Movements of Ocean Water, Class 11 Geography: Waves, Tides and Currents

What Movements of Ocean Water is about

Weightage: This chapter is part of Unit V, Water (Oceans), of Fundamentals of Physical Geography, which carries 4 of the 70 theory marks in the school annual exam together with Water (Oceans). Map work carries a further 5 marks for each book.Source: CBSE Geography (029) syllabus 2026-27, Class XI course structure

Key concepts

Types of ocean water movement

NCERT section Movements of Ocean Water (introduction)

Influences: physical characteristics (temperature, salinity, density) and external forces (sun, moon, winds).

Motion	Form	Key point
Horizontal	Ocean currents	Continuous flow of huge amounts of water in a definite direction; water moves from place to place
Horizontal	Waves	Horizontal motion of water; the water does not move ahead, the wave trains do
Vertical	Tides	Rise and fall of water, twice a day, due to the sun and moon
Vertical	Upwelling and sinking	Cold subsurface water rises; surface water sinks

Worked example

A floating bottle at sea bobs up and down as waves pass but stays roughly in place; a week later it is found 200 km away. Explain both observations. (2 marks)

Try it first, then show the solutionSolution

1. Waves move energy, not water: water particles travel in small circles, so the bottle bobs and returns.
2. Its long journey is due to an ocean current, a continuous flow of water in a definite direction.

Answer: Waves made it bob; a current carried it away.

Waves and their characteristics

NCERT section Waves

Nature: waves are energy, not water, moving across the surface; particles move in a small circle (carried up and forward as the wave approaches, down and back as it passes; Figure 13.1).

Formation and behaviour:

• Wind supplies energy; it is released on shorelines. Surface motion seldom affects the stagnant deep water.
• A breeze of 2 knots or less over calm water makes ripples, which grow with wind speed until white caps appear.
• Waves can travel thousands of km before breaking as surf.
• The largest waves are in the open ocean; they keep growing as they absorb wind energy.
• Near the beach they slow down (friction with the sea floor) and break when depth is less than half the wavelength.
• Steep waves are young, probably from local wind; slow, steady waves come from far away, possibly another hemisphere.
• Maximum height depends on wind strength, duration and the area over which it blows in one direction.
• Waves travel because wind pushes the water while gravity pulls crests down; falling water pushes former troughs up.

Characteristics:

Term	Meaning
Crest / trough	Highest / lowest point
Wave height	Vertical distance from trough bottom to crest top
Amplitude	Half the wave height
Wave period	Time between two successive crests (or troughs) passing a fixed point
Wavelength	Horizontal distance between two successive crests
Wave speed	Rate of movement through water, in knots
Frequency	Number of waves passing a point in one second

Worked example

A wave has a height of 4.2 m and a wavelength of 60 m. Find its amplitude and the water depth at which it will break. (2 marks)

Try it first, then show the solutionSolution

1. Amplitude = height ÷ 2 = 4.2 ÷ 2 = 2.1 m.
2. A wave breaks when depth is less than half the wavelength: 60 ÷ 2 = 30 m, so it breaks in water shallower than 30 m.

Answer: Amplitude 2.1 m; breaks in depths below 30 m.

Tides and their causes

NCERT section Tides

Tide: sea level rises and falls periodically, once or twice daily, chiefly because the moon and sun attract the water. Surges are movements caused by meteorological effects (winds, pressure changes); they are not regular.

Causes (Figure 13.2):

• The moon's gravitational pull (mainly) and the sun's (less).
• Centrifugal force, which counterbalances gravity.
• Together they create two tidal bulges:
• On the side facing the moon, the moon's pull exceeds centrifugal force: net force towards the moon, a bulge.
• On the opposite side, the moon's pull is weaker (farther away), centrifugal force dominates: net force away from the moon, a second bulge.
• The tide-generating force is the difference between the moon's gravitational attraction and centrifugal force. Horizontal tide-generating forces matter more than vertical ones.

Effect of coast shape:

• Bulges are higher on wide continental shelves, low at mid-ocean islands.
• Bays and estuaries, especially funnel-shaped bays, magnify tides.
• Tides channelled between islands or into bays and estuaries are tidal currents.

Bay of Fundy (Nova Scotia, Canada): the highest tides in the world; bulge 15-16 m. With two highs and two lows a day, the tide comes in within about 6 hours: roughly 240 cm per hour (1,440 cm ÷ 6 h).

Worked example

The sun is far larger than the moon, yet the moon has the greater influence on the tides. Why? Name the tides produced when their pulls combine and when they act at right angles. (2 marks)

Try it first, then show the solutionSolution

1. Tides are caused to a great extent by the moon's gravitational pull and to a lesser extent by the sun's, because the moon is much closer to the earth.
2. When the sun, moon and earth are in a straight line the pulls combine to give spring tides; when sun and moon are at right angles they partly cancel, giving neap tides.

Answer: The much nearer moon dominates; aligned pulls give spring tides, pulls at right angles give neap tides.

Types of tides

NCERT section Tides

By frequency (per day):

Type	Pattern
Semi-diurnal	Most common: two high and two low tides daily; successive highs (or lows) about the same height
Diurnal	One high and one low daily; successive tides about the same height
Mixed	Tides with variations in height; west coast of North America and many Pacific islands

By sun-moon-earth positions:

• Spring tides: sun, moon and earth in a straight line; higher tides; twice a month, at full moon and new moon.
• Neap tides: about seven days after spring tides; sun and moon at right angles; their forces counteract. The moon's attraction (more than twice the sun's) is reduced by the sun's opposing pull.

Distance effects:

• Perigee (moon closest, once a month): unusually high and low tides, greater range; apogee (moon farthest, two weeks later): smaller range.
• Perihelion (earth closest to sun, around 3 January): much greater ranges; aphelion (around 4 July): much smaller ranges.

Ebb and flow: ebb = falling water, from high to low tide; flow or flood = rising water, from low to high tide.

Worked example

On which days of the lunar month are spring tides expected, and why are they higher? (2 marks)

Try it first, then show the solutionSolution

1. Spring tides occur twice a month, at full moon and new moon.
2. Then the sun, moon and earth lie in a straight line, so the pulls of the sun and moon combine, raising the tide higher.

Answer: At full and new moon, because the sun and moon pull in line.

Importance of tides

NCERT section Tides

• Predictable: earth-moon-sun positions are known accurately, so tides can be predicted well in advance; this helps navigators and fishermen plan.
• Navigation: tidal flows matter greatly; tidal heights are vital for harbours near rivers and in estuaries with shallow 'bars' at the entrance that block ships at low water.
• Desilting: tides help remove sediments and polluted water from river estuaries.
• Tidal power: electricity is generated from tides in Canada, France, Russia and China; in India, a 3 MW tidal power project is under way at Durgaduani (Sunderbans, West Bengal).

Worked example

A cargo ship heading for Kolkata port must cross shallow sandbars at the mouth of the Hooghly. How can the tide timetable help the captain, and what else do tides help with near such ports? (2 marks)

Try it first, then show the solutionSolution

1. Tides are predictable, so the captain can time the crossing for high tide, when the water over the bars is deep enough; harbours on rivers and estuaries with shallow bars can be entered only then.
2. Tidal flows also help to desilt the sediments and carry polluted water out of estuaries.

Answer: Plan to cross the bars at high tide; tides also flush silt and pollution from estuaries.

Ocean currents: causes and types

NCERT section Ocean Currents

Ocean currents are like rivers in the ocean: a regular volume of water in a definite path and direction.

Primary forces (initiate movement):
1. Solar heating: water expands; near the equator the sea is about 8 cm higher than in middle latitudes, giving a slight gradient down which water flows.
2. Wind: pushes surface water; friction between wind and water drives it.
3. Gravity: pulls water down the 'pile', creating gradients.
4. Coriolis force: deflects water right in the northern hemisphere, left in the southern. Large accumulations of water and the flow around them are gyres, producing large circular currents in all ocean basins.

Secondary forces influence how currents flow.

Density and vertical movement: saltier water and colder water are denser and sink; lighter water rises. Cold currents form as polar water sinks and moves slowly towards the equator; warm currents move from the equator along the surface towards the poles to replace it.

Types:

By depth	Share	Features
Surface currents	About 10% of ocean water	Upper 400 m
Deep water currents	About 90%	Move by density and gravity; sink at high latitudes where cold raises density

By temperature	Where
Cold	West coasts in low and middle latitudes (both hemispheres); east coasts in higher latitudes (northern hemisphere)
Warm	East coasts in low and middle latitudes (both hemispheres); west coasts in high latitudes (northern hemisphere)

Drift: the speed of a current; measured in knots. Currents are strongest at the surface (can exceed 5 knots); at depth usually below 0.5 knots; most are 5 knots or less.

Worked example

Why is sea level near the equator about 8 cm higher than in middle latitudes, and what does this cause? (2 marks)

Try it first, then show the solutionSolution

1. Solar heating makes equatorial water expand, raising its level.
2. This creates a very slight gradient, and water tends to flow down it, helping set currents in motion.

Answer: Heating expands the water; the slope makes water flow away from the equator.

Major ocean currents and their effects

NCERT section Ocean Currents

Pattern of major currents (Figure 13.3):

• Shaped by prevailing winds and the Coriolis force; roughly matches the atmospheric circulation.
• Middle latitudes: mainly anticyclonic circulation (more pronounced in the southern hemisphere); higher latitudes: cyclonic.
• In monsoon regions, monsoon winds influence currents.
• Warm currents from low latitudes turn right in the NH, left in the SH.
• Oceanic circulation transports heat between latitudes, like the atmosphere: cold polar water moves towards the tropics, warm water polewards.

Effects on human activities:

• West coasts in tropical and subtropical latitudes (except near the equator): bordered by cool waters; relatively low temperatures, narrow ranges, fog, generally arid.
• West coasts in middle and higher latitudes: bordered by warm waters; distinct marine climate: cool summers, mild winters, narrow annual range (e.g. north-west Europe, warmed by the Gulf Stream and North Atlantic Drift as noted in Chapter 8).
• East coasts in tropical and subtropical latitudes: warm currents run parallel, giving warm and rainy climates (western margins of subtropical anticyclones).
• Fishing: mixing of warm and cold currents replenishes oxygen and favours plankton, the primary food of fish; the best fishing grounds are in these mixing zones.

Map list: Cold: Humboldt, California, Falkland, Canaries, West Australian, Oyashio, Labrador. Warm: Alaska, Brazilian, Agulhas, Kuroshio, Gulf Stream.

Worked example

Why are the best fishing grounds found where warm and cold currents meet? (2 marks)

Try it first, then show the solutionSolution

1. Mixing of warm and cold currents replenishes oxygen in the water.
2. This favours the growth of plankton, the primary food for fish, so fish populations are large.

Answer: Mixing adds oxygen and plankton, the base of the fish food chain.

Movements of Ocean Water in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Ocean Currents: Causes, Warm and Cold Currents, Gyres and Their Effects
• Ocean Waves and Tides: Wave Characteristics, Causes and Types of Tides, and Their Importance

Movements of Ocean Water: key facts

Amplitude

$Amplitude=waveheight÷2$

Height = trough bottom to crest top.

Breaking depth

A wave breaks when water depth < wavelength ÷ 2

Friction with the sea floor slows it first.

Period and frequency

$Period=timebetweensuccessivecrests;frequency=wavespassingpersecond$

Wave speed in knots.

Tide-generating force

Moon's gravitational attraction - centrifugal force

Net towards the moon on the near side, away on the far side.

Fundy tide rate

1,440 cm ÷ 6 h ≈ 240 cm per hour

Bulge 15-16 m; highest tides in the world.

Tide types

Semi-diurnal	2 high, 2 low
diurnal	1 and 1
mixed	unequal heights

Spring at full and new moon; neap about 7 days later.

Range extremes

Perigee and perihelion (3 Jan): greater range | apogee and aphelion (4 Jul): smaller range

Ebb = falling; flow/flood = rising.

Current forces

Solar heating (equator 8 cm higher) + wind + gravity + Coriolis → gyres

Density drives vertical motion.

Current shares and speeds

Surface 10% (upper 400 m); deep 90%; surface drift up to > 5 knots, deep < 0.5 knots

Drift = speed of a current.

Movements of Ocean Water: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Movements of Ocean Water: map work

The places on the official CBSE map list for this chapter. Find each one on an outline map of India and practise marking it.

How the school exam asks Movements of Ocean Water

The question patterns to expect, and the method that works for each.

Tricks to remember Movements of Ocean Water

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Wave terms

  'Height Halves to Amplitude; Length is crest to crest; Period is time'.

  Use it when: Wave characteristics.

• Tide types

  'Semi = 2 + 2; Di = 1 + 1; Mixed = mismatched'.

  Use it when: Tides by frequency.

• Spring vs neap

  'Spring in line, Neap at ninety (degrees)'.

  Use it when: Spring and neap tides.

• Current forces

  'Sun, Wind, Gravity, Coriolis = SWGC'.

  Use it when: Primary forces of currents.

• Warm currents on the map

  'All Brave Agents Know Gulf': Alaska, Brazilian, Agulhas, Kuroshio, Gulf Stream.

  Use it when: Warm currents list.

Movements of Ocean Water: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Movements of Ocean Water

The slips examiners see most often, and what to write instead.

• ✗Mistake: Saying water moves forward with waves

  Waves look like moving water.

  Wrong working

  Waves carry water from the open sea to the beach.

  Right working

  Waves move energy; water particles move in small circles and stay roughly in place.

  ✓Do this: Energy travels, water circles.

  Usually costs: 1 mark in a definition.

• ✗Mistake: Confusing perigee with perihelion

  Similar prefixes.

  Wrong working

  The moon is closest to the earth at perihelion.

  Right working

  Perigee: moon closest to earth. Perihelion: earth closest to sun (3 January).

  ✓Do this: -gee = Geo (earth); -helion = Helios (sun).

  Usually costs: 1 mark per MCQ.

• ✗Mistake: Explaining the far-side bulge by the sun

  Students look for a second pulling body.

  Wrong working

  The second bulge is caused by the sun pulling on the other side.

  Right working

  The far-side bulge is due to centrifugal force exceeding the moon's weaker pull there.

  ✓Do this: Far side = centrifugal wins.

  Usually costs: 1-2 marks.

• ✗Mistake: Putting cold currents on east coasts in the tropics

  Reversing the coast rule.

  Wrong working

  Cold currents flow along east coasts in low latitudes.

  Right working

  Cold: west coasts in low and middle latitudes; warm: east coasts in low and middle latitudes.

  ✓Do this: In the tropics, west coasts are the cool, dry, foggy ones.

  Usually costs: 1 mark, and map marks.

• ✗Mistake: Mixing up warm and cold currents on the map

  Twelve names to learn.

  Wrong working

  Kuroshio shown as a cold current.

  Right working

  Warm: Alaska, Brazilian, Agulhas, Kuroshio, Gulf Stream. Cold: Humboldt, California, Falkland, Canaries, West Australian, Oyashio, Labrador.

  ✓Do this: Learn the 5 warm ones; everything else on the list is cold.

  Usually costs: 1 map mark each.

NCERT exercise guide: Movements of Ocean Water

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Practice questions on Movements of Ocean Water

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   A fisherman notices that tides are highest just after full moon and new moon. This is because:
   (a) the sun, moon and earth are in a straight line
   (b) the sun and moon are at right angles to the earth
   (c) the moon is at apogee
   (d) the coastline is indented

   Hint

   Spring tides.

   Answer

   (a) The sun, moon and earth are in a straight line, giving spring tides.

2. Q2 · 1 mark · MCQExam level

   Tides are unusually large when the moon is nearest the earth in its orbit. That position is called:
   (a) apogee
   (b) perigee
   (c) aphelion
   (d) perihelion

   Hint

   -gee for the earth, -helion for the sun.

   Answer

   (b) Perigee: the moon is closest to the earth, giving unusually high and low tides.

3. Q3 · 1 mark · Assertion-reasonHarder exam level

   Assertion (A): Surges are not regular like tides.
   Reason (R): Surges are caused by meteorological effects such as winds and pressure changes.
   Choose (a)-(d).

   Hint

   Weather is irregular.

   Answer

   (a).

4. Q4 · 2 marks · Short answerExam level

   Distinguish between ebb and flow. (2 marks)

   Hint

   Falling versus rising.

   Answer

   Ebb is the time between high tide and low tide, when water level falls. Flow (flood) is the time between low tide and high tide, when the tide rises.

5. Q5 · 3 marks · Short answerHOTS / competency

   Why are cold currents found on the west coasts of continents in low and middle latitudes? Use the chapter's ideas of gyres and Coriolis force. (3 marks)

   Hint

   Circular currents in ocean basins.

   Answer

   Wind, gravity and Coriolis force create large circular gyres in each ocean basin, anticyclonic in middle latitudes. Warm water moves poleward along the east coasts (deflected right in the NH, left in the SH), and cold water from higher latitudes returns equatorward along the eastern side of the ocean basin, i.e. the west coasts of continents.

6. Q6 · 2 marks · Short answerHarder exam level

   Suppose the depth of water off a beach decreases steadily from 50 m to 5 m. Where will waves of wavelength 40 m begin to break, and what slows them before that? (2 marks)

   Hint

   Half the wavelength.

   Answer

   They break where depth falls below 40 ÷ 2 = 20 m. Before that, friction between the moving water and the sea floor slows them down as they approach the beach.

7. Q7 · 2 marks · Short answerHarder exam level

   Why are mixed tides found along the west coast of North America? Explain what mixed tides are. (2 marks)

   Hint

   Height variation.

   Answer

   Mixed tides are tides with variations in height between successive highs and lows. NCERT notes they generally occur along the west coast of North America and on many Pacific islands; the shape of coasts and basins changes tidal magnitudes there.

8. Q8 · 5 marks · Long answerHOTS / competency

   Explain the factors that make tides higher or lower than average at a place. (5 marks)

   Hint

   Positions, distances, coast shape.

   Answer

   Sun-moon-earth alignment: spring tides (straight line, full and new moon) are higher; neap tides (right angles) lower. Moon's distance: perigee gives a greater range, apogee less. Earth's distance from the sun: perihelion (3 January) gives greater ranges, aphelion (4 July) smaller. Coast: wide continental shelves raise bulges, mid-ocean islands lower them; funnel-shaped bays and estuaries magnify tides (Bay of Fundy, 15-16 m).

9. Q9 · 2 marks · Short answerExam level

   A surfer says the best waves come after strong winds have blown for days far out at sea. Use the chapter to explain why. (2 marks)

   Hint

   Energy source and distance.

   Answer

   Most waves get their energy from the wind blowing over the water. Out in the open ocean waves keep absorbing wind energy as they travel long distances, so after long, strong winds they grow large and arrive at the coast as big swells.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.When does a wave break?Show answer

   When water depth is less than half the wavelength.

2. 2.What is wave amplitude?Show answer

   One-half of the wave height.

3. 3.What is a surge?Show answer

   A movement of water caused by meteorological effects such as winds and pressure changes; not regular.

4. 4.How high is the tidal bulge in the Bay of Fundy?Show answer

   15-16 m.

5. 5.How long after spring tides do neap tides normally occur?Show answer

   About seven days.

6. 6.Where is a 3 MW tidal power project under way in India?Show answer

   Durgaduani in the Sunderbans, West Bengal.

7. 7.What are gyres?Show answer

   Large accumulations of water and the circular flow around them in ocean basins.

8. 8.What share of ocean water is in surface currents?Show answer

   About 10 per cent (the upper 400 m).

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Horizontal: currents and waves; vertical: tides, upwelling and sinking.
• ☐Waves are energy; particles move in circles; wind gives energy; break when depth < half wavelength.
• ☐Wave terms: crest, trough, height, amplitude (half height), period, wavelength, speed (knots), frequency.
• ☐Tides: moon (mainly), sun and centrifugal force; two bulges; surges are irregular.
• ☐Bay of Fundy: 15-16 m bulge; about 240 cm per hour rise.
• ☐Semi-diurnal (most common), diurnal, mixed (west coast of North America).
• ☐Spring tides at full and new moon; neap tides about 7 days later at right angles.
• ☐Perigee/perihelion: greater range; apogee/aphelion: smaller; ebb falls, flow rises.
• ☐Tides: navigation, fishing, desilting, tidal power (Durgaduani, 3 MW).
• ☐Currents: solar heating (8 cm higher at equator), wind, gravity, Coriolis (gyres); density drives sinking.
• ☐Surface 10% (400 m), deep 90%; cold on west coasts and warm on east coasts in low-middle latitudes.
• ☐Mixing zones = best fishing grounds. Map: 7 cold, 5 warm currents.

Movements of Ocean Water: frequently asked questions