Hydrosphere is the name given to all the water of the Earth in solid, liquid and gaseous forms. It thus includes the water of the atmosphere, water on the Earth’s surface (e.g. oceans, rivers, ice-sheets and ground water). Oceans, which are interconnected, cover about 70.8 percent of the surface of the Earth. Pacific Ocean, which is the largest among the oceans, sprawls over an area of about 16,57,60,000 sq km, an area which is more than the total combined area of all the continents.
The oceans have an average depth of 3.5 km but their depth varies from place to place. The deepest known point is the Challenger Deep, a part of the Mariana Trench in the Pacific Ocean, which is 11.776 km deep.
The water in the oceans totals over 1,300 million cubic km, which is more than 97 percent of world`s total water. The balance of water resources are contributed by glaciers, ice and snow, fresh water lakes, rivers and the underground water.
The ocean floor consists of three main zones, viz., the continental shelf, the continental slope and the abyss. The continental shelves are, in fact, the submerged parts of the continents that gentally slope into the oceans bordering these continents.
The true edge of the continents is, however, the continental slope which begins from the point where the continental shelf ends.
The abyss contains large sediment covered plains below the oceans. These plains are often interspersed by lofty volcanic mountains some of which surface as islands and long broad ridges which are in some places 2 to 4 kilometres high and up to 4,000 kilometres wide. The abyss also contains yawning chasms called deep sea trenches.
Continental Shelf (Littoral)) is the sea bed bordering the continents, which is covered by shallow water up to about 100 fathoms (600 feet) beyond which is the continental slope.
Continental Slope is the region of the sea extending next to the continental shelf and having a depth up to 2,000 fathoms.
Continental Drift is a theory or hypothesis that continents have moved relative to each other across the surface of the earth. The idea was originally put forth by Antonio Snider-Pellegrini in 1858 and developed by the German geologist Alfred Wegner from 1910. He started that there was just one supercontinent, Pangaea which began to break up about 200 million years ago, since then the continents have drifted to their present positions.
Isohaline is the line which joins, on a map points of the sea / oceans having equal salinity.
Ocean Current is the movement of a sizeable body of water as a current for fairly long distances along a specific path. It is known as ‘drift current’ when caused by the winds and as ‘convection current’ when brought about by variations in temperature. A ‘warm current’ is the one which flows from a warm to a cold region. The current flowing from a cold to a warm region is called a ‘cold current’.
Stream refers to any body of running water that flows on or under the surface of the water.
Swamp is a portion of wet, waterlogged or flooded land.
Gulf Stream refers to the warm ocean current which starts from the Gulf of Mexico and flows along the eastern coast of North America. Influenced by the westerly winds, it crosses the Atlantic, moves along the north-west coast of Europe and helps to keep the British and Norwegian coastal waters warm and navigable during the winter months.
Kuro Siwo (Black Current or Japanese Current) is the warm ocean current which flows up the Asian east coast and is driven by westerly winds towards North America.
Tide is the periodic rise and fall of sea water. Rise and fall occur alternately twice a day. The rising of water is called the Flood Tide and the falling of water is termed as the Ebb Tide.
Spring Tides are caused as a result of the Moon and the Sun pulling the Earth gravitationally in the same direction. They occur twice a month around full moon and new moon.
Neap Tides are caused when the Moon and the Sun pull the Earth gravitationally in opposite directions. They occur twice a month during first and last quarters of the moon, when Sun, Earth and Moon are at right angles.
Lagoon is a shallow stretch of Water which is partly or completely separated from sea by a narrow strip of land.
Reef is a ridge of submerged rock or other hard substance in sea water. It becomes visible at low rides.
Coral Reef is a ridge of coral and other organic material consolidated into lime stone lying near the sea level.
Bay is a wide curving indentation in a coastline lying between two head lands.
Atoll is a circular or horse shoe shaped coral enclosing within it a lagoon.
Fjord is a shallow stretch of river that may be crossed on foot or in a vehicle, commonly found in Norway or Sweden.
Strait is a narrow sea passage that links two large areas of sea, for example the Strait of Gibraltar.
Isthmus is a narrow strip of land connecting two large areas of land (e.g., Isthmus of Panama joining the North and South American continents).
Hinterland is the land which lies behind a seaport or seaboard and supplies the bulk of the exports and in which are distributed the bulk of the imports of that seaport or seaboard.
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