Class 9 Geography: Chapter 04 By the Hands of the Nature - Questions and Answers

Study Notes for Class 9th Social Science II (English Medium) പ്രകൃതിയുടെ കൈകളാൽ | Geography: Chapter 04 By the Hands of the Nature

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Social Science II Chapter 4: By the Hands of the Nature
1. Formation of Landforms. 
- The forces acting on the earth's surface create many various landforms. These are formed as a result of the processes of erosion and deposition of external forces over millions of years. 

2. Forces that cause changes in the Earth's surface 
- External forces
- Internal forces

3. What are the various landforms on earth.
- The mountains, valleys, plains, plateaus, waterfalls, etc. 

4. What are geomorphic processes?
- The processes that help in the formation of landforms are called geomorphic processes

5. What are geomorphic agents? Write examples.
- Varied landforms are created by the continuous processes carried out by external agencies, these agencies are often called geomorphic agents.
- Running water, wind, glaciers, sea waves, etc. 

6. Name the branch of geography which deals with the study of origin and evolution of landforms.
- Geomorphology

7. What is weathering?
- Disintegration or decomposition of rocks is known as weathering.

8. What are the different processes of weathering?
- Physical, chemical and biological weathering

9. What is the difference between erosion and deposition?
- The transfer of rock particles from one place to another by external agencies such as running water, wind, glaciers, sea waves, etc. is called erosion
- The materials carried by external agencies will be deposited in low-lying regions and this process is called deposition

10. Observe the picture below and name the processes marked as 'A' and ‘ B’
A – Erosion
B – Deposition

11. What is the difference between source and mouth of a river?
- The place of origin of a river is called its source and the place at which it discharges into the sea or to a water body is called the river mouth.

12. Name the factors that determine the flow of a river.
- Volume of water, Rock structure, Slope of the terrain, Amount of sediments

13. The course of a river can generally be divided into three stages. Which are they? Compare the three-course of a river
- Upper course
The upper course is that part of the river where it rapidly flows down along steep slopes from the place of origin. The intensity of erosion is severe in this course.
• Place of origin of the river
• River flows through steep slopes
• Intense rate of erosion
• No deposition
• Landforms such as valley, waterfall, etc are seen
- Middle course
Middle course is that stage of the river where it flows through gently sloping foothills. As the velocity of the flow decreases, the intensity of erosion declines and deposition begins.
• Flows through the foothills
• Both erosional and depositional processes are active
• Features such as meanders and oxbow lakes are seen
- Lower course
The lower course is the stage where the river flows through the plains. The rate of deposition will be higher due to the slow pace of the river and the increase in the number of sediments during this stage.
• Flows through the plains
• Active depositional processes
• Depositional landforms such as flood plains and deltas are seen

14. In which stage is the intensity of erosion more?
- Upper course

15. Which process results in the landforms developed in the lower course?
- Depositional processes

16. What are the factors affecting the intensity of river erosion.
- Velocities of water flow, the slope of the terrain, and rock structure

17. What do you meant by abrasion or corrosion?
- The rock particles like gravel, sand, pebbles, etc. carried by the river rub against the rocks along the bed and both sides of the river. This results in the wearing down of rocks. Such erosion is known as abrasion or corrosion.

18. What could be the reason behind the round shape and polished surface of the pebbles?
- Abrasion or corrosion

19. How the erosion alters the bed and valleys of the river?
- Erosion along with the bed results in deepening of rivers
- Erosion along the valleys results in widening of rivers

20. What are fluvial landforms?
- Landforms created by the erosion and depositional activities of rivers are
called fluvial landforms.

21. How V-shaped valleys are formed?
- The valleys take a distinct shape as a result of the intensity of Erosion along the river bed. Such valleys are called V-shaped valleys.

22. How Waterfalls are formed?
- Waterfalls are generally formed at the upper course of rivers as a result of erosion.
- Soft rocks are easily eroded in the valleys where soft and hard rocks are found intermingled. This results in the formation of waterfalls.

23. What are meanders?
- The sinuous curves formed along the river course are called meanders.

24. How oxbow lakes are formed?
- Meanders may further curve through continuous erosion and deposition. Finally, the river takes a straight course. Due to deposition, the curves may get detached from the main river form isolated water bodies. Such water bodies are called oxbow lakes

25. What are flood plains? Write the importance of floodplains
- The deposition of alluvium along both the flooded banks may cause the formation of plains. Such plains are called floodplains
- Flood plains are very significant as they are suitable for agriculture because of the presence of alluvial soil, water availability, physiography(plains)

26. Many of the famous civilizations took birth along flood plains. Why? 
- The deposition of alluvium and the growing availability of water in flood plains caused for the spread of agriculture has resulted in the development of civilizations.

27. How deltas are formed? Write an example.
- At the river mouth the sediments brought by the river are deposited between the distributaries forming almost triangular-shaped landforms called deltas
- The Sundarbans in West Bengal which is the largest delta in the world

28.Complete the table based on the landforms created by rivers.

29. Write the features of Karst topography?
- Rocks like limestone easily dissolve in rainwater which percolates to form underground water.
- The erosional and depositional landforms of underground water are mainly confined to limestone regions. Such landform features are generally called Karst topography

30. Write a short note about landforms created by underground water.
1) Limestone caves - Caves formed by the solution of limestone in underground water.
2) Stalactites - The deposit of lime grows upside down due to the long-continued depositional process in limestone caves. These are called Stalactites. 
3) Stalagmites - The deposit of lime on the floor of the cave also grows upward as a result of the deposition from above. These are called stalagmites
4) Limestone pillars - Stalactites and stalagmites do merge together with to form pillars.

31. Write an example for limestone caves.
- The Borra caves near Vishakapatnam in Andhra Pradesh is an example for
limestone caves (tourist hotspot)

32. Coastal landforms are created by the erosional and depositional processes carried out by waves. Which are they? How they are formed?
1) Sea Cliffs -The steep hillocks facing the sea are called sea cliffs.
- They are formed by the crumbling of the sea-facing slopes due to wave erosion
Eg: Varkala beach in the Thiruvananthapuram district
2) Stacks - Pillar-like rocks standing upright along the coastline are called stacks.
- The strong blast of sea waves on the rocky coasts causes the wearing down of rocks. As a result of such abrasion by waves, isolated rock pillars are formed from coastal rocks.
Eg: Stacks were found along the coast of Thalassery in the Kannur district.
3) Beaches -They are depositional landforms along the coastlines formed with sand, gravel etc.
Eg: Kovalam, Cherai

33. Which is the major geomorphic agent creating landforms in deserts?
- Winds

34. List the features that distinguish deserts from other places.
• High temperature
• Strong winds
• Less vegetation
• Barren area of landscape 

35. What is deflation?
- The strong whirlwinds carry away the dry desert sands from one place to
another. This process of wind erosion is called deflation.

36. What do you mean by the term abrasion?
- As a result of the continued erosion caused by sand and other rock particles carried by strong winds, rocks in deserts get worn down. This process of wind erosion is called abrasion.

37. Landforms created by wind are mostly seen in deserts. Justify
1) Mushroom rocks - As a result of the continued erosion caused by sand and other rock particles carried by strong winds, rocks in deserts get worn down. Such rocks seen in deserts resembling mushrooms are called mushroom rocks.
2) Sand dunes -The sand dunes formed in the deserts are a result of the deposition by wind
3) Barchans -The sand dunes commonly formed in crescent shapes are called barchans

38. Name the only continent where the deserts are absent.
- Europe

39. What is a glacier?
- Slow-moving mass of ice is called a glacier

40. Which is the major geomorphic agent creating landforms in high mountain ranges and the poles?
- Glacier

41. What are cirques?
- Armchair-like valleys formed by glacial erosion are called cirques

42. How are U-shaped valleys formed?
The erosion caused by the continuous movement of glaciers along the valleys carves out steep-sided and flat-bottomed U-shaped valleys.

43. Name the depositional landform created by glaciers? How it will be formed?
- Moraines
- The sediments carried down by the glaciers will be deposited in various parts of the valley. These depositional features by glaciers are called moraines 

44. Identify the various portions of the valley in which moraines are formed?
• Along the sides of the valley
• At the middle of the valley
• At the foot of the valley

45. What is the difference between degradation and aggradation?
• The elevated regions are levelled down by erosion and low-lying regions are filled by deposition. These processes are called degradation and aggradation respectively.
• The processes together are generally called gradation

46. List out the human activities that bring changes to the earth's surface
• Reclamation of agricultural fields
• Deforestation
• Mining

47. 'The erosion, as well as deposition carried out by external agencies, create varied landforms.' Explain these processes?
- Erosion: The transfer of rock particles formed by weathering processes from one place to another by external agencies is called erosion.
- Deposition: The rock particles transfer due to erosion will be deposited in low lying regions and this process is called deposition.

48. Arrange the items in B' and 'C' columns, appropriate to column 'A'.
Answer

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