Descripción de Casos de Uso

Extent: On high mountain slope of both hemispheres. Himalayas and Andes have vertical zonation of climate from tropical to ice-cap type. Windward slope receives heavy rainfall while the leeward sides are dry. In the N-Hemisphere southern slopes are warmer.

CHRONICLE IAS

ACADEMY

HYDROSPHERE CHRONICLE

IAS ACADEMY

A CIVIL SERVICES CHRONICLE INITIATIVE

All the water of the earth including the oceans, lakes, rivers, ice sheets and the water in the atmosphere is called hydrosphere and it covers about 71% of the earth's surface. The ocean predominates over land areas in the S-Hemisphere far more than that in the N-Hemisphere.

Major Oceans

The Pacific Ocean: It is the largest and deepest ocean covering one third of the globe. Its average depth is 4200 m. The deepest parts are the Philippine Trench about 10,380 m. and the Marina Trench about 10,800 m. The Pacific -Ocean has a string of volcanoes along the coastal margins of the conti-nents known as 'The Ring of Fire'.

The Atlantic Ocean: Though the Atlantic is smaller than the Pacific, its total coastline is more than that of the Pacific and the Indian Ocean combined. There is a long submarine ridge run-ning north to south in the middle of Atlantic. It is the greatest mountain chain in the world (16,000 km long). It is known as the Dolphin Ridge in the North Atlantic and the Challenger Ridge in the South Atlantic. There are also con-tinental islands such as the British Isles, New-foundland, the West Indies etc. The Atlantic is the greatest commercial highway of the world.

Indian Ocean: It is small in size but has an average depth of 4,000 m. The two great bays on either side of the peninsula of India, namely the Bay of Bengal and the Arabian Sea belong to the India Ocean. The Indian Ocean is dotted with thousands of small islands some of which are of coral formation, e.g. the Maldives and Lakshadweep islands, while other like the Mauritius and the Reunions are volcanic. Sri Lanka and Malagasy are continental islands.

Arctic Ocean: It is found around the North Pole. It covers only one thirtieth of the sea area.

It is almost completely covered with ice to a depth of about 3 m.

Antarctic Ocean: The remaining area of the sea is included in the Antarctic Ocean surround-ing the Antarctic Continent.

Ocean Area in Percentage

sq. km of sea area

Pacific 1, 66,240,000 46.0

Atlantic 86,560,000 23.9

Indian 430,000 3.7

Profile of Ocean Floor

The ocean basins are in many ways similar to the land surface. There are submarine ridges, plateau, canyons, plains and trenches. The great variety of relief is largely due to the interaction of tectonic, volcanic, erosional and depositional processes. In general the ocean floor can be divided into four major divisions - the continental shelf, the continental slope, the continental rise and the Abyssal Plain.

Continental Shelf: It is the land portion, submerged under sea water and is a transitional zone between the land and the actual sea bottom.

1. The isobath of 100 fathoms (around 200m) demarcates the continental shelf.

2. The average width is about 70 km. and the mean slope is less than 1°.

3. About 7.5 percent of the total ocean area is covered by it.

4. It is almost absent in the eastern Pacific ocean, especially in South America.

5. At the eastern coast of USA it is about 120 km wide and also very wide on the eastern coast of India.

6. Individually it covers about 13.3% part of Atlantic Ocean, 5.7% of Pacific Ocean and 4.2% of Indian Ocean.

7. It is the area of terrigenous deposits i.e.

sediments are derived from land.

8. They provide the richest fishing ground in the world.

CHRONICLE IAS

ACADEMY

9. About 20% of world petroleum and natural gas are found here.

Continental Slope: It lies at the edge of the continental shelf, generally up to the depth of 2000 fathoms (3660 m) from the mean sea level.

1. It has a steep slope with the angle of slope varying from 2° to 5°.

2. It covers about 8.5% of the total oceanic area and individually about 12.4% of the Atlantic Ocean, 7.1% of the Pacific Ocean and 6.5% of the Indian Ocean.

3. The continental blocks are supposed to end at the site of continental slope.

4. The continental slope along the many coasts of the world is furrowed by deep canyons like trenches terminating as fan-shaped deposits at the base.

Continental Rise: The place where the continental slopes end, the gentle sloping continental rise begins. The average slope is between 0.5° and 1° & its general relief is low. With increasing depth the Continental Rise becomes virtually flat and it merges with abyssal plain.

Abyssal/Deep Sea Plains: Beyond Continental Rise, it is found at the depth of 3000 to 6000 m. They cover about 40% of the total ocean floor and generally are bounded by hills (ridges) on the seaward side. They are almost flat with a gradient less than 1:100. The irregular topography of the abyssal plain are buried forming relatively flat areas due to large supply of sediments.

Submarine Ridges: These are the mountain ranges on the ocean floor and some of them are the largest mountain system on the earth.

1. A large number of submarine ridges are placed centrally in the oceans.

2. At some places their summits may rise above the sea level forming islands.

Abyssal Hills: A deep sea floor also contains numerous isolated abyssal hills, sea-mounts and guyots.

1. A submarine mountain peak rising more than 1000 m above ocean floor are known as "seamount".

2. Flat topped seamounts are known as

"Guyots".

3. All the above features are volcanic in origin, very common in Pacific Ocean.

Submarine Trenches or Deeps: A long narrow and steep sided depression on the ocean floor is called trench. These are the deepest part of the ocean.

1. They lie along the fringes of the deep sea plains and usually run parallel to the bordering fold mountains or the island claims.

2. They are believed to have resulted from faulting or down folds of the earth crust and so tectonic in origin.

3. They are most common in the Pacific Ocean like "Mariana Trench" off the Guam Island Chain which is deepest (11 km) in the world.

Submarine Canyons: These are the deep gorges on the ocean floor and are restricted to the continental shelves, slopes and rises.

1. Some canyons begin at the edge of the continental shelf and extend down the continental slope. For example

-"Oceanographer Canyon" near New England.

2. Some canyons have dendritic appearance like off the east coast of Southern California.

3. Some begins at the river mouth and extends over the continental shelf as "Zaire",

"Mississippi" and "Indus" canyons.

Bank, Shoal & Reef: Banks are almost flat topped elevation located in the continental margin. Shoals are detached elevation with shallow depth. Reefs are the mound or rocky elevation like ridges made of organic deposit.

CHRONICLE IAS

ACADEMY

1. The depth of water is relatively small in banks but adequate for navigation.

2. These are sites of rich fishing e.g. "Dogger Bank" (North Sea), "Grand Bank" (off Newfoundland).

3. Shoals are dangerous for navigation as they are only 18-20 m below the sea level.

4. 'Great Barrier Reef' (off Queens land, Australia) is the largest reef in the world.