8th Standard, Social, Geography, CHAPTER 26
HYDROSPHERE
EXERCISES
I Fill in the blanks with suitable words:
1. The average depth of the continental shelf is 100 fathoms (1 fathom is equal to 6 ft.).
2. One fathom is equal to 6 ft.
3. The deepest place in the Pacific Ocean is The Challenger deep of Mariana trench.
4. The average salinity of the ocean water is 35 PPT (Parts per thousand) or 35 grams/1000 grams).
5. Spring tides occur during full moon.
II Answer the following questions briefly:
6. What is hydrosphere?
Answer: The Earth is popularly called ‘Blue planet’ or ‘Watery planet’ because about 70.78% of the total area of the earth or 361 million sq. km is covered by water. The hydrosphere is the total amount of water on, under, and above the Earth’s surface. It includes all forms of water—solid (ice), liquid (oceans, lakes, rivers, groundwater), and gas (water vapor)—and covers about 71% of the Earth’s surface.
7. Mention the four major parts of the ocean floor.
Answer: The ocean floor is divided into four major parts. They are
a) The continental shelf
b) The continental slope
c) The deep sea plain
d) The ocean deeps
8. State the difference between ocean currents and tides.
Answer: The difference between ocean currents and tides are as follows.
- Ocean currents are the regular movement of ocean water from one region to another. Tides are the periodic rise and fall in the sea or ocean level. They occur due to, gravitational attraction by the moon, gravitational force by the sun, rotation of the earth and, centrifugal force of the earth.
- The two types of Ocean currents are Warm currents and Cold currents. There are two types of tides are Spring Tide and Neap Tide.
- Factors that influence ocean currents are Rotation of the Earth, Temperature, Wind, Salinity, Shape of the landmasses, etc. But the Tides influenced by the basis of the positions of the Moon and the Sun.
9. Distinguish between spring tide and neap tide.
Answer:
- Spring tides take place when the earth, the moon and the sun are in the same straight line, eg, New moon and Full moon. Neap tides occur on the first quarter and last quarter days in the phase of the Moon. During neap tides the sun and the earth are in the same straight line and moon is in right angle to the earth.
- When the spring tides take place, high tides are the highest and low tides are the lowest. In Neap tides the high tides are not very high and low tides are not very low.
- Spring Tide: The gravitational pulls of the Sun and Moon combine, leading to a greater pull on the Earth’s oceans.
Neap Tide: The gravitational pulls of the Sun and Moon work against each other, partially cancelling out the effect.
10. How can we conserve the oceans?
Answer: The following are the important methods of conservation of oceans.
1. Oil transportation should be done through pipelines.
2. Nuclear waste should not be dumped into the sea or ocean.
3. Petro-chemical industries in the coastal regions must avoid dumping effluents into the sea or ocean.
4. Dumping of any waste near the ports and harbours must be controlled.
5. Ore deposition and mineral exploitation along the coast must be controlled.
6. Exploitation and destruction of beaches must be controlled.
III Match the following:
A B
i. fathom a) deep sea plain
ii. oyashio b) eastern coast of USA
iii. gulf stream c) cold current
iv. sea mounts d) Indian ocean current
v. agulhas current e) Measuring the depth of ocean
Answer:
A B
i. fathom e) Measuring the depth of ocean
ii. oyashio c) cold current
iii. gulf stream b) eastern coast of USA
iv. sea mounts a) deep sea plain
v. agulhas current d) Indian ocean current
IV Define the following:
11. Continental shelf 14. High tide and low tide
12. Salinity 15. benguela current
13. Warm and cold currents 16. Tides
11. Continental shelf: This is the shallow area along the sea coast. This part is bordered by the sea coast on one side and continental slope on the other side. The average depth of the continental shelf is 100 fathoms (1 fathom is equal to 6 ft). The depth of the sea in this region gradually increases towards the continental slope. The continental shelf is very important for fishing, aquaculture, navigation and extraction of minerals.
12. Salinity: Salinity is the percentage of salts dissolved in the sea or ocean water. The average salinity of the ocean water is 35 PPT (Parts per thousand) or 35 grams/1000 grams). The salinity of ocean water is very high near the tropics and it is very low near the poles.
13. Warm and cold currents: Warm currents: These currents originate and flow from the equatorial regions to sub-polar regions.
Cold currents: These currents originate in the polar regions and flow towards the equatorial region.
14. High tide and low tide: Tides are of two types. High tide, also known as Flood tide and Low tide, also known as Ebb tide. On the water bodies of the earth there are alternate high tides and low tides. Between one high tide and a low tide the time is 6 hrs, 13 minutes. Between one high tide and another, the timegap is 12 hrs, 26 minutes. In 24 hrs, 52 minutes there are 2 high tides and 2 low tides.
15. Benguela current: This is one of the cold current is found in South Atlantic Ocean. These Cold currents originate in the Polar Regions and flow towards the equatorial region.
16. Tides: Tides are the periodic rise and fall in the sea or ocean level. They occur due to, gravitational attraction by the moon, gravitational force by the sun, rotation of the earth and, centrifugal force of the earth.
V Terms to remember:
1. Gulf: Gulf is a part of an ocean or sea that penetrated into the land. It is smaller than a sea. The size, shape and depth of a gulf varies from one to another, e.g., the Gulf of Mannar, the Persian Gulf, the Gulf of Mexico.
2. Salinity: Salinity is the percentage of salts dissolved in the sea or ocean water. The average salinity of the ocean water is 35 PPT (Parts per thousand) or 35 grams/1000 grams). The salinity of ocean water is very high near the tropics and it is very low near the poles.
3. Warm currents: These currents originate and flow from the equatorial regions to sub-polar regions.
4. Kuroshio current: Kuroshio Current is one of the warm currents is found in North Pacific Ocean.
5. High tide and low tide: Tides are of two types. High tide, also known as Flood tide and Low tide, also known as Ebb tide. On the water bodies of the earth there are alternate high tides and low tides.
6. Tidal energy: Tidal energy is a renewable energy source generated from the natural rise and fall of ocean tides, driven by the gravitational pull of the moon and sun.
VI Activity:
- List out the cold and warm currents in Atlantic Ocean.
Answer: The cold and warm currents in Atlantic Ocean are as follows.
The cold currents in Atlantic Ocean: Labrador current, Norwegean current, Canary current, Falkland current, Benguela current
The warm currents in Atlantic Ocean: North equatorial current, Gulf stream, North Atlantic drift, South equatorial current, Brazilian current
