The rise and fall of seawater because of the gravitational forces of the Sun and the Moon are called tides. Sea waves produced by tides are known as tidal waves. The rise of seawater and its movement towards the coast is called tide. As a result, when the water level is high, it is known as high water tide. The fall of seawater and its movement towards the sea is called ebb. The resultant low water level is called low tidewater. The difference between high tidewater and low tide water is called tide range.
Factors Causing Tides
- They are basically caused by the gravitational pull of the Moon and the Sun.
- The Earth revolves round the Sun and the Moon revolves around the Earth in an elliptical orbit. The distance between the Earth and the Moon changes many times during a month.
- The surface of the Earth which faces the Moon experiences maximum gravitational pull of the Moon. As a result, the water of the Earth’s surface gets pulled up and thus high tides occur.
- High tides also occur in the part of the Earth which is facing away from the Moon because of the centrifugal force (the force which draws a rotating body away from the centre of rotation) of the gravitational pull of the Moon causing an outward bulge of water.
- The period of farthest distance between the Moon and the Earth is called apogee. The period of the nearest distance between the Moon and the Earth is known as perigee.
Some Facts about Tides
- Tides and ebbs occur twice on the Earth’s water surface in 24 hours. High tides take place when the Sun, the Earth and the Moon are in the same line. When their gravitational forces work together, high tides are formed.
- When the Sun and the Moon are at the position of right angles with reference to the Earth, the gravitational forces of the Sun and the Moon work against each other resulting in low tides.
- Every place experiences tides twice a day.
- When the Sun, Moon and Earth are in the same line, the tides are highest and they are called spring tides.
- When the Moon is in its first and last quarter, the ocean water gets pulled in the opposite direction of the Moon by the Sun’s and Earth’s gravitational force causing low tides. These tides are also known as neap tides.
Importance of Tides
- They can cause a change in the landforms of the Earth. While they can destroy the coastlines, they also help in the formation of creeks and inlets.
- Strong tides help in building lower floodplains of rivers. These are very fertile.
- Because the debris is swept away by them, they help keep the harbours clean.
- In cold countries, they bring in saltwater to the shore and their continuous movement prevent the harbour from becoming ice bound.
- The low-lying areas of the sea coast during high tides trap water which is used for the manufacturing of salt. Salt is manufactured along the west coast of India in this manner.
- The alternate rise and fall of them help fisherman to sail out and return to the coast.
- Tidal energy is fast becoming an important source of non-convectional sources of energy. They are used in the production of electricity along the Gulf of Kachchh in Gujarat.
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