The periodic short term rise and fall in the sea level is known as Tide. It is produced due to the gravitational interaction of earth, sun, and moon. The main two types of Tides: Spring and Neap
- It is caused by the combined effects of :
- The gravitational force exerted on Earth by the Sun
- The gravitational force exerted on Earth by the Moon
- Rotation of the Earth
Types of Tides
Based on Frequency
Semi-Diurnal Tides
- Each day, a semi-diurnal tidal cycle has two almost equal high tides and two low tides.
- The time between high and low tides is around 12 hours and 25 minutes.
- The Indian Ocean is home to the most Semi-Diurnal Tides.
- The following are some of the most common coasts where semidiurnal tides occur: Eastern African Coast and Bay of Bengal.
Diurnal tide
- There is only one high tide and one low tide during each day. The successive high and low tides are approximately of the same height.
Tides based on the Sun, Moon and the Earth Positions
The height of rising water (high tide) varies appreciably depending upon the position of the sun and moon with respect to the earth. Spring tides and neap tides come under this category.
Spring Tides
- When the sun and the moon are in alignment, spring tides form, pulling the water surface in the same direction.
- A spring tide occurs when high tides are higher and low tides are lower as a result of this. It happens twice in a lunar month.
- The term ‘King Tide‘ has also been given to it.
Neap Tides
- Seven days following the spring tide, it occurs.
- The fact that the sun and the moon are at a right angle to each other is the most noticeable feature.
- The first and last quarters of the moon are when this tide happens.
- The moon’s gravitational pull and accompanying oceanic bulge are canceled out by the sun’s gravitational pull and resulting oceanic bulge.
- In addition, in neap tides, the high tides are ‘lower’ and the low tides are ‘higher’ than in spring tides.
Importance of Tides
- Since tides are caused by the earth-moon-sun positions which are known accurately, the tides can be predicted well in advance. This helps the navigators and fishermen plan their activities.
1. Navigation
2. Fishing
3. Desilting
Characteristics of Tides
- The tidal bulges on wide continental shelves have greater heights.
- In the open ocean, tidal currents are relatively weak.
- When tidal bulges hit the mid-oceanic islands they become low.
- The shape of bays and estuaries along a coastline can also magnify the intensity of tides.
- Funnel-shaped bays greatly change tidal magnitudes.
- Example: the Bay of Fundy –– Highest tidal range.
- The large continents on the planet, however, block the westward passage of the tidal bulges as the Earth rotates.
- Tidal patterns differ greatly from ocean to ocean and from location to location.
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