WBBSE Solutions For Class 10 Geography And Environment Chapter 3 Hydrosphere

Class 10 Geography West Bengal Board Chapter 3 Hydrosphere True Or False Type:

Question 1. Floods occur in India during the years of El Nino.
Answer: False

Question 2. The position of the sun, moon and earth along a straight line is known as syzygy.
Answer: True

Question 3. The salinity of seawater is maximum in the Equatorial region.
Answer: False

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Question 4. Change of seasons is observed in the Equatorial region.
Answer: False

Question 5. The drought conditions develop in the western coast of South America due to the influence of El Nino in the Pacific Ocean.
Answer: False

Question 6. ‘Chinook is an example of seasonal wind.
Answer: False

Question 7. Kuro Shio current flows near the coast of China & Japan.
Answer: True

Geography Class 10 West Bengal Board

Question 8. Flumbolt current flows along the West Coast of South America.
Answer: True

Question 9. Gulf Stream flows towards the North through the Gulf of Mexico.
Answer: True

Question 10. Guinea current flows towards the West Africa Coast.
Answer: True

Question 11. The Sargasso Sea is situated at the middle of the North Atlantic Ocean.
Answer: True

Question 12. Labrador is a cold current from the Arctic Ocean.
Answer: True

Question 13. Venezuela currently flows near the coast of South-West Africa.
Answer: True

Question 14. Peru is a cold current of the Pacific Ocean.
Answer: True

Question 15. Madagascar current flows along the East coast of Madagascar Island.
Answer: True

Question 16. Mozambique current is a warm current.
Answer: True

Question 17. Madagascar and Mozambique currents unite together to form Agulhas current.
Answer: True

Question 18. The wind is responsible for the origin of ocean current
Answer: True

Question 19. Brazilian Current occurs in the Atlantic Ocean.
Answer: True

Question 20. The shape of the coastline exerts some influence in the direction of the currents.
Answer: True

Question 21. Benguela current is found on the South Eastern coast of Africa.
Answer: False

Question 22. The planetary winds play a major role in the formation of ocean currents.
Answer: True

Question 23. Monsoon wind is an example of local wind.
Answer: False

Question 24. The polar region has a low-pressure belt.
Answer: False

Geography Class 10 West Bengal Board

Question 25. Tropical cyclone causes disasters.
Answer: True

Question 26. The stratosphere is the lowest layer of the atmosphere above the earth’s crust.
Answer: False

Question 27. In the confluence of warm and cold currents fishes are abundant.
Answer: True

Question 28. A Humboldt current is a warm current.
Answer: False

Chapter 3 Hydrosphere Fill in The Blanks Type:

Question 1. With the increase of air pressure gradient, wind velocity ______.
Answer: Increase.

Question 2. The cold ocean water from the polar region flows as ______ current towards equator.
Answer: Under Current.

Question 3. ______current causes snowfall in New Foundland.
Answer: Labrador.

Question 4. During high tide huge tidal waves entering through the mouth of a river from the sea are called ______
Answer: Tidal bore.

Question 5. ______ force of the earth causes secondary high tide.
Answer: Centrifugal.

Question 6. Air conditioners emit ______ gas into the atmosphere.
Answer: CFC.

Question 7. Pull of the ______ is responsible for tides.
Answer: Moon.

Question 8. The Sargasso Sea is found in the ______ ocean.
Answer: Atlantic.

Question 9. Tidal bores are common in the ______ river of China & Hooghly in India.
Answer: Yangtze Kiang.

Question 10. The interval between two high tides is ______.
Answer: 12 hrs 26 m.

Geography Class 10 West Bengal Board

Question 11. ______ tides are caused by the gravitational pull of the sun &the moon.
Answer: Spring/High.

Question 12. Tides occurring at the opposite side of the spring tide are called ______ tides.
Answer: Secondary.

Question 13. Alternate rise and fall of sea water are called _______.
Answer: Tides.

Question 14. Primary tides are also known as ______ tides.
Answer: Direct.

Question 15. Tides make rivers ______.
Answer: Navigable.

Question 16. The interval between high trades and low tides is ______.
Answer: 5 hrs 13 ms.

Question 17. Warm currents keep the coastal areas ______.
Answer: Warm.

Question 18. Cool currents keep the coastal areas ______.
Answer: Cool.

Question 19. Labrador is a cold current of the ______.
Answer: Atlantic ocean.

Question 20. ______ flows along the southwest coast of South America.
Answer: Humboldt current.

Question 21. Grand Bank is famous for ______.
Answer: Commercial fishing.

Question 22. North Indian ocean currents are dominated by ______.
Answer: Monsoon wind.

Question 23. ______ is responsible for the origin of ocean currents.
Answer: Prevailing winds.

Question 24. Ocean currents deflect due to the movement of the earth’s gravitational.
Answer: Rotational.

Geography Class 10 West Bengal Board Chapter 3 Hydrosphere Very Short Answer Type:

Question 1. Name the southernmost mountain pass of the Western Ghats.
Answer: Palghatgap

Question 2. What is the local name of the lagoons in the Kerala coast?
Answer: Koyal

Question 3. On which quarters of the moon, does Neap tide occur?
Answer: Dark and White Half of a lunar month.

Question 4. What is the main food of marine fish?
Answer: Planktons.

Question 5. What type of current originates in the tropical oceans?
Answer: Warm Current

Question 6. What is the time interval between two primary high tides and two secondary high tides?
Answer: 24 hrs 52 mins.

Class 10 Geography West Bengal Board

Question 7. What is the time interval between two low tides?
Answer: 12 hrs 26 mins.

Geography Class 10 West Bengal Board

Question 8. What is drift?
Answer: If the mass of water moving on the surface of an ocean is broad, slow and shallow, it is termed as drift.

Question 9. What is Tide?
Answer: The alternative rise and fall of seawater is called Tide.

Question 10. Name three forms of movement of oceanic water.
Answer: Waves, currents, and tides.

Question 11. Give one term for each of the following statements:
1. The time taken by two consecutive crests to pass any fixed point.
2. Vertical distance between a trough and a crest of a wave.
3. An oscillatory movement in a body of water manifested by an alternate rise and fall of the surface.
4. The breaking waves in a coastal region.
5. Currents flow from low latitudes to higher ones.
6. A vertical wall of tidal waters moving upstream in the river channel.

Answer:
1. Wave period.
2. Wave height.
3. Ocean wave.
4. Surf.
5. Warm currents.
6. Tidal bore.

Question 12. Name three types of waves generated by wind.
Answer: Sea, Swell and Surf.

Question 13. What are the different types of currents?
Answer: Warm currents and cold currents.

Class 10 Geography West Bengal Board

Question 14. What are warm currents?
Answer: Warm Currents: Currents flowing from equatorial regions to polar regions on the surface of the oceans due to their lightness.

Question 15. What are cold currents?
Answer: Cold Currents: Currents flow from polar regions to equatorial regions under the surface of the oceans due to the cold water being heavy.

Question 16. Why are oceans and seas often called inner space?
Answer: Oceans and seas are sometimes called ‘inner space’ because the space occupied by them is covered with water.

Question 17. What do you mean by ‘Sargasso Sea’?
Answer: Sargasso Sea is stagnant water where seaweeds grow and accumulate and it is found in the North Atlantic and North Pacific Oceans.

Question 18. In which ocean ‘the Cold Wall’ is found?
Answer: ‘The Cold Wallis is found in the Atlantic Ocean.

Question 19. Name the deepest lake in the world.
Answer: Lake Baikal is the deepest lake (1620 m) in the world.

Geography Class 10 West Bengal Board

Question 20. How much is the gap of time between the two primary tides?
Answer: The gap of time between the two primary tides is 24 hours and 52 minutes.

Question 21. What is an iceberg?
Answer: An iceberg is a broken mass of ice from a coastal glacier floating in the ocean.

Question 22. Which ocean current keeps the coastline of Japan warm?
Answer: The warm Kuroshio Current keeps the Japanese coast warm.

Class 10 Geography West Bengal Board

Question 23. Which one is the largest lake in the world?
Answer: The Caspian Sea (4,38,700 sq. km) is the largest lake in the world.

Question 24. Name the saltiest lake in the world.
Answer: Dead sea is the saltiest lake in the world; even fish cannot live in it.

Question 25. What do you know about evaporation regarding ocean currents?
Answer: Evaporation: More evaporation reduces the amount of water and lowers its level. In order to maintain the balance, water from other areas starts flowing in the form of a current.

Question 26. What is ocean current and how does it differ from the wave?
Answer: The regular movements of water from one part of the ocean to another are called ocean currents. They differ from waves. The waves are the movements of surface water of the ocean and sea with only rise and fall of the water surface and there is no onward motion as in ocean current.

Question 27. Mention one cause of ocean currents.
Answer: Planetary wind.

Question 28. Where do you find the Sargasso Sea?
Answer: In the North Atlantic Ocean.

Class 10 Geography West Bengal Board

Question 29. In which sea the salinity is maximum-Baltic Sea/Mediterranean Sea?
Answer: Mediterranean Sea.

Question 30. Name the longest lake in the world.
Answer: Lake Tanganayika.

Question 31. What is Grand Bank?
Answer: A fishing centre near Newfoundland.

Question 32. Mention the factors affecting ocean currents.
Answer: Temperature, wind velocity, salinity and rotation of the earth.

Question 33. Name one man-made lake in India.
Answer: Govind Sagar (Himachal Pradesh).

Geography Class 10 West Bengal Board

Question 34. Name one tidal river.
Answer: The Hugli (Hooghly) river is a tidal river.

Question 35. How many times a place on the globe experiences high or low tides in a day?
Answer: A place on the earth experiences one high tide and one low tide in a day.

Question 36. How much percentage of the earth is covered with water?
Answer: 71 per cent.

Question 37. Name the deepest place in the ocean.
Answer: Mariana Trench of the Guam Islands (11,033 metres).

Question 38. How much part of the earth’s surface is covered by the Pacific ocean?
Answer: 1/3rd part.

Question 39. What percentage of the ocean floor is covered by the continental shelf?
Answer: 7.5%.

Question 40. What is the length of the Mid-Atlantic Ridge?
Answer: 14,000 km.

Class 10 Geography West Bengal Board

Question 41. Name the most common features found on the ocean floors.
Answer: Continental shelf, Continental slope, Continental rise and Abyssal Plain.

Question 42. Why is the earth known as ‘Watery Planet’?
Answer: Because 71% of its surface area is covered by water.

Question 43. Give one term for each of the following statements:
1. A gently seaward sloping surface extending between the shoreline and the continental slope.
2. A flat, nearly level area in the ocean, lying beyond the continental slope.
3. A submarine mountain or peak rising more than 1,000 metres above the ocean floor.

Answer:
1. Continental shelf.
2. Abyssal plain.
3. Seamount.

Question 44. What are the processes heating ocean water?
Answer:
1. Absorption of heat radiation from the sun.
2. Convection of heat through the ocean bottom from the interior of the earth.

Question 45. Name the processes of cooling ocean water.
Answer: Back radiation of heat, convection and evaporation.

Question 46. Name the factors affecting the temperature of ocean water.
Answer: Latitude, prevailing winds, ocean currents, adjacent land waters, salinity and icebergs.

Question 47. At what temperature the density of pure water is maximum?
Answer: At 4°C

Class 10 Geography West Bengal Board

Question 48. Name the two most important factors which affect the density of ocean water.
Answer: Temperature and salinity.

Question 49. Give one term each for the following:
1. Floating or stranded masses of ice at least five metres above the level of the sea.
2. Index of the amount of total dissolved solids in seawater.
3. Mass per unit volume of a substance.

Answer:
1. Iceberg.
2. Salinity.
3. Density.

Question 50. Name three forms of movement of oceanic water.
Answer: Waves, currents and tides.

Question 51. Give the formula for finding the velocity of a wave.
Answer:  Velocity of wave (C) = Wavelength(L)/Period(T)

Question 52. Name three types of waves generated by wind.
Answer: Sea, Swell and Surf.

Question 53. What are the different types of currents?
Answer: Warm currents and cold currents.

Question 54. When does spring tide occur?
Answer: On a full and new moon when the earth, moon and the sun are in line with the earth.

Class 10 Geography West Bengal Board

Question 55. When does neap tide occur?
Answer: In the first and the last quarter of the moon when the sun and the moon make a right angle at the earth’s centre. ”

Question 56. What is the time interval between two successive tides?
Answer: 12 hours and 25 minutes.

Question 57. What is a Bay?
Answer: It is a wide indentation into the land produced by the sea. E.g. Bay of Bengal.

Question 58. What are waves?
Answer: Waves are the oscillatory movements in water, manifested by an alternate rise and fall of the sea surface.

Chapter 3 Hydrosphere 2 Marks Questions And Answers:

Question 1. What do you mean by Perigean Spring tide?
Answer:

Perigean Spring tide:

A Perigean spring tide occurs when the moon is either new or full and closest to Earth. Often between 6-8 times a year, the new or full moon coincides closely in time with the perigee of the moon — the point when the moon is closest to the Earth. These occurrences are often called Perigean Spring tides.

Question 2. What is an Inter-tropical convergence zone?
Answer:

Inter-tropical convergence zone:

Inter-Tropical Convergence Zone: In the winter the Indian climate is influenced by the western disturbances originating from the Mediterranean sea and is characterised by snowfall or rainfall (its influence is seen sometimes up to the plains of West Bengal also). Kashmir, Punjab, and Western U.P. receive snowfall or rain during this time.

Question 3. State the definition of ocean current.
Answer:

ocean current:

The stream of water that flows from one place to another, regularly within the ocean itself, is called an ocean current. Ocean currents are of two types – warm currents and cold currents.

Class 10 Geography WBBSE

Question 4. What is the apogean tide?
Answer:

Apogean tide: When the moon is farthest from the earth (4,03,320 km), this position is known as Apogee. Due to the reduced attraction of the moon, the tide is also 20% less high. This is known as Apogean tide.

Question 5. What is a tidal bore?
Answer:

Tidal Bore: When a tide enters the narrow and shallow estuary of a river, the front of the tidal wave appears to be vertical, owing to the piling of water of the river against the tidal wave and friction against the river bed. The steep-nosed tide crest looks like a vertical water of water rushing upstream. This is called a Tidal Bore.

Question 6. Explain the types of ocean currents.
Answer:

Types of Currents:

Ocean currents are, in broad terms, of two types:

1. Warm currents and
2. Cold currents.

Warm Currents: Movement of ocean water from low latitudes to higher latitudes on the ocean surface.

Cold Currents: Movement of ocean water from high latitudes to low latitudes under the ocean surface.

Question 7. What is Neap tide?
Answer:

Neap tide:

When the sun, the moon and the earth are in the position of right angle, the attractions of the sun and the moon oppose each other which makes the tide weaker and this type of tide is called neap tide, This situation occurs at the first and the third quarters of the moon.

Class 10 Geography WBBSE

Question 8. What is SYZYGY?
Answer:

SYZYGY:

SYZYGY is a position in which the sun, the moon and the earth lie in the same straight line.

Question 9. what is the Great Barrier Reef?
Answer:

Great Barrier Reef:

Great Barrier Reef, situated in the Pacific Ocean, is the world’s largest coral reef.

Question 10. Differentiate between warm currents and cold currents.
Answer:

Difference between warm currents and cold currents

Question 11. Ships prefer to sail along ocean currents. Why?
Answer:

Ships prefer to sail along ocean currents

Ships prefer to sail along the ocean currents because ships sailing down the currents surely go faster, which saves time and fuel.

Question 12. What is a tidal bore?
Answer:

Tidal bore:

When a high tidal wave in shallow water reaches the mouth of a river, it causes the water to pile up across the river and water moves along like a broken wave and advances upstream like a wall of water. This is known as a tidal bore. It occurs in the Hooghly, the Amazon, the Yang-tse-kiang, etc,

Question 13. What is the Sargasso Sea?
Answer:

Sargasso Sea:

In the Atlantic Ocean the North equatorial current, the Gulf current and the Canary current move in a circular way. In between these currents water is stagnant. Seaweeds and other elements gather here. And in these elements weeds known as ‘Sargasso’ are found. That is why the region is known as the Sargasso sea.

Question 14. What is Spring tide?
Answer:

Spring tide:

At full moon and new moon the sun and the moon are more or less in a straight line with the earth. Due to this combined pull of the sun and the moon the highest high tides are produced on the earth. These highest tides are known as ’Spring Tide1.

Class 10 Geography WBBSE

Question 15. Why does tidal bore occur in the Ganga?
Answer: Tidal bores occur in those rivers which have certain conditions. In the case of the Ganga (Hooghly) river, the river mouth is funnel-shaped and especially in monsoon season the river is already filled with water and so tidal bores are common, especially in the Ganga river.

Question 16. What is a ‘Cold wall’?
Answer:

‘Cold wall’:

A cold wall is a discontinuity layer between any cold and warm current, e.g. between the Labrador current and the Gulf stream.

Question 17. Name the types of movements in ocean water.
Answer:

Three types of movements in ocean waters are:

1. Waves.
2. Tides and
3. Ocean currents.

Question 18. What do you mean by ocean currents?
Answer:

Ocean currents

Regular movement of a mass of water in a fairly defined direction over great distances is known as current.’Water in the current moves forward while water on its sides and below it remains more or less stationary. Thus, an ocean current can be compared with rivers on the land.

Question 19. What is Gulf?
Answer:

Gulf:

A deep inlet of the sea almost surrounded by land, with a narrow mouth is called Gulf, e.g. Gulf of Mannar, Gulf of Kutchchh.

Class 10 Geography WBBSE Chapter 3 Hydrosphere 3 Marks Questions And Answers:

Question 1. Mention the relationship between the Jet stream and the Indian Monsoon system.
Answer:

Influence of jet stream on monsoon winds: The westerly jet stream causes high pressure on the Indian sub-continent in winter. Hence the monsoon winds start retreating. During the summer, the Tibetan plateau gets excessively heated and drives the subtropical westerly jet stream north of the Himalayas. The tropical easterly jet stream blows through the centre of the Indian sub-continent, causing low-pressure conditions. This gradually attracts the monsoon wind. The onset of the monsoon depends on the shifting of the sub-tropical westerly.jet stream northwards, which allows the easterly jet to set in. A sudden shift of the westerly jet stream may cause a huge monsoon Burst’.

Question 2. Why does the interval between two primary tides exceed 24 hours?
Answer:

Interval Between Primary Tides Exceeds 24 Hours: High tides (Primary and Secondary) do not occur regularly every twelve hours. They occur at an interval of 12 hours and 26 minutes. This is because the moon is revolving around the earth in the same direction as the earth’s rotation, i.e., from west to east, and completes one revolution in 28 days (approximately). If the moon had been stationary, each place on the earth’s surface would have come exactly under it after 24 hours and the next primary high tide would have occurred just after 24 hours. But the moon revolves around the earth for almost 28 days. So in a day, the moon moves farther 13° [360 28 = 12.8 or 13° (approx.)] on its way. Therefore, it takes an extra time of about 52 minutes [13°x 4 = 52] to reach that place. For this, the time of high tides changes every day and the interval between the corresponding high tides (primary) at a particular place of two following days is about 24 hours and 52 minutes. Thus, an interval between two high tides (primary & secondary) is about 12 hours and 26 minutes.

Class 10 Geography WBBSE

Question 3. Why is Grand Bank famous for fishing?
Answer:

The shallow sea of the eastern coast of New Foundland is called the Grand Bank region. It is famous for fishing due to the following reasons:

(1)The sea near New Foundland is shallow because pebbles, sand clay, stones, etc. are collected over a long period. Such a shallow sea is ideal for fishing.
(2)Being located in a temperate region, the fish are very tasty.
(3)The meeting of warm and cold currents in the region gives birth to microscopic organisms called Plankton. Phytoplankton and zooplankton form the main food for fish.
(4)There is a huge demand of fish in nearly located U.S.A Canada and many countries.
(5)Fishing facilities: The fishermen of this region have been provided with modern boats, fish-catching nets and other modern equipment for better fishing.
(6)Others: There are also other causes like port facility, freezing facility, broken coastline, etc. which made this region suitable for fishing.

Question 4. What are primary tides and secondary tides?
Answer:

Primary Tide and Secondary Tide: Due to the rotation of the earth tides occur twice a day at a place. One tide occurs in the water of the earth facing the Moon; the other tide occurs at the diametrically opposite sides of the earth.
Primary Tide or Direct Tide: Ocean water of the earth nearest to the moon swells up by the gravitational of the moon. It happens when the moon is directly overhead and its attraction forces the water to pile up on that place to form high tide. The tide is known as Primary Tide or Direct Tide.
Secondary Tide or Indirect Tide: At the same time, there is a piling up of ocean water on the other side of the earth. The solid earth on the opposite side is near the moon and is pulled by the moon which causes the water to pile up again on the opposite side. Thus another high tide occurs on the opposite side. This is known as Secondary Tide or Indirect Tide.

Question 5. Why does the tide not occur at the same time in any place every day?
Answer:

Tide does not occur at the same time in any place every day because with the movement of the earth moon also revolves in the same direction as the earth. So a place comes in front of the moon every day after 52 minutes. Hence tide occurs every 24 hrs 52 minutes at a place.

Question 6. What are Perigean and Apogean Tides?
Answer:

Perigean and Apogean Tides:

Perigean and Apogean tides When the moon comes to its nearest point (Perigee) its tide-producing effect is more pronounced. The tides so developed are called Perigean tides which are about 20% higher than high tides. When the moon is at its farthest distance from the earth, its tide-producing effect is less. At this stage tides produced are lower than usual high tides. If they coincide with neap tides, small tidal ranges occur. They are known as Apogean tide.

Class 10 Geography WBBSE

Question 7.” Dense fog occurs at the Newfoundland coast very often”. Why? Or, Why does the Newfoundland coast remain foggy around the year?
Answer:

Dense fog occurs at the New Foundland coast very often

The cold Labrador Current and the Warm Gulf Current (stream) meet near the coast of Newfoundland. The wind which that blows over the cold current is cold and dry; but the wind that blows over the warm current is hot and moist. As a result of the mixing of these two different types of winds, fog is formed along the coast of Newfoundland throughout the year. Because of this, the coast of Newfoundland remains foggy around the year.

Question 8. What do you know about the Gulf Stream?
Answer:

Gulf Stream: Gulf Stream has the following characteristics-
1. It is a warm current and originates in the Gulf of Mexico.
2. It flows northward along the east coast of North America.
3. It comes under the influence of the westerly winds and flows north-eastwards as North Atlantic Drift. Near New Foundland its water mixes with the cold water current of Labrador which results in the formation of dense fog.

Question 9. What are the effects of tide?
Answer:

Effects of Tide: The effects of the tide are as follows-
1. Large ships can enter into rivers during high tide and leave the river harbour during low tide.
2. At ebb tide loads deposited by the river on its bed (sand, silt, etc.) are carried away to the sea by the dragging power of the ebb tide. So the depth of the river increases.
3. High tide brings salty sea water into the river which makes the river water change from sweet to salty. Such water can be used for farming & industrial purposes.
4. High tide often causes siltation on the river beds decreasing the depth of the rivers. E.g. – Hooghly.
5. At many places tidal energy is produced by the power of high and low tides.
6. During high tide many fishes enter in the rivers.
7. The saltwater entering ports and rivers during high tide in high latitudes keeps them ice-free often as salt water does not get frozen easily.
8. Very high tides often damage the land on either side of a river; huts and houses become submerged as the water rises several metres.

Class 10 Geography WBBSE

Question 10. How was the Sargasso Sea formed?
Answer:

Sargasso Sea: The centre of the North Atlantic Ocean lying between 20°N and 45°N latitudes is encircled by clockwise gyral ocean currents namely, the North Equatorial Current and Cayenne Current on the South, the Caribbean and Gulf Stream on the West, the North Atlantic Drift on the North and the Canary Current on the East, forming a region of stagnant water. This region also coincides with the location of the subtropical High-Pressure Belt or Horse latitude, where there is little wind movement. Thus, the region forms a calm sea with no surface currents. Tropical brown seaweeds grow and accumulate and navigation is difficult due to the lack of surface current. The growth of sea weed of sargassum (from the Portuguese language) has probably given the name Sargasso Sea to this part of the North Atlantic Ocean.

Question 11. Distinguish between Spring tide and Neap tide.
Answer:

Difference between Spring tide and Neap tide

Question 12. Point out some of the influences of the Gulf Stream on climate.
Answer:

Influence of Gulf Stream: It exerts great influence on the climate of the Southeastern U.S.A. and Western Europe. Norway and Sweden are the most northern countries lying beyond 74° North, but still, they enjoy mild winters when compared to eastern Canada and Siberia. London is on 51° north latitude as against New York’s 40° North latitude, yet New York has freezing temperatures in winter while London is comparatively warmer. Due to the influence of warm currents, the ports of Western Europe remain open for trade all year round. The westerlies blowing over these warm currents bring plenty of rainfall to Western Europe.

School Geography Class 10 WBBSE

Question 13. Distinguish between warm and cold currents.
Answer:

Difference between warm and cold currents:

Question 14. Explain the characteristics of ocean currents.
Answer:

Characteristics of Ocean Currents:

1. Ocean currents move to their right in the Northern hemisphere and to their left in the Southern hemisphere due to the effect of Coriolis effect and Ferrel’s law. This general law does not have any effect on currents prevailing in the Indian Ocean. They follow the reversal of monsoon winds.
2. Warm or hot currents move towards cold oceans and seas and cool or cold currents towards warm oceans and seas.
3. Coldwater with high density occur near the surface in middle latitudes on the western coasts of continents.
4. Coldwater with less density in higher latitudes moves towards warm oceans along eastern coasts.
5. Warm currents move along the western coasts and cold currents along eastern roasts in higher latitudes.

School Geography Class 10 WBBSE

Question 15. What are the effects of tides?
Answer:

The effects of tides:

Tide exerts influence over the coastal areas and the lower courses of the river, it also influences the economic activities of man. The effects are the following :
1. Tides clear out the refuse materials and wastes from the river mouth.
2. Tides make some of the rivers navigable. They help many big ships to reach the ports located in shallow water in the interior. At high tides, ships can enter the harbour, such as at Kolkata on the river Hugli, at London on the river Thames and others.
3. Due to natural flushing action, the mouths of the rivers and estuaries deepen.
4. The waters of the river remain clear due to tidal action.
5. Silts and mud cannot accumulate on the river mouth; they are washed away by the tides.
6. Tides make river water salty; they keep the water in motion and so water does not freeze easily.

Question 16. State three factors affecting the salinity of the water.
Answer:

The salinity of the seawater changes from place to place and is affected by the following factors :

1. Fresh Water: Fresh water in the sea comes from rivers and melted ice and reduces salinity. This is the reason that river mouths and polar areas have less salinity.
2. Evaporation: Fresh water is evaporated by the process of evaporation and salt is left behind. So the areas of high evaporation will have a high proportion of salinity.
3. Ocean Currents: Warm currents from the equator carry more saline water to polar areas and cold currents carry less saline water to equatorial areas. Thus, ocean currents also influence the distribution of salinity.

Question 17. Distinguish between waves and currents.
Answer:

Difference between Waves and Currents: The only similarity between waves and oceans is that they have their origin in the ocean. Otherwise, they are quite different from each other as is clear from the following description:

Question 18. What do you understand by ‘Syzygy’?
Answer:

‘Syzygy’:

Syzygy, is a straight-line configuration of three celestial bodies in a gravitational system. The word is often used in reference to the sun, earth, and either the moon or a planet, where the latter is in conjunction or opposition. Solar and lunar eclipses occur at times of syzygy, as do transits and occultations. The term is often applied when the sun and the moon are in conjunction (new moon) or opposition (full moon).

School Geography Class 10 WBBSE

Effects: There is no controversy about the effect of a syzygy on ocean tides. The syzygy produces the more powerful spring tide due to the combined gravitational effect of the sun with that of the moon. The spring tides (highest tides) occur at the full moon and new moon times while the neap tides (lowest tides) occur when the sun and the moon are at right angles in the first and third quarters of the moon’s cycle. Spring and neap tides are about 20% higher and lower, respectively than the average tide. Syzygy also produces stronger earth tides, although there is controversy about the tidal triggering of earthquakes.

WBBSE Class 10 Geography Solutions Chapter 3 Hydrosphere 5 Marks Questions And Answers:

Question 1. Mention the location of the Mediterranean climatic region and discuss its major climatic characteristics.
Answer:

Location: The Mediterranean climate is the climate typical of the lands in the Mediterranean basin. The lands around the Mediterranean Sea form the largest area where this climate type is found, but it also is found in most of California, in parts of Western and South Australia, in southwestern South Africa, and in central Chile.

Characteristics:
1. The Mediterranean climate is characterised by dry summers and wet winters.
2. Due to the shifting of pressure belts, dry trade winds blow over the region during summer.
3. The westerlies bring rainfall in the region during winter.
4. During summer the climate is pleasant with an average temperature of 54°C.
5. Bright sunshine throughout the year is another feature of the climate.

Question 2. Discuss the influences of ocean currents on global climate.
Answer:

Influence of Ocean Currents: The various influences of ocean currents are as follows:
1. temperature difference: The regions where warm ocean currents pass, become comparatively warmer, while the regions where cold ocean currents pass become comparatively cooler.
2. Rainfall: Winds crossing warm ocean currents gather enough moisture and cause much rainfall. But winds causing cold currents do not gather much moisture, hence do not cause much rainfall.
3. Fog and Storms: Regions where warm and cold currents meet remain foggy almost throughout the year and often face storms.
4. Frost-free harbours: Warm currents help to keep the mouths of the harbours of higher latitudes frost-free even in winter.
5. Navigation: Ships can move faster and easily along ocean currents. The movement against the direction of currents is difficult, time-consuming and fuel-consuming.
6. Sandbars: When warm and cold currents meet, the icebergs carried by cold currents melt. The sand, pebbles, etc. being carried by the icebergs get deposited at the base, creating sandbars. These are economically useful as the low depth of the sea in this region attracts many fish which can be easily acquired.
7. Business and commerce: Sandbars are good for the growth of plankton, which is a favourite fish food. A huge number of fish are attracted to these regions. This leads to a huge catch of fish, naturally leading to good business and commerce.

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Question 3. Explain the causes responsible for the development of high tides and ebb.
Answer:

Tides are the periodic rise and fall of the ocean twice in about 24 hrs. Tides are formed because of the following factors

1. Rotation of the earth: The earth is continuously spinning on its axis. This movement causes the development of centrifugal force. Due to the effect of centrifugal force, the water on the earth’s surface tends to move away. This causes high tides to be formed in the seas.
2. Attraction of the Earth by the Sun & the Moon: According to Newton’s law of gravity, all objects in the universe attract another object. The attraction of the moon is much more effective because the sun is 380 times further than the moon. Therefore, high and low tides are influenced by lunar attraction.

3. When the moon is directly over the sea, water piles up and causes high tide there. The tides move in a great wave around the earth following the movement, of the moon except where the presence of land stops them. Places on the rotating earth facing the moon experience maximum pull by the moon and enjoy high tide. This is known as Primary tide. Places of the earth opposite to places experiencing primary tides enjoy secondary tides due to the centrifugal force of the earth.

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Question 4. Explain the factors responsible for the origin of ocean currents.
Answer:

Causes of Origin of Ocean Currents: The main causes of the origin of ocean currents are:

1. Prevailing winds: The planetary winds or prevailing winds push the surface layers of the ocean water in front of them in a constant flow. If due to seasonal changes, the direction of the wind is changed, the currents also have a similar change in their direction. In Tropical areas, the equatorial currents moving along with trade winds move from east to west. In Temperate regions, westerlies drive the seawater from west to east.
2. Difference in temperature: Temperature is low at the poles and high at the equator. The polar water is cool and becomes heavy and sinks. The equatorial water is warm, light and floats. This creates a convectional current and the polar water moves towards the equator and vice versa.
3. Difference in salinity: The salinity of ocean water varies from place to place. Water of high salinity is denser than water of low salinity. Hence, water of high salinity flows on the surface while the water of high salinity flows at the bottom of the oceans.
4. Rotation of the earth: The rotation of the earth generates a centrifugal force, which causes the generation of currents in the ocean water.
5. Shape of coasts: The shape and direction of the coasts of the landmasses also change the direction of the currents.
6. Centrifugal force: The centrifugal force of the earth is greater at the equator than at the poles. Hence, water currents move from the equatorial region to the poles.
7. Evaporation and rainfall: Evaporation decreases the water level and increases salinity while rainfall increases the water level and decreases salinity. This influences the flow of ocean currents.
8. Melting of ice: Melting of ice raises the sea level and reduces salinity, influencing the ocean currents.

Question 5. Give a brief account of the influences of global warming.
Answer:

The influences of global warming are discussed below:

1. Melting of glaciers: Global warming increases the average temperature of the earth’s atmosphere, which results in the melting of ice caps and glaciers. This will submerge coastal areas due to an increase in the level of seawater. The fluvial cycles will be disturbed and landforms will change. Many flora and fauna may be destroyed.
2. Climatic change: The northern hemisphere will become hotter than the southern hemisphere due to the presence of more landmasses here. The amount of rainfall in Tropical, regions will increase by 10-15%. The northern countries may experience flood and the southern countries will experience drought in the northern hemisphere. Summers will be longer. Chances of thunder storms and cyclones will increase.
3. Ecosystem: Change in climate due to global warming may result in the extinction of many species of birds, animals and plants.
4. Spread of diseases: The germs and bacteria will become highly active and spread diseases like Dengue, Malaria, Yellow Fever, Encephalitis, etc. Some tropical diseases may spread to higher latitudes also.
5. Spread of deserts: High temperatures and high rates of evaporation will turn many places arid and hence boost the spread of deserts.
6. Effect on vegetation and agriculture: Excessive heat may hamper the growth of coniferous trees in hilly areas. Mangroves may be drowned due to the rise in sea water level. Some crops like rice, wheat, barley, soybean, tobacco, jute, etc. will reduce their growth.

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Question 6. What are the effects of ocean currents?
Answer:

The ocean currents have much importance for humans as they influence climate, navigation, marine life and trade. Ocean currents have the following effects:

1. Climate:
(1) The warm current makes the climate of its surroundings warmer, e.g. the Kuroshio current in the Pacific ocean modifies the climate of southern japan.
(2)The ocean currents have an influence on the amount of rainfall received by a country; e.g. Eastern USA, Ireland and Britain receive more rainfall because winds passing over them absorb a lot of moisture.

2. Marine life: The area of mixing of warm and cold currents provides plankton which are food for fish.
3. Navigation: The ocean currents influence navigation as a ship sailing down the current goes faster which saves time and fuel both.
4. Fishing: The area of mixing of warm and cold ocean currents is a golden place for fishing. The Grand Bank of New Foundland is a great example.
5. Power: The currents are a huge source of hydroelectric power.
6. Storms: Violent storms follow the line of the meeting of cold and warm currents, e.g. Hurricanes which occur off the coast of the United States follow the line where the Gulf stream mingles with the cold current.
7. Port Facility: The warm currents keep the ports of the polar region free from ice during winter.

Question 7. Give an account of the major currents of the Atlantic ocean.
Answer:

Currents of the Atlantic Ocean

1. North Equatorial Current It is a warm current that flows from east to west under the influence of trade winds. It flows parallel to the equator.
2. South Equatorial current is a warm ocean current flowing south of the equator parallel to it. It flows under the influence of trade winds and the earth’s rotation.
3. Counter Equatorial current is a warm ocean current. It flows between north and south equatorial currents towards the east.
4. Brazilian Current is a warm current. South equatorial current flows towards South America and at Cape, de Sao Roque divides into two parts. The part that flows along the east coast of Brazil is known as the Brazil Current.

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5. Guinea current is a warm current. A part of the Atlantic Equatorial Counter Current that flows towards the coast of Africa is called Guinea Current.
6. Gulf StreamThis is a famous warm current. Actually, it takes its origin from the Gulf of Mexico, hence it is known as Gulf Stream. The North Equatorial current and rivers like Mississippi, etc. as well as the waters of the Gulf of Mexico together accumulate and the outlet of water gets its way through the Florida Strait. From here it is known as Gulf Stream. Due to enormous quantities of water, it flows at about 8 km per hour and the width of the current is about 60 km and its depth is about 600 metres. The current has a temperature of 27°C and at a given point it carries about 7 crore tons of water per second. Its colour is brilliant deep blue. After coming out from the strait of Florida, the Gulf Stream flows along the eastern coast of the U.S.A. north up to Newfoundland.
7. North Atlantic Drift Under the influence of the Westerlies and rotation of the earth at 40° North latitude the Gulf Stream deflects towards the east, crosses the North Atlantic diagonally and is known as North Atlantic Drift.
8. Norwegian Current After reaching the eastern part of North-West Europe the North Atlantic Drift is divided into three parts.
The part that flows towards the Arctic ocean along the coast of Britain it is known as the Norwegian Current. The second part that flows southward is known as Canary Current and the third one flows northward between Iceland and Greenland and mixes with the Labrador current.
9. Falkland CurrentIt is a cold current. This current flows from Cape Horn towards the north along the South-East coast of South America. Dense fog is produced when this cold current meets the warm Brazilian current.
10. Labrador current is a cold current flowing from the Arctic Ocean. It flows along the eastern coast of Labrador and meets with the warm Gulf Stream current near the coast of Newfoundland. As a result of the meeting of warm and cold currents, dense fog is produced which causes navigation difficulties.
9. Venezuela CurrentAfter reaching the coast of South-West Africa, the Antarctic ocean current turns North and is known as Venezuela current.
10. Antarctic CurrentNear Antarctica this cold ocean current flows from west to east under the influence of the Westerlies.

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Question 8. Give a brief description of the currents of the South Atlantic Ocean.
Answer:

The major currents of the South Atlantic Ocean are:

1. The South Equatorial current lies in the South of the Equator and flows almost parallel to it from East to West.
2. Brazil CurrentThe South Atlantic Current splits into two branches near Cape-de- Sao Roque (Brazil). The northern branch joins the North Equatorial Current, whereas the southern branch turns southward and flows along the Brazilian coast as the Brazil Current.
3. South Atlantic CurrentThe Brazil current swings eastward at about latitude 35° S to join the West-wind Drift flowing from West to East.
4. Venezuela CurrentNear the Cape of Good Hope, a branch of the South Atlantic current flows northward along the west coast of South Africa. It is a cold current and is known as the Venezuela Current. It finally joins the South Equatorial Current, thus completing the circuit.
5. Falkland CurrentAnother cold current, known as the Falkland Current, flows along the south-eastern coast of South America from South to North. This brings huge icebergs from the Antarctic region and creates thick fog when it joins the warm water.

Question 9. Describe the circulation of water in the North Atlantic Ocean.
Answer:

Circulation of water in the North Atlantic Ocean may be described as under

1. North Equatorial current flows from the coast of Africa in the East to the West Indies in the West parallel to the equator under the influence of the trade winds.
2. Antilles Current: The South Equatorial current bifurcates into two branches near Cape-de-Sao Roque (Brazil). Its Northern branch reinforces the North Equatorial Current. Part of the combined current enters the Caribbean Sea and the Gulf of Mexico, while the remainder passes along the Eastern side of the West Indies as the Antilles Current.
3. Florida CurrentThe branch entering the Gulf of Mexico is reinforced by a great bulk of warm ocean water driven by the trade winds and by the water brought by the Mississippi River. As a result, the water level in the Gulf rises as compared to that of the Atlantic Ocean. This difference in water level is compensated by the current flowing through the Strait of Florida and this branch is joined by the Antilles current. From the Cape of Florida, the combined current moves along the south-eastern coast of the United States and is known as the Florida Current up to the Cape Hatteras.
4. Gulf StreamBeyond the Cape Hatteras up to the Grand Banks of Newfoundland, it is known as the Gulf Stream. The Gulf Stream receives plenty of warm water from the Gulf of Mexico and carries it to cold areas. In the beginning, it flows along the East Coast of America from southwest to northeast direction. Near Halifax, it comes under the influence of the Westerlies and reaches the Gulf of St. Lawrence. The Gulf Stream is well-defined in deep waters.
5. North Atlantic DriftFrom the Grand Banks, the Gulf Stream flows eastward across the Atlantic under the influence of the prevailing Westerly winds. Here it is known as North Atlantic Drift. Its speed is quite large in the open ocean.
6. Norwegian Current: The North Atlantic Drift is divided into two branches when it reaches the European Coast. The Northern branch reaches the British Isles from where it flows along the coast of Norway as the Norwegian current and enters the Arctic Ocean.
7. Canaries Current: The second branch of the North Atlantic Drift takes a southerly turn and flows between Spain and Azores as the cold Canary current. This current finally joins the North Equatorial current completing the circuit in the North Atlantic. A part of this current enters the Guinea current from the African coast. Some of the above-mentioned currents carry large quantities of water to the Arctic Ocean. In order to maintain the balance, two currents flow from the Arctic Ocean towards the South. They are cold currents because they originate in polar areas.
8. East Greenland CurrentThis current flows from North to South along the eastern coast of Greenland.
9. Labrador CurrentThis current starts from the Baffin Bay and Davis Strait and flows along the coast of Labrador. It brings a large number of icebergs from Baffin Bay. The East Greenland current joins it at the southern tip of Greenland. The joint current moves. further southwards and joins with the Gulf Stream. The confluence of the warm Gulf Stream and cold Labrador Current produces thick fog near Newfoundland which causes great hindrances in navigation.

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Question 10. Describe the currents of the Indian Ocean.
Answer:

The currents of the Indian Ocean

In the Indian Ocean the South Equatorial current, the South-West Monsoon drift, the North-East Monsoon drift, and the Somali current are the noteworthy warm currents. The West Australian Current and Antarctic Drift are cold ones. There are regional currents such as Agulhas, Mozambique and Madagascar. The monsoon winds influence the currents of the Indian Ocean to a large extent.

1. Somali Current: It is a warm current. In the northern part of the Indian Ocean, the current moves toward the southwest influenced by the southwest monsoon from June to September every year, the branch of the South Equatorial current flows towards the Eastern coast of Africa as Somali Current.
2. South-West Monsoon Drift: It is a warm current. After crossing the Arabian Sea and the Indian Ocean, the Somali current flows with the influence of the southwest monsoon.

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3. North-Eastern Monsoon Drift: During the winters, the prevailing monsoons blow in the north-east direction and there is a clear. reversal in the direction of ocean currents. The warm northeast monsoon drift flows from the Bay of Bengal to the Arabian Sea and the east coast of Africa.
4. South Equatorial Current: This warm current flows in the south of the Equator from Indonesia in the East to the east coast of Africa in the west.
5. Mozambique Current, Madagascar Current, Agulhas Current:- It is a warm current. After receiving the West Australian drift, the south equatorial current is divided into two branches by Madagascar Island namely the Mozambique current and Madagascar current. These two currents meet near Agulhas strait in the Southern tip of Africa and here the current is known as Agulhas Current. After flowing towards the East it ultimately merges with Antarctic Drift.
6. West Australian current is a cold current. A branch of cold Antarctic Drift enters into the Indian Ocean and flows along the west coast of Australia and merges with the South Indian Equatorial Current.
7. Antarctic Drift: This drift flows across the Indian Ocean, Pacific Ocean and Atlantic Ocean without any interference from the West to East direction. Due to the vast snow and ice around the Antarctic, it becomes a cold current.

Question 11. How are ocean currents caused?
Answer:

The causes of the formation of ocean currents are given below:

1. Prevailing Winds: Prevailing winds influence ocean currents more than any other single factor. These winds blow consistently in a particular direction and drag the surface water due to the force of friction. This leads to the formation of ocean currents. Within the tropics, there are trade winds blowing from the East. They are responsible for North Equatorial and South Equatorial currents flowing from East to West. The temperate lands are under the influence of westerlies and the ocean currents flow from West to East. The best example of the influence of winds on the currents is found in the North Indian Ocean where the ocean currents change their direction with seasonal changes in the direction of monsoon winds.

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2. Temperature Differences: Temperature is high at the equator and low at the poles. The equatorial water becomes lighter on heating while water in polar areas becomes heavy due to cooling. The warm light water floats and the cool heavy water sinks. This makes a difference in the level of the sea. To maintain the balance, water from equatorial areas moves towards the polar areas in the form of currents. To counter this, polar currents flow towards the equator under the surface.

3. Salinity Differences: Water having high salinity is heavier and it subsides. As a result, light water with less salinity rushes towards the area of high salinity and the current is formed. To maintain the balance, an undercurrent of high saline water moves towards the area of lower salinity. For example, the water of the Mediterranean Sea has more salinity than that of the Atlantic Ocean. This results in the flow of a surface current from the Atlantic towards the Mediterranean and an undercurrent from the Mediterranean to the Atlantic.

4. Evaporation: More evaporation reduces the amount of water and lowers its level. In order to maintain the balance, water from other areas starts flowing in the form of a current. For example, evaporation is more in the Mediterranean Sea than in the Atlantic Ocean. This lowers the water level in the Mediterranean sea and a current flows from the Atlantic Ocean.

5. Rotation of the Earth: The earth rotates around its axis due to which Coriolis force becomes effective. Thus, according to Ferrel’s law, currents move to their right in the Northern Flemisphere and to their left in the Southern Hemisphere. This results in the formation of new currents. For example, a part of the North Atlantic is turned towards the South and Canary current is formed.

6. Shape of the Coasts: The shape of coasts also influences ocean currents. The currents of the North Indian Ocean follow the coastline of the Indian subcontinent. The South equatorial current of the Atlantic Ocean is divided into two parts on reaching the Brazilian coast. One branch turns northwards and reaches the Caribbean Sea. The other branch turns southwards and flows along the coast of Brazil in the form of Brazil current.

7. Change of Season: Change of season changes the direction of the flow of the currents. The best example is offered by the currents of the North Indian Ocean. In winter, the monsoon drift flows from East to West and in summer it flows from West to East. The counter equatorial current is found in winter only and the equatorial current in summer only.

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Question 12. Explain the influence of salinity & prevailing winds regarding ocean currents.
Answer:

Prevailing Winds: Prevailing winds influence ocean currents more than any other single factor. These winds blow consistently in a particular direction and drag the surface water due to the force of friction. This leads to the formation of ocean currents. Within the tropics, there are trade winds blowing from the east. They are responsible for North Equatorial and South Equatorial currents flowing from East to West. The temperate lands are under the influence of westerlies and the ocean currents flow from West to East.

Temperature Differences: Temperature is high at the equator and low at the poles. The equatorial water becomes lighter on heating while water in polar areas becomes heavy due to cooling. The warm light water floats and the cool heavy water sinks. This makes a difference in the level of the sea. To maintain the balance, water from equatorial areas moves towards the polar areas in the form of currents. To counter this, polar currents flow towards the equator under the surface.
Salinity Differences: Water having high salinity is heavier and it subsides. As a result, light water with less salinity rushes towards the area of high salinity and a current is formed. To maintain the balance, an undercurrent of high saline water moves towards the area of lower salinity.

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Question 13. Explain the effect of ocean currents on man.
Answer:

Effect of Ocean currents on man:

1. Currents influence climate, trade and the presence of organisms in oceans.
2. Oceans supply food to a man in large quantities.
3. Currents affect precipitation, temperature and humidity of coastal areas.
4. Cold currents decrease the temperature of these areas and decrease the water-bearing capacity of the winds blowing over them. So, these winds give almost no rain on the windward side.
5. Peruvian cold current decreases the temperature of the western coast of Chile.
6. On the other hand, waters of the warm North Atlantic Drift raise the temperature of coastal areas of North Western Europe up to the Lofoten Isles (Norway). The North West coast of Western Europe upto Lofoten Isles does not freeze even in winter and trade and shipping activities remain in full swing throughout the year.
7. In the same latitudes the eastern coasts of Labrador and Greenland are frozen in winter due to the effect of the cold Labrador current.
8. North Atlantic Drift also increases the rate of evaporation and the water-bearing capacity of the westerlies blowing over the East North Atlantic. These westerlies cause rain throughout the year on the West European Coasts.
9. Warm Gulf Stream and Cold Laborador currently meet each other near the New Foundland Island on the east coast of North America. They create dense fog, sometimes resulting in ship collisions and their sinking. These regions are also prone to storms and high-velocity winds. Continental shelves and banks adjoining New Foundland and Japan Coasts abound in fish.
10. Warm and Cold currents also carry various types of fish with them and their confluence is the storehouse offish. Currents from warmer regions bring Sargassum, which serves as food for fish.
11. Currents carry various types of organisms from one place to another. Equatorial currents and warm currents are a very good sources of these organisms which thrive in warm water Tropical areas obtain fish in abundance as the cold currents carry fish from high-latitude regions.
12. Warm and cool currents provide oxygen to ocean organisms. Organisms also develop on them.

Question 14. (1)What is a hydrosphere? What are the divisions of the Hydrosphere?
(2)Mention the importance of the hydrosphere.
(3)What are the causes of temperature variations of seawater?
Answer:

(1) Hydrosphere includes all the waterbodies of the earth as distinct from the atmosphere and lithosphere. It includes both the comparatively shallow layer of water, which covers nearly three-quarters of the earth’s surface, forming the oceans, seas, lakes, ice sheets, etc., and also the water that is present in the atmosphere. The largest divisions of water are called Oceans which are five in number; these are the Pacific, Atlantic, Indian, Arctic and Southern Ocean or Antarctic Ocean. The Pacific is the largest ocean. It is ringed by mountains, 10 km deep trenches, and volcanoes. The Atlantic is a great highway linking the people and resources of Europe, America, and Africa. The Indian Ocean is the only ocean to be named after a country. The largest sea.is the China Sea and the Bay of Bengal is the largest Bay. But they are only extensions of the ocean.
(2)The importance of the hydrosphere as a highway, as a moderator of climate, as a reservoir of water, as a source of food and raw materials for a number of industries, is certainly great.
(3)The temperature of the seawater on earth’s surface depends mainly on two factors-latitudes and seasons. Within the tropics, the temperature of the seawater is always high. But it decreases towards the poles. In the polar regions, the temperature of the seawater may reach a freezing point. The sea gets warm during the day, but it loses its heat slowly at night. So, the daily range of temperature is very small. In winter, the temperature of the seawater is higher than that on land. The temperature of the seawater decreases towards the bottom except in the polar seas. The temperature of the bottom of all seas is almost the same everywhere.

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Question 15. Give a concise description of the Pacific Ocean currents.
Answer:

From the point of view of the study of ocean currents, the Pacific Ocean is divided into North Pacific and South Pacific.

Currents of the North Pacific Ocean:

1. North Equatorial Current: It flows across the ocean from East to West, increasing in volume as it flows West. Starting from the West coast of Central America, it reaches the Philippine Islands in the Western Pacific Ocean.
2. Kuro Shio Current: On reaching the Philippine Islands, the north equatorial current turns towards the North along the coasts of Taiwan and Japan and is known as Kuro Shio current.
3. North Pacific Current: After reaching the South-East coast of Japan the Kuro Shio current comes under the influence of the prevailing westerlies and flows from East to West. Here it is known as North Pacific Current.
4. Californian Current: The North Pacific Current is bifurcated into two currents on reaching the west coast of North America. It’s one branch goes towards the North and the other is turned towards the South. The southward current flows along the coast of California as a cool current. It is known as California Current.
5. British Columbia or Alaska Current: The northern branch of the North Pacific Current flows anti-clockwise along the coast of British Columbia and Alaska, and is known as the British Columbia current or Alaska Current. The water of this current is relatively warm as compared to that of the sea in this zone.
6. Oya Shio Cold Current: It starts from Bering Strait and flows southwards as a cold current along the East coast of the Kamchatka Peninsula.
7. Okhotsk Current: Another cold current in the North Pacific is the Okhotsk Current which flows past Sakhalin to merge with the Oya Shio Current of Hokkaido. The Oya Shio finally merges with and sinks beneath the warmer water of the Kuro Shio.

Currents of the South Pacific Ocean:
(1)South Equatorial Current: It is a warm current that flows almost parallel to the equator from the coast of Central America in the East towards the East coast of Australia.
(2)East Australian Current: The south equatorial current turns towards the South on reaching the coast of New Guinea under the influence of Coriolis force. It is a warm current which flows along the East coast of Australia. Hence, it is known as East Australian Warm Current.
(3)South Pacific Current: The East Australian current turns towards the east under the influence of the westerlies and is known as South Pacific Current.
(4)Peru Current: On reaching the south-western coast of South America the South Pacific current turns northward and flows along the Peru Coast as the Peru Current. It is also known as the Humboldt current because it was discovered by Alexander Von Humboldt of Germany. It is a cold current which finally meets the South Equatorial Current, completing the great circuit.
(5)Counter Equatorial Current: Between the North and the South Equatorial Currents, a current flows from West to East which is known as the Counter Equatorial Current. The North and the South Equatorial Currents cause an accumulation of water in the western parts which disturbs the surface level. This difference in level makes the Counter Equatorial current flow eastward.

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Question 16. (1) What do you know about the importance of ocean currents?
(2)Why is there always dense fog along the coasts of New found land?
(3)What is Cold Wall?

Answer:
(1) Importance of Ocean Currents: Ocean currents are important to mankind as they influence the weather, climate, navigation, and the character and quality of marine life. Warm currents tend to have to modify and warming effects on the coasts of countries along which they flow. Cold currents tend to produce a drying and cooling effect on coastal countries along which they flow. Ocean currents have been helping trade and commerce for thousands of years as boats and ships sail with the ocean currents. The density of ocean water is associated with down-swelling and up-swelling.

Up- swelling brings water rich in nutrients and dissolved gases to the surface. The food pyramid of marine life grows here. Plankton germinates here. Most of the fishing grounds of the ocean are situated at the converging points of cold and warm ocean currents. Phytoplankton and Zooplankton constitute the essential food of fish. Warm currents help many ports in the Arctic region to function even in winter. Hydroelectricity is generated. from the ocean currents.

(2)Dense fog along the costs of the new Foundland: The cold Labrador Current and the Warm Gulf Current (stream) meet near the coast of Newfoundland. The wind that blows over the cold current is cold and dry, but the wind that blows over the warm current is hot and moist. As a result of the mixing of these two different types of winds, fog is formed along the coast of Newfoundland throughout the year. Because of this, the coast of Newfoundland remains foggy all year round.

(3)Cold wall: The cold wall is a discontinuity layer between Cold Labrador Current and the Warm Gulf Stream. The Labrador current carries meltwater of Greenland’s icebergs southward. The Gulf stream transports high temperatures northward. The water of the Labrador Current is nearly 80 to 110 degrees Celsius cooler. Individual water masses of Gulf-Stream, Labrador Current are of different temperatures and salinity and of the opposite direction of movement from the Cold wall.

Question 17. Give an account of the different oceans of the world.
Answer:

Different oceans of the world

All the oceans of the world are connected. They cover 361,000,000 sq. km out of the earth’s total surface of 501,000,000 sq. km. The important oceans are described below.
1. The Pacific Ocean: The Pacific Ocean is oval in shape with the greatest length from east to west. It has North America and South America on its east. and Asia and Australia on its west. It is the biggest ocean in the world and is double the size of the Atlantic Ocean. It is believed that all the land of the world could be placed in it and still a portion of the Ocean as big as Africa will be left over. It has a much shorter and regular coastline and fewer harbours than the Atlantic Ocean. Its shores are bordered by less fertile and less commercial lands. It has consequently less commerce than the Atlantic Ocean. It has, however, great resources of fish. It is the deepest ocean, with an average depth of 4,200 m. There are greater deeps in this ocean than in the Atlantic. The greatest known depth of the sea in the world is at the Mariana Trench, 320 km southwest of Guam.

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2. The Atlantic Ocean: The Atlantic Ocean is “S” shaped with the greatest length from north to south. It is the second-largest ocean in the world. There is a ridge of the same shape running almost in the middle, called the Central Ridge. Most of the islands of the Atlantic lie on this ridge. The Atlantic coastline is greatly broken and is bordered by the most fertile lands of Europe. The Atlantic Ocean is the biggest highway of commerce. It covers an area of about 82,160,000 sq. km. The average depth of the ocean is between 3 and 5 km or 2,200 fathoms (4092 metres). The greatest depth lies off the Dominican Republic and is 9,400 metres.

3. The Indian Ocean: It is the third largest ocean in the world, covering approximately 20 per cent of the water on the earth’s surface. It is bounded on the north by the Indian subcontinent, on the west by East Africa, on the east by Indochina, the Sunda islands and Australia. It is the only ocean to be named after a country, India. The greatest known depth of 7,067 metres lies in the Sunda Trench, south of Java.
The Suez Canal connects the Indian Ocean with the Mediterranean Sea, therefore, its trade has greatly increased during the last century.

4. The Arctic Ocean: It is situated around the North Pole and remains perpetually frozen. It is connected to the Atlantic Ocean by the Eastern and Western Greenland Channels and to the Pacific Ocean by the Bering Strait.
There are some geographers who regard the area around the continent of Antarctica as the Antarctic ocean. But most experts think that this part of the globe has no natural boundaries on the north, and consists largely of the southern extremities of the three major oceans—Pacific, Atlantic and Indian. The Arctic is strictly not an ocean as it is not navigable. It winds around the North Pole and is completely frozen in winter and covered with drifting ice for the rest of the year. Its separate existence and its area of over 13 million sq km entitle it to be called an ocean.

Class 10 Geography Book West Bengal Board

The marginal seas like the Caribbean, the Mediterranean and the Bering seas are not included in the above water surface. Sea is described as a saltwater body usually on the margins of the continents. Besides the above three seas, other important seas are the Arctic Sea, Sea of Japan, Barents Sea, Kara Sea, East China Sea, Andaman Sea, Arabian Sea and Red Sea. The average depth of oceans is 3800 m against the average height of 840 m of the lithosphere. The highest summit on land surface is Mount Everest – 8848 metres above sea level. The deepest bottom of the ocean is Mariana Trench -11,033 metres below sea level. The difference in height between the greatest depth and the highest summit on the surface of the earth is thus only 19.9 km. This is very small in relation to the earth’s diameter.