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Hydrosphere – Ocean Floor Division

Ocean Floor Division

Ocean Floor Division


Continental Self

      • Basically the seaward extension of the continent from the shoreline to the continental edge approx. 200 m deep
      • Continental shelf is thus a shallow platform, whose width varies greatly from a few miles in North Pacific off the continent of North America to over 100 miles off North West Europe
      • In some places, where the coasts are extremely mountainous, such as at Rocky Mountains, the continental shelf may be entirely absent
      • The angle of slope is also variable with most common of 1 in 500 & is normally the least, where the continental shelf is widest

        Continental Self - Ocean Floor Division

      • Continental shelves may be formed by submersion of part of continent due to increase in sea level or by wave erosion or conversely by off-shore deposition
      • Continental shelves shallowness enables sunlight to penetrate through the water, which encourages the growth of minute plants & other microscopic organisms such as planktons, on which millions of fishes & polyps survive. The continental shelves are therefore the richest fishing grounds in the world.

 


Continental Slope

  • At the southern edge of continental self, seaward slope immediately becomes steep & gradient to about 1 in 20 with average depth 200 – 3000 m.
  • Most of the canyons & trenches are observed in this region

 


Continental Rise

  • Beyond the continental slope is continental rise, an area of gentle slope with angle varying from .5 – 1*
  • With increasing depth, it virtually becomes flat & merges with abysmal plains

Continental Slope - Ocean Floor Division


Abysmal Plains

  • Where the continental rise end, deep sea plains begin covering 2/3rd of the ocean floor
  • Average depth is of 3000 – 6000 m
  • Flattest & smoothest surfaces of the world

 


Some important terms

Oceanic Deeps or Trenches

      • Deepest part of the oceans
      • Generally steep sided narrow basins, deeper then oceanic floors
      • Occurs at the base of continental slopes & associated with active volcanos & strong earthquakes
      • Hence, Contrary to our expectations, most of the deepest trenches are not located in the midst of the oceans but found close to the continents
      • Deepest trench of the world Marina trench (11 km) of Guam islands (Pacific Ocean)
      • Hence we can see that ocean trenches are greater in magnitude than the highest mountains on the land

 

There are thousands of hills on ocean floors which are submerged under ocean water. A submarine peak rising > 1000 m above the ocean floor is called a seamount. Flat topped seamounts are known as Guyots (Volcanic in origin)

Gorge vs Canyon

      • Gorge / Trench → Narrow & steep side valley formed by down cutting action of river
      • Canyon Magnified form of Gorge. Ex. Grand canyon of river colarado (US) Largest one

 

Difference between Straits & Isthmus

Straits 

  • Narrow channel of water connecting 2 large land bodies
  • Strait of Gibraltar Connects Atlantic ocean & Mediterranean sea and separates Spain (Europe) from Morocco (Africa)
  • Palk Strait Separates India & Srilanka

 

Isthmus 

  • Opposite of strait i.e. narrow channel of land connecting 2 large water bodies
  • Panama Canal crosses Isthmus of Panama, connecting the North Atlantic & Pacific Oceans
  • Suez Canal crosses isthmus of Sinai Peninsula connecting Mediterranean Sea & Indian Ocean

Oceanic Deposits on Ocean Floor

Muds
  • These are terrigenous deposits as they are derived from land
  • Are mainly deposited on the continental shelves
Oozes
  • These are pelagic deposits as they are derived from the oceans
  • They are made of shelly & skeletal remains of marine micro-organisms with calcareous or siliceous parts
  • Oozes have very fine, flour like texture which either occur as accumulated deposits or float as suspension
Clays
  • These occur mainly as red clays in the deeper parts of ocean basins
  • Are particularly abundant in Pacific Ocean
  • Red clay is believed to be an accumulation of volcanic dust blown out from volcanoes during volcanic eruptions
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