Transcript Mapping the Ocean Floor

Mapping the Ocean Floor
Essential Questions
 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
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.
Continental Rise
 The slope moderates to a mere
degree or two from horizontal which
is called the continental rise
 Joins abyssal plain to continental
slope
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.
Oceanic Trench
 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.
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.
Rift Valley
 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.
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
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
Interesting facts
 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
 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
 SONAR
 acronym for SOund Navigation And
Ranging
 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