CBSE Board Exam: Oceanography Relief Geography Notes on Relief Features of Ocean, Continental Shelf, Continental Slope and Trenches

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Introduction to Oceanography

Distribution of Sea

  • Hydro sphere is36, 10,60, 000 sq. km about 71 % of the lithosphere (3/ 4th of the globe) .
  • Total surface area of the globe is 5, 09,950, 000 sq. km. (Lithosphere) .
  • Important oceans are Pacific Ocean (16, 50,00, 000 sq. km) ; Atlantic ocean (8, 20,00, 000 sq. km) ; Indian Ocean (7, 30,00, 000 sq. km) .
  • Average depth of the ocean (hydrosphere) 3800 m and average height of lithosphere is 840 m from the sea level.
  • The height and depth of lithosphere and hydrosphere are represented by HYPSOGRAPHIC or HYPSOMETRIC CURVE.
  • The ocean basins have 4 relief zones: Continental shelves, Continental slopes, Deep Sea plains and Oceanic Trenches

Continental Shelf

  • It is partly submerged in water while partly exposed;
  • Its average depth is 100 fathoms;
  • Its slope is gentle i.e.. from to towards the sea;
  • It is 8.6 % of total area of ocean basins, but the highest area is in Atlantic i.e.. 13.3 % , 5.7 % in Pacific and 4.2 % in Indian ocean;
  • The shelves are narrow where high mountains are close and parallel to the coast;
  • The narrowest shelf is in western coast of South America i.e.. 16 km. because of Andes mountain;
  • The shelves are wider where the coast lands are wide plains. The average width is 48 km. The widest is in North America i.e.. from 96 to 120 km. ;
  • It is mainly created by marine erosion and fluvial deposits;

Continental Slope

  • Slope is
  • near St. Helena; at the Spanish Coast; near St. Paul; near Calicut.
  • It constitutes 8.5 % of total area of the ocean basin: Atlantic ocean 12.4 % , Pacific ocean 7 % and Indian ocean 6.5 % .
  • Most extensive continental slope are found between N latitude and on N and S. Most important continental slope is the SubMarine Canyons.
  • Due to steep slope, marine deposits doesnttake place; Deep Sea Plains:
  • Found in the depth of 3000 m. to 6000 m. and constitutes 75.9 % of total ocean basin;
  • 80.3 % in Pacific, 80.1 % in Indian Ocean, 54.9 % in Atlantic Ocean.
  • Ocean Deep or Trenches:
  • There are 57 deeps in the world;
  • Highest in Pacific i.e.. 32,19 in Atlantic and 6 in Indian Ocean;


  1. Mariana or Challenger Trench North Pacific 11,022 m.
  2. Aldrich or Tonga Central South Pacific i 0,882 m.
  3. Swire or Philippine Trench N. West Pacific 10,475 m.
  4. Nares or Puerto Rico Trench West Indian Island 8,385 m.
  5. Kurile Trench Kamchatka 10,498 m.
  6. Tizard or Romanche Trench S. Atlantic 7,631m.
  7. Java Trench Indian Ocean 7,450 m.
  8. Karmadee Pacific Ocean 10,447 m.
  9. PeruChile Trench Pacific 8,025 m.
  10. Aleutian Trench Pacific 7,679 m.
  11. Middle America Pacific 6,562 m.

Submarine Canyons

  • It has originated because of various types of earth movement
  • Are long narrow and very deep valleys or trenches located on the continental shelves and slopes with vertical walls resemblirflefriecontinental Canyon.

Submarine Canyon

  1. It is similar lot the youthful river valleys on the land but are deeper
  2. The course is generally straight
  3. The gradient of are steeper near islands i.e. 13 8 %
  4. They have a coarser material which includes clays, silts, gravels and pebbles.

Distribution of Submarine Canyons

  • There are as many as 102 submarine canyons.
  • Generally they are more abundantly found along the straight coast than highly indented and crenulated coastline.
  • They are more commonly found Off the east mm of US from Canada to Cape Hatteras.
  • They are also found off the Californian and Mexican coast, Mediterranean, east coast of India, Aleutian lands, Japan, Philippines.

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