Mapping the Ocean Floor
Essential Questions
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What are some of the features found
on the ocean floor?
What technology is used to map the
ocean floor?
What are some of the features
found on the ocean floor?
Continental Shelf
A flat, wide margin is found around
every continent
 The average width of a continental shelf
is 70 kilometers
 Slopes at an angle of 0.1°, or 1.7
meters per kilometer
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Continental Slope
The continental slope is about 16
kilometers wide, on average, and
descends to a depth of about 2.4
kilometers
 The slope of the ocean floor becomes
much steeper, typically a 4° slope, or 70
meters per kilometer.
 is grooved by submarine canyons and
gullies.
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Continental Rise
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The slope moderates to a mere degree
or two from horizontal which is called
the continental rise
Submarine Canyon
is a steep-sided valley on the sea floor
of the continental slope
 cutting the continental slopes have
been found at depths greater than 2 km
below sea level.
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Oceanic Trench
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Is where an oceanic crust plate begins to
descend beneath another oceanic crust plate
Oceanic trenches typically extend 3 to 4 km
below the level of the surrounding oceanic
floor.
Trenches are generally parallel to a volcanic
island arc, and about 200 km from a volcanic
arc.
The greatest ocean depth to be sounded is in
the Challenger Deep of the Mariana Trench,
at a depth of 10,911 m below sea level.
Abyssal Plain
The abyssal plain, which is the deepest,
most level part of the ocean, is found
where the continental rise ends, at a
depth of about 4 kilometers.
 The abyssal plain is dotted with
thousands of small, extinct volcanoes
called abyssal hills.
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Mid-Ocean Ridge
a long, undersea mountain chain that
usually extends down the middle of the
ocean
 The Mid-Atlantic Ridge, for example,
snakes down the middle of the Atlantic
most of the way from the North Pole to
Antarctica.
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Rift Valley
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Along the center of the mid-ocean ridge is the
rift valley, a deep V-shaped notch.
From this valley, new oceanic crust is
constantly being extruded from Earth's
mantle by processes not yet fully understood.
In the case of the Mid-Atlantic rift valley, one
sheet flows east and the other west, each
moving at about half an inch per year.
This causes sea floor spreading.
Guyot
is an isolated underwater volcanic
mountain, with a flat top over 200
meters (660 feet) below the surface of
the sea.
 the diameters of these flat summits can
exceed 10 km.
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Seamount
is a mountain rising from the ocean
seafloor that does not reach to the
water's surface, and thus is not an
island.
 these are typically formed from extinct
volcanoes, that rise abruptly and are
usually found rising from a seafloor of
1,000–4,000 metres depth
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Hydrothermal vent
is a fissure in a planet's surface from
which geothermally heated water issues
 are commonly found near volcanically
active places, areas where tectonic
plates are moving apart, ocean basins,
and hotspots
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Interesting facts
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Mauna Kea, Hawaii, rises 33,474 feet from its
base on the ocean floor; only 13,680 feet are
above sea level
The ocean ridges form a great mountain
range, almost 64,000 km long, that weaves
its way through all the major oceans. It is the
largest single feature on Earth
Deepest point - 36,198 feet in the Mariana
Trench in the western Pacific.
What technology is used
to map the ocean floor?
Historically
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For hundreds of years, the only way to
measure ocean depth was the sounding line,
a weighted rope or wire that was lowered
overboard until it touched the ocean floor.
Not only was this method time-consuming, it
was inaccurate; ship drift or water currents
could drag the line off at an angle, which
would exaggerate the depth reading.
It was also difficult to tell when the sounding
line had actually touched bottom
Present Day
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SONAR
– acronym for SOund Navigation And
Ranging
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is a technique that uses sound
propagation
– SONAR waves are sent from a ship and the
time for the waves to return is measured
– the farther the distance the longer the
time, the shorter the distance the smaller
the time
Sea 3-D: Charting the
Ocean Floor - KQED
QUEST
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http://www.youtube.com/watch?v=1h4
vaERMNbs
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5:59
Oceanfloor Legacy
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http://video.google.com/videoplay?doci
d=862857452234843312#
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28:
America's New Frontier
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http://video.google.com/videoplay?doci
d=-7837963317498620058#
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27:30