• Water is absolutely essential for survival. Water alone can quench our thirst when we are thirsty.
• March 22 is celebrated as World Water Day when the need to conserve water is reinforced in different ways.

• Waves are formed when gentle winds scrape across the ocean surface. The stronger the wind blows, the bigger the wave becomes.
• When the water on the surface of the ocean rises and falls alternately, they are called waves.
• Tsunami is a Japanese word that means “Harbour waves” as the harbours get destroyed whenever there is tsunami.
• During a storm, the winds blowing at very high speed form huge waves. These may cause tremendous destruction. An earthquake, a volcanic eruption or underwater landslides can shift large amounts of ocean water. As a result a huge tidal wave called tsunami, that may be as high as 15m., is formed. 
• The largest tsunami ever measured was 150m. high. These waves travel at a speed of more than 700 km. per hour. The tsunami of 2004 caused wide spread damage in the coastal areas of India. 
• The Indira point in the Andaman and Nicobar islands got submerged after the tsunami. 

 

Tides

• The rhythmic rise and fall of ocean water twice in a day is called a tide. It is high tide when water covers much of the shore by rising to its highest level. It is low tide when water falls to its lowest level and recedes from the shore.
• The strong gravitational pull exerted by the sun and the moon on the earth’s surface causes the tides. 
• The water of the earth closer to the moon gets pulled under the influence of the moon’s gravitational force and causes high tide. 
• During the full moon and new moon days, the sun, the moon and the earth are in the same line and the tides are highest. These tides are called spring tides. 
• But when the moon is in its first and last quarter, the ocean waters get drawn in diagonally opposite directions by the gravitational pull of sun and earth resulting in low tides. These tides are called neap tides. 
• High tides help in navigation. They raise the water level close to the shores. This helps the ships to arrive at the harbour more easily. The high tides also help in fishing. Many more fish come closer to the shore during the high tide. This enables fishermen to get a plentiful catch. The rise and fall of water due to tides is being used to generate electricity in some places. 

 

OCEAN CURRENTS

• Ocean currents are streams of water flowing constantly on the ocean surface in definite directions. The ocean currents may be warm or cold. 
• Generally, the warm ocean currents originate near the equator and move towards the poles. The cold currents carry water from polar or higher latitudes to tropical or lower latitudes. 
• The Labrador Ocean current is cold current while the Gulf Stream is a warm current. 
• The ocean current influence the temperature conditions of the area. Warm currents bring about warm temperature over land surface. The areas where the warm and cold currents meet provide the best fishing grounds of the world. Seas around Japan and the eastern coast of North America are such examples. 
• The areas where a warm and cold current meet also experience foggy weather making it difficult for navigation.

 

 

Questions and Answers

 

Ques 1 The process by which water continually changes its form and circulates
between oceans, atmosphere and land 

(a) Water cycle 

(b) Tides 

(c) Ocean currents 

Ans- (a) Water cycle

 

Ques 2 Generally the warm ocean currents originate near 

(a) Poles 

(b) Equator 

(c) None of these 

Ans- (b) Equator

 

Ques 3 The rythmic rise and fall of ocean water twice in a day is called 

(a) Tide 

(b) Ocean current 

(c) Wave

Ans- (a) Tide

 

 

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