Ocean Tides : Causes, Types, Tidal Bulge

What is the Ocean Tide ?

The periodical rise and fall of the sea level, once or twice a day, mainly due to the attraction of the Sun and the Moon, is called a Tide.

What causes Tides ?

• Tides are caused mainly by the gravitational forces.

• The gravitational pull on the Earth by the Sun.

• The gravitational pull on the Earth by the Moon.

• The Centrifugal force of the Earth (It is act as gravitational pull of the earth against Sun and Moon).

• Rotation of the Earth.

What are the types of the tides ?

It is based on the frequency of tides and the height of tides.

Tides Based on Frequency :

1. Diurnal Tide : There is only one high tide and one low tide during each day. The height of low and high tide approximately same.

2. Semi-Diurnal Tide : The most common tidal pattern, featuring two high tide and two low tide each day. The height of low and high tide approximately same.

3. Mixed Tide : Tides having variations in height are known as mixed tides. These  tides generally occur along the west coast of North America and many Islands of the Pacific Ocean.

Tide Based on the Sun, Moon and the Earth Positions (Based on Height) :

1. Flood Tide : The time between the low tide and high tide, when the tide is rising, is called flood Tide or flow tide.

2. Ebb Tide : The time between the high tide and low tide, when the water level is falling, is called the ebb tide.

3. Spring Tides : When the Sun, the Earth and the Moon are in straight line (it known as Sygyzy), the height of the tide will be higher. These are called spring tides and they occur twice a month, one on full Moon period and another during new moon period.

What is full moon day and new moon day ?

Full Moon Day : When the Earth comes between the Sun and the Moon is known Lunar Eclipse.

Note : Lunar Eclipse always occur on Full Moon Day.

New Moon Day : When the Moon comes between the Sun and the Earth is known as Solar Eclipse.

Note : Solar Eclipse always occur on New Moon Day.

4. Neap Tides : At this time the Sun and the Moon are at right angles to each other and the forces of the Sun and Moon tend to counteract one another. Due to more distance of the Sun from the Earth, the Moon attraction more than twice as strong as the Sun.

Also Read : Ocean Current

How are the tidal bulge formed ?

• The gravitational pull and the centrifugal force are together responsible for creating the major tidal bulges on the Earth.

• On the side of the Earth facing the Moon or the Sun, a tidal bulge occurs while on opposite side, the gravitational force of the Earth i.e. Centrifugal force causes tidal bulge on other side. 

What are Challenges of Tides ?

• Erosion of coastal area.

• It can be catastrophic in cases where the tide gets too huge.

• Some time, it is unpredictable that caused loss of life at the shore area.

What are the benefits of Tides ?

• According to new technology, tide helps navigators and fishermen plan their activities. 

• The tidal heights are very important, especially harbours near rivers and within estuaries having shallow 'bars' at the entrance, which prevent ships and boats from entering into the harbour.

• Tides are also helpful in desilting the sediments and I removing polluted water from river estuaries.

• It helps to grow mangrove at the coast. e.g. Largest mangrove forest of India at West Bengal coast.

• Tides are used to generate electricity power. e.g. in Canada, France... in India (in West Bengal, Kerala, Tamil Nadu...).

Mains based Questions :

1. How are tides caused and impact on navigation ?

2. What are the benefits and challenges of tides ?

Also Read : Oceans Topography

References

E-book

NCERT