This MCQ module is based on: Floods, Droughts, Earthquakes & Tsunami in India
TOPIC 15 OF 17
Floods, Droughts, Earthquakes & Tsunami in India
🎓 Class 11
Social Science
CBSE
Theory
Ch 6 — Natural Hazards and Disasters
⏱ ~28 min
🌐 Language: [gtranslate]
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Chapter 6 · Natural Hazards and Disasters — Floods, Droughts, Earthquakes & Tsunami
You may have watched television footage of tsunami waves swallowing the Tamil Nadu coast in 2004, or seen a Bhuj school crumble during the Gujarat earthquake of 2001. Why does the same Earth that grows our crops sometimes turn into a destroyer? Are hazards and disasters the same thing? Why do floods drown Assam every monsoon while Rajasthan goes thirsty in the same year? In this chapter we read the language of disaster — and the science of mitigation that humanity is slowly learning.
6.1 Change, Hazards and Disasters — Reading the Difference
Change is the law of nature. Some changes are slow, like the rise of the Himalayas; others are sudden, like a volcanic eruption, a tsunami or a flash of lightning. Some changes are tiny in scale, like a hailstorm over one village; others are global, like ozone-layer depletion. From a purely natural perspective these changes are value-neutral; from a human perspective some are good (the change of seasons) and some are dreaded (earthquakes, floods, wars).
📖 NCERT Definition
A disaster? is an undesirable occurrence resulting from forces that are largely outside human control, that strikes quickly with little or no warning, causes or threatens serious disruption of life and property including death and injury to a large number of people, and requires mobilisation of efforts in excess of those normally provided by statutory emergency services.
For a long time, scholars treated disasters purely as the work of nature, with humans as helpless victims. That picture is no longer accurate. Bhopal Gas tragedy, the Chernobyl nuclear accident, wars, the release of CFCs and the rise of greenhouse gases, plus pollution of air, water, soil and noise — all are disasters caused directly by human actions. Even classical “natural” disasters like landslides and floods are accelerated indirectly by deforestation, unscientific land-use and reckless construction in fragile zones.
6.1.1 Natural Hazards vs. Natural Disasters
The two terms are often used interchangeably, yet they are distinct. Natural hazards? are elements of the natural environment that have the potential to harm people, property or both. They may be permanent features such as ocean currents, steep unstable slopes in the Himalayas or the extreme cold of glaciated areas. Natural disasters, by contrast, are sudden, large-scale events that cause widespread death, destruction of property and disruption of social systems — events over which people have little or no control.
Put briefly: every disaster grows out of a hazard, but not every hazard becomes a disaster. A hazard becomes a disaster only when its magnitude of destruction is very high — usually when it strikes a region of high population density or low coping capacity.
🌍 International Action
In recognition of rising losses, the U.N. General Assembly (1989) declared the decade 1990–2000 the International Decade for Natural Disaster Reduction (IDNDR). The World Conference on Natural Disaster Reduction at Yokohama, Japan (May 23–27, 1994) adopted the Yokohama Strategy and Plan of Action for a Safer World, urging every country to give priority attention to disaster prevention, mitigation and preparedness, and to support developing and least-developed countries, land-locked countries and small-island states.
6.2 Classification of Natural Disasters
Identification and classification of disasters is a scientific first step toward managing them efficiently. Broadly, natural disasters fall into four categories as recognised in NCERT Table 6.1.
| Atmospheric | Terrestrial | Aquatic | Biological |
|---|---|---|---|
| Blizzards, Thunderstorms, Lightning, Tornadoes, Tropical Cyclones, Drought, Hailstorm, Frost, Heat Wave (Loo), Cold Wave | Earthquakes, Volcanic Eruptions, Landslides, Avalanches, Subsidence, Soil Erosion | Floods, Tidal Waves, Storm Surge, Tsunami | Plants and Animals as colonisers (locusts, etc.); insect infestation; fungal, bacterial and viral diseases such as bird flu, dengue, etc. |
India experiences nearly every category in this table. Every year the country loses thousands of lives and property worth millions of rupees to one or more of these calamities — floods in Assam and Bihar, droughts in Rajasthan, cyclones along the eastern coast, earthquakes in the Himalayas and Kachchh, landslides in the Western Ghats, and the once-in-a-generation tsunami of 2004.
Activity 6.1 · LET'S EXPLORE — Mapping Change in Your Life
- List five changes you observe in your environment that take place over a long period of time.
- List five changes that take place within a short period of time (seconds to days).
- Beside each change, mark whether you consider it good (G), bad (B) or value-neutral (N) and explain why.
- Identify two human activities going on in or around your school that could lead to a disaster in the near future. Suggest one prevention measure for each.
Pointers: Slow changes — ageing of trees, soil erosion, weathering of buildings, urban expansion, climate-shift evidence. Sudden changes — storms, road accidents, earthquakes, floods, lightning. “Good” vs “bad” depends on perspective: a heavy monsoon rain is good for farmers but bad for low-lying slum residents. Risk activities near schools may include construction without earthquake-resistant designs, dumping of waste into drains, deforestation of slope-side land. Mitigation: enforce building codes, plant trees, clean storm drains.
6.3 Natural Disasters and Hazards in India
India's vastness, environmental diversity and cultural pluralities are exactly what make it a land of unity in diversity — and what make it deeply vulnerable to disasters. Its prolonged colonial past, continuing social discrimination, and a population of more than 1.4 billion all enhance the country's vulnerability. About two-thirds of India's geographical area and roughly the same proportion of its population are vulnerable to one disaster or another, according to the National Institute of Disaster Management.
6.4 Earthquakes
Earthquakes are the most unpredictable and highly destructive of all natural disasters. You have already learnt their physical causes in Fundamentals of Physical Geography (NCERT, 2024). Tectonic earthquakes — the most devastating and far-reaching kind — occur when sudden release of energy along faults shakes the Earth's crust. Earthquakes associated with volcanic eruptions, rock-falls, landslides, subsidence in mining areas, and the impounding of dams and reservoirs are smaller in their footprint and damage.
6.4.1 Why India trembles
The Indian plate is moving northward and north-eastward at a speed of about one centimetre per year, and is being constantly obstructed by the Eurasian plate. The two plates lock against each other, energy accumulates, stress builds up, and when the lock finally breaks, a sudden release of energy unleashes earthquakes along the Himalayan arc.
The most vulnerable Himalayan zone covers Jammu & Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, the Darjeeling sub-division of West Bengal, and all seven north-eastern states. Beyond the Himalayas, the central-western parts of India — Gujarat (1819, 1956 and 2001) and Maharashtra (1967 and 1993, the Latur earthquake) — have also been hit by severe earthquakes. The reasons remain debated; one recent theory points to a fault line along the Bhima river (a Krishna tributary) near Latur and Osmanabad, where the Indian plate may itself be breaking up.
6.4.2 The Five Earthquake Zones of India
The National Geophysical Laboratory, the Geological Survey of India, the IMD (Department of Meteorology) and the recently formed National Institute of Disaster Management have analysed more than 1,200 earthquakes in India to divide the country into five earthquake hazard zones:
| Zone | Risk Level | Major Areas Covered |
|---|---|---|
| (i) Very High | Very high damage risk | North-east states; areas north of Darbhanga & Araria along Indo-Nepal border (Bihar); Uttarakhand; Western Himachal Pradesh (around Dharamshala); Kashmir Valley; Kachchh (Gujarat) |
| (ii) High | High damage risk | Remaining parts of J&K, Ladakh, Himachal Pradesh; Northern Punjab; Eastern Haryana; Delhi; Western Uttar Pradesh; Northern Bihar |
| (iii) Moderate | Moderate damage risk | Parts of central India and the Peninsular plateau margins |
| (iv) Low | Low damage risk | Most of the central and eastern peninsular plateau |
| (v) Very Low | Very low damage risk | Stable Deccan plateau core — the safest zone |
Figure 6.A: India — Earthquake hazard zones (schematic, after NCERT Figure 6.2). The Himalayan arc, the NE states and Kachchh share the highest damage risk.
6.4.3 Major Indian Earthquakes — A Painful Timeline
| Year | Event | Magnitude (approx.) | Note |
|---|---|---|---|
| 1819 | Kachchh (Gujarat) | ~7.7 | Created the Allah Bund — an uplifted ridge on the Rann of Kachchh |
| 1956 | Anjar (Gujarat) | ~6.1 | Severe damage to Kachchh region towns |
| 1967 | Koyna (Maharashtra) | ~6.5 | Reservoir-induced; led to redesign of dam safety norms |
| 1993 | Latur (Maharashtra) | ~6.4 | About 9,000 lives lost; surprised seismologists in the “stable” Peninsula |
| 2001 | Bhuj (Gujarat) | ~7.7 | Devastated Kachchh; tens of thousands killed; revolutionised India's disaster law |
| 2005 | Kashmir (along the LoC) | ~7.6 | Massive damage on both sides of the Line of Control |
| 2011 | Sikkim | ~6.9 | Damaged Sikkim and parts of north Bengal |
| 2015 | Nepal (Gorkha) | ~7.8 | Felt across Bihar, UP, Delhi; widespread tremors in N. India |
6.4.4 Socio-Environmental Consequences of Earthquakes
Earthquakes are particularly feared because of their scale, magnitude and suddenness. They become a calamity when they strike a densely populated region. They damage settlements, infrastructure, transport and communication networks, industries and developmental activities; they destroy material and socio-cultural gains preserved over generations; they render millions homeless and put extra stress on the weak economies of developing countries. Their effects fall under three heads: on the ground, on man-made structures, and on water.
| On Ground | On Man-made Structures | On Water |
|---|---|---|
| Fissures, settlements, landslides, liquefaction, earth pressure, possible chain-effects | Cracking, slidings, overturning, buckling, collapse, possible chain-effects | Waves, hydro-dynamic pressure, tsunami, possible chain-effects |
Beyond these, earthquakes carry far-reaching environmental consequences. Surface seismic waves can produce fissures on the upper crust through which water and volatile materials gush out, inundating neighbouring areas. Earthquakes commonly trigger landslides; landslides can dam rivers and form temporary reservoirs; rivers can change course, causing fresh floods elsewhere.
6.4.5 Earthquake Hazard Mitigation?
It is not yet possible to prevent an earthquake. The next-best option therefore is preparedness and mitigation, not cure. NCERT recommends four pillars:
Seismological Centres
Establish earthquake monitoring centres for regular surveillance and fast dissemination of information among people in vulnerable areas. GPS aids in tracking tectonic plate movement.
Vulnerability Mapping
Prepare a national vulnerability map. Disseminate risk information and educate people on minimising adverse impacts of disasters.
Modify Building Designs
Modify house types and building designs in vulnerable areas. Discourage high-rise buildings, large industrial establishments and big urban centres in such zones.
Earthquake-Resistant Codes
Make earthquake-resistant designs and the use of light materials mandatory in major construction activities in vulnerable areas.
Figure 6.B: Approximate magnitudes of major Indian earthquakes since 1819. Bhuj 2001 and Nepal 2015 stand out as the strongest of recent decades.
6.5 Tsunami
Earthquakes and volcanic eruptions on the sea-floor can suddenly displace huge volumes of ocean water, generating high vertical waves called tsunamis? — literally “harbour waves” in Japanese, also called seismic sea waves. After the first disturbance the ocean throws up a series of after-waves that oscillate between high crest and low trough until water level is restored.
The speed of a tsunami wave depends on the depth of water; it is greater in shallow water than in the deep ocean. Out at sea the wave-length is enormous and the wave-height is limited — just a metre or two — so a ship feels little. As the wave enters shallow water near the coast, the wave-length shortens, the period stays unchanged, and the height shoots up to 15 m or more — producing the “Shallow Water Waves” that smash into the shore.
⚠ The 26 December 2004 Tsunami
Triggered by a magnitude-9 sub-marine earthquake off Sumatra, the tsunami that struck on 26th December 2004 killed more than 3,00,000 people across the Indian Ocean rim. India lost thousands of lives along Tamil Nadu, Kerala, Andhra Pradesh, Puducherry and the Andaman & Nicobar Islands. India subsequently joined the International Tsunami Warning System. Tsunamis are common around the Pacific Ring of Fire (Alaska, Japan, the Philippines, Indonesia, Malaysia, Myanmar, Sri Lanka and India). Mitigation is difficult because losses are on a scale beyond any single nation; only combined international action helps.
6.6 Floods
Inundation of land and human settlements by the rise of water in channels and its spill-over presents the condition of flooding?. Unlike other disasters, the causes of floods are well-established. Floods occur when surface run-off exceeds the carrying capacity of river channels and streams and overflows into low-lying flood plains. They can also be caused by:
- Storm surge in coastal areas (often from a cyclone)
- High-intensity rainfall continuing over long periods
- Melting of ice and snow
- Reduction in the rate of infiltration
- Eroded material in water from accelerated soil erosion
Floods occur frequently across the world, but the South, Southeast and East Asian countries — particularly China, India and Bangladesh — suffer the most. Unlike other natural disasters, human beings play an important role in the genesis as well as the spread of floods: indiscriminate deforestation, unscientific agricultural practices, disturbances along natural drainage channels, and colonisation of flood-plains and river-beds all increase flood intensity and gravity.
6.6.1 Flood-Prone Areas of India
The Rashtriya Barh Ayog (National Flood Commission) has identified 40 million hectares of land as flood-prone in India. Assam, West Bengal and Bihar are among the most flood-prone states. Most rivers of the northern states such as Punjab and Uttar Pradesh are also vulnerable to occasional floods.
In recent decades, even Rajasthan, Gujarat, Haryana and Punjab are getting inundated by flash floods — partly due to changing monsoon patterns and partly because human activities have blocked many streams and channels. Tamil Nadu sometimes experiences flooding during November–January due to the retreating monsoon.
Figure 6.C: Flood-prone areas of India (schematic, after NCERT Figure 6.6). Brahmaputra (Assam), Ganga (Bihar, UP, WB) and the eastern delta coasts dominate. Rajasthan and Punjab now face flash floods.
6.6.2 Consequences and Control of Floods
Floods drown agricultural land and human settlements year after year — especially in Assam, West Bengal, Bihar and Eastern UP (river floods); coastal Odisha, Andhra Pradesh, Tamil Nadu and Gujarat (cyclonic floods); and Punjab, Rajasthan, Northern Gujarat and Haryana (flash floods). They destroy crops, infrastructure, roads, rails, bridges and human settlements; they wash millions of people and their cattle downstream and trigger water-borne diseases such as cholera, gastro-enteritis, hepatitis and others.
Yet floods bring some benefits too. Every year they deposit fertile silt over agricultural fields. Majuli in Assam — the world's largest riverine island — produces excellent paddy thanks to the annual flooding of the Brahmaputra. But these benefits are insignificant beside the grave losses.
Government responses include construction of flood-protection embankments in flood-prone areas, building of dams, afforestation, and discouraging major construction activities in the upper reaches of flood-creating rivers. Removing human encroachment from river channels and depopulating flood plains — especially in western and northern India where flash floods strike — are equally urgent. Cyclone centres can provide relief in coastal areas hit by storm surges.
Activity 6.2 · THINK ABOUT IT — Why Are Floods “Predictable”?
- List three reasons why floods are described in NCERT as “relatively slow in occurrence and within expected time in a year”.
- Identify five human activities that worsen floods. Suggest one solution for each.
- Compare floods in eastern India (Assam) with flash floods in western India (Rajasthan): list two differences in cause and two in consequence.
Pointers: (1) Floods follow the seasonal monsoon, occur in the same river basins each year, and develop over hours to days — unlike sudden quakes. (2) Deforestation, encroaching flood-plains, river siltation, blocking of natural drains, unscientific dam release. (3) Eastern floods follow heavy summer monsoon and last weeks; flash floods in the West follow short cloud-bursts in arid catchments and last hours but cause sudden devastation.
6.7 Droughts
The term drought? applies to an extended period when there is a shortage of water due to inadequate precipitation, excessive evaporation rates, and over-utilisation of water from reservoirs and groundwater storages. Drought is a complex phenomenon — it involves precipitation, evaporation, evapo-transpiration, ground-water, soil moisture, surface run-off, the kinds of crops grown, the agricultural and socio-economic practices of the area, and ecological conditions.
6.7.1 The Four Types of Drought
| Type | Definition / Trigger |
|---|---|
| Meteorological | Prolonged period of inadequate rainfall, marked by mal-distribution of the rains over time and space. |
| Agricultural (Soil-moisture) | Low soil-moisture necessary to support crops, resulting in crop failures. An area with more than 30 % of its gross cropped area under irrigation is excluded from the drought-prone category. |
| Hydrological | Availability of water in aquifers, lakes and reservoirs falls below what precipitation can replenish. |
| Ecological | Productivity of a natural ecosystem fails due to shortage of water; ecological distress damages the ecosystem. |
6.7.2 Drought-Prone Areas of India
Indian agriculture is heavily dependent on the monsoon; droughts and floods are the two accompanying features of Indian climate. According to NCERT estimates, nearly 19 per cent of the total geographical area of the country and 12 per cent of its total population suffer from drought every year. About 30 per cent of the country's total area is identified as drought-prone, affecting around 50 million people. On the basis of severity, India is divided into:
Extreme Drought
Most parts of Rajasthan west of the Aravalis — Marusthali; Kachchh region of Gujarat; districts of Jaisalmer and Barmer (Indian desert) that get less than 90 mm average annual rainfall.
Severe Drought
Parts of eastern Rajasthan, most of Madhya Pradesh, eastern parts of Maharashtra, interior Andhra Pradesh, Karnataka Plateau, northern interior Tamil Nadu, southern Jharkhand, interior Odisha.
Moderate Drought
Northern Rajasthan, Haryana, southern districts of UP, the rest of Gujarat, Maharashtra except Konkan, Jharkhand, Coimbatore plateau of Tamil Nadu, interior Karnataka.
Free / Less Prone
The remaining parts of India — especially the eastern Himalayan foothills, the Northeast, Konkan, Kerala, deltaic eastern coast — are largely free of severe drought.
Figure 6.D: Drought-prone areas of India (schematic, after NCERT Figure 6.7). The Marusthali and Kachchh stand at the harshest end; the NE foothills, Konkan and Kerala are largely safe.
6.7.3 Consequences of Drought
Droughts have cascading effects. Crop failures cause scarcity of food grains (akal), of fodder (trinkal), and of water (jalkal); when all three combine, the result is trikal — the most devastating form. Large-scale death of cattle and other animals, and migration of humans and livestock, are common sights in drought-affected areas. Scarcity of clean water forces people to consume contaminated water, spreading water-borne diseases like gastro-enteritis, cholera and hepatitis.
Drought planning must consider both short-term and long-term aspects. Immediate measures include distribution of safe drinking water, medicines, fodder and water for cattle, and shifting people and livestock to safer places. Long-term measures include identification of ground-water aquifers, transfer of river water from surplus to deficit areas, planning for inter-linking of rivers, construction of reservoirs and dams (with the aid of remote sensing and satellite imagery), dissemination of drought-resistant crops, and rooftop rainwater harvesting.
Activity 6.3 · SOURCE BOX — Yokohama Strategy 1994
Read this extract carefully and answer below:
The World Conference on Natural Disaster Reduction (Yokohama, 23–27 May 1994) resolved that each country has the sovereign responsibility to protect its citizens from natural disasters; that priority attention will be given to developing countries, particularly the least developed, land-locked countries and small-island developing states; that national capacities for natural and other disaster prevention, mitigation and preparedness will be developed; and that sub-regional, regional and international cooperation will be strengthened with emphasis on capacity-building, technology sharing and resource mobilisation. The decade 1990–2000 was declared the International Decade for Natural Disaster Reduction.
- What is the “sovereign responsibility” described above?
- Why does the document single out land-locked countries and small-island states?
- List the three pillars of international cooperation it recommends.
Pointers: (1) Each country must protect its citizens from natural disasters — with international help, but not in place of national action. (2) These countries are most vulnerable: land-locked countries depend on neighbours for relief logistics, while small-island states face existential risks from cyclones and sea-level rise. (3) The three pillars are capacity-building, technology sharing, and resource mobilisation.
📋
Competency-Based Questions — Floods, Droughts, Earthquakes & Tsunami
Case Study: Sneha is preparing a presentation on India's most vulnerable natural disaster zones. She has these notes: Bhuj earthquake (2001) measured ~7.7 magnitude; the 2004 Indian Ocean tsunami killed more than 3,00,000 people; Rashtriya Barh Ayog identifies 40 million hectares as flood-prone; about 30 % of India is drought-prone. Help her assign each fact to the right disaster category and reason about mitigation.
Q1. Which one of the following is not a category in NCERT's classification of natural disasters?
L1 RememberAnswer: (D) — The four NCERT categories are Atmospheric, Terrestrial, Aquatic and Biological. “Magnetic” is not a category.
Q2. The Indian plate is moving northward at a speed of about:
L2 UnderstandAnswer: (B) — About 1 cm per year. The slow but persistent collision with the Eurasian plate locks energy along the Himalayan arc and is the root cause of Indian earthquakes.
Q3. Sneha reads that an area with more than 30 % of its gross cropped area under irrigation is excluded from the drought-prone category. This rule applies to:
L3 ApplyAnswer: (B) — Agricultural (soil-moisture) drought. The 30 % irrigation cutoff is a direct exclusion rule used in the official drought-prone classification of agricultural drought.
Q4. Why does a tsunami appear small at sea but becomes destructive near the coast? Pick the best explanation.
L4 AnalyseAnswer: (B) — Out at sea, tsunami wavelength is huge and wave-height is barely 1–2 m. As the wave enters shallow water near the shore, wave-length shortens while period is unchanged — so the wave is squeezed upward, sometimes to over 15 m. This is why these are also called “Shallow Water Waves”.
HOT Q. Imagine you are a planner in Kachchh, where the soil is parched, the population is rising and seismic risk is the highest in India. Sketch a one-page integrated plan combining (i) earthquake-resistant building design, (ii) rainwater harvesting and drought mitigation, and (iii) public communication for both quake and drought preparedness.
L6 CreateHint: (i) Light-weight roofs, base-isolation foundations, retrofit of public buildings, BIS-2002 codes; discourage high-rise. (ii) Roof-top rainwater harvesting in every household; revival of kunds and tankas; community check-dams; drought-resistant millets (bajra, jowar). (iii) Bilingual posters at panchayat level; quarterly mock drills; SMS alert system tied to IMD and seismological centres; school curriculum modules. The integrated theme: a Kachchh resident must know what to do when the ground shakes and when the rains fail — both within the same year.
⚖ Assertion–Reason Questions — Hazards & Disasters
Options:
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is NOT the correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.
(A) Both A and R are true, and R is the correct explanation of A.
(B) Both A and R are true, but R is NOT the correct explanation of A.
(C) A is true, but R is false.
(D) A is false, but R is true.
Assertion (A): The Himalayan arc and the north-eastern states of India are placed in the very high earthquake hazard zone.
Reason (R): The Indian plate is moving roughly one centimetre per year toward the north and is constantly obstructed by the Eurasian plate, building up energy along the Himalayan arc.
Answer: (A) — Both A and R are true and R correctly explains A. The slow tectonic collision is the very mechanism that places the Himalayan arc and NE states in the highest hazard category.
Assertion (A): A tsunami is barely noticed by ships in the deep ocean.
Reason (R): In deep water the tsunami has a very long wavelength and limited wave-height, raising the ship only a metre or two over a period of several minutes.
Answer: (A) — Both A and R are true; R is the correct explanation of A. The geometry of a tsunami in the deep sea makes it almost invisible to ships, a fact that complicates early warning.
Assertion (A): Floods in India are entirely natural in origin.
Reason (R): Indiscriminate deforestation, unscientific agricultural practices, disturbances in natural drainage, and colonisation of flood-plains worsen the intensity, magnitude and gravity of floods.
Answer: (D) — A is false, R is true. NCERT clearly states that human beings play an important role in the genesis as well as spread of floods; the activities listed in R are the very reason A is false.
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Class 11 Geography — India: Physical Environment
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