Deck 11: The Ocean Floor

Question 1

Which one of the following would typically have the widest continental shelf?

A)a tectonically passive, trailing continental margin
B)a tectonically passive, mid-ocean ridge and trench system
C)a tectonically active continental margin next to a deep ocean trench
D)an atoll

Answer 1

A

Question 2

On average, the continental shelf is about ________ kilometres wide and ________ metres deep.

A)20; 50
B)80; 130
C)400; 2000
D)1800; 80

Answer 2

B

Question 3

If you are sailing across the continental shelf in Queen Charlotte Sound and your echo sounder reported the bottom at 200 milliseconds (0.200 sec)at the maximum depth crossing the axis of Mitchell Trough, how deep is the seabed in the middle of this drowned submarine valley? Use the equation: depth (m)= 0.5 * (1500 m/s * total 2-way travel time in sec)

A)150 metres
B)15 metres
C)1500 metres
D)50 0 metres

Answer 3

A

Question 4

You are doing a hydrographic survey by the Sand Heads Light, off the mouth of the Fraser River in very silty green water.You lower a bar to check its reflection and calibrate your sounder.You find that the fresh river water has dropped the speed of sound to 1483 m/sec.If the bottom registers at 15 milliseconds (0.015 sec), how deep is the top of the Fraser delta? Use the equation: depth (m)= 0.5 * (1500 m/s * total 2-way travel time in sec)

A)11.12 metres
B)11.25 metres
C)22.25 metres
D)2250 metres

Question 5

In the 1870s, the ________ was involved in the first far-reaching, comprehensive study of Earth's oceans.

A)H)M.S.Beagle
B)H)M.S.Challenger
C)H)M.S.Endeavour
D)U)S.S.Enterprise

Question 6

An echo sounder operates by measuring the time required for a ________.

A)light beam to travel from a satellite at a known altitude to the sea bottom and back
B)radar beam to travel from a harbour patrol boat to a fuzz-buster on a speeding yacht
C)radar beam to travel from a ship to the seafloor and back
D)sound pulse to travel from a ship or survey towfish to the seafloor and back

Question 7

Satellites like SEASAT can observe the ocean using ________ to measure sealevel to +/- 2 cm and infer the seabed bathymetry from the ________ exerted by the variable elevation and mass of seabed features.

A)accelerometers, magnetism
B)infrared radiation, temperature and heat effects
C)microwave beams, gravitational pull
D)surveying telescopes, tidal pull

Question 8

Geologically, ________ are actually submerged parts of the continents.

A)coastal guyots
B)continental shelves
C)continental trenches
D)abyssal plains

Question 9

The ________ lies at the base of the continental slope.

A)offshore shelf
B)off-slope reef
C)continental rift
D)continental rise

Question 10

The geologic process responsible for the most rugged relief on the seabed of a passive continental margin is ________.

A)active explosive submarine volcanism
B)deposits of major river deltas
C)dredging and bottom dragging in shelf fisheries for scallops and groundfish
D)glacial erosion and deposition modified by rising sea levels.

Question 11

What was the latest technologic addition to seafloor mapping, developed in response to mapping the ocean floor for national security, resource development, and directing seabed cable and pipeline crossings?

A)airborne sounding methods, by overflying the oceans
B)fleets of remotely telemetered, miniature drifter buoys
C)swath echo sounding by mechanical multi-beam sonar
D)walking it off one step at a time by the "Pirates of the Caribbean"

Question 12

If your ship is out in the middle of the North Pacific Ocean on the edge of the abyssal plain south of the Aleutian trench, how deep is the seabed if it took 6 seconds to get a bottom return from your 3500 kilohertz echo sounder? Use the equation: depth (m)= 0.5 * (1500 m/s * total 2-way travel time in sec)

A)4500 metres
B)1286 metres
C)2625 metres
D)6000 metres

Question 13

Water depths and seafloor bathymetry (submarine topography)are now routinely determined by ________.

A)ship-mounted radar with fiber-optical satellite uplink systems
B)computerized, satellite-mounted, weighted lead-lines
C)ship-mounted or towed echo sounders
D)by satellite-linked, laser reflector systems

Question 14

________ is the oceanward edge of a continental shelf.

A)The deepest portion of a deep-ocean trench
B)The top of the abyssal plain
C)The base of the continental rise
D)The top of the continental slope

Question 15

The geologic process responsible for the most rugged relief to be found on a passive margin's continental shelf is ________.

A)eustatic sea level changes
B)glacial erosion and deposition
C)earthquake induced submarine landslides
D)turbidity currents

Question 16

________ marks the edge of a continent.

A)An offshore, barrier island system
B)The lowest part of the continental slope
C)The centre of an abyssal plain
D)The highest part of the continental shelf

Question 17

Which one of the following would typically have the narrowest continental shelf?

A)a tectonically passive, trailing continental margin
B)a tectonically passive, mid-ocean ridge and trench system
C)a tectonically active continental margin next to a deep ocean trench
D)an atoll

Question 18

On average, the slope across a continental shelf is about ________.

A)0)001°
B)0)1°
C)1)5°
D)5°

Question 19

How thick are the accumulations of shallow water sediments on passive continental margins like the Scotian Shelf?

A)several kilometres
B)several metres
C)several hundred metres
D)several tens of metres

Question 20

How were water depths and seafloor bathymetry (submarine topography)determined by the Challenger surveys?

A)by early deep sea divers
B)hand thrown and retrieved weighted lead-lines
C)multi-beam, towed echo sounders
D)timing the descent of heavy bricks with sand glasses and listening for the echoes with early hydrophones

Question 21

How deep is the deepest portion of the ocean floor and what are these regions called?

A)2000 metres, submarine canyons
B)2500 metres, rift zones
C)4000 metres, abyssal plains
D)>10,000 metres, trenches

Question 22

How broad an area of seafloor was covered by the 1929 Grand Banks turbidite deposit?

A)2,500 km³
B)25,000 km³
C)250,000 km³
D)2,500,000 km³

Question 23

The largest regions underlain by deformed marine sediments occur on ________.

A)active continental margins
B)mid-ocean ridges
C)passive continental margins
D)deep ocean basins

Question 24

________ develop where oceanic lithosphere bends downward and sinks into the mantle.

A)Submarine canyons
B)Abyssal seamounts
C)Deep ocean trenches
D)Rift valleys on mid-ocean ridges

Question 25

Which one of the following would most likely be covered with thick turbidite layers?

A)axial rift zone of an active mid-ocean spreading centre
B)upper flanks of a steep, narrow, submarine canyon
C)deep-sea fan at the base of a continental slope
D)lagoon floor inside an atoll

Question 26

The chaotic accumulation of deformed sediments and tectonic slices of oceanic crust plastered onto the edge of a continent is called ________.

A)an accretionary wedge
B)an agglutinated foram
C)a deep sea fan
D)a guyot

Question 27

What is meant by graded bedding?

A)Particle sizes in a single, sedimentary bed change from pebbles and coarse sands at the base to silt and mud at the top.
B)Muddy and silty strata grade upward into sandy and pebbly strata.
C)Strata have the same thicknesses and bedding contacts are smooth and flat.
D)Thin, laminated, storm-beds slope gently back towards the land.

Question 28

How does the continental rise form?

A)tectonic uplift and tilting of the edge of the continental margin
B)outbuilding of major river deltas
C)deep sea pelagic oozes that drape guyots and seamounts
D)coalescing deep-sea fans built from turbidites

Question 29

Which one of the following is not typical of sandy turbidite deposits?

A)They contain land-derived and shallow-water fossil materials, even deposited in deep waters.
B)They form very gently sloping deep-sea fans at the mouths of submarine canyons.
C)Within a depositional layer, they show graded bedding but little stratification.
D)They occur on the continental shelf in cross-stratified dunes with very low silt and clay contents.

Question 30

What was the original cause of the 1929 turbidity currents that cut submarine cables off Newfoundland?

A)a ML 7.2 earthquake
B)a tsunami
C)a submarine landslide
D)the grounding of a massive iceberg that caused the seafloor to fail

Question 31

Active continental margins are found ________.

A)around the Arctic Ocean
B)mainly around the Pacific Ocean
C)surrounding Africa
D)underneath passive continental margins

Question 32

Where are the greatest number of deep ocean trenches found?

A)along the western edge of North America
B)along the western edge of the Pacific
C)along the eastern margins of the Atlantic
D)around the rim of the Arctic

Question 33

Which of the following about deep ocean trenches is false?

A)They are long and narrow depressions.
B)They are sites where plates plunge back into the mantle.
C)They are geologically very stable.
D)They may act as sediment traps.

Question 34

Which one of the following statements concerning submarine canyons is not true?

A)They extend from the continental shelf to the base of the continental slope.
B)They channel turbidity currents down the continental slope to deeper waters.
C)They generally connect across the continental shelf to specific river valleys on land.
D)They were cut by streams and rivers during the Pleistocene when sea level had dropped to the base of the continental slope.

Question 35

Which one of the following did not accompany the 1929 Newfoundland ML 7.2 earthquake?

A)Submarine telegraph cables were broken on the floor of the North Atlantic.
B)Explosive volcanic eruption of pillow basalts occurred on the west edge of the Grand Banks.
C)Turbidity currents moved down the continental rise to the edges of the North Atlantic abyssal plain.
D)A tsunami struck the Burin Peninsula of Newfoundland.

Question 36

Which one of the following statements regarding turbidity currents is true?

A)They form on the continental shelf and flow down submarine canyons to deeper water.
B)They are shaken loose by earthquakes and move from abyssal plains to the continental shelf.
C)They flow down submarine canyons to estuaries at the edge of the continental shelf.
D)The moving sediment-laden waters are less dense than the surrounding seawater.

Question 37

Which is the deepest ocean trench?

A)Aleutian
B)Kurile-Kamchatka
C)Mariana
D)Peru-Chile

Question 38

How much of the Earth's surface is covered by the deep ocean basins?

A)15%
B)30%
C)50%
D)65%

Question 39

The continental rise is located ________.

A)at the top of a mid-ocean ridge
B)at the top of the continental slope
C)between an abyssal plain and continental slope
D)at the seaward edge of a deep ocean trench

Question 40

Graded bedding is ________.

A)a Canadian quality-rating scale for different brands of mattresses
B)an upwards decrease in clastic particle size within a single sediment layer
C)an accumulation of sedimentary beds beginning with sandy beds at the bottom and ending with clayey beds at the top
D)the layering in coral limestone produced by the combined chemical action of living coral animals and submarine, hot spring emissions

Question 41

Why are the deep sea clays mostly red or brown?

A)They are eroded mostly from desert areas and carried to the sea by winds or rainstorms.
B)They are mostly volcanic ash particles erupted onto the seafloor; this is their colour.
C)Slow settling of fine clay-sized mineral particles allows for complete oxidation of their iron by dissolved oxygen.
D)These are the residues of red algae blooms, dispersed by ocean currents to settle out everywhere.

Question 42

What are the flattest and most level places on Earth?

A)abyssal plains
B)continental shelves
C)oceanic volcanic plateaus
D)mid-ocean ridges

Question 43

Below the coral limestone, surface rocks of an atoll, what would you find?

A)an upraised, abyssal plain covered with turbidites
B)basaltic volcanic rocks of a truncated seamount
C)a magma chamber of an active shield volcano
D)a slab of rifted, continental crust extending down to ocean floor depths

Question 44

What sedimentary process is mainly responsible for the accumulation of up to 9 kilometres of sediment in deep ocean trenches?

A)pelagic, biogenous ooze slowly settling from the top of the water column
B)offshore dumping of unending bargeloads of garbage from major cities
C)turbidity currents and submarine landslides from the continental slope and trench walls
D)sunken or subsided coral reefs

Question 45

For its size, which ocean has the largest proportion of abyssal plains?

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

Question 46

What sedimentation rates typify the red or brown clays of the abyssal plains?

A)> 5 metres per year
B)1-5 centimetres per year
C)1 centimetre per 500 years
D)1 centimetre per 5,000 to 50,000 years

Question 47

Seamounts ________.

A)are a special type of oceanic trench
B)are volcanoes that form on the ocean floor
C)form only in the Pacific Ocean basin
D)are submarine canyons found near Australia

Question 48

Geologically, what is the best way to explain the thousands of metres of coral limestone beneath most atolls?

A)Sea level has fallen thousands of metres since the reef began to grow.
B)An eroded volcanic seamount rose thousands of metres after the limestone formed.
C)The eroded volcano slowly sank as sea level remained steady or rose gradually.
D)The volcano never reached the surface, but built a very thick cap of coral limestones from its deep submarine hot springs emissions.

Question 49

________ sediments represent weathered rock and mineral particles eroded mainly from land areas.

A)Exogenous
B)Hydrogenous
C)Terrigenous
D)Biogenous

Question 50

As a result of the 1831 expedition of the H.M.S.Beagle, ________ proposed the correct theory of how atolls formed.

A)Isaac Newton
B)Charles Darwin
C)James Hutton
D)Charles Lyell

Question 51

________ are highly detrimental to healthy growth of coral reefs.

A)Clear, sunlit waters
B)Nutrient-rich waters, cloudy with luxuriant plankton growth
C)Warm water temperatures
D)Vigorous wave action and water circulation

Question 52

A(n)________ is a low lying, coral reef island perched above a sunken, truncated volcano.

A)guyot
B)seamount
C)re-entry cone
D)atoll

Question 53

Which ocean floor sediment type includes quartz sand?

A)terrigenous
B)biogenous
C)hydrogenous
D)orogenous

Question 54

Which is the longest ocean trench?

A)Aleutian
B)Java
C)Kurile-Kamchatka
D)Peru-Chile

Question 55

Trenches are often parallel to, and genetically related to ________.

A)mid-ocean ridges
B)hot spot volcanic island chains
C)oceanic transform faults
D)volcanic island arcs or continental margin mountain belts with active volcanism

Question 56

Which ocean floor sediment type includes turbidity currents?

A)terrigenous
B)biogenous
C)hydrogenous
D)orogenous

Question 57

What thicknesses of unconsolidated sediment typically covers the deep abyssal plains?

A)<100 metres
B)about 500 to 1000 metres
C)about 1500 to 4500 metres
D)about 5000 to 9000 metres

Question 58

What is the most abundant sediment type on the deep ocean floor for most locations in the world?

A)carbonate ooze
B)diatom and radiolarian ooze
C)mud
D)sand

Question 59

Which ocean floor sediment type includes abyssal plain clay?

A)terrigenous
B)biogenous
C)hydrogenous
D)orogenous

Question 60

What geologic studies finally confirmed Darwin's hypothesis that coral atolls all had a volcanic substrate underneath that formed the original platform for corals to colonize?

A)exploration drilling of the Great Barrier Reef by Petro Canada for offshore oil production
B)scientific drilling of Eniwetok and Bikini Atolls by the U.S.government in preparation for nuclear weapons tests
C)submersible traverses down the flanks of North Atlantic atolls by the C.S.S.Hudson
D)seismic imaging of the West Pembina Pinnacle Reefs in the Alberta Basin by Amoco

Question 61

________ are not associated with a mid-ocean ridges.

A)Very thin, ocean floor sediment layer
B)Submarine basaltic lava eruptions
C)Shallower depths than abyssal plains
D)Deep ocean trenches

Question 62

What is the most active, long term, deep diving, manned submersible used for studying the seafloor and deep ocean depths?

A)Alvin
B)Nautilus
C)Simon
D)Theodore

Question 63

Calcareous ooze is composed of ________ sediment.

A)androgynous
B)terrigenous
C)biogenous
D)hydrogenous

Question 64

Oceanic ridges are elevated compared to the surrounding ocean floor because ________.

A)newly formed lithosphere is hotter and therefore less dense than the surrounding rocks
B)the older, colder lithosphere is less dense and tends to rise
C)the mantle is pushing up the lithosphere along the ridge
D)of the shield volcanoes that develop due to seafloor spreading

Question 65

Which method did not contribute significant geologic knowledge about the rocks, structures, and mineral deposits of the mid-ocean ridges?

A)deep diving submersibles traverses by manned and unmanned subs
B)geophysical surveys and soundings of the ocean floor
C)mapping of slices of ocean crust added to the continents by tectonic activity
D)remote sensing and mapping of mineral deposits by satellites

Question 66

Which sediment type comprises rounded blackish lumps of metallic compounds on the seafloor?

A)biogenous
B)manganese nodules
C)androgynous
D)terrigenous

Question 67

Which ocean floor sediment type includes calcareous ooze?

A)biogenous
B)terrigenous
C)hydrogenous
D)orogenous

Question 68

Which ocean floor sediment type comprises complex metallic lumps?

A)manganese nodules
B)terrigenous
C)biogenous
D)orogenous

Question 69

What kinds of materials account for the phosphate rich sediments?

A)calcareous ooze
B)diatoms and radiolarians
C)mineral rich turbidites
D)hard residues of teeth, scales, bones, and fecal pellets of fish and other marine animals

Question 70

How do calcareous oozes form?

A)The particles are biogenically or chemically precipitated in warm, surface waters and sink to the bottom.
B)The particles are precipitated by deep-ocean, bottom-dwelling, carbon-fixing bacteria.
C)The particles are precipitated in the water column below the depth of sunlight penetration and then sink to the bottom.
D)The particles settle out from calcite-rich turbidity currents at depths greater than 4,500 metres.

Question 71

Which ocean floor sediment type includes diatom ooze?

A)biogenous
B)terrigenous
C)hydrogenous
D)orogenous

Question 72

Seafloor spreading occurs along relatively narrow areas at the crests of oceanic ridges called ________.

A)trenches
B)submarine canyons
C)rift zones
D)seamounts

Question 73

What is the heat source for "black smokers"?

A)biologic heat from thermophyllic bacteria and densely populated vent communities
B)chemical oxidation of sulphide minerals below the seafloor
C)deeply circulating currents of hot, dense ocean brines, deflected to follow the ridge system
D)magmatic heat below the seafloor

Question 74

What do the tube worms of the hydrothermal vent communities directly rely on for their survival?

A)direct chemical oxidation of sulphide minerals by their root-like, chitinous tube-feet
B)pelagic organic debris settling slowly from the sea surface and local decaying organic matter from crabs, clams, fish, and stupid marine biologists
C)photosynthesis from weak sunlight filtering down to the seafloor
D)symbiotic chemosynthetic (sulphur based)bacteria residing in their trophosomes (guts)

Question 75

Which one of the following statements concerning actively spreading mid-ocean ridges is false?

A)They are sites for submarine eruptions of basaltic lava.
B)They are places where young lithosphere is added to the edges of spreading, oceanic plates.
C)Terrigenous sediment coverings are very thin or absent.
D)Sediments include thick siliceous ooze deposits and sandy turbidite beds.

Question 76

________ is/are most soluble in cold seawater at ocean depths in excess of 4500 metres.

A)Clay minerals
B)Quartz
C)Calcite
D)Manganese oxides

Question 77

________ consists of diatom and radiolarian remains.

A)Siliceous ooze
B)Terrigenous ooze
C)Reddish clay ooze
D)Calcareous ooze

Question 78

Which is the best description of a mid-ocean ridge?

A)thick sequences of folded and faulted sedimentary rocks pushed up 500-1000 metres above the regional seafloor
B)narrow ridges 5-10 kilometres wide, 3-4 kilometres high, and 10-50 kilometres long with active erupting volcanoes every 1-2 kilometres of ridge length
C)1000 to 4000 kilometre wide, block faulted regions of sparsely sedimented, basaltic seafloor raised 2-3 kilometres above the regional abyssal plains
D)50-200 metre-wide rough mounds of metal sulphides that encircle the globe continuously for more than 70,000 kilometres

Question 79

Which one of the following is not connected in any way with submarine, hot spring vents?

A)sediment rich in metallic sulphides
B)ecological communities living without photosynthesis
C)thick turbidites on the continental rise
D)black smokers on a mid-ocean ridge

Question 80

Where in the oceans are biologic communities thriving without sunlight?

A)in shallow water, coral reefs
B)in muds of deep-ocean trenches
C)around seafloor, hot spring vents in areas of active volcanism
D)around fissure vents for flood basalts