On 6 October 2026, after days of clashes in Siang and Upper Siang districts, the All Adi Youth Association asked the government to withdraw the central and State police deployed, it alleges, to put down protests against surveys for the Siang Upper Multipurpose Project (The Hindu). It said the Adis settle disputes through customary councils such as the Kebang, and that memoranda signed with some villagers do not speak for all 27 affected villages. NHPC's project is estimated at at least 11,000 MW; the Centre and the State call it a counter to China's 60,000 MW Medog station upstream on the Yarlung Tsangpo, which enters Arunachal Pradesh as the Siang.
Behind consent and strategy lies a physical fact every officer in the North-East must grasp: the ground under this dam is moving. The Siang flows out of the place where the Indian plate pushes into Asia. That push built the Himalaya, bends the river around Namcha Barwa, and caused the 1950 Assam–Tibet earthquake, one of the strongest recorded on land. To judge whether, where and how such a dam can be built, start with plate tectonics.
Concept Booster · Officer's Lens · Geography & Environment · Class 1
Can you build a dam on a moving continent? Plate tectonics, the Himalaya and the Siang
क्या खिसकते महाद्वीप पर बाँध बनाया जा सकता है? प्लेट विवर्तनिकी, हिमालय और सियांग
KnowDrift, sea-floor spreading and plate tectonics: the evidence, the plates, the three boundaries, and India's journey to the Himalaya.
LinkHow one moving plate explains the Himalaya, the Brahmaputra's course, the North-East's earthquakes and the risk to every Himalayan dam.
FeelLife in an Adi village on the Siang, where the ground shakes and strangers arrive with drills and guards.
DecideThe note a Deputy Commissioner writes when a dam survey in a seismic valley must go on without losing the people's trust.
1The file on your desk
URGENT · FOR DECISION
To: The Deputy Commissioner, a district in the Siang valley, Arunachal Pradesh
Subject: Pre-feasibility surveys for a large storage dam: how to proceed after the clashes
It is the first week of October. Surveys for a large hydropower project on the Siang have led to clashes, and armed police are posted in the valley. Five papers are on your table.
(1) The developer: drilling teams must test the rock at the dam site before the next monsoon; they want police escort to every site.
(2) The district geologist: the site lies near the eastern end of the Himalaya, where the Indian and Eurasian plates meet. The great 1950 earthquake struck this region; the slopes are steep, fractured and landslide-prone.
(3) A resolution of a village council (Kebang): "No survey on our land without the agreement of all our villages. Who will answer if the dam breaks in an earthquake?"
(4) A downstream district in Assam: its people fear sudden releases from China's upstream project, and a dam break on the Siang. They ask to see what the survey finds.
(5) The State government: the project is of national importance; the surveys must not stop.
The Chief Secretary wants one page: how the surveys go on, how seismic risk is judged and shared, and what you tell the villages. You have 24 hours.
To: The Deputy Commissioner, a district in the Siang valley, Arunachal Pradesh
Subject: Pre-feasibility surveys for a large storage dam: how to proceed after the clashes
It is the first week of October. Surveys for a large hydropower project on the Siang have led to clashes, and armed police are posted in the valley. Five papers are on your table.
(1) The developer: drilling teams must test the rock at the dam site before the next monsoon; they want police escort to every site.
(2) The district geologist: the site lies near the eastern end of the Himalaya, where the Indian and Eurasian plates meet. The great 1950 earthquake struck this region; the slopes are steep, fractured and landslide-prone.
(3) A resolution of a village council (Kebang): "No survey on our land without the agreement of all our villages. Who will answer if the dam breaks in an earthquake?"
(4) A downstream district in Assam: its people fear sudden releases from China's upstream project, and a dam break on the Siang. They ask to see what the survey finds.
(5) The State government: the project is of national importance; the surveys must not stop.
The Chief Secretary wants one page: how the surveys go on, how seismic risk is judged and shared, and what you tell the villages. You have 24 hours.
The file is a composite for teaching; no real office or person is described.
2The story
3The skeleton: the theory, the plates and the institutions
3a. Three ideas, one ladder
| Idea | What it says |
|---|---|
| Continental drift (Alfred Wegener, 1912) | All continents once formed one supercontinent, Pangaea, in one ocean, Panthalassa. About 200 million years ago it split into Laurasia (north) and Gondwanaland (south), and then into today's continents. Evidence: the jigsaw fit (best along the continental shelf edge); same-age rock belts in Brazil and West Africa; glacial deposits (tillite) in India and other southern continents; Ghana's placer gold with its source rock in Brazil; shared fossils such as the reptile Mesosaurus in southern Africa and Brazil. His forces (a pole-fleeing force and a tidal force) were far too weak, so the theory was rejected. |
| Convection currents (Arthur Holmes, 1930s) | Heat from radioactive decay drives slow currents in the mantle, which could drag the crust: a plausible engine for drift. |
| Sea-floor spreading (Harry Hess, early 1960s) | Magma rises at mid-ocean ridges, forms new ocean floor that moves away on both sides, and is destroyed at trenches. Evidence: rocks get older away from the ridge; sediments are thin near it; magnetic stripes lie symmetrically on both sides; ocean-floor rocks are nowhere older than about 200 million years, while some continental rocks exceed 3,000 million. |
| Plate tectonics (1967 onwards) | The lithosphere (crust plus rigid upper mantle) is broken into plates that move as rigid units over the softer asthenosphere. Continents are passengers; the ocean floor moves too. Most earthquakes, volcanoes and young fold mountains lie along plate boundaries. |
3b. The plates and their boundaries
NCERT lists seven major plates: Antarctica with its surrounding ocean; North American; South American; Pacific; India–Australia–New Zealand; Africa; Eurasia. Minor plates include Cocos, Nazca, Arabian, Philippine and Caroline. The Pacific plate is almost all ocean floor; the Indian plate carries both continent and ocean. NCERT gives the Arctic Ridge as the slowest-spreading (under 2.5 cm a year) and the East Pacific Rise near Easter Island as the fastest (over 15 cm a year).
| Boundary | What happens · example |
|---|---|
| Divergent (constructive) | Plates move apart; new crust forms. Mid-Atlantic Ridge; the East African Rift on land. |
| Convergent (destructive) | Ocean–ocean: subduction, island arcs and trenches (Japan, the Mariana Trench). Ocean–continent: volcanic fold mountains (the Andes). Continent–continent: neither sinks easily; the crust crumples into great fold mountains (the Himalaya). The Andaman–Nicobar arc is a subduction zone, with Barren Island, India's only active volcano. |
| Transform (conservative) | Plates slide past each other; crust is neither made nor destroyed. The San Andreas Fault; the faults that offset mid-ocean ridges. |
3c. The Indian plate, the Himalaya and the Brahmaputra
• India lay far south, beside Africa, Antarctica and Australia, separated from Asia by the Tethys Sea. As Gondwanaland broke up, it moved north; on the way, lava outpourings formed the Deccan Traps (NCERT: from about 60 million years ago; modern dating puts the main eruptions near 66 million).
• India met Asia about 40–50 million years ago. Tethys sediments were squeezed and lifted into the Himalaya. The push continues by a few centimetres a year, and the Himalaya still rises.
• The join is the Indus–Tsangpo Suture Zone. South of it, great thrust faults cut the range: from north to south the Main Central, Main Boundary and Main Frontal thrusts. Big Himalayan earthquakes release stress locked on them.
• Plate edges (NCERT): the Himalaya (north); Arakan Yoma and the Java Trench (east); Kirthar range and Makran coast (west); Indian Ocean ridges (south).
• The Brahmaputra rises in the Chemayungdung glacier near Lake Mansarovar, flows east along the suture zone in Tibet as the Tsangpo, turns sharply around Namcha Barwa through one of Earth's deepest gorges, and enters Arunachal Pradesh as the Siang (Dihang). Joined by the Dibang and Lohit in Assam it becomes the Brahmaputra, a braided, silt-laden river (Majuli is its great river island), fed on the right bank by the Subansiri and the Manas. In Bangladesh, where the Teesta joins, it is the Jamuna, and meets the Padma. Like the Indus and the Sutlej, it is antecedent: older than the Himalaya, it kept cutting down as the mountains rose.
• India met Asia about 40–50 million years ago. Tethys sediments were squeezed and lifted into the Himalaya. The push continues by a few centimetres a year, and the Himalaya still rises.
• The join is the Indus–Tsangpo Suture Zone. South of it, great thrust faults cut the range: from north to south the Main Central, Main Boundary and Main Frontal thrusts. Big Himalayan earthquakes release stress locked on them.
• Plate edges (NCERT): the Himalaya (north); Arakan Yoma and the Java Trench (east); Kirthar range and Makran coast (west); Indian Ocean ridges (south).
• The Brahmaputra rises in the Chemayungdung glacier near Lake Mansarovar, flows east along the suture zone in Tibet as the Tsangpo, turns sharply around Namcha Barwa through one of Earth's deepest gorges, and enters Arunachal Pradesh as the Siang (Dihang). Joined by the Dibang and Lohit in Assam it becomes the Brahmaputra, a braided, silt-laden river (Majuli is its great river island), fed on the right bank by the Subansiri and the Manas. In Bangladesh, where the Teesta joins, it is the Jamuna, and meets the Padma. Like the Indus and the Sutlej, it is antecedent: older than the Himalaya, it kept cutting down as the mountains rose.
3d. The legal and institutional frame
| Provision or body | What it does for this concept |
|---|---|
| Seventh Schedule; Art 262; Art 371H | Water: State List Entry 17, subject to Union List Entry 56 (inter-State rivers); Article 262 for inter-State water disputes; rivers shared with China and Bangladesh are foreign affairs, a Union subject. Article 371H: Arunachal's Governor has special responsibility for law and order. |
| Geological Survey of India (1851); National Center for Seismology (MoES) | GSI maps geology, faults and landslides and studies project sites; NCS is the nodal agency for earthquake monitoring. |
| BIS: IS 1893 (Part 1) | The earthquake design code and zone map. From 2002 there have been four zones (II to V), Zone V the highest, with the whole North-East in Zone V; the edition in force is IS 1893 (Part 1):2016. A 2025 revision that added a Zone VI for the Himalayan arc was withdrawn by BIS in March 2026. |
| DM Act, 2005; Dam Safety Act, 2021 | Disaster authorities at national (Prime Minister), State (Chief Minister) and district (Collector or Deputy Commissioner) levels. A National Dam Safety Authority and State bodies; owners of specified dams must do safety reviews and keep emergency action plans. |
| EIA Notification, 2006; Forest Rights Act, 2006 | Hydro projects of 50 MW or more are Category A, appraised at the Centre after a public hearing; forest land is diverted only after rights are settled and the gram sabha consents. |
| CWC; CEA | The National Committee on Seismic Design Parameters, serviced by the Central Water Commission, vets and recommends site-specific seismic design parameters for river valley projects; large hydro schemes need the Central Electricity Authority's concurrence (Section 8, Electricity Act, 2003). |
4The fine print — what separates a topper from the rest
1. Drift is not plate tectonics. Wegener moved continents through a fixed ocean floor; plate tectonics moves whole slabs of lithosphere, ocean floor included, driven by mantle convection, ridge push and slab pull. His evidence survived; his engine did not.
2. Plates are lithosphere, not crust. A plate includes the crust and the rigid top of the mantle, moving over the weak asthenosphere. NCERT gives plate thickness as roughly 5–100 km under oceans and about 200 km under continents. "Crustal plates" is loose language.
3. Why the Himalaya has no active volcanoes. Continental crust is too light to sink deep, so a continent–continent collision builds mountains and earthquakes, not volcanic arcs. Where an ocean plate sinks, as along the Andaman–Sumatra arc, come volcanoes (Barren Island) and great quakes like 2004.
4. The interior of a plate is not safe ground. The "stable" peninsula has had deadly quakes on old faults within the plate: Koyna (1967), Latur (1993), Bhuj (2001). Koyna is India's classic case of reservoir-triggered seismicity: filling a reservoir changes water pressure in faults and can release stress already stored. A dam cannot create plate stress, but it can trigger its release.
5. The eastern Himalaya is special. Around Namcha Barwa and the Mishmi Hills the mountain belt bends sharply: the eastern Himalayan syntaxis. The 1950 Assam–Tibet earthquake (magnitude 8.6) struck here; its landslides dammed rivers, and the debris dams later burst. The 1897 earthquake hit the Shillong Plateau, a block of the old peninsula pushed up between faults. The North-East faces both kinds of quake.
6. Antecedent rivers carry a warning. The Siang cut its gorge as the Himalaya rose; the steep valley that suits hydropower also breeds landslides and sudden floods.
7. Floods can come from above the dam. In October 2023 a glacial lake outburst from South Lhonak Lake in Sikkim swept down the Teesta and destroyed the Chungthang dam of the Teesta III project. A Himalayan dam must survive not only shaking but floods released upstream by quakes, landslides or glaciers.
8. Courts weigh the mountain and the people. In the Alaknanda Hydro Power case (13 August 2013), after the Kedarnath floods, the Supreme Court halted fresh environmental and forest clearances for hydro projects in Uttarakhand and asked an expert body whether such projects had worsened the disaster. In the Niyamgiri case (Orissa Mining Corporation v. Ministry of Environment and Forests, 2013) it upheld the gram sabha's say over forest diversion under the Forest Rights Act.
5How the idea grew
1596The Dutch map-maker Abraham Ortelius suggests that the Americas, Europe and Africa were once joined, as the coastlines seem to fit.
1897The great Shillong (Assam) earthquake shakes the North-East.
1912Alfred Wegener, a German meteorologist, proposes continental drift; his book follows in 1915.
1930sArthur Holmes suggests that convection currents in the mantle could move the continents.
1950The Assam–Tibet earthquake (15 August, magnitude 8.6) devastates the eastern Himalaya and blocks rivers with landslides.
Early 1960sOcean-floor mapping and Harry Hess's sea-floor spreading; magnetic stripes on the sea floor confirm it.
1967Plate tectonics is formulated (McKenzie and Parker, and Morgan). In December, the Koyna earthquake makes reservoir-triggered seismicity an Indian concern.
2001 → 2002The Bhuj earthquake (26 January 2001); IS 1893 revised, merging Zone I into Zone II.
2004 → 2005The Sumatra–Andaman earthquake and tsunami (26 December 2004); the Disaster Management Act, 2005; later, a tsunami warning centre at INCOIS, Hyderabad.
2021 → 2023The Dam Safety Act, 2021; the South Lhonak glacial lake outburst destroys the Teesta III dam (October 2023).
2025 → 2026China begins building the Medog project; surveys for the Siang Upper project meet protests, and in October 2026 clashes and an armed deployment.
6One issue, six lenses
Polity & law
Water is a State subject, inter-State rivers fall to the Union, and a river shared with China is foreign policy. The Forest Rights Act, the EIA Notification and the Dam Safety Act each govern a step. Arunachal is outside the Fifth and Sixth Schedules, so the gram sabha and the Kebang are the main local voice.Carry: geology and consent are both legal gates for a Himalayan dam.
Social justice
The plate shakes everyone, but risk falls unequally: villages in steep valleys, with weak houses and few roads, suffer most. The Adis would carry the submergence and the seismic risk, while most of the power and strategic gain go elsewhere.Carry: natural hazards are equal; disasters are not. Who bears the risk is a justice question.
Governance
India knows where the hazard is: the zone map, GSI's landslide maps, the NCS network. The gap is use: rushed site studies, unenforced codes, dam-break plans not shared downstream.Carry: hazard knowledge saves lives only when it reaches the person at risk.
Economy
The young, steep, wet mountains that make the North-East seismic also hold India's largest untapped hydropower. Storage offers clean power, flood moderation and a buffer against upstream releases; landslides and delays can multiply its cost.Carry: in the Himalaya, geology is part of every project's cost; price it in early.
Ethics
The precautionary principle: where harm could be serious and irreversible, uncertainty is no excuse for delaying care. A dam outlives its planners. Telling people the truth about risk, and asking for consent, is a duty, not public relations.Carry: honesty about risk is the first condition of consent.
Citizen & nation
The nation needs water security and an answer to upstream works; the Adis are citizens whose land and safety are part of that nation. A project that splits the valley weakens the border region it is meant to secure.Carry: national security on the frontier is built with the people of the frontier.
7From paper to village — the implementation chain
1
Science: the NCS records earthquakes; the GSI maps faults, rocks and landslides. Breaks if: the network is thin in remote valleys and small quakes go unrecorded.
2
Standards: the BIS code and zone map; NDMA guidelines. Breaks if: a zone map is read as a site study; it says "high hazard", not how one slope will behave.
3
Project design: drilling and rock tests, site-specific seismic parameters vetted through the CWC, dam-break and landslide-lake studies, then the project report and CEA concurrence. Breaks if: studies are rushed or done under guard, and the people who must live with them doubt them.
4
Clearances: EIA with a public hearing; forest clearance after gram sabha consent. Breaks if: memoranda with some households are treated as the consent of whole villages.
5
Dam safety: reviews, instruments and an emergency action plan under the 2021 Act. Breaks if: the emergency plan is a document in an office and never a drill in a village.
6
District: the Deputy Commissioner, chairing the District Disaster Management Authority, links the project, police, Kebangs and downstream Assam. Breaks if: the district acts as the developer's security, not the people's guardian.
7
The household: a family that knows the warning signals, the safe route uphill and who to call. Breaks if: warnings are in a language or form the village does not use, or arrive too late.
8Who wants what
| Stakeholder | Wants | Fears | Their fair point |
|---|---|---|---|
| Adi villages in the valley | Their land, river and way of life; a collective say through the Kebang | Submergence, displacement, a dam failing in an earthquake | They will live with the risk for generations; their consent should be collective and informed. |
| The Centre | Water security, flood control and a strategic counter to the Medog project | Sudden releases or diversion upstream with no treaty to restrain them | A large Indian reservoir could buffer the river against upstream actions. |
| The State government | Revenue, power, roads and jobs | A stalled project | Hydropower is one of its few large revenue sources. |
| Downstream Assam | Flood moderation and early warning | A dam break or a sudden release in a quake-prone valley | They bear the flood risk and should see the dam-break studies. |
| Bangladesh | Steady flows and data on the Jamuna | Upstream projects in China and India | The lowest riparian bears every upstream decision. |
9The human side — EQ, citizen first, nation first
The people behind the file. An elderly woman in a Siang village remembers her parents' stories of 1950: the roar, the hillsides sliding into the river, the flood days later. For her, "seismic risk" is family memory, not a map colour. A young engineer sees jobs in the project but cannot say so in his village. A policeman from another State, posted on the bank, does not know why the villagers are angry with him.
An officer with emotional intelligence starts by listening: she goes to the Kebang without an escort and lets the elders speak first. She promises neither that the dam is safe nor that it will be stopped; she promises honest studies, results explained in the village, and no survey by force. She brings the geologist to answer questions in plain words.
Citizen first: the valley's people have the first right to know what lies beneath their land and what the dam would mean. Nation first: India's position on the Brahmaputra is strongest when the people of the frontier stand with it. The officer's task is to let science and consent move together, so that whatever is built stands for a century, on the ground and in people's trust.
An officer with emotional intelligence starts by listening: she goes to the Kebang without an escort and lets the elders speak first. She promises neither that the dam is safe nor that it will be stopped; she promises honest studies, results explained in the village, and no survey by force. She brings the geologist to answer questions in plain words.
Citizen first: the valley's people have the first right to know what lies beneath their land and what the dam would mean. Nation first: India's position on the Brahmaputra is strongest when the people of the frontier stand with it. The officer's task is to let science and consent move together, so that whatever is built stands for a century, on the ground and in people's trust.
10The concept web — where this sits in your mind
Earth's interior — the crust, mantle, lithosphere and asthenosphere, and how seismic waves revealed them (geoenv-002).
Earthquakes & tsunamis — focus, epicentre, magnitude; why most quakes lie on plate boundaries; 2004 (GS1, GS3).
Himalaya & physiography — the Himalaya, the Indo-Gangetic plain and the peninsular plateau: three products of one plate's journey (GS1).
Brahmaputra system — Tsangpo–Siang–Brahmaputra–Jamuna; tributaries, braiding, floods (GS1).
Volcanoes & traps — the Deccan Traps, hotspots, island arcs and Barren Island (geoenv-007).
Disaster management — the DM Act, 2005, seismic codes, landslides and glacial lake outbursts (GS3). Darpan Lens: horizon.
Hydropower & dams — energy security, EIA, dam safety, forest-rights consent (GS3). Darpan Lens: sustain.
India–China rivers — no water-sharing treaty; an Expert Level Mechanism and flood-season data; Medog (GS2 IR). Darpan Lens: global.
On the website, each of these opens its own class as the library grows. Each new class adds lines to this web.
11Your decision — back to the file
You are the Deputy Commissioner. Choose the plan you will send to the Chief Secretary:
The note an officer would write
1. The site lies where the Indian plate pushes into Asia, in the highest seismic hazard zone of the BIS map; it saw the 1950 earthquake (magnitude 8.6) and its landslide floods. Only honest site studies can show whether a safe dam can be built here, and they need the villages' cooperation.
2. Immediate: surveys paused in villages that saw clashes; forces moved to standby; injuries to be inquired into. No land to be surveyed without the village's agreement.
3. Within 7 days: meetings in each Kebang with the engineers and the district geologist; the survey explained in the local language, objections recorded, agreements only after open village meetings.
4. Safety first: the developer to share its plan for site geology, site-specific seismic parameters (vetted through the CWC), dam-break and landslide-lake analysis, and an emergency action plan under the Dam Safety Act, 2021. Results to be explained in the villages.
5. Downstream: the Deputy Commissioners of the Assam districts to be briefed; a joint early-warning and data-sharing arrangement proposed.
6. Public message: "No survey by force. The ground here moves; we will study it honestly and share what we find."
7. Submitted for approval.
12How the exam asks it
| Paper | How this concept serves you |
|---|---|
| Prelims | Evidence for drift and spreading; plates and boundary types; why the Himalaya has no volcanoes; antecedent rivers; seismic zones; India's only active volcano. |
| GS1 — Geography | "Salient features of world's physical geography"; "Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity"; the physiography and drainage of India. |
| GS3 | Disaster and disaster management; infrastructure (energy); environmental impact assessment. |
| Essay | "The mountains do not negotiate"; "Development that does not listen to the land, or to its people, does not last." |
| Interview | "You are posted to a district in the highest seismic zone where a large dam is planned. What would you need to know before you support it, and how would you find out?" |
Trap: "Wegener explained drift by mantle convection currents." — False; that was Arthur Holmes. Wegener proposed pole-fleeing and tidal forces.
Trap: "Like the Andes, the Himalaya has active volcanoes, being on a convergent boundary." — False; continent–continent collision builds no volcanic arc.
Trap: "The oldest rocks on Earth are found on the ocean floor." — False; ocean-floor rocks are no older than about 200 million years; the oldest rocks are on the continents.
Trap: "Since the Indian peninsula is a stable shield, it has no major earthquakes." — False; Koyna (1967), Latur (1993) and Bhuj (2001) were all within the plate.
Mains practice 1 (GS1)
How does the theory of plate tectonics explain the origin of the Himalaya and the high seismicity of north-east India? (15 marks, 250 words)Model approach
Directive — Explain: cause and effect. Introduction: moving plates; India leaves Gondwanaland and moves north. Body — origin: the Tethys closes; collision 40–50 million years ago; sediments folded and lifted; the Indus–Tsangpo suture; the MCT, MBT and MFT; still rising. Body — the North-East: continuing convergence; the eastern syntaxis; 1950; the Shillong Plateau and 1897; the Arakan Yoma link to Andaman subduction. Diagram: a cross-section of India sliding under Tibet, thrusts marked. Conclusion: the process that made the mountains makes the hazard; planning must start from it.Mains practice 2 (GS3)
"Large dams in the Himalaya stand on a moving plate." Discuss the geological risks to hydropower projects in the Brahmaputra basin and the safeguards India needs. (10 marks, 150 words)Model approach
Directive — Discuss: both sides, then a view. Introduction: the basin's hydro potential; Siang Upper as an answer to Medog. Risks: great earthquakes (1950); landslide dams; glacial lake outbursts (South Lhonak, 2023); silt; reservoir-triggered seismicity (Koyna). Safeguards: site-specific seismic design; dam-break and GLOF studies; the Dam Safety Act, 2021; warnings shared with Assam; forest-rights consent. Conclusion: build only where science supports it and the people have agreed; size the project to both.13Check yourself
1. List four kinds of evidence Wegener used for continental drift.
Answer
Any four: the jigsaw fit; same-age rock belts in Brazil and West Africa; tillite in India and other southern continents; Ghana's placer gold traced to Brazil; shared fossils such as Mesosaurus.2. Why did most scientists reject Wegener's theory at first?
Answer
Because the forces he proposed, a pole-fleeing force and a tidal force, were far too weak to move continents.3. Give three pieces of evidence for sea-floor spreading.
Answer
Rocks age away from the ridges; symmetric magnetic stripes; thin sediments near ridges; no ocean floor older than about 200 million years.4. Name the three types of plate boundary, with one example each.
Answer
Divergent (Mid-Atlantic Ridge); convergent (the Himalaya, the Andes, the Japan trench); transform (the San Andreas Fault).5. Why are there no active volcanoes in the Himalaya, though it lies on a convergent boundary?
Answer
Both plates carry continental crust, too light to sink deep, so there is no subduction melting to feed volcanoes.6. Trace the Brahmaputra from its source to the sea, naming it in each stretch.
Answer
Chemayungdung glacier → Tsangpo (Tibet) → gorge around Namcha Barwa → Siang/Dihang (Arunachal) → with the Dibang and Lohit, the Brahmaputra (Assam) → Jamuna (Bangladesh) → meets the Padma → Bay of Bengal.7. What is an antecedent river? Give two Indian examples.
Answer
A river older than the mountains across its path, cutting down as they rose. The Indus, Sutlej and Brahmaputra.8. As Deputy Commissioner, why should a seismic survey not be carried out under armed escort against a village's will, even for a project of national importance?
Answer
The dam needs the valley's trust for a century, for warnings and drills. A forced survey yields data people will not believe, breaks the consent the Forest Rights Act requires, and turns a safety role into a security role.“Know it, link it, feel it, decide it.”
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