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Features of the Seafloor

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Parts of the Seafloor

How parts of the seafloor are classified is fairly simple:  the continental margin and the deep seafloor.

Do you remember the densities of continental and oceanic crust?  Which one is heavier?  If you don't, review Plate Tectonics: The Layers of the Earth page.

There is a height difference between the top of the continental crust and the top of the oceanic crust due to the difference in densities.  All of the oceanic crust is located under water, but not all of the continental crust is. 

Profile extending from the continental margin (left), dropping off to the deep sea floor, where there is a spreading center in the middle.  The abyssal plain continues to the left before subducting beneath another continental plate on the right.

Image source:  Sonjia Leyva, own work, © 2020.

 

The portion of the continental crust that is under water is called the continental margin.  The amount of continental crust that is under water is dependent upon a few factors:

 

Take a look at these two Google Earth images.  The first shows the Doggerland region in Europe.  Archaeology shows that this area was inhabited by Mesolithic people as far back as 12,000 years ago.  Melting of the ice sheets began to inundate this area, causing people to migrate elsewhere around 6,000 years ago.  Today, the region is covered in approximately 100 meters of seawater.  The Doggerland area is referred to as a "Land Bridge".  On the image, the light blue areas represent shallow water - the continental margin and, in this case, a land bridge.

Eduard Suess believed that South America, Africa, and India were once connected and were separated as sea levels rose and a land bridge was connected between them.  You learned in the Plate tectonics lecture why this isn't true - those continents were separated by mid-ocean ridges.  The Doggerland area is a true land bridge, creating a nice, wide continental margin for western Europe.

Satellite image of the Doggerland region

Image source:  "Satelite Imagery" Google Data: SIO, NOAA, U.S. Navy, NGA, GEBCO, IBACO, Landsat / Copernicus, ORION-ME, U.S. Geological Survey by is in the Public Domain

 

Next is the Bering Land Bridge.  Like the Doggerland area, this land bridge formed as sea levels rose as the ice sheets melted.  The area between Russia (left) and Alaska (right) has formed a wide continental margin.  Now, look south (bottom of image) where the Aleutian Islands form an arc below the land bridge.  Recall that the light blue areas represent shallow water - the continental margin.  Note that the amount of light blue south of the island chain is very narrow;  this area has a narrow continental margin.

Satelite image of the Bering Sea

Image source:  "Satelite Imagery" by Google Data: SIO, NOAA, U.S. Navy, NGA, GEBCO, IBACO, Landsat / Copernicus is in the Public Domain


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