Important Questions: Water (Oceans) | Geography Class 11 - Humanities/Arts PDF Download

Very Short Answer Type Questions

Q1: How would you classify the large water bodies?
Ans: The large water bodies can be classified into four groups, viz., oceans, intercontinental seas, enclosed seas and fringing seas.

Q2: Give three examples of intercontinental seas.
Ans: They are Malays Sea, Central American Sea and the Mediterranean Sea.

Q3: Identify some fringing seas.
Ans: Baring Sea, Japan Sea, East China Sea, Andaman, California, North Sea, Laurentian Sea, Bass Sea, English Channel and Irish Seas.

Q4: What are the first order relief features of the earth?
Ans: Continents and ocean basins are the first order relief features of the earth.

Q5: Mention three types of features of the ocean basin floor.
Ans: The ocean basin floor contains three types of features, viz.,

• abyssal plains and hills,
• oceanic rise and
• seamounts.

Q6: What is the major salt presents in the seawater?
Ans: The major salt present in seawater is sodium chloride.

Q7: Where is the tallest sea mount situated?
Ans: The tallest seamount is situated between Samoa and New Zealand which is 8690 m. high from the surrounding ocean floor.

Q8: What is residence time?
Ans: The average time that an element remains dissolved in the ocean before removal is known as residence time.

Short Answer Type Questions

Q9: What are oceanic deeps?
Ans: The oceanic deeps are deeper than the abyssal plains. They occupy 2% of the oceanic area. Although deeps are found in the Pacific ocean. Mariana deep is the deepest deep in the Pacific Ocean.

Q10: Define the continental shelf.
Ans: From the coasts towards the open sea, there often exists a stretch of the shallow sea. The bed of this shallow sea bordering the continental platform is known as the continental shelf. It is a continuation of the continental block submerged below the sea. It slopes gently towards the sea, the angle of slope usually being less than one degree. The depth of the shallow seas rushing over a continental shelf varies from low tide to about 100 fathoms. Along the eastern coast of India, there exists a fairly wide strip of the continental shelf.

Q11: What are seamounts?
Ans: Seamounts are topographical features rising from the ocean floor. A seamount is an isolated peak, usually a volcano, with a pointed summit, usually lies below the ocean surface, sometimes 3000 m. below.

Q12: Write a short note on the continental rise.
Ans: Continental rise is a submarine feature of the continental margins. Along its seaward margin, the continental shelf gives way to the continental slope. The slope is abruptly replaced by the continental rise. Continental rise is a surface of much gentler slope decreasing in steepness toward the ocean basin floor. It generally has a moderate to low relief.

Q13: Why is the seawater saline?
Ans: The seawater is saline because a number of salts are dissolved in it. The total weight of salts dissolved in the sea is 4800 million tonnes. Of these, sodium chloride, or common salt, accounts for 3800 million tonnes, sulphate for 3000 million tonnes, magnesium for 1600 million tonnes, potassium for 480 million tonnes and bromide for 83 million tonnes. The seawater may be less saline or more saline depending upon the extent of evaporation, river discharge and precipitation, but salt composition remains invariable.

Long Answer Type Questions

Q14: What type of relief features exists in the ocean basin floor?
Ans: The ocean basin is an extensive region of the basin floor, generally lying at a depth ranging between 2,500 and 6,000 m. It covers about 76.2% of the ocean’s area.
The ocean basin floor contains three types of relief features:

• abyssal plains and hills,
• oceanic rise and
• seamounts.

An abyssal plain is an area of the deep ocean floor having a flat bottom with a very faint slope. Characteristically situated at the foot of the continental rise, the abyssal plain is present in all ocean basins. Abyssal plains are surfaces formed by long-continued deposition of very fine sediments and, therefore, have a nearly perfect flatness. Abyssal hills are small hills rising to heights of a few tens of metres to a few hundred metres above the sea basin floor. The ocean rise is an area hundreds of km. in the breadth over which the surface rises several hundred metres above the surrounding abyssal plain. Within the rise, the relief may range from subdued to very rugged. Seamounts are the isolated peaks that rise 1000 ms. or more above the seafloor. Many of the seamounts are conspicuously flat-topped and extremely steep riched, named guyot.

Q15: Describe the hydrological cycle in brief.
Ans: The hydrological cycle is the continuous circulation of water from the earth’s surface to the atmosphere. Water from the oceans is evaporated and lifted into the atmosphere. It is eventually condensed and is returned back to the earth’s surface in the form of rain, hail, snow or sleet. Some of the precipitation, after wetting the foliage and ground, runs off over the surface to the streams. It is the water that sometimes causes erosion and is the main contribution to floods. Of the precipitation that soaks into the ground, some are available for growing plants and for evaporation. Some reach the deeper zones and percolates through springs and seeps to maintain streams during the dry period. The streams, in turn, eventually return the water back to the oceans where it originated. It is because of this never-ending circulation that the process has come to be known as the hydrological cycle.
The hydrological cycle is mathematically expressed as:

• RF = RO + ET, where RF-includes all types of precipitation, RO is runoff and ET is evapotranspiration.

Runoff occurs when precipitation, that does not have an opportunity to infiltrate into soil, flows across the land surface. However, most of it enters the stream channel ultimately, which carries it to the oceans. A part of precipitation that infiltrates the soil percolates downward to the water table through springs. Broadly speaking, runoff is composed of water from both surface flow and seepage flow. It is an extremely important segment of the hydrological cycle. Rainwater that reaches the soil surface is wholly or partly absorbed by the soil in the process of infiltration. The amount of rainfall entering the soil depends upon the s* rate of rainfall and infiltration rate of the soil.

Q16: Prepare a map of the Atlantic Ocean floor, mentioning ocean basins and mid-Atlantic ridges.
Ans: The Atlantic Ocean covers about one-sixth of the earth’s area. Resembling ‘S’ in shape, the ocean is bounded on the west by North America and South America, and On the east by Europe and Africa. To the south, it extends up to Antarctica and in the north, it is bounded by Greenland and Iceland. The mid-Atlantic ridge, running from north to south in ‘S’ form is about 14,450 km. long and about 4000 m. high. The ridge has a broad fracture in the middle and slopes on both sides gently. The mid-oceanic ridge in the North Atlantic is known as Dolphin Ridge, and that in the South Atlant ic as the Challenger Ridge. A number of islands are located on the ridge.
The mid-Atlantic ridge divides the ocean into two major basins, namely, the East and West Atlantic basins. Some other basins in the Atlantic are the North American basin, The Labrador basin, The Brazil basin. The Argentina, Agulhas, Angola, and the West.

Q17: Identify various layers of the ocean based on the level of salinity.
Ans: The salinity of the water is the ratio of the total weight of dissolved solids to the weight of water. It is variable in quantity, differentiating in value from place to place over the oceans and at various depths. The average salinity is 35 per thousand. The relationship of salinity to depth is analogous with the three-layer temperature systems.

• First and the topmost layer is the shallow surface layer of high salinity (35.0 to 36.5 per thousand)
• Below this layer is a zone of rapid decrease in salinity, called a halocline. It corresponds with the thermocline.
• Below the halocline, differences in salinity’ are very small and salinity lies in the range of 34.6 to 34.9 per thousand for most of the ocean body. Thus, the salinity decreases with the increasing depth.