Structure of the Ocean Floor | Class 8 | Geography | Chapter 4| Maharashtra State Board
Explore the fascinating structure of the ocean floor. Learn about landforms like continental shelves, slopes, abyssal plains, and marine trenches, their significance, and their impact on marine life and human activities.
Questions & Answers
1. Choose the correct option:
a. Like there are landforms on land, ocean floor also has submerged landforms because ………….
(i) there is land under water
(ii) there are volcanoes under water
(iii) land is continuous and there is water in deeper parts
(iv) though land is continuous, its level is not the same everywhere like that of water
Ans.
(iv) though land is continuous, its level is not the same everywhere like that of water
b. Which part of the ocean floor is most useful to the man?
(i) Continental shelf
(ii) Continental slope
(iii) Abyssal plains
(iv) Marine deeps
Ans. (i) Continental shelf
c. Which one of the following option is related to marine deposits?
(i) Rivers, glaciers, continental shelf, remains of plants and animals
(ii) Volcanic ash, continental shelf, remains of plants and animals
(iii) Volcanic ash, lava, fine particles of soil
(iv) Volcanic ash, remains of plants and animals, abyssal plants
Ans.
(iii) Volcanic ash, lava, fine particles of soil
2. a. Name the landforms shown in the following figure.
Ans.
b. Which of these landforms are useful for deep sea research?
Ans.
Submarine plateau and marine trench are the landforms useful for deep sea research.
c. Which of these are appropriate to be used for the protection of marine borders and naval base building?
Ans.
Continental shelf is appropriate to be used for the protection of marine borders and naval base building.
3. Give geographical reasons:
a. The study of ocean floor is useful to man.
Ans.
Various minerals, rocks, fine I soil particles are found on the sea floor.
Remains of marine plants and animals are also found on the ocean floor.
To study the marine life, mineral wealth as well as the process of volcanic eruption, the study of ocean floor is useful to man.
b. The continental shelf is a paradise for fishing activity.
Ans.
Being a shallowest part of the ocean bed, sunlight reaches up to continental shelf easily.
As its effect, algae, plankton, etc. grows on a large scale on continental shelf.
Algae, plankton, etc. is food for fish. Therefore, fish are found on a large scale on continental shelf. Therefore, the continental shelf is paradise for fishing activity.
c. Some marine islands are actually the peaks of sea mountains.
Ans.
The hundreds of kilometres wide and thousands of kilometres long hills found on the ocean bed are called submerged hills.
Peaks of some of the submerged hills come above the sea level.
These peaks are the visible land areas surrounded from all sides by water. These peaks are called islands. Thus, some marine islands are actually the peaks of sea mountains.
d. The continental slope is considered to be the boundary of continents.
Ans.
Continental slope lies beyond the continental shelf.
The deep abyssal plain begins beyond the continental slope. Therefore, the continental slope is considered to be the boundary of continents.
e. The disposal of waste materials in the oceans by man is harmful to the 1 environment.
Ans.
The disposal of waste materials in the oceans by man increases the pollution of sea water.
This disposed waste materials harm the life of marine animal life and marine plant. Thus, the disposal of waste materials in the oceans by man is harmful to the environment.
4. Observe the map on Pg 27 in ‘Give it a try’ and answer the following questions:
a. Madagascar and Sri Lanka are related to which landform of the ocean floor?
Ans.
Madagascar and Sri Lanka are related to island of the ocean floor.
b. Near which continent are these landforms located?
Ans.
Madagascar is located near the continent of Africa and Sri Lanka is located near the continent of Asia.
c. Which islands in our country are examples of peaks of submerged mountains?
Ans.
Andaman and Nicobar islands in our country are examples of peaks of submerged mountains.
E X T R A
1. Choose the correct answer and complete the sentences:
a. Continental slope has slope.
(a) flatter
(b) broader
(c) steeper
(d) lower
Ans.
(c) steeper
b. The average depth of the oceans is around metres.
(a) 7300
(b) 3700
(c) 3900
(d) 3300
Ans.
(b) 3700
2. Examine the following statements and correct the incorrect ones:
a. Abyssal plain lies beyond the continental shelf.
Ans.
Incorrect.
Correct statement: Abyssal plain lies beyond the continental slope.
b. Around 51 per cent of the surface of the earth is covered by water.
Ans.
Incorrect.
Correct statement: Around 71 per cent of the surface of the earth is covered by water.
c. Natural gas and mineral oil can be obtained from the continental shelf.
Ans.
Correct.
d. For survey purpose in India, the height of sea level at Kanyakumari is considered to be zero.
Ans.
Incorrect.
Correct statement: For survey purpose in India, the height of sea level at Chennai is considered to be zero.
e. Active volcanoes are mostly seen in marine trenches.
Ans.
Correct.
3. Answer the following questions in one sentence each:
a. What is called continental shelf?
Ans.
The land near the coast and submerged under the sea is called continental shelf.
b. What is called continental slope?
Ans.
The steeper slope of the sea bed beyond the extent of continental shelf is called continental slope.
c. What is called abyssal plain?
Ans.
The flat part of the sea bed that liesbeyond the continental slope is called abyssal plain.
d. What is called submerged hills?
Ans.
The hundreds of kilometres wide and thousands of kilometres long hills found on the ocean bed are called submerged hills.
e. What is called marine islands?
Ans.
Peaks of some of the submerged hills that come above the sea level are called marine islands.
f. What is called submarine plateau?
Ans.
The flat and extensive summit of marine island is called submarine plateau.
g. What is called marine deep?
Ans.
The landforms on the ocean bed that are comparatively less extending and shallower ones are called marine deep.
h. What is called marine trench?
Ans.
The landforms on the ocean bed that are comparatively more extending and deeper ones are called marine trench.
4. Answer the following questions in brief:
a. What is marine deposits?
Ans.
Marine deposit is a type of marine deposition.
The rivers and glaciers flowing from the continent bring pebbles, clay, soil, etc. with them when they meet sea or ocean.
These materials get deposited on the continental shelf. The deposits are known as marine deposits.
Due to pressure of sea water and deposition of layers over layers of sediments, sedimentary rocks are formed.
Marine life and the availability of minerals in the sea bed can be studied with the help of marine deposits.
b. What is marine oozes?
Ans.
Marine oozes is a type of marine deposit.
Lava and ash erupting out of volcano, fine soil particles, remains of plants and animals, etc. get deposited on marine abyssal plains. Deposits of these materials on the abyssal plains are known as marine oozes.
Marine oozes are in the form of fine clay. The percentage of remains of plants and animals in marine oozes is up to 30 per cent.
Marine oozes are also useful to study marine life and the availability of minerals in the sea bed.
c. Write in brief about the continental shelf.
Ans.
The land near the sea coast and submerged under the sea is called continental shelf. The depth of continental shelf is about 200 metres below the sea level.
Continental shelf is found to be narrow along the coasts of some continents and broad along the coasts of some other continents.
Being a shallowest part of the ocean bed, sunlight reaches up to continental shelf easily. As its effect, the food for fish like algae, plankton, etc. grows on a large scale on continental shelf. Therefore, continental shelf is useful for fishing occupation.
Various minerals, natural gas and mineral oil, etc. can also be obtained from mining the continental shelf. For example, Mumbai High located on the continental shelf of the Arabian Sea is a source from where the mineral oil and natural gas is obtained.
d. Write in brief about the continental slope.
Ans.
The steep slope of the sea bed beyond the extent of continental shelf is called continental slope.
The depth of the continental slope is from 200 metres to 3600 metres below the sea level.
The continental slope is found to be comparatively narrower.
The lower boundary of the continental slope is considered as the boundary of 1 continent.
f. Write in brief about the abyssal plains.
Ans.
The flat part of the sea bed that lies beyond the continental slope is called abyssal plains.
Various submerged landforms likesubmerged hills, submerged mountains, etc. are seen on abyssal plains.
Submarine plateaus are also found on the abyssal plains.
g. Write in brief about mean sea level.
Ans.
The average of the highest high tide and the lowest low tide is considered to calculate the mean sea level.
This average is considered to be zero sea level.
The altitude of any place above the sea level is measured and expressed in positive value. (For example, Mount Everest is 8848 metres high.)
The depth of any place below the sea level is measured and expressed in negative value. (For example, Mariana Trench is 11034 metres below sea level.)
Note: If you have any additional questions or feedback, please leave them in the comment section below. We will try to answer them and update this blog accordingly as soon as possible.
Comments