Deck 15: Ocean Basins

Question 1

A/an __________ __________ is a shallow, gently sloping submarine surface on the submerged edge of a continent.

Answer 1

continental shelf

Question 2

A flat-topped seamount is called a __________.

Answer 2

guyot

Question 3

California, Oregon, Washington, and western British Columbia were added to North America as __________ __________.

Answer 3

accreted terranes

Question 4

The Mid-Oceanic Ridge rises high above the surrounding sea floor because new lithosphere forming at the ridge axis is __________ and of relatively __________ density.

A) hot, low
B) hot, high
C) cool, high
D) cool, low

Question 5

Modern sea-floor maps are made with __________ __________ instruments.

Question 6

The __________ __________ emits a high-energy signal from a research ship that penetrates and reflects from layers in sediment and rock.

Question 7

A/an __________ __________ is an open-mouthed steel net dragged along the sea floor behind a research ship.

Question 8

A chain of volcanic islands that form along a subduction zone is called a/an __________ __________.

Question 9

A/an __________ is a submarine mountain that rises 1 kilometer or more above the surrounding sea floor.

Question 10

Oceanic crust is __________ than continental crust and therefore __________ isostatically.

A) denser, sinks
B) denser, rises
C) lighter, sinks
D) lighter, rises

Question 11

The depth of the central parts of the ocean basins is about __________ kilometers.

A) 6
B) 5
C) 4
D) 3

Question 12

A circular coral reef that forms a ring of island around a central lagoon is a/an __________.

Question 13

Oceans cover about __________ percent of the Earth's surface.

A) 91
B) 81
C) 71
D) 61

Question 14

__________ __________ is a mixture of clay carried from continents and the remains of tiny plants and animals that live in the surface waters of the oceans.

Question 15

Oceanic crust is mostly composed of __________.

Question 16

The average thickness of oceanic crust is about __________, whereas the average thickness of continental crust is about __________.

A) 20-10 km, 1-2 km
B) 1-2 km, 10-20 km
C) 20-40 km, 4-7 km
D) 4-7 km, 20-40 km

Question 17

Beyond the Mid-Oceanic Ridge system are flat, level, featureless submarine surfaces called __________ __________.

Question 18

A/an __________ __________ is a deep trough in the crest of many mid-ocean ridges.

Question 19

Continental margins on both sides of the Atlantic Ocean are __________ __________ __________.

Question 20

Deep, V-shaped, steep-walled valleys called __________ __________ are eroded into continental shelves and slopes.

Question 21

Moving away from mid-ocean ridges, oceanic crust becomes:

A) older, sinks, and forms the abyssal plains.
B) younger, sinks, and forms the abyssal plains.
C) older, rises, and becomes part of the continental shelf.
D) younger, rises, and becomes part of the continental shelf.

Question 22

When two oceanic plates converge, the sinking plate drags the sea floor down to create:

A) a black smoker.
B) a rift valley.
C) accreted terranes.
D) an oceanic trench.

Question 23

At sea-floor vents, bacteria produce energy from hydrogen sulfide in a process called:

A) sea-floor spreading.
B) photosynthesis.
C) subduction.
D) chemosynthesis.

Question 24

The part of oceanic crust made up of pelagic and terrigenous sediment is __________.

A) layer 1
B) layer 2
C) layer 3
D) the deepest layer

Question 25

The part of oceanic crust made up of pelagic and terrigenous sediment is:

A) layer 2.
B) layer 1.
C) layer 3.
D) composed mainly of basalt pillows.

Question 26

A circular coral reef that forms a ring of islands around a central lagoon is a/an __________.

A) guyot
B) atoll
C) barrier island
D) pillow reef

Question 27

Most of layer 3 of the oceanic crust is composed of __________.

A) pelagic sediment
B) pillow basalt
C) gabbro
D) terrigenous sediment

Question 28

The flattest surfaces on Earth are __________.

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

Question 29

Sand, silt, and clay that erodes from the continents and is carried to the deep sea floor is called __________.

A) zooplankton
B) terrigenous sediment
C) pelagic sediment
D) pillow basalt

Question 30

Submarine canyons on continental shelves and slopes are cut by __________.

A) longshore currents
B) turbidity currents
C) deep-sea currents
D) sharks
Multiple Choice

Question 31

A/an __________ is a submarine mountain that rises 1 kilometer or more above the surrounding sea floor.

A) seamount
B) white smoker
C) island arc
D) pillow basalt

Question 32

Most of the water that fills the Earth's oceans came from:

A) interplanetary space.
B) outside of our solar system.
C) volcanoes.
D) a gigantic flood.

Question 33

The age of the oldest ocean floor is about __________ million years.

A) 400
B) 300
C) 200
D) 100

Question 34

If a series of island arcs collide with a continent over a long period of time, they add to a continent as:

A) accreted terranes.
B) mid-oceanic ridges.
C) abyssal plains.
D) high plains.

Question 35

Samples can be taken from the deep sea floor by:

A) coring devices.
B) echo sounders.
C) seismic profilers.
D) remote sensing.

Question 36

Rift valleys are characterized by __________ faults and __________ earthquakes.

A) reverse, shallow
B) normal, shallow
C) reverse, very deep
D) normal, very deep

Question 37

Remote sensing devices used to study the ocean floor are:

A) magnetometers.
B) echo sounders.
C) microwave radar instruments.
D) all of these

Question 38

A magnetometer could be used to:

A) take a sample of the Earth's core.
B) measure sea-floor topography.
C) determine the orientation of the Earth's magnetic field at the time the mineral cooled.
D) picture the layering at the mantle-core boundary.

Question 39

The Mid-Oceanic Ridge is composed mainly of:

A) basalt.
B) ocean floor sediments.
C) folded and faulted sedimentary rocks.
D) granite.

Question 40

Island arcs grow from __________.

A) atolls
B) passive continental margins
C) submarine volcanoes near a subduction zone
D) abyssal fans

Question 41

Oceans do not affect global climate.

Question 42

Studying the sea floor requires direct physical contact with the ocean floor.

Question 43

A continental shelf on a passive margin is usually a wide bathymetric feature.

Question 44

An active continental margin commonly has a much narrower continental shelf and a considerably steeper continental slope than does a passive margin because:

A) the subducting plate forms a steep-sided trench.
B) undersea volcanoes form steep-sided slopes.
C) turbidity currents erode terrigenous sediment.
D) abyssal fans are common.

Question 45

The west coast of South America is a passive continental margin.

Question 46

Atolls are volcanic peaks on the ocean floor.

Question 47

Some of the world's richest offshore petroleum reserves are found on continental shelves.

Question 48

Active continental margins do not have continental rises.

Question 49

Shallow earthquakes and faults commonly occur at the Mid-Oceanic Ridge.

Question 50

Pillow basalt comprises most of layer 2 of oceanic crust.

Question 51

An active continental margin forms:

A) at mid-ocean ridges.
B) at continent-continent margins.
C) where an oceanic plate sinks beneath a continental plate at a subduction zone.
D) in a rift valley.

Question 52

If the modern Mid-Oceanic Ridge system were to disappear completely, sea level would rise by about 400 meters.

Question 53

Where two oceanic plates converge, subduction generates huge amounts of magma that erupt to form submarine volcanoes, and eventually island arcs.

Question 54

The continental rise on a passive continental margin is a/an:

A) apron of terrigenous sediment that was transported across the continental shelf and deposited on the deep ocean floor at the foot of the continental slope.
B) rugged surface formed by erosion of sediment near the abyssal plain.
C) topographic surface formed as a portion of a lithospheric plate dives into the mantle.
D) steep surface formed by accumulation of basalt near the continental margin.

Question 55

At present, the Atlantic Ocean is growing, while the Pacific is shrinking.

Question 56

An oceanic island:

A) rises isostatically as it becomes older.
B) is a seamount that rises above sea level.
C) is a guyot that forms adjacent to a hot spot.
D) is composed entirely of terrigenous sediment. True/False

Question 57

The Mid-Oceanic Ridge system is the Earth's largest mountain chain.

Question 58

Hot seawater dissolves metals as it circulates through oceanic crust.

Question 59

Continental crust and oceanic crust firmly join together at a/an:

A) convergent plate boundary.
B) active continental margin.
C) passive continental margin.
D) Mid-Oceanic Ridge.

Question 60

A turbidity current can travel at speeds greater than 100 kilometers per hour and for distances up to 700 kilometers.