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Waves and Tides – UPSC Geography Notes
Overview: Waves and tides are important movements of ocean water that influence coastal landscapes, navigation, fisheries, and climate. Understanding them is essential for UPSC Physical Geography and Oceanography.
Table of Contents
- 1. Introduction
- 2. Waves – Meaning and Characteristics
- 3. Types of Waves
- 4. Causes of Waves
- 5. Effects of Waves
- 6. What are Tides?
- 7. Causes of Tides
- 8. Types of Tides
- 9. Tidal Cycles
- 10. Importance of Tides
- 11. UPSC Quick Revision Notes
- 12. Previous Year Question
1. Introduction
Waves and tides are natural movements of ocean water caused by wind and gravitational forces. They shape coastlines, influence marine life, and affect human activities like fishing, shipping, and coastal development.
2. Waves – Meaning and Characteristics
Waves are oscillatory movements of water on the ocean surface. They transfer energy, not water, horizontally.
Key Characteristics of Waves
- Crest: Highest point of the wave.
- Trough: Lowest point of the wave.
- Wave Height: Vertical distance between crest and trough.
- Wavelength: Horizontal distance between two crests or troughs.
- Wave Period: Time taken for two crests to pass a point.
- Wave Velocity: Distance traveled per unit time.
3. Types of Waves
- Sea Waves: Generated by local winds.
- Swell Waves: Long-distance waves formed by storms and cyclones.
- Tsunami: Seismic waves caused by earthquakes, volcanic eruptions, or landslides.
- Tidal Waves: Misleading term; actually large tides caused by gravitational forces, not by earthquakes.
4. Causes of Waves
- Wind: Main cause of surface waves.
- Earthquakes: Cause tsunamis.
- Earth’s rotation: Impacts wave direction.
- Gravitational pull: Affects tidal waves.
5. Effects of Waves
- Cause coastal erosion and deposition.
- Form landforms like beaches, cliffs, and sandbars.
- Help in sediment transport.
- Influence navigation and fishing.
6. What are Tides?
Tides are periodic rise and fall of sea level caused by the gravitational forces of the Moon and Sun, along with Earth’s rotation.
- High Tide → Sea level rises
- Low Tide → Sea level falls
7. Causes of Tides
(A) Gravitational Pull
- Moon: Main cause (closer to Earth → stronger pull).
- Sun: Less influence but important during syzygy (alignment).
(B) Centrifugal Force
- Caused by Earth-Moon system’s rotation.
- Creates a bulge of water on the opposite side of Earth.
(C) Positions of Moon and Sun
- New Moon & Full Moon → strong tides.
- Quarter Moon → weak tides.
8. Types of Tides
(A) Based on Frequency
- Semidiurnal Tides: Two high & two low tides per day (most common).
- Diurnal Tides: One high & one low tide per day.
- Mixed Tides: Different heights of high and low tides.
(B) Based on Sun-Moon Alignment
1. Spring Tides
- Occur during New Moon and Full Moon.
- Moon + Sun align → higher gravitational force.
- Highest high tides & lowest low tides.
2. Neap Tides
- Occur during First Quarter & Last Quarter Moon.
- Moon & Sun at right angles.
- Lowest tidal range.
(C) Based on Water Movement
- Flood Tide: Rising tide.
- Ebb Tide: Falling tide.
9. Tidal Cycles
- Lunar Day: 24 hours 50 minutes.
- Tides follow the movement of the Moon.
- High tide occurs roughly every 12 hours 25 minutes.
10. Importance of Tides
- Navigation: Ships navigate safely using high tides.
- Fishing: Tides influence fish movement.
- Tidal Energy: A renewable energy source.
- Coastal Geomorphology: Forms tidal flats, mudflats, and estuaries.
- Marine Life: Nutrient mixing boosts productivity.
11. UPSC Quick Revision Notes
Tides → rise and fall of sea level due to Moon & Sun.
Spring Tide → highest tidal range (New + Full Moon).
Neap Tide → lowest tidal range (Quarter Moons).
Semidiurnal = most common tidal pattern.
Tsunami = seismic wave, not a tide.
Tides help navigation, fishing & energy generation.
Gravitational pull + centrifugal force → two tidal bulges.
12. Previous Year Question
Q. Spring tides occur when:
(a) Earth, Moon, and Sun form a right angle
(b) Earth is farthest from the Sun
(c) Earth, Moon, and Sun are in a straight line
(d) Moon is in its first quarter
Answer: (c) Earth, Moon, and Sun are in a straight line
Related Keywords
Waves and Tides UPSC Notes, Ocean Movements, Spring Tide, Neap Tide, Semidiurnal Tide, Oceanography UPSC, Physical Geography Notes.
Sources: NCERT Class XI – Fundamentals of Physical Geography, NOAA Ocean Data (Simplified for UPSC), Goh Cheng Leong.
Next Topic → Marine Resources and Ocean Exploration – UPSC Geography Notes
