CLASS 7 CHAPTER-5

CBSE Notes Class 7 Geography Chapter 5 – Water PDF Overview Water Cycle: The process by which water continually changes its form and circulates between oceans, atmosphere and land is known as the water cycle. The major sources of freshwater are the rivers, ponds, springs and glaciers. The ocean bodies and the seas contain salty water. Most of the salt is sodium chloride or the common table salt that we eat. Distribution of Water Bodies Three-fourth of the earth’s surface is covered by water. Water is absolutely essential for survival. Water alone can quench our thirst when we are thirsty. Ocean Circulation The movements that occur in oceans can be broadly categorised as waves, tides and currents. 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 is formed. 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 waterfalls 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 cause the tides. 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. 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. 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. 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 meets experience foggy weather making it difficult for navigation.