Continental Margins

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Chapter 14
The Ocean Floor
Section 14.2
Ocean Floor
Features
Ocean Floor Features
• Mapping the ocean Floor
– The ocean floor regions are the continental
margins, the ocean basin floor and the mid-ocean
ridge.
Ocean Floor Features
Continental Margins
• A continental margin is the zone of transition
between a continent and the adjacent ocean
basin floor.
• In the Atlantic Ocean, thick layers of
undisturbed sediment cover the continental
margin. This region has very little volcanic or
earthquake activity.
Atlantic Continental Margin
Ocean Floor Features
Continental Margins
• In the Pacific Ocean, oceanic crust plunges
beneath continental crust. This force results
in a narrow continental margin that
experiences both volcanic activity and
earthquakes.
Which of the following areas is NOT
one of the three main regions of the
ocean floor?
A.
B.
C.
D.
Ocean floor basin
Continental margins
Continental rock
Mid-ocean ridge
The continental margins of the Pacific
Ocean are
A. Wider than those of the Atlantic and have
more earthquake activity.
B. Narrower than those of the Atlantic and
are not covered with thick layers of
sediment.
C. Wider than those of the Atlantic and have
no volcanic or earthquake activity.
D. Narrower than those of the Atlantic and
are covered with thick layers of sediment.
Ocean Floor Features
Continental Margins
• Continental Shelf
– A continental shelf is the gently sloping
submerged surface extending from the shoreline
– Continental shelves contain important mineral
deposits, large reservoirs of oil and natural gas,
and huge sand and gravel deposits.
Ocean Floor Features
Continental Margins
• Continental Slope
– A continental slope is the steep gradient that
leads to the deep-ocean floor and marks the
seaward edge of the continental shelf.
– A submarine canyon is the seaward extension of
a valley that was cut on the continental shelf
during a time when sea level was lower—a canyon
carved into the outer continental shelf, slope, and
rise by turbidity currents.
Ocean Floor Features
Continental Margins
• Continental Slope
– A turbidity current is the downslope movement of
dense, sediment-laden water created when sand
and mud on the continental shelf and slope are
dislodged and thrown into suspension.
Submarine Canyons
Ocean Floor Features
Continental Margins
• Continental Rise
– A continental rise is the gently sloping surface at
the base of the continental slope.
• Located in regions where trenches do not exist.
Which area of the continental margin
contains mineral deposits, large
reservoirs of oil and natural gas, and
huge deposits of sand and gravel?
A.
B.
C.
D.
Continental shelf
Continental slope
Continental rise
Continental plain
Which area of the continental margin
are submarine canyons cut into?
A.
B.
C.
D.
Continental shelf
Continental slope
Continental rise
Ocean floor basin
What are turbidity currents?
A. Fast moving currents near the shoreline
B. Sediment-rich water that moves down
the continental slope
C. Currents that carry trash out to the
open ocean
D. Currents that wear aware the shoreline
Ocean Floor Features
Ocean Basin Floor
• The ocean basin floor is the area of the deepocean floor between the continental margin
and the oceanic ridge.
• Deep-Ocean Trenches
– Trenches form at the sites of plate convergence
where one moving plate descends beneath
another and plunges back into the mantle.
Ocean Floor Features
Ocean Basin Floor
• Abyssal Plains
– An abyssal plain is a very level area of the deepocean floor, usually lying at the foot of the
continental rise.
– The sediments that make up abyssal plains are
carried there by turbidity currents or are
deposited as suspended sediment settles out.
Ocean Floor Features
Ocean Basin Floor
• Seamounts and Guyots
– A seamount is an isolated volcanic peak that rises
at least 1000 meters above the deep-ocean floor,
and a guyot is an eroded, submerged seamount.
Abyssal Plain Cross Section
Trenches form at sites where
A.
B.
C.
D.
One plate descends beneath another.
Erosion cuts into the continental shelf.
Two plates diverge under the sea.
The tops of undersea volcanoes
collapse.
Abyssal plains are very flat features
that form when
A. Volcanoes spread lava on the ocean
bottom.
B. Turbidity currents deposit sediments on
the ocean floor.
C. Ocean waters flood plains on land.
D. Plates diverge on the ocean floor,
causing seafloor spreading.
Guyots are
A. Active underwater volcanoes
B. Volcanoes that have turned into islands
C. Eroded, flat topped, underwater
volcanoes
D. Underwater volcanic craters
Ocean Floor Features
Mid-Ocean Ridges
• A mid-ocean ridge is found near the center of
most ocean basins. It is an interconnected
system of under water mountains that have
developed on newly formed ocean crust.
• Seafloor Spreading
– Seafloor spreading is the process by which plate
tectonics produces new oceanic lithosphere at ocean
ridges.
– New ocean floor is formed at mid-ocean ridges as
magma rises between the diverging plates and cools.
Ocean Floor Features
Mid-Ocean Ridges
• Hydrothermal Vents
– Hydrothermal vents form along mid-ocean ridges.
These are zones where mineral-rich water, heated
by the hot, newly-formed oceanic crust, escapes
through cracks in the oceanic crust into
surrounding water.
Hydrothermal Vents
Which of the following forms at midocean ridges?
A.
B.
C.
D.
Island arcs
Deep-sea trenches
Guyots
New ocean floor
Where do hydrothermal vents form?
A.
B.
C.
D.
Near subduction zones
Near deep-ocean trenches
Along mid-ocean ridges
In the deep-ocean basin floor
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