NCERT Solutions Class 9 Social Science (Understanding Society: India and Beyond, Part I) Chapter 2 – Shaping of the Earth's Surface
Circle of Learning • New NCERT textbook (2026-27) • In-text questions, activities and end-of-chapter questions – complete answers
The Big Questions
Answer
What shapes the Earth's surface?
The Earth's surface is shaped by two sets of forces. Internal forces such as earthquakes, volcanic eruptions, folding and faulting (driven by plate movement) build mountains, valleys and ocean basins. External forces such as weathering, erosion and deposition by running water, glaciers, wind, waves and groundwater slowly wear these down and reshape them.
What is plate tectonics? What are the effects of plate movement?
Answer
Plate tectonics, given by W.J. Morgan, is the theory that the Earth's lithosphere is broken into large and small tectonic plates that move slowly (a few centimetres a year) over the semi-molten asthenosphere. Plate movement forms fold mountains, mid-ocean ridges, volcanoes, valleys and ocean basins, causes earthquakes, and explains the distribution of continents and oceans.
Answer
How are landforms formed and how are they classified?
Landforms are natural features formed by processes such as weathering, erosion, deposition and movement of the crust. Large landforms like mountains and ocean basins are formed mainly by internal forces. Smaller landforms are classified by the agent of gradation that forms them: running water (waterfall, meander, delta), waves (beach, cliff, stack), glaciers (U-shaped valley, cirque, moraine), wind (yardang, dunes) and underground water (caves, sinkholes).
How are humans and other living beings connected to these landforms?
Answer
Landforms influence where people live and what they do. Fertile plains, meanders and deltas support farming and dense settlements; waterfalls give hydroelectric power and tourism; beaches and fjords support fishing and harbours; glaciers feed rivers with fresh water. Historically, river plains gave rise to early cities, mountains acted as barriers and protectors, and coasts supported trade.
How do disasters associated with different landforms impact human lives?
Answer
Landslides on hill slopes, avalanches on snowy slopes, glacial lake outburst floods (GLOFs) in glaciated valleys, and dust storms in dry areas can kill people and livestock, destroy houses, roads, bridges and hydel projects, and cut off villages. They also damage farmland and livelihoods, so understanding landforms helps us prepare and reduce disaster risk.
Let's Map
Pick any two plates from the map (Fig. 2.3) and complete the table (Name of the plate, Continents, Ocean).
Answer
Sample answer:
Name of the plate | Continents | Ocean |
|---|---|---|
African Plate | Africa | Parts of the Atlantic Ocean and the Indian Ocean |
Indo-Australian Plate | Australia and the Indian subcontinent (Asia) | Indian Ocean and part of the Pacific Ocean |
Let's Explore
Examine the plate map (Fig. 2.3) with the earthquake and volcano map (Fig. 2.4). What correlation do you observe?
Answer
Most earthquakes and active volcanoes lie along plate boundaries, where plates collide, move apart or slide past each other. The strongest concentration is around the edges of the Pacific Plate, the belt called the Ring of Fire. Other belts follow the Himalaya–Alpine collision zone and the mid-ocean ridges such as the Mid-Atlantic Ridge. The interiors of plates have far fewer earthquakes and volcanoes.
Observe the map showing the distribution of earthquakes and volcanoes (Fig. 2.4). Can you identify which continents and countries are located around the Ring of Fire with the help of an atlas or a globe?
Answer
The Ring of Fire surrounds the Pacific Ocean. It touches the continents of North America, South America, Asia, Australia (Oceania) and Antarctica. Countries along it include the USA (Alaska and the west coast), Canada, Mexico, Guatemala, Colombia, Ecuador, Peru, Chile, Russia (Kamchatka), Japan, the Philippines, Indonesia, Papua New Guinea and New Zealand.
Does India have a risk of earthquakes? Can you find out which region is more vulnerable to earthquakes? Why do you think human lives are at risk?
Answer
Yes. India has experienced major earthquakes, such as the one in Gujarat in 2001 that caused extensive damage. The most vulnerable regions are the Himalayan belt (Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim), the north-eastern states, the Kutch region of Gujarat, and the Andaman and Nicobar Islands, because the Indian plate is still pushing against the Eurasian plate. Human lives are at risk because India is densely populated, many buildings are not earthquake-resistant, and collapsing structures, landslides and fires cause most deaths.
Look carefully at the photograph (Fig. 2.6) and answer: What do you think caused this situation? What could that grey powder be? What does it tell us about the Earth's internal forces?
(i) The situation was caused by a volcanic eruption, which threw out material that settled over the area.
(ii) The grey powder is volcanic ash – tiny fragments of rock and glass blasted into the air and deposited on the ground.
Answer
(iii) It shows that the Earth's interior is extremely hot and has great pressure; molten magma can force its way to the surface, showing how powerful internal forces are in changing the surface.
Observe the photographs (Fig. 2.9) and also note the types of erosion. How are farmers affected by erosion due to water and wind?
Answer
Fig. 2.9 shows (a) water erosion and (b) wind erosion. Water erosion by rain and rivers cuts gullies and washes away the fertile topsoil; wind erosion in dry, sandy areas blows the loose topsoil away. In both cases farmers lose the fertile layer needed for crops, so yields fall, fields become uneven or covered with sand, and more money must be spent on fertilisers and land repair.
Have you heard about the Sundarbans delta? Try and explore its uniqueness and find out why it is popular with tourists.
Answer
The Sundarbans is formed by the Ganga, Brahmaputra and Meghna rivers in West Bengal (India) and Bangladesh, and is one of the largest deltas in the world. It is unique for its vast mangrove forests (named after the sundari tree), its network of tidal creeks and islands, and the Royal Bengal tiger that can swim in its waters. It is a National Park, Tiger Reserve and UNESCO World Heritage Site. Tourists visit for boat safaris, tiger and crocodile sightings, bird-watching and its rich biodiversity.
Observe the landforms around your school or residence and try to identify which agent may have created them.
Answer
Sample answer: Near a river, you may see a floodplain or meander formed by running water. Small gullies on bare slopes are created by rain water. In dry areas, sand heaps and dunes are formed by wind. In hilly areas, V-shaped valleys are made by rivers. Students should list each landform with the agent (running water, wind, waves, glacier or underground water) that formed it.
Complete the exercises given at the end of each type of disaster (prone areas, mitigation measures, recent examples) with the help of newspapers, atlases and books. Make a list of disaster-prone areas from India and the world and enlist mitigation measures quoting recent examples.
Answer
Disaster | Prone areas | Mitigation measures | Recent examples |
|---|---|---|---|
Landslides | Himalayan states (Uttarakhand, Himachal Pradesh, Sikkim, J&K), North-East, Western Ghats (Kerala, Konkan); world: Nepal, Andes, Japan | Afforestation, retaining walls, proper drainage, no construction on steep slopes, early warning, controlled road cutting | Wayanad (Kerala) landslides, July 2024; Joshimath land subsidence, 2023 |
Avalanches | Snow-covered Himalaya: J&K, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim; world: Alps, Rockies | Avalanche forecasting and warnings, snow fences and barriers, planting trees on slopes, avoiding trekking after heavy snowfall | Avalanches in Ladakh and Uttarakhand affecting army personnel and mountaineers in recent winters |
GLOFs | Glaciated Himalaya: Sikkim, Uttarakhand, Himachal Pradesh, Ladakh; Nepal, Bhutan | Monitoring glacial lakes by satellite, lowering lake water levels, early warning systems, avoiding settlements and dams in danger zones | South Lhonak lake outburst, Sikkim, October 2023; Chamoli flood, Uttarakhand, February 2021 |
Dust storms | Rajasthan (Thar), Punjab, Haryana, Uttar Pradesh, Delhi; world: Sahara, Middle East, China | Shelterbelts and tree planting, preventing overgrazing, covering soil with vegetation, weather warnings | Severe dust storms in Rajasthan and Uttar Pradesh in May 2018 |
Students should update the examples with the latest events from newspapers.
Don't Miss Out
The "Don't Miss Out" boxes are information boxes. Key points to remember:
(i) In ancient India earthquakes were called 'bhūkampa'. In the Bṛihatsaṁhitā, Varāhamihira linked them to changes in wind, rain, clouds, animal behaviour and planetary alignments, and to four forces – Vāyu, Agni, Indra and Varuṇa.
(ii) Baratang Island in the Andaman and Nicobar Islands has India's only mud volcano, where mud bubbles out due to underground gases and pressure.
(iii) The Sindhu-Sarasvatī civilisation used contouring, bunding, terracing, dams and canals for water management; the Zabo system of Nagaland uses earthen bunds on hillslopes.
(iv) Landforms shaped history: river plains gave rise to early cities, the Himalaya protected India but allowed exchange through passes like the Khyber pass, and coasts supported trade.
Think About It
A devastating flood struck the Chamoli district in Uttarakhand in February 2021, causing loss of lives and damage to buildings, roads, bridges and hydel projects. Can you find out the reasons that led to the sudden and unexpected flood?
Answer
On 7 February 2021, a huge mass of rock and glacier ice broke off from a slope near Ronti peak in the Nanda Devi region. It fell into the valley, turned into a fast-moving flood of water, mud and debris, and rushed down the Rishiganga and Dhauliganga rivers. It was sudden because it happened in winter without heavy rain. Contributing factors include steep, unstable mountain slopes, weakening of ice and rock due to rising temperatures and freeze-thaw weathering, and the presence of hydel projects and settlements right in the narrow river valleys.
Questions and activities
What are the sources of energy that are required to cause movements associated with the internal forces of the Earth?
Answer
The main source is the heat inside the Earth, coming from the very hot core (and heat released by radioactive elements in the interior). This heat makes molten material in the mantle rise while cooler material sinks, creating convection currents. These currents push and pull the tectonic plates, causing earthquakes, volcanoes, folding and faulting.
Relate various physiographic divisions you have studied in the earlier grades with various endogenic forces responsible for their origin.
Answer
Physiographic division of India | Endogenic (internal) force responsible |
|---|---|
The Himalaya | Convergence: collision of the Indo-Australian (Indian) plate with the Eurasian plate caused folding, forming young fold mountains. |
Northern Plains | Formed in the depression (trough) created in front of the rising Himalaya during plate collision, later filled by river deposits. |
Peninsular Plateau | A very old, stable block of the ancient landmass; parts were raised and broken by faulting, and the Deccan Traps formed from volcanic lava flows. |
Coastal Plains | Formed by faulting and the drifting away of landmasses, along with uplift and sinking of the coast. |
Islands (Andaman and Nicobar; Barren Island) | Plate convergence and volcanic activity; Barren Island is an active volcano. |
Why and where do earthquakes occur frequently? Is it possible to predict earthquakes?
Answer
Earthquakes occur when tectonic plates collide, move apart or slide past each other, releasing stored energy that shakes the ground. They occur most frequently along plate boundaries, especially around the Pacific Ocean (the Ring of Fire), in the Himalaya–Alpine belt, along mid-ocean ridges such as the Mid-Atlantic Ridge and transform faults such as the San Andreas Fault. Scientists can identify earthquake-prone regions, but the exact time, place and strength of an earthquake cannot yet be predicted accurately. So preparedness and safe construction are the best protection.
"Plate movements are responsible for the distribution of earthquakes and volcanoes." Explain.
Answer
(i) Earthquakes and volcanoes are not spread randomly; most occur along plate boundaries.
(ii) At convergent boundaries, when an oceanic plate sinks beneath a continental plate, rock melts into magma, causing volcanoes and earthquakes (as around the Pacific Ring of Fire). When two continental plates collide, as in the Himalaya, strong earthquakes occur.
(iii) At divergent boundaries, plates move apart and magma rises to form new crust, such as the Mid-Atlantic Ridge, with volcanic activity and earthquakes.
(iv) At transform boundaries, plates slide past each other, mainly causing earthquakes, as along the San Andreas Fault in the USA.
(v) Plate interiors are comparatively stable. Thus the pattern of plate movement explains where earthquakes and volcanoes are concentrated.
Draw and label a diagram of a meander and a delta.
Answer
Guidance (students should draw the diagrams in their notebooks, following Fig. 2.11 and Fig. 2.12):
Meander – labels: River; steep bank (outer bank, where erosion occurs); bar (inner bank, where sediment is deposited); oxbow lake (a cut-off loop of the old meander). Draw a winding river with a large loop, the steep outer bank, the deposit on the inner bend, and a crescent-shaped lake left beside the river.
Delta – labels: River; distributaries; islands/bars; sea. Draw the main river splitting into many distributaries that spread out in a fan or triangle shape, with islands of sediment between them, ending at the sea.
How are deforestation and erosion associated with each other? Explain.
Answer
Tree roots hold soil together, and leaves and plant cover break the force of rain and wind. When forests are cut, the soil is left bare, so rain water and wind easily wash or blow away the fertile topsoil. On slopes, deforestation also makes the land unstable and causes landslides, while in dry areas it increases wind erosion and dust storms. Thus deforestation speeds up erosion, which reduces farm yields and damages land.
Develop a plan to protect the land in your local area from erosion.
Answer
Sample plan:
(i) Plant trees and grass on bare land, slopes and river banks so roots hold the soil.
(ii) Contour ploughing, bunding and terracing on sloping fields to slow down running water.
(iii) Continuous contour trenches and check dams on small streams to reduce water speed and recharge groundwater.
(iv) Shelterbelts (rows of trees) in windy, dry areas to reduce wind erosion.
(v) Avoid overgrazing and keep soil covered with crops or mulch after harvest.
(vi) Proper drainage along roads and buildings so water does not cut gullies.
(vii) Awareness campaigns through the school eco-club and panchayat or ward committee.
Which disasters do you think you might experience in your region? Discuss a mitigation plan in your classroom.
Answer
Sample answer (for a hilly region such as Uttarakhand; students should choose their own region): Likely disasters are landslides during the monsoon, earthquakes and flash floods. Mitigation plan: plant trees and avoid construction on steep slopes and river banks; keep drains clean; follow weather warnings from the radio, TV and mobile alerts; identify safe assembly points and evacuation routes; build earthquake-resistant houses; keep an emergency kit (torch, water, first-aid, documents); and hold regular mock drills in school.
Prepare a model of landforms created by underground water.
Answer
Guidance: Use a cardboard base, clay or plaster of Paris, and paint. Make a limestone hill with a hollow cave inside. Show stalactites hanging from the cave ceiling and stalagmites rising from the floor (use clay drips or melted candle wax), a pillar where they join, a cave mouth, an underground river flowing through the cave (blue paint or cellophane), and a sinkhole depression on the surface. Label each feature and add a note that these form by chemical weathering of limestone, called Karst topography.
What precautionary measures will you take if you are staying in an earthquake-prone region?
(i) Live in an earthquake-resistant building and fix heavy furniture and shelves to walls.
(ii) Keep an emergency kit with water, food, torch, medicines and important documents.
(iii) During shaking, follow "Drop, Cover and Hold" under a sturdy table, staying away from windows and heavy objects.
(iv) If outdoors, move to an open area away from buildings, trees and electric poles.
(v) Do not use lifts; after the shaking, leave the building carefully and switch off gas and electricity.
(vi) Take part in mock drills and know the safe assembly points.
Answer
Prepare a map showing landform-associated disasters that happened in the current calendar year.
Answer
Guidance: Take an outline map of India (or the world). Collect news reports of landslides, avalanches, GLOFs, dust storms and earthquakes from this year. Mark each event at its location with a different symbol or colour (for example, brown triangle for landslides, white star for avalanches, blue drop for GLOFs, yellow circle for dust storms), write the date beside it, and add a legend and title. Then note which landforms (hill slopes, glaciated valleys, deserts) the disasters cluster in.
Create a poster showing landforms that are considered to be sacred or important in your region, and add the folk stories associated with them.
Answer
Sample ideas: Students may show rivers like the Ganga (believed to have descended from heaven through Lord Shiva's hair), mountains such as Govardhan hill (lifted by Lord Krishna to shelter people from rain), Kailash, Arunachala hill in Tiruvannamalai, sacred caves like Amarnath, or a local hill, lake or grove. The poster should include a picture or sketch of each landform, its location, the folk story in a few lines, and how people protect it.
Document a case of a disaster that hit your region in the past, highlighting its effects on various human activities.
Answer
Sample case: Gujarat earthquake, 2001. A major earthquake struck the Kutch region of Gujarat on 26 January 2001.
(i) Housing and settlements: Thousands of houses and buildings collapsed, especially in Bhuj, leaving many people homeless.
(ii) Loss of life: Thousands of people were killed and many more injured.
(iii) Economy: Shops, small industries and handicraft work stopped; roads, bridges and power lines were damaged.
(iv) Services: Schools and hospitals were destroyed, disrupting education and health care.
(v) Recovery: Rebuilding was done with earthquake-resistant designs, and Gujarat set up a disaster management authority.
Students can document any disaster from their own region in a similar format.
Translate the given poster on landslide into your native language and display it in your home.
Answer
Sample translation into Hindi of the NDMA poster "Landslide – Ready Now to stay secure":
भूस्खलन – अभी तैयार रहें, सुरक्षित रहें
पहले: मिट्टी को बाँधने वाले अधिक पेड़ लगाएँ; किसी भी चेतावनी के लिए रेडियो, टीवी और अख़बार पर ध्यान दें; नालियाँ साफ़ और खुली रखें; ज़मीन धँसने, चट्टानों में दरार और नदी का पानी मटमैला होने जैसे संकेतों पर नज़र रखें; खड़ी ढलानों और नालों के पास निर्माण न करें।
दौरान: शांत रहें, घबराएँ नहीं, अफ़वाहों पर ध्यान न दें; अपने साथियों के साथ रहें; पेड़ टूटने या पत्थरों के टकराने जैसी असामान्य आवाज़ें सुनें तो भूस्खलन के रास्ते से या नीचे की घाटी से तुरंत हट जाएँ; नज़दीकी तहसील/ज़िला मुख्यालय को सूचित करें।
बाद में: ढीली सामग्री और बिजली के तारों या खंभों को न छुएँ, उन पर न चलें; भूस्खलन के रास्ते से दूर रहें; घायल और फँसे लोगों की जाँच करें; घायल व्यक्ति को प्राथमिक उपचार दिए बिना न हिलाएँ, जब तक तत्काल ख़तरा न हो; नदियों, झरनों और कुओं का दूषित पानी सीधे न पिएँ।
समझदार बनें, तैयार रहें।
Divide the class into three groups. Each group will work on one project (water, wind, and glacier). The project should highlight the causes, impact on human life and the environment, and mitigation measures.
Answer
Group / Agent | Causes | Impact on human life and environment | Mitigation measures |
|---|---|---|---|
Water | Heavy rainfall, fast-flowing rivers, ocean waves; deforestation and bare soil | Loss of fertile topsoil, lower yields, floods, gullies, washing away of houses, roads and coastal land | Afforestation, contour bunding, terracing, check dams, embankments, mangrove plantation on coasts |
Wind | Strong winds in dry, sandy areas; drought, overgrazing and sparse vegetation | Topsoil blown away, spreading sand dunes, desertification, dust storms harming health and visibility | Shelterbelts, stabilising dunes with vegetation, controlled grazing, keeping soil covered |
Glacier | Moving ice scraping valleys; rising temperatures melting glaciers | U-shaped valleys and moraines; fresh water for rivers; but GLOFs, avalanches and floods downstream | Monitoring glacial lakes, early warning systems, avoiding construction in danger zones, reducing greenhouse gas emissions |
Extra Important Questions
Multiple Choice Questions
1. The theory of plate tectonics was given by
(a) Varāhamihira (b) W.J. Morgan (c) Alfred Wegener (d) Kauṭilya
Answer: (b) W.J. Morgan
The semi-molten layer beneath the lithosphere on which plates move is the:
Answer
(a) Crust (b) Inner core (c) Asthenosphere (d) Outer core
Answer: (c) Asthenosphere
3. The San Andreas Fault is an example of a
(a) Convergent boundary (b) Divergent boundary (c) Transform boundary (d) Mid-ocean ridge
Answer: (c) Transform boundary
4. An oxbow lake is formed by
(a) Glaciers (b) A meandering river (c) Wind (d) Sea waves
Answer: (b) A meandering river
Isolated pillars of rock left standing after sea arches collapse are called:
Answer
(a) Stacks (b) Cirques (c) Yardangs (d) Levees
Answer: (a) Stacks
6. India's only mud volcano is located at
(a) Barren Island (b) Baratang Island (c) Kutch (d) Chamoli
Answer: (b) Baratang Island
Short Answer Questions
Distinguish between weathering and erosion.
Answer
Weathering | Erosion |
|---|---|
Breaking down of rocks into smaller pieces on the surface. | Wearing away and carrying of soil and rocks from one place to another. |
Does not involve movement of the broken material. | Involves movement by agents like water, wind, ice or waves. |
Types: physical, chemical and biological. | Types: water, wind, glacial and coastal erosion. |
Name the three types of tectonic plates and give two examples of major plates.
Answer
The three types are continental plates, which carry continents; oceanic plates, which carry ocean floors; and mixed plates, which carry both. Examples of major plates are the Pacific Plate and the Eurasian Plate (others include the African, Indo-Australian and Antarctic Plates).
Answer
How are deltas useful to humans? Why can they be risky?
Deltas have rich alluvial soil that supports crops such as rice and jute, and the mix of fresh and salt water supports fishing. They support dense settlements and are centres of trade and transport because rivers provide navigable routes. However, they are low-lying and prone to flooding.
What are moraines? Name their types.
Answer
Moraines are landforms made of rocks, soil and debris (called till) deposited by a glacier when it melts. The types are lateral moraines along the sides of glaciers, terminal moraines at the end of a glacier marking its furthest advance, and medial moraines formed when two glaciers meet and their lateral moraines join.
Long Answer Questions
Describe the landforms formed by a river in its upper, middle and lower course and explain their importance to humans.
Answer
(i) Upper course: Due to steep gradient and strong erosion, the river forms V-shaped valleys, rapids and waterfalls. Waterfalls form where hard rock resists erosion and softer rock below is worn away. They attract tourists and can be used for hydroelectric power.
(ii) Middle course: The river loses energy and begins to meander, eroding outer banks and depositing on inner banks. Oxbow lakes and floodplains form. The fertile soil supports farming and settlements; the Grand Anicut (Kallanai) in Tamil Nadu shows the use of rivers for irrigation.
(iii) Lower course: The river slows further and deposits large amounts of sediment, forming deltas, levees and alluvial fans. Deltas support rice and jute farming, fishing, dense settlements and trade, though they are flood-prone.
Explain the causes of landslides and GLOFs.
Answer
Landslides
(i) Heavy, continuous rainfall seeps into soil and rock, increasing weight and reducing friction.
(ii) Earthquakes and volcanic eruptions shake and weaken slopes.
(iii) Steep slopes and loose or weathered rocks increase risk.
(iv) Human activities like deforestation, mining, road building and unplanned construction, along with poor drainage, cause sudden slope failure.
GLOFs (Glacial Lake Outburst Floods)
(i) Rising temperatures melt glaciers rapidly, enlarging glacial lakes and pressuring their natural dams of ice or loose moraine.
(ii) Heavy rainfall or snowfall adds excess water.
(iii) Earthquakes, avalanches or landslides may strike the lake or weaken the dam.
(iv) The dam collapses and water is released suddenly, causing destructive floods downstream.