Questions Answers Class 8 Chapter 4 Geography Maharashtra Board

Questions Answers For All Chapters – Geography Class 8

Structure of Ocean Floor

Q1. 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 .

Answer: (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

Answer: (i) Continental shelf.

(c) Which one of the following option is related to marine deposits?

(i) Rivers, glaciers, 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 plains

Correct option: (i) Rivers, glaciers, remains of plants and animals.

Q 2. (a) Name the landforms shown in the figure.

Answer:

Based on the structure of the ocean floor and typical landforms, here are the probable names of the landforms shown in the figure:

1. Continental Shelf – The shallow, gently sloping area near the coast.
2. Continental Slope – The steep slope that descends from the continental shelf.
3. Abyssal Plain – The deep, flat region of the ocean floor.
4. Oceanic Trench – A deep, narrow depression in the ocean floor.
5. Mid-Ocean Ridge – An underwater mountain range formed by tectonic activity.
6. Seamount or Volcanic Island – An underwater volcanic peak, sometimes emerging above sea level.

(b) Which of these landforms is useful for deep-sea research?

Answer: Marine trenches and marine deeps are useful for deep-sea research as they are geologically active areas and contain valuable marine deposits.

(c) Which of these are appropriate to be used for the protection of marine borders and naval-base building?

Answer:Continental shelf and islands formed by submerged mountains are appropriate for the protection of marine borders and for naval-base building.

Q3. Give geographical reasons:

(a) The study of the ocean floor is useful to man.

Answer:

• The ocean floor contains valuable resources such as mineral deposits, oil, and natural gas (e.g., Mumbai High).
• Studying the ocean floor helps in understanding marine biodiversity, ocean currents, and climate patterns.
• It provides knowledge about geological activities like earthquakes and tsunamis, helping in disaster preparedness.

(b) The continental shelf is a paradise for fishing activity.

Answer:

• The shallow waters of the continental shelf allow sunlight to reach the ocean bed, supporting plankton growth.
• Rich in marine biodiversity, making it a prime area for commercial fishing.
• Many fishing grounds worldwide are located on the continental shelf.

(c) Some marine islands are actually the peaks of sea mountains.

Answer:

• Certain islands are the emerged peaks of submerged mountains, formed by volcanic activity.
• Example: Iceland, Andaman and Nicobar Islands.
• These peaks extend from the ocean floor to above sea level.

(d) The continental slope is considered to be the boundary of continents.

Answer:

• The continental shelf transitions into a steep slope, known as the continental slope.
• This marks the end of the continental landmass and the beginning of the deep ocean floor.

(e) The disposal of waste materials in the oceans by man is harmful to the environment.

Answer:

• Waste like plastic, sewage, and chemicals disrupts marine ecosystems.
• Pollutants harm marine life, leading to species decline.
• The presence of radioactive and industrial waste affects water quality and food chains.

Q4. 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?

Answer: Marine islands formed by the peaks of submerged mountains.

(b) Near which continent are these landforms located?

Answer: Madagascar is near Africa, and Sri Lanka is near Asia (India).

(c) Which islands in our country are examples of peaks of submerged mountains?

Answer: Andaman and Nicobar Islands and Lakshadweep Islands.