OCE 1001 Chapter 3

How do turbidity currents affect canyons?

Turbidity currents erode material from canyons as currents move downslope.

Expanding Ocean Basin

-Atlantic Ocean Basin

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

Identify the major feature of a slow-spreading mid-ocean ridge.

rift valley

Measurement of ocean floor bathymetry from satellites relies on ___________.

sea surface elevation, which varies depending on the shape of the underlying sea floor

On the diagram of a passive continental margin shown below, match the letters with the correct features.

A: Graded bedding D: submarine canyons B: deep-sea fans C: turbidity current

On the cross-section shown below, correctly identify the following features.

A: magma C: metal sulfide deposits B: black smoker

The image below shows a perspective view of a mature ocean basin. Match the letters with the correct marine provinces or features listed below.

C: Ocean basin B: continental margin A: mid-ocean ridge

On this perspective view of a passive continental margin, match the following letters with the correct features.

D: continental slope G: shelf break A: continental shelf C: continental crust B: Abyssal plain F: continental rise E: oceanic crust

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

PDR

Can you explain why atolls extend from the surface of the ocean down to great depths into the sea? Corals, which make up these ring-shaped structures, can only live where water is warmed and illuminated by sunlight, no more than approximately 45 meters deep. How do you explain an atoll that extends thousands of meters deep?

The coral reef once formed around an active volcano. The reef became a barrier reef, with hard skeletons of previous colonies acting as the scaffolding for new ones on top. The volcano gradually sank into sea, moving with the plate it rested on, as the coral continued to grow upward, leaving the atoll as a ring structure at the top.

What statement correctly distinguishes an ocean trench from a submarine canyon?

Trenches descend deep beyond the abyssal plains. Submarine canyons are part of the shallower continental margins.

Match the term with the appropriate phrase. continental shelf

a generally flat zone extending from the shore to the shelf break

Extending from the base of the continental rises into the deep-ocean basins are flat depositional surfaces called:

abyssal plains

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

Match the term with the appropriate phrase. ocean trench

deep linear scars on the deep-ocean floor caused by plate convergence

Older lithosphere is destroyed in association with:

deep-sea trenches

Passive continental margins are characterized by all the following except:

deep-sea trenches

What are turbidity currents?

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

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

false

Seamounts form from ancient tablemounts.

false

The three major provinces of the ocean floor are continental margins, deep-ocean basins, and submarine canyons.

false

Turbidity currents are highly erosive and are thought to be responsible for the creation of deep-sea trenches.

false

Match the term with the appropriate phrase. abyssal plain

flat depositional surfaces that cover extensive portions of the deep-ocean basins

All the following are considered part of the continental margin except the:

fracture zone

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

graded bedding that begins as coarse material and becomes finer upward

On a deep-sea voyage in the North Pacific, near the Aleutian Islands of Alaska, you begin to explore a deep, long, narrow region in the ocean floor. You begin to discuss what this is with a partner and come up with the theories below. Determine whether each of the statements below presents a likely scenario.

-It is most likely a deep-ocean trench because they are common along the active continental margins. -The feature was most likely caused by one oceanic crust subducting under a leading edge of a continent. -It is most likely a deep-ocean trench because they are common along the margins of the Pacific Ocean.

Shrinking Ocean Basin

-Pacific Ocean Basin

Of the following statements about Earth's hypsographic curve (figure shown below), which is/are true?

-The hypsographic curve shows that a majority of the exposed land is below 1 kilometer in elevation. -The hypsographic curve shows the percentage of Earth's surface area that is covered by ocean waters. -The hypsographic curve shows that a majority of the ocean floor is below 4 kilometers deep. -The hypsographic curve shows that the average depth of the ocean is about four times the average height of the continents.

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

-The ocean's great depth and opaque character have hindered mapping efforts. -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.

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

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

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

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

Passive Continental Margins

-continental margin A -continental margin B -continental margin C

What process(es) affect the shape and structure of continental shelves?

-erosion of sediment -eposition of sediment -large fluctuations in sea level -major climate changes, such as ice ages

The majority of ocean trenches are associated with ___________.

-narrow or no continental shelves -very deep ocean water depths -volcanic arcs and active continental margins -subduction zones and associated faults -the Pacific Ring of Fire

Imagine you are a geological oceanographer. As an expert, you are asked by a student to recommend the technique that would produce the most detailed map of a deep-water seamount near Hawaii. Which instrument would you recommend?

side-scan sonar

Black smokers are hydrothermal vents that discharge superheated water with high concentrations of metal sulfides.

true

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

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

Nearly all oceanic islands are __________.

volcanic in origin

Active Continental Margins

-continental margin D -continental margin E

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

continental slope

How often do turbidity currents occur?

infrequently

Match the term with the appropriate phrase. submarine canyon

narrow and deep valleys on continental slopes

The features of active and passive continental margins and the characteristics of ocean basins are evidence for existence, or absence of a plate boundary. Read the sentences below, and fill in the blanks to make them complete and correct.

1. Oceanic crust spreads at mid-ocean ridges, creating new crust and slowly enlarging the ocean basin. 2. submarine canyons are deep valleys at passive continental boundaries. They are likely carved out by turbidity currents, which occur when sediment-laden water rapidly moves down slope. 3. Melt from the subducting plate rises to the surface, erupts through the crust on the overriding plate and forms continental volcanic arcs on continents, or volcanic island arcs in the ocean. 4. Subduction zones surrounding the Pacific Ocean give rise to volcanoes. This area surrounding the Pacific Ocean is called the Ring of Fire.

The greatest proportion of Earth's surface lies in this elevation/depth interval.

4,000-5,000 m below sea level

A ship's fathometer (an echo sounder) transmits a sound pulse and records the return of an echo 7.4 seconds later. If the speed of sound in water is 1,500 m/second, what is the water depth in meters?

5,550 meters

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. A. abyssal plain B. continental flood basalt C. continental rise D. continental shelf E. continental slope

B

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. black smoker B. deep focus earthquake C. hydrothermal vent D. rift valley E. white smoker

B

The image below shows a close-up view of a mid-ocean ridge that is offset by a linear fault/fracture. Match the letters with the correct features.

B: fracture zone D: transform fault A: rift valley of a mid-ocean ridge E: lithosphere C: asthenosphere

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. abyssal hill B. abyssal plain C. submarine canyon D. seamount E. tablemount

C

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. turbidity currents B. graded bedding C. turbidite deposits D. abyssal plains E. deep-sea fans

D

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. metal sulfide deposits B. pillow basalts C. rift valley D. seamounts E. trenches

E

The direction of motion along a seafloor transform fault is:

in the same direction as the plates are spreading.

New lithosphere is produced in association with:

oceanic ridges

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

perpendicular to the ridge axis

Most ocean floor features owe their origins to _________.

plate tectonic processes

Volcanic peaks on the deep-ocean floor with conical tops are called:

seamounts

In comparison with other ocean basins, major sedimentary features such as continental rises and abyssal plains are relatively rare in the Pacific. The primary reason for their scarcity in the Pacific is that __________.

sediment is trapped within the trenches of the convergent plate boundaries ringing the Pacific

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

shelf, slope, rise, abyssal plain.

The method that is used most frequently to investigate sediment and rock layers of the sea floor is:

sound waves