Transcript Continental Margins & Ocean Basins

Continental Margins & Ocean Basins
Chapter 4
Sea Floor Topography
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Topography is the detailed representation
of relief (elevation) of an area.
Sea floor topography is a result of the
combination of erosion and plate
tectonics.
The ocean floor is divided into two main
categories:
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Continental Margins (edge of continent)
Ocean Basins (deep ocean floor)
Pie chart showing
the percentage
features that cover
the Earth’s surface.
Of all the features:
•What feature
covers the most
area on Earth?
Hypsographic curve
represents the
distribution of
elevations and depths
on the Earth.
Notice the average
depth of the ocean is
much greater than the
average elevation of
the land.
Continental Margins
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Submerged part of the continent
Topography influenced by changes in sea
level
Two types 
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Active Margin (Pacific Type)
Passive Margin (Atlantic Type)
Diagram of a continental margin
Continental Shelf
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Generally located parallel to the coast.
Characteristics:
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Includes near shore islands
Width varies
Shallow with an average depth of 250 ft
Has a gentle slope (1.7m/km).
Contains resources like oil and minerals.
Formed by down-warping of the continents
during the break-up of Pangaea.
Continental Shelf
Continental Slope
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Generally located at the edge of the
continental shelf. True edge of continent.
Transition zone between continental
margin and ocean basin
Characteristics include:
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Steep slope (70 m/km)
Average 13 miles wide
Depth average is 12,000 ft
Cut by submarine canyons.
Continental Slope
Submarine Canyons
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Located perpendicular to the continental shelf.
Cuts through the shelf and the slope.
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Characteristics:
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On Pacific coast, canyons are close to shore.
Atlantic, canyons are far off shore.
Some are size of the grand canyon
Narrow with steep walls
Depths in excess of 3,000 m or 10,000 ft
Formed by turbidity currents that scour out the
canyons as they flow down the continental
slope.
Turbidity Current
Submarine Canyons
Examples of submarine
canyons. One of the
largest submarine
canyons off the California
is the Monterey Canyon.
Continental Rise
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Generally located at the base of the continental
slope.
Sediment is transported by turbidity currents.
Characteristics include:
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Width varies from 100 – 1,000 km
Slope is gradual
Mud waves & dunes form by strong ocean currents
Formed from the accumulation of continental
sediments.
Absent where there are trenches. Why?
Continental Rise
Deep Ocean Basin
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Constitutes more than a third of the
Earth’s surface.
Composed of basalt (volcanic) which is
blanketed with sediment up to 3 miles
thick (mud & clay).
Contains abyssal plains, mid-ocean ridges,
seamounts, and guyots.
Mid-Ocean Ridge
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Generally located in the center of most ocean
basins.
Mountainous chain of young basaltic rock and
active volcanoes at spreading center.
Characteristics include:
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Stretching 40,000 miles long!!
Average height of about 1.25 miles above sea floor
Accounts for 22% of the worlds solid surface
Devoid of sediments.
Formed: Volcanic activity & sea floor spreading
Mid-Ocean
Ridge
Hydrothermal Vents
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Volcanic hot springs on the ocean floor.
Characteristics:
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hydrothermal fluid is so hot (350 to 400°C),
it can melt metal.
The hydrothermal fluids include dissolved
copper, zinc, and iron, from the ocean
crust.
Build chimneys over 50 ft tall
Formed from the interaction of seawater
and magma near MOR’s and hotspots.
Abyssal Plains & Hills
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Abyssal plains are large, flat sedimentcovered areas of the seafloor.
Abyssal plains are usually located on
either side of a mid-ocean ridge.
Characteristics
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Depth – 10,000 – 16,500 ft
Extraordinarily flat!!!!
Largest features on the deep ocean floor
Covered with sediment up to 3,300 ft thick
Abyssal Hills
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Abyssal hills are small sediment-covered
extinct volcanoes near MOR’s.
Characteristics –
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Usually less than 650 ft high
Buried in sediment
Abyssal hills formed from sea floor
spreading.
Abyssal Plains & Hills
Formed: Sediment covers the irregular basaltic seafloor
burying the hills until the seafloor is flat. Some abyssal hills
still protrude above the plain.
Seamounts & Guyots
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Seamounts and guyots are volcanic mountains
that rise above the ocean floor.
Characteristics:
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Circular in shape
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Seamounts are cone shaped (never above surface)
Guyots are flat-topped (top eroded by waves)
More than a kilometer in height
Steep slopes
Over 10,000 found in the Pacific Ocean
Seamounts & Guyots
Seamounts are
conical shaped
and guyots are
flat-topped.
isobaths
Bathymetric map of an under-sea volcano near Samoa. Lines
are isobaths and the contour interval is 200 meters.
Guyots