravitational attraction, they produce depressed areas on the ocean's surface.

Question 56

Abyssal plains are flat areas of the ocean floor that are likely the most level places on Earth.

Question 57

What kind of subduction occurs when younger, warmer, less-dense lithosphere dips under another plate at shallower angles because it is too buoyant to sink?

A)Forced subduction
B)Mantle plume subduction
C)Spontaneous subduction
D)Overriding subduction

Question 58

A passive continental margin is located hundreds of miles away from the nearest tectonic boundary.

Question 59

What kind of subduction occurs when old, dense lithosphere sinks into the mantle by its own weight rather than by compressional force?

A)Forced subduction
B)Mantle plume subduction
C)Spontaneous subduction
D)Overriding subduction

Question 60

Which of the following locations is an example of spontaneous subduction?

A)Mariana Trench
B)Peru-Chile Trench
C)East African Rift
D)Cascadia Trench

Question 61

What feature in this image is indicated with arrow X? (Note: it is made of sediments.)

A)Deep-sea fan
B)Accretionary wedge
C)Turbidity current
D)Deep-ocean trench

Question 62

Oceanic Ridge A has slow spreading rates of 2-5 cm/yr.Oceanic Ridge B has intermediate spreading rates of 6-9 cm/yr.Oceanic Ridge C has fast spreading rates of 10-11 cm/yr.Compare and contrast the topography and structure that would be present at all three spreading centers.

Question 63

Compare and contrast the formation of accretionary wedges and the process of subduction erosion.

Question 64

Discuss how oceanic crust forms.What process generates the necessary magma? Also, be sure to discuss ophiolite sequences and discuss how the formation of each layer contributes to the formation of the crust.

Question 65

Give a location of where one might find the continental margin in this image.

A)Off the coast of southern California
B)Eastern margin of North America
C)Western margin of South America
D)Northern margin of North America

Question 66

How are sound waves used to detail the shape of the seafloor?

Question 67

Why does the lithosphere thicken as it moves away from a mid-ocean ridge?

Question 68

Black smokers can be found along subduction zones.

Question 69

Based on the seafloor features labeled on this map, what kind of tectonic boundary would you say surrounds the Pacific Ocean basin?

A)Convergent
B)Divergent
C)Transform

Question 70

What three major features comprise a passive continental margin?

Question 71

Explain the process of accretionary wedge.

Question 72

Describe the appearance of a rift valley that has started on land.How do these valleys form?

Question 73

Which location possesses the continental margin in this image?

A)Western margin of South America
B)Eastern margin of North America
C)East of Japan
D)Around the Philippines

Question 74

Compare seamounts and guyots.How do the two features differ?

Question 75

Why does the Atlantic Ocean have the most extensive abyssal plains?

Question 76

Based on its slow rate of spreading, the East Pacific Rise has a gradual profile with gently sloping sides.

Question 77

Assume the Mid-Continental Rift were to reactivate and divergence were to occur.What sequence of events would unfold as rifting began and what would eventually happen to the landmass?

Question 78

What kind of continental margin is visible in this image?

A)Active
B)Rift
C)Passive
D)Transform

Question 79

What kind of continental margin is visible in this image?

A)Active
B)Rift
C)Passive
D)Transform

Question 80

Why are oceanic ridges elevated above the rest of the seafloor?