INTRODUCTION

When there is a gravitational pull of celestial bodies on the planet, the ocean leads to the formation of something called tides. It is, essentially, the recurrent ascent and fall of the ocean level, which happens principally because of the force of attraction between the sun and the moon. The topic of tides is a fundamental topic in the subject of Geography and this article will help understand what causes tides, the different types of tides, and their characteristics.

WHAT CAUSES TIDES?

Tides occur due to the regular ascent and fall of the ocean level, which happens principally because of the force of attraction between the sun and the moon. The movement of the water is caused by meteorological effects like the winds, atmospheric pressure, which is also known as surges. Three important forces cause the occurrence of tides: The Moon’s gravitational pull, the sun’s gravitational pull, and the centrifugal force which acts as the opposite to the gravitational pull of the Earth.

Tides occur due to an imbalance between the forces acting on the water at any point in time. The tide generating force is the difference between the gravitational attraction due to the mass of the moon and the centrifugal force that occurs due to the rotation of the earth. When these two forces are not balanced, then it gives rise to a tide-generating force. The side of the earth that is closest to the moon has the strongest attraction towards the moon, while the water on the other side of the earth has a weaker gravitational force.

The reason that the moon’s gravitational force is higher than the sun’s gravitational force is because of the distance between the two.

WHAT ARE THE DIFFERENT CATEGORIES OF TIDES?

The types of tides can be grouped according to the frequency, direction, and movement from place to place and time to time.

Based on frequency, tides are classified into:

• Semi-diurnal tides – This is considered to be the most common tidal pattern that features two high tides and two low tides each day. Both the high and low tides are of the same height. The interval of the low and high tides is 12 hours and 25 minutes. These tides occur in areas of the Bay of Bengal and the Eastern African Coast
• Diurnal tide – In this classification, there is only one high tide and one low tide each day and the heights of both are approximately the same
• Mixed tide – The tides that have variations in their heights are known as mixed tides. These types of tides usually occur on the west coast of North America and the islands of the Pacific Ocean

Based on the position of the sun, moon, and earth, there is:

• Spring tides – When the position of the sun, earth, and moon are aligned in a way that it forms a straight line, then the height of the tide is higher than normal. This is called a spring tide. These tides occur twice a month, once during the full moon and the other during the new moon. These tides are also known as ‘King Tide’
• Neap tides – seven days after the spring tides occur, the sun and the moon form a 90-degree angle between each other, and this results in a gravitational force that gives rise to a very low magnitude tide which is called the neap tide. This also occurs twice a month

Based on the magnitude, there is:

Once a month, when the orbit of the moon is closest to the sun, there is the unusual occurrence of high and low tides. This is known as perigee. The tidal range during this time is greater than normal.

Two weeks after this, the distance between the moon and the Earth is largest. Due to this the force of gravitation present between the moon and Earth is limited. Further, the range of the tides becomes smaller than their average heights. This phenomenon is known as apogee.

When the earth is closest to the sun (around 3rd January), there is an unusual occurrence of low and high tides. This is called Perihelion.

When the position of the earth is farthest from the sun, (around 4th July), the tidal ranges are less than average during this period. This is called Aphelion.

The time between high and low tide:

• The time between high and low tide when the water is falling is called the ebb
• The time between the high and low tide when the water is rising is called the flow

IMPORTANCE OF TIDES

• Tides are very useful in navigation. When there are high tides, the large ships can enter the harbor safely
• Tides are also very useful in helping ships travel the mouth of the river in the case of river ports. The high tides increase the volumes of water so that the large ships can pass safely
• Tides help in removing silts. The rivers carry down a lot of soil and sand and the tides help in washing away these deposits by keeping the mouth of the river clear
• Tides also help bring in huge amounts of fish and these areas serve as fishing zones for fishermen
• There are edible sea creatures like crabs, snails, seaweed, etc. that inhabit a tidal zone. Without the regular washing of tides, these abundant creatures would be found nowhere, and food resources would diminish
• Tidal energy is highly used as a source of producing electricity and is also considered to be a renewable source of energy