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Movements of Ocean Water

NCERT Class 11 · Geography Based on NCERT Class 11 Geography textbook · Free CBSE study kit

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Chapter Notes

Overview
This chapter explains the dynamic nature of ocean water, focusing on three main movements: waves, tides, and ocean currents. It exists in the syllabus to help students understand how physical characteristics like temperature, salinity, and density, along with external forces like the sun, moon, and wind, drive these movements. The one big idea a student must walk away with is that ocean water is in constant motion—horizontally as waves and currents, and vertically as tides—and these movements are governed by predictable forces and have significant impacts on climate, navigation, and human activities.
Key Concepts (29)
Ocean currents
The continuous flow of huge amount of water in a definite direction.
e.g. The Gulf Stream is a warm ocean current that flows from the Gulf of Mexico across the Atlantic Ocean.
Waves
The horizontal motion of water; actually the energy, not the water as such, which moves across the ocean surface.
e.g. When wind blows over a calm sea, ripples form and grow into waves that travel towards the shore.
Tides
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.
e.g. High tide at Mumbai's coastline occurs twice daily, allowing ships to enter the harbour.
Wave crest
The highest point of a wave.
e.g. The top of a breaking wave at a beach is its crest.
Wave trough
The lowest point of a wave.
e.g. The dip between two successive wave crests is the trough.
Wave height
The vertical distance from the bottom of a trough to the top of a crest of a wave.
e.g. A wave with a crest 3 metres above the trough has a wave height of 3 metres.
Wave amplitude
One-half of the wave height.
e.g. If wave height is 4 metres, the amplitude is 2 metres.
Wave period
The time interval between two successive wave crests or troughs as they pass a fixed point.
e.g. If 10 seconds pass between two crests, the wave period is 10 seconds.
Wavelength
The horizontal distance between two successive crests.
e.g. The distance from one crest to the next crest is the wavelength.
Wave speed
The rate at which the wave moves through the water, measured in knots.
e.g. A wave moving at 20 knots travels 20 nautical miles per hour.
Wave frequency
The number of waves passing a given point during a one-second time interval.
e.g. If 5 waves pass a point in one second, the frequency is 5 Hz.
Surges
Movement of water caused by meteorological effects (winds and atmospheric pressure changes).
e.g. A storm surge during a cyclone can raise sea levels dramatically along the coast.
Semi-diurnal tide
The most common tidal pattern, featuring two high tides and two low tides each day, with successive high or low tides approximately of the same height.
e.g. Most Indian coasts experience semi-diurnal tides.
Diurnal tide
There is only one high tide and one low tide during each day, with successive high and low tides approximately of the same height.
e.g. Some parts of the Gulf of Mexico experience diurnal tides.
Mixed tide
Tides having variations in height are known as mixed tides.
e.g. The west coast of North America and many islands of the Pacific Ocean have mixed tides.
Spring tides
When the sun, the moon and the earth are in a straight line, the height of the tide will be higher; they occur twice a month, one on full moon period and another during new moon period.
e.g. During a full moon, spring tides cause higher high tides and lower low tides.
Neap tides
When the sun and moon are at right angles to each other, the forces of the sun and moon tend to counteract one another, resulting in lower tidal ranges.
e.g. Seven days after a spring tide, neap tides occur with minimal tidal variation.
Perigee
The point when the moon's orbit is closest to the earth, causing unusually high and low tides.
e.g. When the moon is at perigee, tidal ranges are greater than normal.
Apogee
The point when the moon is farthest from earth, causing tidal ranges less than their average heights.
e.g. Two weeks after perigee, the moon at apogee results in smaller tides.
Perihelion
When the earth is closest to the sun, around 3rd January each year, tidal ranges are much greater.
e.g. In early January, unusually high and low tides occur due to perihelion.
Aphelion
When the earth is farthest from the sun, around 4th July each year, tidal ranges are much less than average.
e.g. In July, tidal ranges are smaller due to aphelion.
Ebb
The time between the high tide and low tide, when the water level is falling.
e.g. Fishermen plan their return during ebb to avoid strong currents.
Flow or flood
The time between the low tide and high tide, when the tide is rising.
e.g. During flow, water enters estuaries and rivers.
Gyres
Large accumulations of water and the flow around them, producing large circular currents in all the ocean basins.
e.g. The North Atlantic Gyre includes the Gulf Stream and the Canary Current.
Drift
The speed of a current, measured in knots.
e.g. A current with a drift of 3 knots moves at 3 nautical miles per hour.
Surface currents
Constitute about 10 per cent of all the water in the ocean, these waters are the upper 400 m of the ocean.
e.g. The Kuroshio Current is a surface current in the Pacific Ocean.
Deep water currents
Make up the other 90 per cent of the ocean water, moving around the ocean basins due to variations in the density and gravity.
e.g. Cold, dense water sinks at high latitudes and flows slowly towards the equator.
Cold currents
Bring cold water into warm water areas; usually found on the west coast of the continents in the low and middle latitudes and on the east coast in the higher latitudes in the Northern Hemisphere.
e.g. The California Current is a cold current along the west coast of North America.
Warm currents
Bring warm water into cold water areas; usually observed on the east coast of continents in the low and middle latitudes.
e.g. The Gulf Stream is a warm current along the east coast of North America.
How It Works
Wave Formation and Movement
  1. Wind blows across the ocean surface, transferring energy to the water.
  2. When a breeze of two knots or less blows over calm water, small ripples form.
  3. As wind speed increases, ripples grow into waves and white caps appear in breaking waves.
  4. Wind pushes the water body forward while gravity pulls the crests downward.
  5. The falling water pushes the former troughs upward, and the wave moves to a new position.
  6. The actual motion of water beneath the waves is circular: things are carried up and forward as the wave approaches, and down and back as it passes.
  7. As a wave approaches the beach, friction with the sea floor slows it down.
  8. When the depth of water is less than half the wavelength, the wave breaks.
💡 Students often think water moves horizontally with the wave, but water particles only travel in a small circle; it is the energy that moves forward, not the water itself.
Tide Generation (Gravitational and Centrifugal Forces)
  1. The moon's gravitational pull attracts the ocean water on the side of the earth facing the moon, creating a tidal bulge.
  2. On the opposite side of the earth, the gravitational attraction of the moon is weaker because it is farther away.
  3. The centrifugal force, which counterbalances gravity, becomes dominant on the far side, creating a second tidal bulge away from the moon.
  4. The 'tide-generating' force is the difference between gravitational attraction and centrifugal force.
  5. On the surface nearest the moon, the net force causes a bulge towards the moon.
  6. On the opposite side, the net force is away from the moon, creating the second bulge.
  7. Horizontal tide-generating forces are more important than vertical forces in generating the tidal bulges.
💡 Students often forget the centrifugal force and think only the moon's gravity causes tides. Both bulges—towards and away from the moon—are equally important.
Spring and Neap Tides Formation
  1. Spring tides occur when the sun, the moon, and the earth are in a straight line (syzygy).
  2. The gravitational pulls of the sun and moon combine, resulting in higher high tides and lower low tides.
  3. Spring tides occur twice a month: during full moon and new moon.
  4. Neap tides occur when the sun and moon are at right angles to each other (quadrature).
  5. The forces of the sun and moon tend to counteract one another.
  6. The moon's attraction, though more than twice as strong as the sun's, is diminished by the counteracting force of the sun's gravitational pull.
  7. Neap tides have lower tidal ranges than average.
💡 Students often confuse spring tides with the season 'spring'. Spring tides occur all year round, not just in spring. Also, neap tides occur seven days after spring tides.
Ocean Current Formation and Circulation
  1. Primary forces initiate the movement of water: heating by solar energy, wind, gravity, and Coriolis force.
  2. Heating by solar energy causes water to expand; near the equator, ocean water is about 8 cm higher than in middle latitudes, creating a slight gradient.
  3. Wind blowing on the surface pushes the water to move; friction between wind and water surface affects movement.
  4. Gravity pulls water down the pile, creating gradient variation.
  5. The Coriolis force causes water to move to the right in the northern hemisphere and to the left in the southern hemisphere.
  6. These forces create large accumulations of water and flow around them called Gyres.
  7. Differences in water density affect vertical mobility: denser water (cold, high salinity) sinks, lighter water (warm, low salinity) rises.
  8. Cold-water currents occur when cold water at the poles sinks and slowly moves towards the equator.
  9. Warm-water currents travel from the equator along the surface, flowing towards the poles to replace sinking cold water.
💡 Students often forget that the Coriolis force is a primary force that influences the direction of currents, not just wind. Also, the 8 cm height difference at the equator is a specific fact often tested.
Wave Breaking Mechanism
  1. As a wave approaches the beach, it slows down due to friction between the dynamic water and the sea floor.
  2. The wave's speed decreases as the water becomes shallower.
  3. When the depth of water is less than half the wavelength of the wave, the wave breaks.
  4. The crest outruns the trough, causing the wave to collapse and release energy as surf.
💡 The condition for wave breaking is depth < half the wavelength. Students often miss the 'half' condition and write 'depth equals wavelength'.
Exam Traps — Don't Make These Mistakes
⚠ Confusing wave motion with water movement
✗ In waves, water moves forward from one place to another.
→ The chapter clearly states that water in waves does not move; the wave trains move ahead. Water particles only travel in a small circle.
✓ In waves, it is the energy that moves across the ocean surface, not the water itself. Water particles move in a circular motion, returning to their original position.
⚠ Attributing tides only to the moon's gravity
✗ Tides are caused only by the gravitational pull of the moon.
→ The chapter states that both the moon's gravitational pull (to a great extent) and the sun's gravitational pull (to a lesser extent) are major causes. Additionally, centrifugal force is equally important in creating the second tidal bulge.
✓ Tides are caused by the combined gravitational pulls of the moon and the sun, along with the centrifugal force that counterbalances gravity. Together, these create two tidal bulges on Earth.
⚠ Mixing up spring tides and neap tides
✗ Spring tides occur only in spring season, and neap tides occur in autumn.
→ Spring tides are named after the concept of 'springing forth' and occur twice a month (full moon and new moon) throughout the year, not just in spring. Neap tides occur seven days after spring tides, regardless of season.
✓ Spring tides occur when the sun, moon, and earth are in a straight line, happening during full moon and new moon. Neap tides occur when the sun and moon are at right angles, happening seven days after spring tides.
⚠ Confusing perigee/apogee with perihelion/aphelion
✗ Perigee is when the earth is closest to the sun.
→ Perigee refers to the moon's orbit being closest to the earth, while perihelion refers to the earth being closest to the sun. Students often swap these terms.
✓ Perigee is when the moon is closest to the earth (causing greater tidal ranges). Perihelion is when the earth is closest to the sun (around 3rd January, also causing greater tidal ranges).
⚠ Misidentifying the location of cold and warm currents
✗ Cold currents are found on the east coast of continents in low latitudes.
→ The chapter states that cold currents are usually found on the west coast of continents in low and middle latitudes, and on the east coast in higher latitudes in the Northern Hemisphere. Warm currents are on the east coast in low and middle latitudes.
✓ Cold currents are typically found on the west coast of continents in low and middle latitudes (e.g., California Current). Warm currents are typically found on the east coast of continents in low and middle latitudes (e.g., Gulf Stream).
⚠ Thinking waves and ocean currents are the same
✗ Waves and ocean currents both involve the horizontal movement of water from one place to another.
→ The chapter distinguishes clearly: in ocean currents, water moves ahead from one place to another. In waves, the water does not move; only the wave trains move ahead.
✓ Ocean currents involve the continuous flow of huge amounts of water in a definite direction. Waves involve the movement of energy across the water surface, with water particles only moving in a circular path.
Compare & Contrast
Position of sun, moon, and earth
Spring tides
Neap tides
Spring tides occur when the sun, moon, and earth are in a straight line (syzygy), resulting in higher tidal ranges. Neap tides occur when the sun and moon are at right angles (quadrature), resulting in lower tidal ranges.
Movement of water
Waves
Ocean currents
In waves, water does not move forward; only energy moves. In ocean currents, water moves ahead continuously from one place to another in a definite direction.
Temperature and location
Cold currents
Warm currents
Cold currents bring cold water into warm areas and are usually found on the west coast of continents in low and middle latitudes. Warm currents bring warm water into cold areas and are usually found on the east coast of continents in low and middle latitudes.
Moon's distance from Earth
Perigee
Apogee
Perigee is when the moon is closest to Earth, causing unusually high and low tides. Apogee is when the moon is farthest from Earth, causing tidal ranges less than average.
Exam Focus
Marks pattern: 2 MCQs (1 mark each), 1 SA of 30 words (3 marks), 1 LA of 150 words (5 marks). Total approximately 10 marks.
Most asked: Types of tides (semi-diurnal, diurnal, mixed, spring, neap) · Causes of tides (gravitational pull of moon and sun, centrifugal force) · Differences between waves and ocean currents · Classification of ocean currents (cold vs warm, surface vs deep) · Effects of ocean currents on climate and fishing grounds · Perigee, apogee, perihelion, aphelion and their effects on tides
Don't skip: Explain the causes of tides with a diagram showing gravitational and centrifugal forces.; Differentiate between spring tides and neap tides.; How do ocean currents affect the temperature of coastal areas? Give examples.; Describe the characteristics and types of waves.
One-Line Revision (read aloud before the exam)
  1. Waves are energy moving across the ocean surface; water particles only move in a circle, not forward.
  2. Wind provides energy to waves; wave size depends on wind strength, duration, and fetch.
  3. A wave breaks when the water depth is less than half its wavelength.
  4. Tides are the periodic rise and fall of sea level caused mainly by the gravitational pull of the moon and sun.
  5. The moon's gravitational pull and centrifugal force together create two tidal bulges on Earth.
  6. Spring tides occur during full moon and new moon when the sun, moon, and earth are aligned.
  7. Neap tides occur when the sun and moon are at right angles, seven days after spring tides.
  8. Perigee (moon closest to Earth) and perihelion (Earth closest to sun) cause greater tidal ranges.
  9. Apogee (moon farthest from Earth) and aphelion (Earth farthest from sun) cause smaller tidal ranges.
  10. Ocean currents are continuous flows of water in a definite direction, unlike waves.
  11. Surface currents make up 10% of ocean water (upper 400 m); deep water currents make up 90%.
  12. Cold currents are found on west coasts in low/middle latitudes; warm currents on east coasts.
  13. The Coriolis force deflects currents to the right in the Northern Hemisphere and left in the Southern Hemisphere.
  14. Mixing of warm and cold currents creates ideal fishing grounds by replenishing oxygen and plankton.
  15. Tides help in navigation, desilting sediments, removing pollution, and generating electricity.
  16. The Bay of Fundy in Canada has the highest tides in the world, up to 15-16 metres.

MCQs — 10 Questions with Answers

Q1. What is the primary source of energy that creates waves in the ocean?

  • A. Wind blowing over water surface ✓
  • B. The moon's gravitational pull
  • C. The sun's heat warming the water
  • D. Underwater earthquakes and volcanic activity

Answer: A — Wind provides the energy that creates waves; the moon and sun drive tides, not waves.

Q2. Which statement correctly describes the motion of water particles in a wave?

  • A. Water particles move forward horizontally with the wave
  • B. Water particles move only in small circles as the wave passes ✓
  • C. Water particles sink deeper into the ocean as the wave travels
  • D. Water particles move upward and outward in straight lines

Answer: B — Water particles follow circular motion; only the wave energy moves horizontally across the ocean.

Q3. A wave will break when entering shallow water because:

  • A. The wind stops pushing the wave
  • B. Water depth becomes less than half the wavelength ✓
  • C. The moon's gravitational pull weakens near the shore
  • D. Friction with the seafloor causes the wave to stop completely

Answer: B — Wave breaking occurs specifically when depth < half wavelength; this is a geometric wave property unrelated to wind, gravity, or complete friction.

Q4. What is the relationship between wave height and wave amplitude?

  • A. Wave amplitude is double the wave height
  • B. Wave amplitude is exactly equal to wave height
  • C. Wave amplitude is half the wave height ✓
  • D. Wave amplitude and height are unrelated measurements

Answer: C — Amplitude is defined as exactly half of wave height; this is a direct mathematical relationship.

Q5. Which of the following is NOT a correct statement about tides? (A) The moon causes tides primarily through gravitational attraction (B) Spring tides occur when the sun, moon, and Earth are in a straight line (C) Neap tides have greater height than spring tides (D) Tidal bulges occur on two opposite sides of Earth simultaneously

  • A. Spring tides occur only during the full moon
  • B. Neap tides have greater height than spring tides
  • C. The sun's gravitational pull is stronger than the moon's on tides
  • D. Diurnal tides have two high tides and two low tides per day ✓

Answer: D — Diurnal tides have only one high and one low tide per day; semi-diurnal tides have two of each, making this a common misconception.

Q6. Spring tides occur approximately twice per month because:

  • A. The sun and moon are always closest to Earth during spring season
  • B. The sun, moon, and Earth align once during a full moon and once during a new moon ✓
  • C. The ocean water temperature increases twice monthly
  • D. Wind patterns over oceans change with lunar phases

Answer: B — Spring tides result from alignment of sun, moon, and Earth during full moon and new moon phases, which occur twice monthly.

Q7. At neap tide, the sun and moon are positioned at approximately:

  • A. 0° (straight line with Earth)
  • B. 45° angle to each other
  • C. 90° angle to each other ✓
  • D. 180° angle to each other

Answer: C — Neap tides occur when sun and moon are at right angles (90°) to each other, causing their gravitational forces to partially counteract.

Q8. Which of the following is true about the Bay of Fundy in Canada? (A) It has the smallest tides in the world (B) Its funnel shape magnifies tidal height to 15-16 metres (C) It experiences only diurnal tides (D) Tides rise at a constant slow rate throughout the day

  • A. It has the smallest tides in the world
  • B. Its funnel-shaped geography magnifies tidal bulges to 15-16 metres ✓
  • C. It experiences only diurnal tides with no variation
  • D. Tides rise slowly and evenly without rapid water movement

Answer: B — The Bay of Fundy's funnel shape channels tidal water into increasingly narrow space, magnifying tides to 15-16 metres—the world's highest.

Q9. Why do slow, steady waves travelling across the ocean differ from steep, white-capped waves? (HOTS - multi-step reasoning)

  • A. Slow waves are formed by strong local winds; steep waves come from far away
  • B. Slow waves are old, formed far away; steep waves are young, formed by local winds ✓
  • C. Slow waves occur in deep water only; steep waves occur only near shores
  • D. Slow waves have greater wavelength but move faster than steep waves

Answer: B — Wave steepness reveals age and origin: steep waves are young with local wind origin; slow, steady waves travel thousands of kilometres from distant origins, transferring energy over long distances.

Q10. The tide-generating force is created by the difference between which two forces? (Assertion + Reasoning)

  • A. Wind pressure and water density
  • B. Moon's gravitational pull and Earth's centrifugal force ✓
  • C. Sun's radiation and moon's orbital velocity
  • D. Ocean current speed and atmospheric pressure

Answer: B — Tide-generating force = moon's gravitational attraction minus centrifugal force; this net force creates the tidal bulges on opposite sides of Earth.

Flashcards

What is the main source of energy for waves in the ocean?

Wind provides energy to create and move waves across the ocean surface.

Define wave height and wave amplitude.

Wave height is the vertical distance from trough to crest; amplitude is exactly half the wave height.

Do water particles in a wave move forward with the wave?

No, water particles move only in small circles as the wave passes; only energy moves forward.

What causes tides on Earth?

The moon's gravitational pull and centrifugal force, combined with the sun's lesser gravitational contribution, create tidal bulges.

Explain the term 'tide-generating force'.

Tide-generating force is the net difference between the moon's gravitational attraction and the centrifugal force acting on Earth's surface.

What is the difference between spring tides and neap tides?

Spring tides occur when sun, moon, and Earth align, producing higher tides; neap tides occur when sun and moon are at right angles, producing lower tides.

Why is the wavelength important in predicting when a wave will break?

A wave breaks when the water depth becomes less than half the wavelength of the wave.

Name three types of tides based on frequency.

Semi-diurnal (two high and two low tides daily), diurnal (one high and one low tide daily), and mixed tides (varying heights).

How do funnel-shaped bays affect tidal bulges?

Funnel-shaped bays greatly magnify tidal intensity and height by channelling tidal water into increasingly narrow spaces.

What physical characteristic determines whether a wave is young or old?

Steep waves are young and formed by local winds; slow, steady waves are old and originate from distant places.

Important Board Questions

Define waves and explain why water particles do not actually move forward as waves travel across the ocean. [2 marks]

State that waves are energy (not water) moving across the surface. Explain that water particles move only in circular motion as the wave passes over them; the wave energy propagates horizontally while particles return to their original positions.

Explain the formation of two tidal bulges on opposite sides of Earth with reference to gravitational pull and centrifugal force. Why is the tide-generating force important in creating tides? [5 marks]

On the moon-facing side, the moon's gravitational pull exceeds centrifugal force, creating a bulge toward the moon. On the opposite side, the centrifugal force dominates over weakened gravitational pull, creating a bulge away from the moon. The tide-generating force is the net difference between these two forces, and it acts horizontally on Earth's surface to create and sustain tidal bulges.

Compare spring tides and neap tides in terms of their occurrence, height, and the positions of the sun, moon, and Earth. Use a diagram to illustrate both types and explain why the Bay of Fundy experiences exceptionally high tides. (6 marks - HOTS) [6 marks]

Spring tides: sun-moon-Earth aligned (new moon or full moon), maximum tidal height, occur twice monthly. Neap tides: sun-moon at 90° (first or last quarter), minimum height, occur between spring tides. Draw both configurations showing aligned vs. perpendicular positions. Bay of Fundy: funnel-shaped geography funnels tidal water into narrowing space, magnifying height to 15-16 metres—geography amplifies the natural tidal force. Connect continental shelf width, bay shape, and island positions as geographic factors.

Assertion-Reason Questions for Movements of Ocean Water

Q1. Assertion (A):

Ocean waves are energy moving through water, not the water itself moving forward in the wave's direction.

Reason (R):

Water particles perform circular motion as waves pass, moving up and forward with the crest, then down and backward, while the wave energy continues forward.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both statements are true and the reason correctly explains why waves are energy transfer: water particles don't translate with the wave; they circle in place while the energy propagates forward. This directly supports the assertion about the nature of waves.

Q2. Assertion (A):

The Bay of Fundy experiences the world's highest tides with a tidal bulge of 15-16 meters.

Reason (R):

The bay's funnel shape channels and concentrates tidal currents, greatly magnifying the tidal bulge height.

Answer: A — Both A and R are true, and R is the correct explanation of A — Both the assertion and reason are true. The reason correctly explains why Bay of Fundy has such extreme tides—the funnel geometry concentrates water flow and tidal forces, magnifying tidal height beyond what geography alone would predict.

Q3. Assertion (A):

Neap tides occur when the sun and moon are at right angles to each other relative to Earth.

Reason (R):

The gravitational forces of the sun and moon cancel each other out during this configuration, resulting in minimum tidal height.

Answer: B — Both A and R are true, but R is NOT the correct explanation of A — Both statements are true, but the reason only partially explains the assertion. Neap tides occur at right angles, but it's more accurate to say the forces counteract rather than cancel. The forces don't fully cancel; they reduce the combined effect, not eliminate it. The assertion is correct; the reasoning is oversimplified.

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Case-Based Questions (CBQ) for Movements of Ocean Water

Case Study:

A maritime research team conducted a study on wave characteristics off the coast of Gujarat. On Day 1, they recorded waves with steep profiles and wavelengths of 50 meters, traveling at 15 knots. These waves caused significant energy release on the nearby coastline within 6 hours. On Day 2, a system of gentle waves with wavelengths of 200 meters and low amplitudes arrived, traveling at 20 knots, but despite higher speed, they produced minimal coastal impact. The team determined that the Day 1 waves originated from a local cyclonic disturbance, while Day 2 waves came from a distant storm system in the Indian Ocean, over 2,000 kilometers away.

Q1. What primary inference can be made about the relationship between wave steepness and origin location based on the research findings?

  • A. Steeper waves always travel faster and cause more coastal damage
  • B. Steep waves indicate local origin, while gentle waves suggest distant origin ✓
  • C. Wave steepness is determined solely by wind speed, not travel distance
  • D. Waves become steeper as they travel greater distances over the ocean

Answer: B

Q2. Why would the Day 1 waves, despite their slower speed (15 knots vs. 20 knots), have greater impact on the coastline than Day 2 waves?

  • A. Steep waves contain more energy and release it more violently upon breaking ✓
  • B. Local waves are always destructive regardless of their characteristics
  • C. Wave speed determines coastal impact, not wave form
  • D. Day 1 waves were created by a more powerful storm system

Answer: A

Q3. If the Day 2 waves traveled 2,000 kilometers in 100 hours, what can be said about the wind system that originally generated them?

  • A. The wind speed was approximately 20 knots when the waves formed
  • B. The distant wind system was stronger than the local Day 1 disturbance
  • C. The waves maintained their initial energy throughout the entire journey
  • D. The waves gradually lost their initial steepness due to energy dissipation over long distance ✓

Answer: D

Q4. Based on wave characteristics, which factor most likely explains why Day 2's gentle waves produced minimal coastal impact despite higher traveling speed?

  • A. Gentle waves have lower amplitude and contain less total energy ✓
  • B. Faster-moving waves automatically cause less coastal damage
  • C. Wave speed is inversely related to coastal impact potential
  • D. Distant-origin waves never cause significant coastal effects

Answer: A

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