Looking for complete, textbook-verified solutions for SEBA Class 9 Social Science Geography Chapter 1 (Changes of Earth’s Surface / ভূ-পৃষ্ঠৰ পৰিৱৰ্তন) for the 2026–27 academic session? Access step-by-step solutions to all official textbook exercises—including Very Short Answer (VSA), Short Answer (SA), and Long Answer (LA) questions. Master high-scoring answers covering internal (endogenous) and external (exogenous) forces shaping the Earth’s lithosphere; mechanical, chemical, and biological weathering processes; differences between weathering, erosion, and denudation; courses of a river and the evolution of erosional and depositional features (gorges, V-shaped valleys, waterfalls, meanders, oxbow lakes, floodplains, and deltas); glacial erosion and deposition forms (U-shaped valleys, hanging valleys, cirques, and moraines); arid aeolian landforms created by wind action (mushroom rocks, yardangs, zeugens, sand dunes, and barchans); coastal wave formations (sea cliffs, sea caves, sea arches, beaches, and spits); and human impact on geomorphic processes, structured strictly according to the Assam Board (SEBA) examination pattern.
Q.1. Give an outline of the distribution of continents and oceans of the world.
Answer: The surface of the earth is composed of continents (landmass) and oceans (hydrosphere). Hydrosphere and landmass cover 71% and 29% of the earth’s surface respectively. In the continents, plains, plateaus, hills and mountains, river valleys, deserts and coastal plains are found to occur. Similarly in the oceans also, submerged plateaus, plains, ridges, trenches, coral reefs are there, along with many islands of various sizes.
Q.2. Explain why there has been change over the earth’s surface.
Answer: The features of the land surface and ocean bottoms are the results of certain processes operating through the ages, and in course of time these features experience changes due to dynamic exogenic and endogenic factors. The plates that constitute the earth’s crust are dynamic, and their movements cause events like earthquakes and volcanic eruptions, while external factors like sunshine, wind, rainfall, river, glacier, and sea-waves continuously modify the surface over space and time.
Q.3. What is meant by exogenic factor? Mention some exogenic factors.
Answer: The exogenic factors are those that operate from outside the earth visibly, with their sources being the sun and the earth’s atmosphere. The exogenic factors mainly include sunshine, wind, rainfall, river, glacier, and sea-waves.
Q.4. Why are earthquakes and volcanic eruption called endogenic factors?
Answer: Earthquakes and volcanic eruptions are called endogenic factors because they work in the earth’s interior and in the ocean bottoms invisibly, being driven by major processes like plate tectonics where dynamic crustal plates move.
Q.5. What do you mean by a river basin? Draw a diagram of a river basin.
Answer: A river basin is an area from where a river along with its tributaries carries water downward.
Class 9 Social Science Geography Chapter 1 Question Answer Assam Board
Q.6. What is a tributary? Name two major tributaries of the Brahmaputra.
Answer: Two major tributaries of the Brahmaputra shown in the chapter maps include the Subansiri and other Himalayan drainage streams.
Q.7. Give an outline of river erosion.
Answer: When a river flows down from a highland, it naturally erodes the surface of its basin, which becomes clearly visible mainly in the river channel. The erosional capacity and power of a river depend on the geological structure of the channel, the hardness of the underlying rocks, the amount of water flow, and the direct mechanical action of water known as hydraulic action. In mountainous regions, the river channel is narrow and deep with high velocity, whereas in plains, the river performs lateral erosion to widen its channel.
Q.8. What do you mean by lateral erosion of a river?
Answer: Lateral erosion refers to the process where a river erodes its banks in the plains (resulting in bank failure and widening of the channel) to carry water down after its velocity decreases due to a decline in slope.
Q.9. What is ox-bow lake? Draw diagram to show how it is formed.
Answer: An ox-bow (or horse-shoe) lake is a lake formed when a highly meandering river course fails to carry a huge amount of water during summer and straightens its course, leaving aside the most winding loop which takes the form of a horse-shoe shaped lake or beel.
Q.10. What is floodplain? Write how it is formed.
Answer: A floodplain is an alluvial plain formed on both the banks of a river. It is formed because, in the middle and lower courses of a river, sediments generated by erosion are deposited on the bed and banks over long periods, and during floods, the sands, mud, and silt carried down spread out over a long distance across the banks.
SEBA Class 9 Geography Chapter 1 Solutions
Q.11. Write how and where sandbars are formed in a river channel.
Answer: Sandbars are formed from sediments deposited on the river bed, occurring both on the sides and in the middle of the channel. When river water becomes weak or subsides (such as during winter), these temporary deposits of various sizes and shapes become visible.
Q.12. How are the deltas formed?
Answer: Deltas are formed in coastal shallow seas where rivers debouch (flow out), as the river deposits sediments at its mouth, creating islands that take the shape of the Assamese letter ‘S’ or the Greek letter delta ().
Q.13. Write why the wind action is strong in the deserts.
Answer: Wind action is strong and has a far-reaching impact in deserts primarily because the vegetal cover is very thin, allowing the wind to easily act upon the surface and blow away sands and dust.
Q.14. What is meant by deflation?
Answer: Deflation is the process of blowing away and transporting sands and dust from one part of the desert to another by wind action, which often creates dust storms and leaves behind relatively depressed areas where temporary lakes may form.
Q.15. How are the sand dunes formed?
Answer: Sand dunes are formed when sands and dust transported through deflation get deposited in certain places where the surface is gradually raised to form hills, with shapes and sizes varying based on the nature, path of flow, and strength of the wind.
Assam Board Class 9 Geography Chapter 1 Solved Textbook Solutions PDF
Q.16. What is inselberg?
Answer: An inselberg is a low erosional hill or isolated island mountain formed in deserts due to the frictional erosional action of speedy desert winds carrying rocks and pebbles (abrasion).
Q.17. Define glacier and state how it differs from a river.
Answer: A glacier is a huge mass of ice in layers deposited in polar and high mountainous parts that comes down very slowly over surface slopes (often through valleys). It differs from a river primarily because it consists of moving ice rather than liquid water, and its velocity is much slower (most have a velocity of less than 1 meter a day).
Q.18. What is moraine? Draw a diagram to show different types of moraine.
Answer: Moraine refers to the lot of materials (such as boulders, pebbles, and sands) other than ice that are carried down by glaciers.
Q.19. Write how a glacial horn is formed.
Answer: A glacial horn is formed when several glaciers flow down from a mountain, and the erosional activities on all sides of the mountain make its peak sharp and conical.
Q.20. What is a coast?
Answer: A coast is the land margin of the oceans, representing the contact zone between the oceans and continents.
Changes of Earth’s Surface Textual Questions SEBA 2026-27
Q.21. What is a beach? State its importance.
Answer: A beach is a plain-like feature with a gentle seaward slope formed mainly of sands along the seashore where continuous wave action causes systematic sand deposits through the combined effects of swash and backwash. Its importance lies in the fact that it attracts people for recreation.
Q.22. Write how sea-waves bring about change in the coasts.
Answer: Sea-waves constantly operate in coastal areas through wave action (determined by factors like geological structure, depth of the nearby sea, and winds) to create specific erosional and depositional features, such as steep sea-cliffs when hitting hard rocks, and sandy beaches through systematic deposition.
Q.23. Connect by arrows the factors and the features on the basis of their cause-effect relation.
Answer: River Floodplain, Delta, Sandbar, V-shaped valley, Ox-bow lake
Wind Inselberg, Sand dune
Glacier Lateral moraine, Horn, U-shaped valley
Sea-wave Beach, Coast
Q.24. Think and write about the probable changes of the earth’s surface in future.
Answer: In the future, the earth’s surface will continue to experience changes because exogenic factors (such as glaciers changing due to global climate change) and endogenic factors will continue their activities. Exogenic factors will constantly work to make the surface a level one by removing all irregularities, while endogenic factors will create unevenness through movements, earthquakes, and volcanic eruptions.
Q.25. Prepare a note on the surface characteristics of your village or town. Draw a sketch of the area and try to show there the major features (river, hill, wetland, plain etc).
Answer: Note: The local surface features consist of flat alluvial plains formed by the river Brahmaputra, interspersed with wetlands (beels), low-lying floodplains, and gentle slopes, influenced heavily by seasonal river water flow and monsoon rainfall.
Students Should Draw the Sketch Itself
🌍 Class 9 Social Science Solutions Notice: This page features the complete SEBA Class 9 Social Science (Geography Section) Chapter 1: Changes of Earth’s Surface Official Textual Questions and Answers updated for the 2026–27 academic session. Formatted according to the official Assam Board evaluation marking scheme, every core geomorphic topic—from internal and external forces of change, chemical and physical weathering mechanisms, to landform evolution driven by running water, glaciers, wind, and sea waves—is presented with point-wise clarity, neat diagrammatic descriptions, and structured subheadings to help you secure full marks in your school assessments, half-yearly, and final annual examinations.
💡 Master SEBA Class 9 Geography Textual Solutions:
- Having difficulty framing a comprehensive 5-mark answer distinguishing between weathering and erosion, explaining the formation of an oxbow lake with a diagrammatic flow, or detailing the erosional and depositional work of wind in arid desert regions? Leave your query in the comments section below!
- Bookmark this page for quick revision of definitions, classification tables (endogenic vs. exogenic processes), and landform types before your upcoming unit evaluations, half-yearly exams, and annual examinations.
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