Chapter 3

A sediment-laden current that flows off the continental shelf is called a turbidity current.

True

What effect do turbidity currents have on the continental slope?

Turbidity currents are erosive to the continental slope and, as a result, carve out submarine canyons.

What are some of the differences between a submarine canyon and an oceanic trench?

A submarine canyon is a steep, V-shaped canyon cut into the continental shelf or slope most likely caused by turbidity currents. An oceanic trench is a long, narrow, and deep depression on the ocean floor with relatively steep sides that is caused by plate convergence.

Direct and indirect observations indicate that rivers on land are responsible for the formation of submarine canyons.

False

Hydrothermal vents are seafloor cold seeps with high concentrations of sulfur and salts.

False

Mid-ocean ridges are rises that occupy a small portion (around 10%) of the deep ocean basins.

False

Older lithosphere is destroyed in association with:

deep-sea trenches.

What are turbidity currents?

dense mixtures of sand, mud, and other debris that move at high speeds down submarine canyons

What is turbidity?

suspended sediment

Relatively few abyssal plains are located in the Pacific Ocean due to:

the presence of convergent active margins.

Directly seaward of the continental shelf is a more steeply sloping region called the:

continental slope.

Trenches are typically associated with ________.

convergent continental margins

Match the term with the appropriate phrase. hypsographic curve

cumulative plot of area versus depth or elevation

The instrument that emits a high-frequency sound beam to measure the depth of the ocean developed in the 1950s is the:

precision-depth recorder (PDR).

Of the following statements about mapping the ocean floor, which is/are true?

-Only 5% of the ocean floor has been mapped as accurately as the Moon. -Radar altimeters on satellites have collected data on sea surface elevation that help produce maps of the sea floor. -There are large areas of the sea floor that remain unmapped by sonar. -The ocean's great depth and opaque character have hindered mapping efforts.

Of the following statements about turbidity currents, which is/are true?

-Turbidity currents are highly erosive and carve submarine canyons. -Turbidity currents move sediment down the continental shelf and the continental slope to be deposited on the continental rise. -Turbidity currents are episodic events (they don't occur all the time but only every so often, like a flash flood). -The material carried by turbidity currents is what builds deep-sea fans.

Which of the following feature(s) is/are associated with the mid-ocean ridge?

-hydrothermal vents -basalt volcanism and pillow lavas -a central rift valley -volcanoes

Of the following items, which is/are associated with a passive continental margin?

-turbidity currents, which are initiated here and flow down submarine canyons -a wide continental shelf

Examine the five words and/or phrases and determine the relationship among the majority of words/phrases. Please identify the word and/or phrase that does NOT fit the pattern. Enter only the letter of the answer (caps, no period, and not the full entry) in the field below.

A. global positioning system (GPS)

Examine the five words and/or phrases and determine the relationship among the majority of words/phrases. Please identify the word and/or phrase that does NOT fit the pattern. Enter only the letter of the answer (caps, no period, and not the full entry) in the field below.

A. passive margin

Describe the process by which abyssal plains are created.

Abyssal plains are formed by fine particles of sediment drifting out onto the deep-ocean floor. Over many years, a thick blanket of sediment is produced as fine particles accumulate on the ocean floor. Eventually, these deposits cover most irregularities of the deep ocean floor.

Satellites are used to map the ocean floor because:

All the above statements are correct.

Examine the five words and/or phrases and determine the relationship among the majority of words/phrases. Please identify the word and/or phrase that does NOT fit the pattern. Enter only the letter of the answer (caps, no period, and not the full entry) in the field below.

B. abyssal hill

Examine the five words and/or phrases and determine the relationship among the majority of words/phrases. Please identify the word and/or phrase that does NOT fit the pattern. Enter only the letter of the answer (caps, no period, and not the full entry) in the field below.

B. continental flood basalt

What is bathymetry?

Bathymetry is the measurement of ocean depths and the charting of shape, or topography, of the ocean floor. Determining bathymetry involves measuring the vertical distance from the ocean surface down to the mountains, valleys, and plains of the seafloor.

Examine the five words and/or phrases and determine the relationship among the majority of words/phrases. Please identify the word and/or phrase that does NOT fit the pattern. Enter only the letter of the answer (caps, no period, and not the full entry) in the field below.

E. trenches

Echo sounding is not a very reliable way to measure ocean depth because water is a poor transmitter of sound.

False

Explain how submarine canyons are created.

Submarine canyons are created on the continental slope most likely by turbidity currents - underwater avalanches of sediment-laden water that flow off the continental shelves.

Describe the origin of the three basic types of oceanic islands.

The three basic types of oceanic islands are (1) islands associated with volcanic activity along the mid-ocean ridge, (2) islands associated with hot spots, and (3) islands that are island arcs associated with convergent plate boundaries.

Abyssal plains are more extensive on the seafloor of the Atlantic Ocean basin as compared to those on the seafloor of the Pacific Ocean basin.

True

Hydrothermal vents are often associated with central rift valleys along the oceanic ridge and rise system.

True

Oceans with passive plate margins have continental slopes with more gradual slopes than oceans with active plate margins.

True

The Pacific Ring of Fire is the seismically active area along the margins of the Pacific Ocean where earthquakes and volcanoes are common.

True

The shape of Earth's hypsographic curve can be used to support the existence of plate tectonics.

True

How do turbidity currents affect canyons?

Turbidity currents erode material from canyons as currents move downslope.

What common item is used in this video to demonstrate a turbidity current?

a large jar filled with water and sediment

Volcanic features on the ocean floor that are less than 1,000 meters (0.6 miles) tall are called:

abyssal hills or seaknolls.

An oceanographic vessel is mapping a section of the ocean floor stretching for tens of miles in all directions. The seafloor is extremely flat, with a slope of less than one degree, and the water depth is about 4,500 meters. The area being mapped is most likely a(n) __________.

abyssal plain

The measurement of ocean depth and the charting of seafloor topography is called __________.

bathymetry

Characteristics of active continental margins include all the following except:

broad continental shelves.

Submarine canyons were most likely formed by:

erosion by turbidity currents.

What is the characteristic layering of an individual turbidity current deposit called?

graded bedding

What types of deposits do turbidity currents leave in alluvial fans?

graded bedding that begins as coarse material and becomes finer upward

How often do turbidity currents occur?

infrequently

Graded bedding provides evidence that __________.

large, heavy particles settle out first as current velocity decreases

Match the term with the appropriate phrase. bathymetry

measurement of ocean depth and seafloor topography

Match the term with the appropriate phrase. submarine canyon

narrow and deep valleys on continental slopes

New lithosphere is produced in association with:

oceanic ridges.

With respect to mid-ocean ridges, transform faults are:

perpendicular to the ridge axis.

What would you look for as evidence that a rock layer formed from materials deposited by ancient turbidity currents?

repeated sequences of graded bedding that begin as coarse material and become finer upward

The reason the deposit on the bottom forms the way it does is a result of __________.

settling velocity

Match the term with the appropriate phrase. continental margin

shallow-water areas close to continents

The correct order of seafloor features from the coast to the mid-ocean ridge is:

shelf, slope, rise, abyssal plain.

Where a mid-ocean ridge is offset, the linear feature connecting and between the crests of the ridge segments is called a __________.

transform fault

Match the term with the appropriate phrase. seismic reflection profile

used to determine ocean structure beneath the sea floor

Of the following techniques, which one(s) can be used to map the sea floor?

using satellites to measure the sea surface direct visitation of the sea floor sending sound through water (sonar) recording many depths using a long cable

Warm water (From 30°C to 350°C) hydrothermal vents form:

white smokers.