Tides
        
  The sea level rises in the gulfs and at sea-coast for 6 hours and 13 minutes and takes the same time in getting down. In other words, the time taken in two consecutive rises or two consecutive falls is about 12 hours and 26 minutes. In 24 hours and 52 minutes, the sea water rises and falls two times each. The successive rise and fall of sea water is called a tide.

          When the water is coming towards a gulf or towards a coast, it is known as Flood or Incoming Tide when the sea water moves away from a gulf or a coast; it is called Ebb or Outgoing Tide.

Causes of the Tides

          The fact is that tides are produced by the gravitational pull, exercised by the sun and the moon on the earth. And the role of moon in causing tides is most significant. The waters of the earth are held together in position due to the gravitational pull of the earth but the attractive power of the sun and the moon counteracts the pull of the earthy and the result is that on opposite sides of the earth water is heaped up in tides.

          The attraction of the moon causes tides. Although the moon is smaller than the sun, it is much nearer the earth. Although the moon attracts all the portions of the earth, its pull is most felt on water which is not so compact as the land. In this connection, a remarkable feature is that due to the attraction of the moon two high tides are caused, one directly in front of it and the other indirectly on the opposite of it. The direct high tide is caused by the attractive pull of the moon on the waters just below it. But due to the moon's attraction the surface of the earth on the opposite side is pulled away from the water. The result is that water begins to heap in a mound and a second high tide is produced indirectly.

          While there are high tides at places facing the moon and on the opposite side to the moon, there are low tides at places lying in between the two high tides. While the water rushes to rise at the high tides on the opposite side of the earth, at two points lying in between the direct and indirect high tides, the water falls and there are low tides. These are also known as flood tides and ebb tides.

Kinds of Tides
1.     High/ Spring Tides
2.     Low/Neap Tides

Spring Tides

          At full moon and new moon, the earth, the sun and the moon are almost in a straight line so that the sun pulls with the moon. The result is that usually high tides-the highest tides-occur and are known as           Spring Tides. As the name indicates, the waters leap or jump to a very great height and this occurs twice a month.

Neap Tides

          During the first and last quarter of the moon, the sun and the moon are almost at right angles to the earth. The result is that the pull of the sun neutralizes the pull of the moon and detracts some water from the pull of the latter. Hence the high tide that occurs is the lowest, as if it had been nipped. This scanty high tide is known as the Neap Tide.

Importance of Tides

1.     In many shallow seas, the harbours are able to receive the ships only when the water is high during the tide.
2.     The tides fulfill another service in keeping the harbours clear of refuse.
3.     In the hot climatic zones tide water be collected produced salt.
4.     In the cold regions because of the tides there may not be frozen the icebergs. So that ships can move easily.

Waves

          Waves are up and down movements of ocean waters caused by the transfer of energy from the wind to the sea.