Our Changing Earth-II- NCERT notes

 4.Our Changing Earth-II

 

I we have read about n the previous chapter, Endogenic processes that take place inside the Earth. Exogenic processes take place on the surface of the Earth and are therefore, also known as external processes. These processes can be quite slow and their effects become visible after many years. Weathering and gradation are the two main exogenic processes which lead to changes on the surface of the Earth, such as breaking up of rocks or formation of landforms like river deltas and plains. These processes are brought about by natural agents, like rivers, winds, sea waves, and glaciers. In this chapter, we will study about all this in detail.

for weathering. They weaken rocks by altering their chemical and physical structure. Plants, animals, and humans also play a role in the process of weathering. Weathering is a slow process When the parent rock breaks down, its pieces remain at the same site. They are not carried away from the site. These weathered rock particles ultimately form soil.

 

WEATHERING

Weathering refers to the process of breaking down of rocks on the Earth's surface into smaller particles or sediments. Temperature, humidity, rainfall, and wind are agents chiefly responsible

Weathering of rocks

 

 

TYPES OF WEATHERING

PHYSICAL WEATHERING

Physical weathering is said to occur when rocks break down as a result of a physical process involving elements, such as temperature, wind, precipitation and frost. No chemical change occurs in the rocks. This type of weathering is also known as mechanical weathering.

 

(a) Exfoliation: In the deserts, the diurnal (daily) range of temperature is very high with temperatures during the day rising above 50° C and dropping to 0° C at night. The high temperatures during the day cause minerals inside rocks to expand, while the low temperatures at night cause them to contract. This alternate expansion and contraction weakens rocks and causes them to crumble.

 

( b) Wind action: Wind serves as another common agent of physical weathering in the deserts. Blowing wind carries sand particles with it. When such sand particles strike against rocks over and over again, they cause them to slowly disintegrate.

 

(c) Frost action: In cold countries and mountains, frost is a common agent of physical weathering. Frost refers to small ice crystals that form on the ground when the temperatures fall below freezing in cold areas. During the day, when the temperatures rise, the ice crystals turn into water and seep into cracks in the rocks. At night, when the temperatures fall, the water turns into ice which exerts great pressure on the rocks. This is because when water turns into ice, it expands by about one-tenth of its volume. Continuous thawing and freezing of water inside the rocks weakens them over time till they crack or break down.

 

CHEMICAL WEATHERING

Chemical weathering is said to take place when rocks break down as a result of a chemical process. Rainwater is an important agent of chemical weathering. It dissolves carbon dioxide present in the air, forming a weak solution of carbonic acid. When rainwater containing carbonic acid seeps into rocks, it causes them to break down.

 

 

Limestone rocks get weathered in this way. When rainwater containing carbonic acid seeps into limestone rocks, the calcium carbonate in the rocks gets dissolved in the rainwater leading to their weathering. Rainwater also contains dissolved oxygen, which breaks down iron-containing rocks when it comes into contact with them. The process is similar to rusting of iron. Chemical weathering is more common in warm tropical climates.

 

BIOLOGICAL WEATHERING

Biological weathering is the process by which rocks break down due to the action of plants, animals, or humans. It can be a physical or chemical process. The roots of plants or trees sometimes grow into the cracks of rocks and force them apart. Burrowing animals like rodents, ants, and worms can break down rocks over time. They also loosen and expose more rock surface to other agents of weathering. Lichens and mosses which grow on rock surfaces produce carbonic acid, that causes weathering in rocks. Human activities such as mining, construction, quarrying, etc., also lead to break down of rocks.

 

GRADATION

erosion Gradation is the process of levelling of the Earth's surface. It involves two processes (degradation) and deposition (aggradation). Erosion is the process by which landforms are slowly worn away by the action of natural agents such as wind, water, ice, etc. These natural agents, also known as agents of gradation, constantly break down and erode different landforms. They transport and deposit the eroded material in different places to create new landforms. The process by which rock particles get accumulated in low-lying areas, gradually raising their level, is known as deposition. Thus, gradation flattens elevated areas and raises low-lying areas to bring them to the same level. Unlike weathering, where rock sediments do not move away from the parent rock, gradation is a dynamic process. It involves the movement of rock particles from the site of erosion to the site of deposition. The lowering of land by the combined action of weathering and erosion is known as denudation.

 

AGENTS OF GRADATION: RIVER

Most of the rivers originate in the mountains and move towards the oceans or seas. In the process, their running water erodes the land or rocks through which they pass. The place where a river originates is called its source. The place where a river falls into the sea is called its mouth. The path or course a river takes to the sea can be divided into three stages upper, middle, and lower. As the landscape is different for the three stages so is the work of the river as an agent of gradation. Let us look at the work of the river in the three stages and the landforms it creates as it runs along its course.

 

UPPER COURSE

The upper course refers to the path the river takes as it flows down mountains. In the upper course, rivers flow at a fast pace and act primarily as agents of erosion. In the process, they help form the following features:

(a) I-shaped valleys: These are formed when river water erodes the river bed to cut a narrow valley. Such valleys have steep walls. They are also known as gorges or canyons.

 

(b) V-shaped valleys: These are formed when river water erodes the bed as well as banks of the river.

 

(c) Waterfalls: When rivers encounter steep valleys or rock faces in the mountains, they often rush down at an angle with great force to form a waterfall. Sometimes, processes such as earthquakes can also create a steep drop in the course of the river to form waterfalls.

Angel waterfall in South America is the highest waterfall in the world.

 

MIDDLE COURSE

The middle course refers to the path the river takes as it flows in the plains. As the slope decreases in the plains, the speed of rivers falls. They act as agents of transportation and deposition in this stage. They help form the following landforms:

 

(a) Meanders: When rivers enter a plain, they often follow a zig-zag pattern to form large bends called meanders. The water of the rivers constantly erodes and deposits material along the sides of the meanders. The Ganga makes a number of meanders in the Northern Plains.

 

(b) Ox-bow lakes: Sometimes, a meander gets cut off from the main river due to constant erosion and deposition of material to form a lake. Such a lake is called an ox-bow lake.

 

 

 

(c) Levees: When the water of a river overflows and floods its banks, it deposits fine soil and sediments on the banks, thereby raising the banks height. Such raised banks are known as levees.

 

(d) Floodplains: The rich deposits from the overflowing rivers also flatten the land around the banks to form fertile floodplains. Whenever river water overflows during floods, it leaves behind fresh layers of alluvial deposits in the floodplains. This makes these areas very fertile.

 

LOWER COURSE

The lower course refers to the path the river takes as it flows towards the seas or oceans. As the rivers come closer to the oceans or seas, the speed with which they flow decreases due to the flatness of the land through which they pass and the heavy load they carry. Rivers mainly act as agents of deposition in this stage. The feature formed in this stage is:

 

Deltas: As rivers slow down on the way to oceans or seas, they begin to deposit eroded material and in the process they break up into smaller branches or streams called distributaries. As the distributaries fall into the sea, their sediments get deposited at the mouths. These sediments collect at the mouth to form a triangular-shaped feature called delta. As they are formed by the deposition of alluvium, deltas are extremely fertile and suitable for agriculture. The Ganga-Brahmaputra Delta is among the largest deltas in the world.

The rivers Ganga, Brahmaputra, and Meghna form the largest delta in the world called the Sunderban Delta. It extends over more than 260 km along the Bay of Bengal.

 

 

AGENTS OF GRADATION: GLACIER

A glacier is a huge slow-moving mass of ice on land. It is formed by the accumulation of snow in mountains or Polar regions. Glaciers can be of two types-mountain glaciers and continental glaciers.

 

Mountain glaciers are found in mountains. They range from a few hundred square kilometres to several hundred square kilometres in area. They give rise to perennial rivers. The Gangotri Glacier and the Siachen Glacier are mountain glaciers.

The Siachen Glacier got its name from the Himalayan wildflowers which bloom in the valleys below the glacier. The word Siachen means 'place of wild roses'.

 

Continental glaciers are found in the Polar regions. They are larger than mountain glaciers, covering thousands of square kilometres of area. There are two major continental glaciers in the world. One covers most of Antarctica and the other covers most of Greenland.

 

Glaciers widen the valleys through which they pass. They also erode landforms and deposit eroded materials to form features such as lakes and moraines. Let us take a closer look at them.

 

(a) U-shaped valleys: When glaciers pass through valleys, they widen and straighten them by eroding their beds and sides to form U-shaped valleys. Such valleys have flat floors and steep sides.

 

( b) Cirques: When glaciers pass over land, they carry away soil and loose stones, exposing the underlying rock. The solid rock surfaces get further eroded by the action of glaciers to form deep, arm-chair shaped hollows called cirques. Once the ice melts, the hollows get filled up with water to form lakes. Such lakes are called tarns or cirque lakes.

 

(c) Moraines: Glaciers often deposit material carried by them like small stones, sand, and silt in different areas. Such deposits are called moraines.

 

AGENTS OF GRADATION: WIND

Erosion and deposition by wind is most commonly seen in deserts. It leads to the formation of features such as mushroom rocks, sand dunes, and loess.

 

( a) Mushroom rocks: These are formed when winds erode rocks in such a way that the lower parts get eroded more than the upper parts. Such rocks are narrow at the base and wide at the top. This is because the sand-carrying capacity of winds decreases with height. As winds carry more sand at lower levels, the lower parts of rocks are eroded more than the upper parts.

(b) Sand dunes: Blowing winds carry sand away from one place and deposit it in another, forming low hill-like features called sand dunes. Winds usually deposit sand when an obstacle comes in their path or their speed decreases. Sand dunes keep shifting their location in keeping with the direction in which the winds blow.

 

(c) Loess: Winds carry fine grains of sand over huge distances. When such fine sand gets deposited over a large area, it forms loess. China has huge deposits of loes.

 

AGENTS OF GRADATION: SEA WAVE

Just like rivers, sea waves also erode surfaces on which they fall and deposit material on them. The process of erosion by sea waves is known as marine erosion. The process of erosion and deposition by sea waves leads to the formation of coastal landforms, such as caves, beaches, and cliffs.

 

 

(a) Beaches: When sea waves strike the shore, they deposit sediments on it. This deposition of sediments lead to formation of beaches.

(b) Sea caves: These are formed when sea waves

strike rocks and cause them to crack. In time, the cracks become bigger and wider to form hollow spaces or caves.

(c) Sea arches: When waves erode sea caves, they get larger and larger till only their roofs remain. Such features are called sea arches.

(d) Sea stacks: These are formed when waves wear away the roofs of caves, leaving only their walls behind.

(e) Sea cliffs: Waves also erode rocks along the coast to form steep rock faces or cliffs that rise almost vertically above the water.

(f) Sand bars: These are formed when waves deposit broken rocks near the coast.

(g) Lagoons: When water gets trapped between the coast and sand bars, it forms a lake. Such lakes are called lagoons.

 

A sea cave is also known as a littoral cave. One of the most famous sea caves is the Blue Grotto. The small sea cave is located in Capri Island. It has a tiny opening, barely 2 m in height. Inside, the cave is 54 metres long, 30 metres broad, and 42 metres high arch.

 

 

New Terms

Weathering: Process of breaking down of rocks on the Earth's surface into smaller particles or sediments.

Physical weathering: Is said to occur when rocks break down as a result of a physical process involving elements, such as temperature, wind, and frost; also known as mechanical weathering.

Chemical weathering: Is said to take place when rocks break down as a result of a chemical process.

Biological weathering: Is the process by which rocks break down due to the action of plants, animals, or humans; it can be a physical or chemical process.

Gradation: The process of levelling of the Earth's surface.

Erosion: Process by which landforms are slowly worn away by the action of natural agents, like wind, water, ice, etc.

Deposition: Process by which rock particles get accumulated in low-lying areas, gradually raising their level.

Denudation: Lowering of land by the combined action of weathering and erosion.

I-shaped valleys: Are formed when river water erodes the river bed to cut a narrow valley; also known as gorges or canyons.

V-shaped valleys: Are formed when river water erodes the bed as well as banks of the river.

Distributaries: Branches or streams formed by rivers as they approach seas or oceans.

Delta: Triangular-shaped feature formed by the deposition of sediments at the mouth of a river.

Glacier: A huge slow-moving mass of ice on land.

Mountain glaciers: Glaciers found in mountains; they range from a few hundred square kilometres to several hundred square kilometres in area.

Continental glaciers: Are found in Polar regions; they are larger than mountain glaciers, covering thousands of square kilometres of area.

 

Exogenic forces

Exogenic forces are responsible for the creation of landforms through the processes of weathering and gradation.

These processes are brought about by natural agents, such as rivers, winds, sea waves, and glaciers.

As they flow down from the mountains to the seas, rivers form waterfalls, I-shaped valleys, V-shaped valleys, meanders, ox-bow lakes, levees, floodplains, and deltas.

Glaciers widen the valleys through which they pass to form U-shaped valleys. Their erosion and depositional action lead to the formation of cirques, lakes, and moraines.

Desert winds help form features such as mushroom rocks, sand dunes, and loess.

Sea waves help form coastal landforms, such as beaches, caves, stacks, arches, and cliffs.

 

 

Exercises: MULTIPLE CHOICE QUESTIONS

 

1. Which of the following processes takes place inside the Earth?

a) Exogenic

b) Endogenic

c) Weathering

d) Gradation

Answer: b) Endogenic

Explanation: Endogenic (or endogenetic) processes originate inside the Earth (e.g., volcanic activity, earthquakes). Exogenic processes like weathering and gradation occur on the Earth’s surface.

 

2. Exogenic processes are also known as:

a) Volcanic processes

b) External processes

c) Internal processes

d) Magmatic processes

Answer: b) External processes

Explanation: Exogenic processes take place on the surface of the Earth; hence, they are called external processes.

 

3. Which two are the main exogenic processes?

a) Weathering and Volcanism

b) Weathering and Gradation

c) Gradation and Folding

d) Weathering and Earthquakes

Answer: b) Weathering and Gradation

Explanation: Weathering (breaking of rocks in place) and gradation (erosion & deposition) are the two major exogenic processes.

 

4. Which of the following is an effect of exogenic processes?

a) Earthquake faults

b) Volcano craters

c) River deltas and plains

d) Mountain building

Answer: c) River deltas and plains

Explanation: Exogenic forces reshape Earth’s surface slowly, leading to landforms like plains, deltas, valleys.

 

5. Weathering results in:

a) Movement of rocks from place to place

b) Breaking of rocks into smaller particles at the same place

c) Volcanic eruption

d) Earthquake cracks

Answer: b) Breaking of rocks into smaller particles at the same place

Explanation: In weathering, rocks break down at their site without being transported.

 

6. Which of the following ultimately forms soil?

a) Glacial erosion

b) Deposition in rivers

c) Weathered rock particles

d) Sea wave erosion

Answer: c) Weathered rock particles

Explanation: Weathering produces smaller rock pieces that later mix with organic matter to form soil.

 

7. Which is NOT an agent of weathering?

a) Temperature

b) Wind

c) Rainfall

d) Earthquakes

Answer: d) Earthquakes

Explanation: Earthquakes are endogenic processes; weathering is caused by external agents like wind, rain, temperature.

 

8. Physical weathering is also known as:

a) Biological weathering

b) Mechanical weathering

c) Chemical weathering

d) Gradation

Answer: b) Mechanical weathering

Explanation: Physical weathering involves only mechanical breakdown of rocks, without chemical change.

 

9. Which of the following is NOT an example of physical weathering?

a) Exfoliation

b) Wind action

c) Frost action

d) Carbonic acid reaction

Answer: d) Carbonic acid reaction

Explanation: Carbonic acid dissolving limestone is chemical weathering, not physical.

 

10. Exfoliation occurs due to:

a) Freezing and thawing

b) Alternate heating and cooling in deserts

c) Plant roots breaking rocks

d) Action of oxygen on rocks

Answer: b) Alternate heating and cooling in deserts

Explanation: Daily temperature changes cause expansion and contraction of minerals, breaking rocks.

 

11. Frost weathering is common in:

a) Deserts

b) Coastal plains

c) Cold regions and mountains

d) Deltas

Answer: c) Cold regions and mountains

Explanation: Freezing and thawing of water in cracks break rocks in cold climates.

 

12. Why does water cause pressure in frost weathering?

a) Because water evaporates

b) Because water contracts on freezing

c) Because water expands when it freezes

d) Because water dissolves rocks

Answer: c) Because water expands when it freezes

Explanation: Water expands by 1/10th volume when frozen, exerting pressure on rocks.

 

13. Which type of weathering dissolves limestone rocks?

a) Physical

b) Chemical

c) Biological

d) Mechanical

Answer: b) Chemical

Explanation: Rainwater with carbonic acid dissolves calcium carbonate in limestone.

 

14. Which process is similar to rusting of iron?

a) Exfoliation

b) Frost action

c) Chemical weathering of iron-rich rocks

d) Biological weathering by roots

Answer: c) Chemical weathering of iron-rich rocks

Explanation: Oxygen in rainwater reacts with iron in rocks like rusting.

 

15. Chemical weathering is more common in:

a) Polar regions

b) Hot deserts

c) Warm tropical climates

d) Mountain peaks

Answer: c) Warm tropical climates

Explanation: Warm and moist conditions enhance chemical reactions.

 

16. Which weathering is caused by roots of plants?

a) Physical

b) Chemical

c) Biological

d) Mechanical

Answer: c) Biological

Explanation: Roots penetrate cracks, forcing rocks apart (physical) and secreting acids (chemical).

 

17. Which of the following is NOT an agent of biological weathering?

a) Ants

b) Worms

c) Oxygen

d) Lichens

Answer: c) Oxygen

Explanation: Oxygen causes chemical weathering, not biological.

 

18. Lichens and mosses cause weathering by producing:

a) Oxygen

b) Carbonic acid

c) Sulphur dioxide

d) Water

Answer: b) Carbonic acid

Explanation: Lichens release carbonic acid that dissolves rock surfaces.

 

19. Human activities such as mining and construction cause:

a) Physical weathering only

b) Biological weathering

c) Endogenic processes

d) Deposition

Answer: b) Biological weathering

Explanation: Humans are biological agents who break rocks by mining, quarrying, etc.

 

20. Gradation refers to:

a) Breaking of rocks at one place

b) Levelling of Earth’s surface by erosion and deposition

c) Mountain building

d) Plate tectonics

Answer: b) Levelling of Earth’s surface by erosion and deposition

Explanation: Gradation lowers highlands and fills lowlands to make surface level.

 

21. Which process involves movement of rock particles from erosion to deposition?

a) Weathering

b) Gradation

c) Exfoliation

d) Frost action

Answer: b) Gradation

Explanation: Unlike weathering (no movement), gradation involves erosion and transportation of particles to new places where they are deposited.

 

22. The combined action of weathering and erosion lowering land is called:

a) Denudation

b) Deposition

c) Transportation

d) Oxidation

Answer: a) Denudation

Explanation: Denudation is the lowering of Earth’s surface due to weathering and erosion.

 

23. The place where a river originates is called its:

a) Mouth

b) Source

c) Meander

d) Tributary

Answer: b) Source

Explanation: A river begins at its source (usually glaciers, springs, or mountains).

 

24. The point where a river falls into the sea is called its:

a) Estuary

b) Mouth

c) Gorge

d) Delta

Answer: b) Mouth

Explanation: The river ends where it joins a larger water body like sea or ocean, known as its mouth.

 

25. In which stage do rivers form I-shaped valleys?

a) Upper course

b) Middle course

c) Lower course

d) Delta stage

Answer: a) Upper course

Explanation: In the mountains, rivers flow fast and cut deep valleys called I-shaped valleys or gorges.

 

26. Which valley has steep walls and is also known as a gorge or canyon?

a) V-shaped valley

b) I-shaped valley

c) U-shaped valley

d) Cirque

Answer: b) I-shaped valley

Explanation: Deep narrow valleys eroded by rivers in upper course are called I-shaped valleys or gorges.

 

27. Which feature is formed when rivers erode both bed and banks?

a) I-shaped valley

b) V-shaped valley

c) Gorge

d) Levee

Answer: b) V-shaped valley

Explanation: When river cuts both its bed and sides, it forms V-shaped valleys.

 

28. Which is the highest waterfall in the world?

a) Niagara Falls

b) Victoria Falls

c) Jog Falls

d) Angel Falls

Answer: d) Angel Falls

Explanation: Angel Falls in South America is the highest waterfall in the world.

 

29. Meanders are formed in which course of the river?

a) Upper course

b) Middle course

c) Lower course

d) Source

Answer: b) Middle course

Explanation: In plains, rivers develop bends called meanders due to erosion and deposition.

 

30. Which landform is formed when a meander is cut off?

a) Delta

b) Ox-bow lake

c) Waterfall

d) Gorge

Answer: b) Ox-bow lake

Explanation: When a river bend gets cut off, it forms a U-shaped lake called ox-bow lake.

 

31. Levees are formed due to:

a) Earthquakes

b) Frost action

c) Deposition of sediments on river banks

d) Glacial erosion

Answer: c) Deposition of sediments on river banks

Explanation: When rivers overflow, they deposit soil along banks, raising them to form levees.

 

32. Floodplains are fertile because of:

a) Rock fragments

b) Lava deposits

c) Fresh layers of alluvial deposits

d) Glacial moraines

Answer: c) Fresh layers of alluvial deposits

Explanation: Floodplains are formed by deposition of alluvium during floods, making them fertile.

 

33. In which course of the river are deltas formed?

a) Upper course

b) Middle course

c) Lower course

d) Source

Answer: c) Lower course

Explanation: At the mouth of rivers, sediments are deposited to form deltas.

 

34. Which is the largest delta in the world?

a) Amazon Delta

b) Sunderban Delta

c) Mississippi Delta

d) Nile Delta

Answer: b) Sunderban Delta

Explanation: The Ganga-Brahmaputra-Meghna river system forms the world’s largest delta called Sunderban.

 

35. Which of the following is a mountain glacier in India?

a) Greenland Glacier

b) Antarctica Glacier

c) Gangotri Glacier

d) Sahara Glacier

Answer: c) Gangotri Glacier

Explanation: Gangotri is a mountain glacier in the Himalayas and source of river Ganga.

 

36. Which glacier is called the “place of wild roses”?

a) Gangotri Glacier

b) Siachen Glacier

c) Lambert Glacier

d) Pindari Glacier

Answer: b) Siachen Glacier

Explanation: Siachen Glacier got its name from Himalayan wild roses (sia).

 

37. Continental glaciers are found in:

a) Himalayas

b) Andes

c) Antarctica and Greenland

d) Alps

Answer: c) Antarctica and Greenland

Explanation: These glaciers cover huge areas of Antarctica and Greenland.

 

38. U-shaped valleys are formed by:

a) Rivers

b) Glaciers

c) Wind

d) Sea waves

Answer: b) Glaciers

Explanation: Glaciers carve out flat-floored, steep-sided U-shaped valleys.

 

39. Cirques are also known as:

a) Tarn lakes

b) Ox-bow lakes

c) Floodplains

d) Moraines

Answer: a) Tarn lakes

Explanation: Armchair-shaped hollows formed by glaciers, filled with water, are called cirques or tarns.

 

40. Moraines are deposits of:

a) Lava

b) Glacial sediments like stones, sand, silt

c) Alluvium

d) Windblown dust

Answer: b) Glacial sediments like stones, sand, silt

Explanation: Glaciers deposit unsorted material called moraines.

 

41. Which landform is created by wind erosion?

a) Mushroom rocks

b) Delta

c) Cirque

d) Levee

Answer: a) Mushroom rocks

Explanation: Wind erodes lower parts of rocks more than upper parts, forming mushroom-shaped rocks.

 

42. Sand dunes are formed when:

a) Winds blow strongly

b) Winds deposit sand when slowed down or blocked

c) Rivers overflow

d) Glaciers melt

Answer: b) Winds deposit sand when slowed down or blocked

Explanation: Wind deposits sand in mounds called sand dunes, common in deserts.

 

43. Loess is formed by deposition of:

a) Ice

b) Fine sand carried by wind

c) Alluvial silt

d) Sea waves

Answer: b) Fine sand carried by wind

Explanation: Loess is fine sand or dust deposited over large areas, e.g., in China.

 

44. Which of these is formed by marine erosion?

a) Meander

b) Sea cave

c) Moraine

d) Sand dune

Answer: b) Sea cave

Explanation: Sea waves erode rocks to form hollow caves.

 

45. Which feature forms when the roof of a sea cave remains?

a) Sea arch

b) Sea cliff

c) Sea stack

d) Lagoon

Answer: a) Sea arch

Explanation: Waves enlarge caves, leaving an arch-shaped roof.

 

46. Sea stacks are formed when:

a) Caves collapse leaving only walls

b) Rivers cut banks

c) Sand dunes harden

d) Loess is eroded

Answer: a) Caves collapse leaving only walls

Explanation: When the roof of a sea arch collapses, walls remain called stacks.

 

47. Steep rock faces along coasts are called:

a) Sea cliffs

b) Beaches

c) Sand bars

d) Lagoons

Answer: a) Sea cliffs

Explanation: Continuous wave erosion creates vertical cliffs on coasts.

 

48. Which feature is formed when waves deposit broken rocks near the coast?

a) Lagoon

b) Sand bar

c) Sea cave

d) Floodplain

Answer: b) Sand bar

Explanation: Waves deposit rocks near the coast to form sand bars.

 

49. Lagoons are formed when:

a) Sand bars trap sea water near coast

b) Rivers form bends

c) Glaciers melt

d) Wind deposits sand

Answer: a) Sand bars trap sea water near coast

Explanation: When sand bars block sea water, it forms shallow coastal lakes called lagoons.

 

50. The famous Blue Grotto sea cave is located in:

a) India

b) China

c) Capri Island, Italy

d) South America

Answer: c) Capri Island, Italy

Explanation: The Blue Grotto is a famous sea cave in Capri Island, Italy, known for its tiny entrance and glowing blue water.