Transcript PowerPoint- Ocean Floor Features

Ocean Features
Bathymetry
 Bathymetry-(Bathos=depth;metry-
measurement) Measurement of
ocean depths and charting the shape
of the ocean floor
 Sounding- Using a line with heavy
weight to probe ocean’s depths
– Fathom- unit of measurement
specifically for ocean depth
measurement (1 fathom=1.8 meters=6
feet)
HMS Challenger
 1872-
made first systematic
measurements using sounding
technology
 Noticed that depth varied indicating
that the ocean floor was not flat, but
had relief just as land does
Advancing Technology


SONAR Technology- Sound, Navigation, And
Range
1900s- Echo Sounders
– Sends a sound signal to determine depth and shape of
ocean floor. Early technology not very accurate

1950s- Precision Depth Recorder (PDR)
– Used high-frequency sound beam to measure depths
within 1 meter accuracy

Current technology- Multibeam Echo Sounders
– Use multiple frequencies of sound simultaneously giving
more precise data

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Ocean Floor Provinces
 Continental
Margins
– Shallow water areas close to continents
 Deep
Ocean Basins
– Deep water areas farther from land
 Mid-Ocean
Ridge
– Shallower areas near the middle of the
ocean
Continental Margins
 Passive
Margins
– Imbedded within the interior of
lithospheric plates and are not in close
proximity to plate margins
– Lack tectonic activity
 Active
Margins
– Associated with lithospheric plate
boundaries and are marked by a high
degree of tectonic activity
Active Margins
 Convergent
Active margins
– oceanic-continental convergent plate
boundaries
– Features
 Continental
arc, narrow shelf, steep
slope, offshore trench
 Transform
Active margins
– Transform plate boundaries
– Faults create linear islands, banks, deep
basins
Features of Continental Margins

Continental shelf- flat zone extending
from the shore beneath the ocean to a
point where slope angle increases
dramatically
– Average width- 70 KM
– Ranges from a meters to 1500 KM

Shelf Break- Point where increase in
slope angle occurs
– Can contain coastal islands, reefs, and raised
banks
Features of Continental Margins
Continental borderland- occurs in
faulted areas (California). High degree of
relief on shelf
 Continental slope- this is where deep
ocean basins begin
 Continental rise- transition zone
between the continental margin and the
deep ocean floor

– Graded bedding, produced by turbidity
currents. Layered sedimentation with heavier
sediments settling out first. Decrease in
sediment size from bottom to top
Underwater Canyons

Submarine canyons- V-shaped and have
branches or tributaries with steep
overhanging walls
– Thought to occur because of turbidity
currents
– Turbidity currents- Underwater avalanches
of muddy water mixed with rocks and other
debris
– Mass moves from earthquakes, hurricanes, or
other disturbance carving the canyon
Deep Ocean
 Abyssal
Plains- Extend from the
base of the continental rise into the
deep-ocean basins.
– Flat, depositional surfaces with very
slight slopes
– Average between 4500 meters and 6000
meters deep
– Suspension Settling- fine particles of
sediment slowly drift onto the deep
ocean floor
 This
is how abyssal plains form
Underwater Volcanoes
Seamounts:
Below sea level,
but rise 1
kilometer above
the deep ocean
floor
 Seaknolls
(abyssal hills)
less than 1
kilometer above
the deep ocean
floor

Ocean Trenches
 Deep
linear scars in the ocean floor.
They are very narrow and steep
 Occurs along active continental
margins, where there is a convergent
plate boundary
 The side nearest to land can be
volcanic arcs (islands of Japan), or
continental arcs (Andes Mountains)
Mid-Ocean Ridge
 Earth’s
longest mountain chain –
75,000 kilometers/46,600 miles
 Divergent boundary
 Entirely volcanic- composed of
basaltic lavas
 Rift valley occurs along its crest
 Underwater lava flows- Pillow lavas
Hydrothermal Vents
Hot springs which occur in the central rift
valley
 Appearance depends on temperature of
water

– Warm-water vents are below 30oC (86oF) and
are clear in color
– White smokers are between 30oC and 350oC
(86oF- 662oF) and are white in color
– Black smokers are above 350oC (662oF) and
are black in color
Mid-Ocean Ridge cont.
 Oceanic
ridges have a rift valley and
steep rugged slopes
 Oceanic rises have slopes that are
gentler and less rugged
Mid-Ocean Ridge
 Transform
Faults cut the mid-ocean
ridge in a number of places
– These faults are perpendicular to the
mid-ocean ridge and give the ridge a
zigzag appearance
– Many earthquakes occur here
 Fracture
Zones also extend from the
mid-ocean ridge, but are much
different from transform faults