Geography ( Tides cause and impact)

1. Introduction

Tides are the periodic rise and fall of ocean water levels caused mainly by the gravitational pull of the Moon and the Sun and the rotation of the Earth. They are among the most regular and predictable natural phenomena, significantly influencing coastal environments, navigation, and marine ecosystems.

Causes of Tides

1. Gravitational Attraction:
• The Moon’s gravitational pull is the primary cause of tides because it is much closer to Earth than the Sun.
• The Sun also exerts a gravitational force on Earth’s oceans, producing solar tides.
3. Centrifugal Force:
• As Earth and the Moon revolve around a common center of mass (the barycenter), the centrifugal force acts outward, balancing gravitational pull and creating bulges of water on opposite sides of Earth.
5. Earth’s Rotation:
• The rotation of Earth on its axis causes different parts of the planet to move through these tidal bulges, leading to two high tides and two low tides each day at most coastal locations.

Types of Tides

1. Based on Frequency:

• Semi-diurnal Tides:
• Two high tides and two low tides each day of almost equal height.
• Common along the Atlantic coasts (e.g., eastern coast of the USA, western Europe).
• Diurnal Tides:
• One high tide and one low tide per day.
• Seen in parts of the Gulf of Mexico and Southeast Asia.
• Mixed Tides:
• Two high and two low tides of unequal height per day.
• Common along the Pacific coast of North America.

2. Based on Sun–Moon–Earth Alignment:

• Spring Tides:
• Occur during full moon and new moon phases when the Sun, Moon, and Earth are in a straight line (syzygy).
• Gravitational forces combine, resulting in highest high tides and lowest low tides.
• Neap Tides:
• Occur during first and third quarters of the Moon when the Sun and Moon are at right angles to the Earth.
• Gravitational forces oppose each other, leading to lowest tidal range.

3. Based on Tidal Range:

• High Tide: When the sea level rises to its maximum.
• Low Tide: When the sea level falls to its minimum.
• Tidal Range: The vertical difference between high tide and low tide levels.

Theories Explaining Tides

1. Equilibrium Theory of Tides (Newton):
• Simplified model assuming a water-covered, non-rotating Earth.
• Explains how gravitational forces and centrifugal forces create two tidal bulges.
• Ideal for understanding basic causes but not actual complex patterns.
3. Dynamic Theory of Tides (Laplace):
• Considers Earth’s rotation, ocean basin shapes, and Coriolis force.
• Explains variations in tidal patterns and amphidromic systems (points with zero tidal amplitude).

Tidal Cycles

• Lunar Day: About 24 hours 50 minutes — the time the Moon takes to return to the same position relative to a point on Earth.
• Due to this, high and low tides occur roughly 50 minutes later each day.

Tidal Currents

• Horizontal movement of water associated with tides.
• Flood current: When water flows toward the coast (rising tide).
• Ebb current: When water flows away from the coast (falling tide).
• Slack water: The moment between ebb and flood when water is stationary.

Importance of Tides

1. Navigation:
• Ships enter and leave ports during high tides to avoid grounding.
3. Fishing:
• Many marine species follow tidal rhythms, aiding fishermen in planning.
5. Tidal Energy:
• Renewable source of power; e.g., La Rance (France), Gujarat and Sunderbans (India) sites proposed for tidal energy.
7. Coastal Erosion and Sediment Transport:
• Tides play a major role in shaping coastal landscapes.
9. Marine and Estuarine Ecology:
• Tidal action maintains nutrient flow and salinity balance in estuaries and mangroves.
11. Climatic Influence:
• Tidal mixing affects ocean circulation and local climate.

Conclusion

Tides are a vital natural phenomenon reflecting the interaction between celestial mechanics and Earth’s ocean systems. Understanding tides not only aids navigation, fishing, and energy generation but also helps in coastal management and climate studies. For UPSC, they are significant under Physical Geography (Oceanography) and questions often focus on their causes, types, and effects.