NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Oceanography Relief Geography Notes on Relief Features of Ocean, Continental Shelf, Continental Slope and Trenches
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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;
Trenches
- Mariana or Challenger Trench North Pacific 11,022 m.
- Aldrich or Tonga Central South Pacific i 0,882 m.
- Swire or Philippine Trench N. West Pacific 10,475 m.
- Nares or Puerto Rico Trench West Indian Island 8,385 m.
- Kurile Trench Kamchatka 10,498 m.
- Tizard or Romanche Trench S. Atlantic 7,631m.
- Java Trench Indian Ocean 7,450 m.
- Karmadee Pacific Ocean 10,447 m.
- PeruChile Trench Pacific 8,025 m.
- Aleutian Trench Pacific 7,679 m.
- 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
- It is similar lot the youthful river valleys on the land but are deeper
- The course is generally straight
- The gradient of are steeper near islands i.e. 13 8%
- 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.