Important Questions: Movements of Ocean Water | Geography Class 11 - Humanities/Arts PDF Download

Very Short Answer Type Questions

Q1: What are the important mechanisms by which ocean currents are generated?
Ans: The important mechanisms are:

• The drag of winds over the ocean surface, and
• Unequal forces set up by differences in water density.

Q2: Give the other name of tropical easterlies.
Ans: Tropical easterlies are also known as trade winds.

Q3: What kind of currents results due to differences in water density?
Ans: Differences in water density set currents in a motion described as thermocline currents.

Q4: Which current flows as Kuroshio current after reaching the coasts of Taiwan and Japan?
Ans: The North equatorial current flows as Kuroshio current after reaching the coasts of Taiwan and Japan.

Q5: Define waves.
Ans: Waves are oscillatory movements in water, where its particles move in a vertical plane, up and down.

Q6: What is the difference between flood tide and ebb tide?
Ans: Rise of sea level is called the flood tide and fall is called ebb tide.

Q7: Up to what depth in water, the photosynthesis is possible for plants?
Ans: The sunlight penetrates water up to 900 metres, but only in the top 100 metres is there enough light for plants to do photosynthesis.

Q8: At what interval of time do the tides occur on each meridian and why?
Ans: Each meridian has a high and a low tide at an interval of 12 hrs. and 26 minutes, due to rotation of the earth.

Short Answer Type Questions

Q9: Give reasons why the height of tidal waves varies from place to place?
Ans: The height of the tidal waves varies from place to place because of the following reasons:

• The relative position of the moon and the sun with respect to the earth,
• Distribution of land and ocean on the earth’s surface, and
• Irregularities in the configuration of oceans.

Q10: What is a tidal bore?
Ans: ‘The tidal waves follow the direction of the moon. In certain inland seas, where tidal waves reach from different directions, one can find a number of high tides and low tides. When such waves enter a gulf or river mouths, the tidal crests look like a vertical wall of water rushing upstream, which is known as the tidal bore.

Q11: Explain how differences in water density set currents in motion?
Ans: Differences in water density can also set currents in motion These are described as thermocline currents. A surface water layer in one place may be less dense because it is warmer, or lower in density than the water layer in adjacent place that is colder or has a higher density. The water then moves gently from the region of less to the higher density.

Q12: Describe the mechanism of origin of sea waves.
Ans: It is commonly believed that the waves are generated due to friction on water surface caused by winds. The height of sea waves depends on:

• The wind speed,
• The duration of wind from a particular direction, and
• The fetch or the expanse of water surface over which the wind blows.

Q13: Discuss the properties of waves.
Ans: Waves are oscillatory movements in water, where its particles move in a vertical plane, up and down. The upper part of the wave is called the crest, and the lower part is called the trough. Each wave has a wavelength, velocity, height and wave period. The distance between two successive crests or two successive troughs is the wavelength. The time taken by a wavelength to pass a fixed point is known as the wave period. The vertical distance between a trough and a crest is called the wave height. The ratio of wavelength to the wave period gives the velocity of the wave.

Q14: Describe the types of ocean currents and their flow mechanism.
Ans: Ocean currents are of two types: warm and cold currents. The main currents flow from the low latitudes in tropical zones towards high latitudes in the temperate and sub-polar zones. The cold currents flow from high latitudes to low latitudes.

Q15: What are tides?
Ans: Tides are periodic rise and fall in the level of water in seas and oceans caused by the differential attraction of the moon and the sun. Twice a day, about every 12 hrs and 26 minutes, the sea level rises and falls. The rise of sea level is called the flood tide and the fall is called the ebb tide.

Long Answer Type Questions

Q16: Write a short note on a spring tide and neap tide.
Ans: Tides are the periodic rise and fall in the level of water in seas and oceans caused by the differential attraction of the moon and the sun. Twice a day, about every 12 hrs and 26 minutes, the sea level rises and falls.

• Tides do not rise to the same height every day. The relative position of the moon and the sun with respect to the earth is responsible for this variation in the height of tides. On the full moon and the new moon, the moon and the sun are almost in line with the earth, and hence, they exert their combined puli. Therefore, on these two days, tides are the highest and are known as spring tides.
• On half-moon, the sun and the moon make a right angle at the earth’s centre. The pulls of the moon and the sun partly cancel each other out. as a result of which there are usually low tides called neap tides. This happens on the first and the last quarter of the lunar month when due to their right angular position to the attraction1 and centrifugal forces of the sun and the moon do not combine. This reduces the height of the tides to the minimum.

Q17: Write a short note on the vertical circulation of ocean water.
Ans: Besides the horizontal movement, the vertical circulation of ocean water is also an important phenomenon. Ocean surface is marked with sinking and upwelling caused by wind action, evaporation of surface water, the addition of surface water by rainfall and changes in density due to cooling or warming of the surface layer. A most important cause of the sinking of ocean water on a large scale is cooling of the surface layer by loss of heat to the overlying atmosphere in high latitudes. During long winters, much heat is lost to space than is gained by solar radiation, thereby the relatively warm surface waters brought polewards v by ocean currents are drilled and increased in density. This water, generally close to the freezing point, sinks to the ocean floor, causing vertical circulation of the water.

Q18: Distinguish between swash and backwash.
Ans: When ocean waves arrive at the coast of a continent or island, they encounter shallow Water. The configuration of coast interferes with the progress of the waives. Waves in shallow water are modified into ellipses that become progressively flattered as the coast is approached, As the steeping waves continue to travel shoreward, encountering still shallower water, the crest height increases sharply and the forward slope of the wave becomes greatly steepened. At a critical point, the ‘ waveform disintegrates into a mass of turbulent water called the breaker. Thereafter, it becomes a landward moving sheet of highly turbulent water known as the swash or uprush.
The water then begins to pour seaward down the slope in a reverse flow termed as backwash or back rush. Thus, backwash is the seaward flow of a body of water down the slope after a wave has broken on the beach, in contrast to swash. It may also be called the drag of a recording wave.

Q19: If there were no ocean currents, what would have happened to the world? Discuss.
Ans: The oceans contain about 3% of the total water on earth. This water is always available for evaporation into the atmosphere and its subsequent precipitation on the land and the seas.
The general movement of a mass of ocean water in a fairly defined direction over great distances is called the ocean current. Current ranges in scale from ocean-wide flow system to local currents of small extent and can be generated by several mechanisms.’ Ocean currents are broad of two types: warm and cold currents. The warm currents flow from the low latitudes in tropical zones towards the high latitudes in the temperate and polar zones. The cold currents flow from high latitudes to low latitudes.
Water has an exceptionally great capacity for absorbing heat. The circulation of ocean water through currents helps in distribution of heat received in low latitudes to certain areas of high latitudes. In this way, the oceans modify the climate of the earth. Without ocean currents, this modification of climate would not have been possible.
The distribution of rich fishing grounds in the oceans and seas depends upon the circulation of water of the oceans as they bring nutrients to the surface in some areas. This process of bringing nutrients – both mineral and organic to the surface through the upwelling of water and its circulation is known as the ploughing action of the seas. Ocean currents aid in these processes. The absence of ocean currents would have hampered this process.
Ocean surface is marked with sinking (surges) and upwelling (swells) caused by wind action, evaporation of surface water, the addition of surface water by rainfall and changes in density due to cooling or warming of the surface layer. A most important cause of the sinking of ocean water on a large scale is cooling of the surface layer by loss of heat to the overlying atmosphere in high altitudes.
During long winters, much heat is lost to space, than is gained by solar radiation, thereby relatively warm surface waters brought poleward by ocean currents are chilled and increased in density. This water may be close to the freezing point and, therefore, sinks to the ocean floor. Without ocean currents, all the above activities of the ocean water would not have taken place.

Q20: Describe the currents of the Pacific ocean in brief.
Ans: The Pacific Ocean is the largest and deepest ocean on Earth, covering an area larger than all the Earth's landmass combined. Its currents play a significant role in regulating the planet's climate and weather patterns. Here's a brief overview of the major currents in the Pacific Ocean:

North Pacific Currents:

• Kuroshio Current: This is a warm north-flowing ocean current on the western side of the North Pacific Ocean. It is analogous to the Gulf Stream in the Atlantic Ocean and is a major driving force behind the region's climate.
• California Current: Flowing southward along the western coast of North America, this current is relatively cold due to upwelling, which brings nutrient-rich waters to the surface, supporting a diverse marine ecosystem.

Equatorial Currents:

• North Equatorial Current: Flowing westward along the equator in the Pacific, this current is part of the subtropical gyre in the northern hemisphere.
• South Equatorial Current: Its counterpart in the southern hemisphere, flowing westward along the equator.

Western Pacific Currents:

• North Pacific Drift: This current flows from the western Pacific Ocean into the Bering Sea, influencing the climate and marine life in the region.
• East Australian Current: Flowing southward along the eastern coast of Australia, this warm current influences the climate of the Australian east coast and the Great Barrier Reef ecosystem.

Southern Pacific Currents:

• East Pacific Current: Flowing from the southern coast of South America to the equator, this current helps regulate the climate of the western coast of South America, including the El Niño and La Niña phenomena.
• Humboldt Current: Also known as the Peru Current, it flows northward along the western coast of South America, bringing cold, nutrient-rich waters to the surface, supporting one of the most productive marine ecosystems in the world.

Central Pacific Currents:

• North Pacific Subtropical Gyre: This large system of rotating ocean currents dominates the central and northern Pacific Ocean. It traps debris, leading to the formation of the Great Pacific Garbage Patch.
• South Pacific Gyre: Similar to its northern counterpart, this gyre influences the central and southern Pacific Ocean, shaping oceanic circulation patterns.

These currents, along with the interactions between them, have a profound impact on the climate, marine life, and weather patterns across the Pacific region and even globally.