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Assam Board SEBA Class 9 Social Science Chapter 6 Solution in English Medium 2026 | SEBA Class 9 Social science Part II Chapter 1 Solution | SEBA Class 9 Social Science Part II Chapter 1 2026

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Assam Board SEBA Class 9 Social Science Chapter 6 Solution in English Medium 2026 | SEBA Class 9 Social science Part II Chapter 1 Solution | SEBA Class 9 Social Science Part II Chapter 1 2026

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&nbsp;changes in the land surface

Practitioner:1 . Give an overview of the distribution of continents and oceans on the Earth's surface.

Answer: The Earth's surface consists of continents (land) and oceans (water). Of this, 71 per cent is covered by water and the remaining 29 per cent by land. The interior of the continents consists of plains, plateaus, mountains, river valleys, deserts, and coastal plains. Similarly, the oceans are flooded with plateaus, plains, mountain ranges, deep canyons, coral reefs, etc. There are also many islands, large and small, in the ocean. These features of the land surface and ocean floor are the result of processes or actions that have been going on for centuries. Some of the factors acting on the Earth's land and water are external and some are internal. External factors include solar heat, wind, rain, rivers, glaciers, and ocean waves. Internal factors include earthquakes and volcanic eruptions. Internal factors can act on the interior of the continent as well as the interior of the ocean floor. These factors usually contribute to the unevenness of the land surface as well as the ocean floor. When an earthquake occurs, part of the continent or ocean floor can rise or sink.

2.   Explain why the surface changes.

Answer: The Earth's surface is variable. Over time, changes occur everywhere on the Earth's surface. Some of the factors that cause land surface changes are external and some are internal. The interaction of external and internal factors has brought the Earth's surface to its present state. The action of these factors will continue to change the surface of the earth in the future. Factors will also change over time. External factors act from the outside so that we can see them and internal factors act inside the world without us seeing them. External factors include solar heat, wind, rain, rivers, glaciers, ocean waves, etc. Internal factors include earthquakes and volcanic eruptions. In addition, biological factors such as plants and animals on the land surface also contribute to land surface changes to a greater or lesser extent.

3. 3. What do external factors mean? Name some external factors.

Answer: External factors on the Earth's surface act mainly from the outside. The sources of these factors are the sun and the atmosphere. External factors include solar energy, wind, rain, rivers, glaciers, and ocean waves.

4. The Why are earthquakes and volcanic eruptions called internal factors?

Answer: Internal factors can act on the interior of the continents as well as the ocean floor. These factors usually contribute to the unevenness of the land surface as well as the ocean floor. When an earthquake occurs, part of the continent or ocean floor can rise or sink. Volcanic eruptions also cause earthquakes and volcanoes in the area. Therefore, earthquakes and volcanic eruptions are called internal factors.

5. What do you mean by a river basin? Draw a diagram of the river basin.

Answer: A river carries water from an area through its tributaries, tributaries, etc. Thus, an area carried by a river is called a basin. The 'action of a river is usually confined to the basin.

6. . What is a tributary? Name the two major tributaries of the Brahmaputra.

Answer: Tributaries are tributaries of major rivers that flow through the plains from their sources.  The two major tributaries of the Brahmaputra are: (i) Puthimari and (ii) Bharlu. or A river carries rainwater, mountain water, snow water, etc. through its tributaries, tributaries, etc. Thus, the area through which a river carries water is called a river basin.

7. Give an overview of river dredging. Answer: After flowing along the steep slopes of the highlands and entering the plains, the drainage strength of the river changes. In the highlands, the river is strong, steep but deep. As the slope gradually decreases to the plains, the sediments carried by the currents from the higher ground begin to accumulate in the plains. As a result, the depth of the river gradually decreases in the plains. As the depth decreases, the river begins to erode on both sides to carry away the water. The river carries water southward by eroding the banks and widening its course. Rivers are mined for such reasons. This type of excavation of a river is called bank excavation or side excavation.

8. What is meant by riverside excavation.  Answer: After flowing along the steep slopes of the highlands and entering the plains, the drainage strength of the river changes. In the highlands, the river is strong, steep but deep. As the slope gradually decreases to the plains, the sediments carried by the currents from the higher ground begin to accumulate in the plains. As a result, the river depth gradually decreases in the plains. As the depth decreases, the river begins to erode on both sides to carry away the water. The river carries water southward by eroding the banks and widening its path. Rivers are mined for such reasons. This type of excavation of a river is called bank excavation or side excavation.

9. What is Ashwakhura Lake? Explain with pictures how it is formed. Answer: Ashwakhura Lake is a horseshoe shaped lake called Ashwakhura Lake.  The river's course is naturally curved as it flows along gentle slopes in the plains. Excavation of the river banks makes its course more curved. Such movement of a river in a single-curved path is called curvilinear or spiral movement. In some parts of the plain, the river course can be very winding. Such paths cannot carry large amounts of water flowing through the river during the rainy season. Then the river leaves the most bent part of its course and moves straight. The remains are usually horseshoe-shaped and later accumulate to form beaches or lakes. This is how the Ashwakhura Lake is formed.

10. Write down what a floodplain is and how it is formed. Answer: Excavation is usually carried out in the upper reaches of the river. In contrast, in the mid- and low-speed sections, gades accumulate on both sides of the path. The sedimentary plains are formed by the accumulation of sediment over the centuries on both sides. This is called a floodplain. During floods, sand, mud, sediment, etc. carried by the currents usually spread far on both sides. These eventually create floodplains.

11 . Write down where and how sand is formed in the course of the river. Answer: Sand dunes are sometimes formed on the banks of rivers and sometimes in the middle of them. These are usually temporary and come in a variety of sizes and shapes. During the monsoon season, strong river currents change the shape of the sand dunes. During the dry season, when the river water drops, the sand dunes are well exposed. There are many sand dunes, both large and small, on the banks of our Brahmaputra. The large river island of Majuli on the banks of the river is also a kind of sandy beach.

12. Write down how the B-Island is formed. Answer: In the shallow sea along the coast, where the river flows, the sediment carried by the river accumulates to form islands. These islands are shaped like a 'bo' in Assamese or a delta in English. Therefore, these islands are called deltas. Most of the world's rivers have formed islands in their estuaries. The world is famous for its islands of the rivers Ganges, Brahmaputra, Nile and Mississippi.

13. Write why the wind is strong in the desert. Answer: In desert environments, wind createsand alters various bodies through excavation, transport and deposition. In deserts, the vegetation cover is very thin and the wind can easily act on the desert surface. Therefore, the wind is strong in the desert.

14 . What does it mean to decline? Answer: In desert areas, dust and sand can be easily carried by the wind from one place to another. The act of blowing dust and sand from a part in this way is called subsidence.

15 . How is sand formed? Answer: The desert surface can gradually rise to form mountains where the dust and sand carried by the subsidence process accumulates. Such mountains form sand dunes or sand dunes.

16. What is Inchelburg? Answer: Inselbergs are the specially shaped eroded arc hills commonly seen in the desert. The German word Inselberg means a lonely hill or mountain like an island.

17 . Define glaciers and write the difference between them and rivers. Answer: The surface of the coldest regions of the Earth is covered with ice. Such regions include the polar regions and the peaks of the highest mountains. These have large amounts of ice accumulated in layers. The ice usually descends slowly according to the slope of the surface. The ice that falls in this way is called a glacier.

The differences between rivers and glaciers are as follows: 1. The river flow is faster in the uplands and slightly slower in the plains. However, glaciers move very slowly. 2. The river carries out its excavation at a rapid pace. But the pace of glacial mining is slow. 18 . Write how sharp peaks are formed by glacial action. Answer: Several glaciers may descend along some mountains. Then, as a result of excavation from all sides, several glaciers can descend along the mountainside. Then, as a result of excavation from all sides, the top of the mountain becomes like a sharp edge. These are called peaks created by glaciers. Thus, the action of glaciers results in the formation of barbed wire. Such sharp peaks are found in the Alps and Himalayas.

19 . What is the coast? Answer: A large part of the Earth's surface is covered by oceans. The shore is the shore of the ocean.

20 . What is the sandbar? Write about its importance. Answer: Gades accumulated on the coastline where waves are always acting, especially when the amount of sand is high, naturally form a flat-like structure. Such sloping formations, mainly formed by the accumulation of sand, are called sandbanks. These structures are formed on the coast by the combined action of ocean waves and returning waves. The sandy beaches of the coast attract people for recreation.

21 . Briefly write about how ocean waves change the coastline. Answer: The waves of the sea constantly act and cause extensive changes in the coastal areas. The action of waves causes the formation of certain bodies on the coasts of oceans. Some of the deposits formed on the coast are erosional and others are sedimentary. When the coastline is made up of hard rocks like granite, basalt, etc., the waves of the sea act on it to form standing cliffs. When a large earthquake occurs on the seabed, special waves are generated in the oceans. On the coast, these waves reach unusual height and strength, causing extensive coastal damage. Such destructive waves are called tsunamis.

22. Indicate with arrows which of the following factors and bodies is created. Answer: You will try this question yourself.

23 . Think about the changes that may occur in the Earth's surface in the future. Answer: The land surface is changing in a continuous process and will continue to do so in the future. The world's agricultural land area and forests are declining at a rapid rate due to rapid population growth. As a result, the rainfall has decreased. More dry areas have been created. The air is being polluted due to the high level of industrialization worldwide. Global warming is rising. The ice in the polar regions and the Himalayas melts more and more water accumulates in the rivers. If the ice melts at such a high rate, it will soon cause devastating floods on Earth. Finally, the water reserves in the polar regions and the Himalayas are decreasing, making the world more likely to face water shortages. As a result, more desert areas are likely to be created on the surface.

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