Water

"Can you think of the various ways in which water is synonymous with life. Water supports all forms of life on Earth and is a very important natural resource. Read the following chapter and understand how water forms an integral part of our lives."

1.0Introduction

The sun's heat causes evaporation of water into vapour. When the water vapour cools down, it condenses and forms clouds. From there it may fall on the land or sea in the form of rain, snow or sleet. The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the Water cycle.

Our earth is like a terrarium. The same water that existed centuries ago still exists today. The water used to irrigate a field in Haryana may have flowed down the Amazon River a hundred years ago. The major sources of fresh water are the rivers, ponds, springs and glaciers. The ocean bodies and the seas contain salty water. The water of the oceans is salty or saline as it contains large amount of dissolved salts. Most of the salt is sodium chloride or the common table salt that you eat.

2.0Distribution of water bodies

• We all know that three-fourth of the earth surface is covered by water.
• If there is more water than land on this earth, why do so many countries face water scarcity?
• Is all the water on earth available to us? The following table gives the distribution of water in percentage.

• Water is absolutely essential for survival. Water alone can quench our thirst when we are thirsty.
• Now don't you think we are wasting a precious resource when we use water carelessly?

Dead sea in Israel has salinity of 340 grams per litre of water. Swimmers can float in it because the increased salt content makes it dense.

3.0Ocean Circulation

There is something magical about walking bare feet on the seashore. The wet sand on the beach, the cool breeze, the seabirds, the smell of the salt in the air and music of the waves; everything is so fascinating. Unlike the calm waters of ponds and lakes, ocean water keeps moving continuously. It is never still. The movements that occur in oceans can be broadly categorised as: waves, tides and currents.

Waves

• When you are playing throw ball on the beach and the ball falls into the water, what happens?
• It is fun to watch how the ball gets washed back to the shore by the waves.
• When the water on the surface of the ocean rises and falls alternately, they are called waves.
• 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 15 m ., is formed.
• The largest tsunami ever measured was 150 m . 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.

Tsunami is a Japanese word that means "Harbour waves" as the harbours get destroyed whenever there is 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 moon 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.

4.0Ocean 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.
  
  Ocean Currents

El Nino is a climate phenomenon characterized by the warming of sea surface temperatures in the central and eastern equatorial Pacific Ocean. In India, El Nino can impact weather patterns, leading to drier-than-normal conditions, affecting rainfall and potentially causing droughts in some regions.

5.0Mind Map