Natural Hazards and Disasters, Class 11 Geography (India: Physical Environment)

What Natural Hazards and Disasters is about

Key concepts

Disaster, hazard and vulnerability

NCERT section Natural Hazards and Disasters

Disaster (NCERT's definition, in summary): an undesirable event from forces largely outside human control that strikes quickly with little or no warning, causes or threatens serious disruption of life and property with many deaths and injuries, and needs efforts beyond normal statutory emergency services.

Natural versus human-made:

• Directly human-made: Bhopal gas tragedy, Chernobyl nuclear disaster, wars, release of CFCs, greenhouse gases, noise, air, water and soil pollution.
• Indirectly intensified by humans: landslides and floods due to deforestation, unscientific land use and construction in fragile areas.
• Human-made disasters can sometimes be prevented; natural ones can mostly only be mitigated and managed.

Hazard versus disaster:

Natural hazard	Natural disaster
Element of the natural environment with potential to cause harm to people or property	Relatively sudden, causes large-scale death, loss of property and disruption over which people have little control
May be swift or permanent: ocean currents, steep and unstable Himalayan slopes, extreme climates of deserts or glaciated areas	An event becomes a disaster when its magnitude of destruction is very high

Changing perception: earlier, people avoided intensive activity in hazard-prone areas, so disasters did less damage. Technology now lets people intensify activities in disaster-prone areas (colonised floodplains; Mumbai and Chennai expanding to the shore because of high land values), raising vulnerability to cyclones, hurricanes and tsunamis. Every disaster is unique in its local socio-environmental factors and the social response.

Three trends noted: magnitude, intensity, frequency and damage of natural disasters have increased; there is growing concern to reduce losses; the pattern of disasters has changed.

International steps: the issue was raised at the UN General Assembly (1989), formalised at the World Conference on Natural Disaster Reduction, Yokohama, Japan (23-27 May 1994): the Yokohama Strategy and Plan of Action for a Safer World; 1990-2000 declared the International Decade for Natural Disaster Reduction (IDNDR). Its resolution stressed each country's sovereign responsibility, priority to developing, land-locked and small-island states, national capacity and community participation, and regional and international cooperation (capacity-building, technology and information sharing, mobilising resources).

Worked example

A steep, crumbling slope above an empty valley is later used for a road and a row of shops. Use this case to explain the difference between a hazard and a disaster. (2 marks)

Try it first, then show the solutionSolution

1. The unstable slope is a natural hazard: an element of the environment with the potential to cause harm.
2. If it fails after people have settled below it, the magnitude of damage to life, property and social systems can be very high, and the hazard becomes a disaster; human settlement in vulnerable areas turns the potential into actual loss.

Answer: The slope alone is a hazard; once people and property are exposed and it fails with heavy loss, it becomes a disaster.

Classification of natural disasters and earthquakes in India

NCERT section Classification of Natural Disasters; Natural Disasters and Hazards in India

Classification (Table 6.1):

Atmospheric	Terrestrial	Aquatic	Biological
Blizzards, thunderstorms, lightning, tornadoes, tropical cyclones, drought, hailstorm, frost, heat wave or loo, cold wave	Landslides, earthquakes, avalanches, volcanic eruptions, soil erosion, subsidence	Tsunami, floods, storm surge, tidal waves	Plants and animals as colonisers (locusts), insect infestation; fungal, bacterial and viral diseases (bird flu, dengue)

Why India is vulnerable: vast area, environmental diversity, long colonial past, continuing social discrimination and a large population.

Earthquakes: the most unpredictable and destructive. Tectonic earthquakes are the most devastating and widespread; those from volcanoes, rock falls, landslides, subsidence (mining) and dams and reservoirs are more limited.

• The Indian plate moves about 1 cm per year north and north-east and is obstructed by the Eurasian plate; the plates are locked, energy accumulates, stress builds, the lock breaks and energy is released along the Himalayan arc.
• Most vulnerable: J&K, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, Darjeeling subdivision, all seven north-eastern states. Severe quakes also in Gujarat (1819, 1956, 2001) and Maharashtra (1967, 1993); a possible fault along the Bhima (Krishna) near Latur and Osmanabad may explain quakes in the stable Peninsula.
• Five zones (from analysis of over 1,200 earthquakes by the National Geophysical Laboratory, GSI, Department of Meteorology and NIDM): very high, high, moderate, low, very low damage risk. Very high: north-eastern states, north of Darbhanga and Araria (Indo-Nepal border, Bihar), Uttarakhand, western Himachal (around Dharamshala), Kashmir valley, Kachchh. High: rest of J&K, Ladakh, Himachal, northern Punjab, eastern Haryana, Delhi, western UP, northern Bihar. Safest: the stable Deccan plateau.
• Effects (Table 6.2): on ground (fissures, settlements, landslides, liquefaction, earth pressure); on structures (cracking, sliding, overturning, buckling, collapse); on water (waves, hydro-dynamic pressure, tsunami), each with possible chain effects; fissures can release water; landslides can dam rivers or shift courses.
• Mitigation: (i) seismological monitoring centres and GPS to track plates; (ii) vulnerability maps and public awareness; (iii) modified house types, discouraging high-rise buildings and big industries and cities in vulnerable areas; (iv) mandatory earthquake-resistant designs and light materials.

Worked example

Seismic zoning maps put most of the north-east and the Himalayan belt in the very high damage-risk zone, but much of the Deccan in low-risk zones. Explain this pattern using plate movement. (2 marks)

Try it first, then show the solutionSolution

1. The Indian plate moves about one centimetre a year towards the north and north-east, and its movement is constantly obstructed by the Eurasian plate, so the plates get locked and energy builds up.
2. When the lock breaks, the stored energy is released suddenly along the Himalayan arc and the north-east, causing frequent earthquakes; the stable Deccan block, away from the collision zone, is relatively safe.

Answer: The Himalayas and north-east lie where the locked Indian and Eurasian plates release energy; the stable Deccan is far from that boundary.

Tsunami and tropical cyclones

NCERT section Natural Disasters and Hazards in India

Tsunami (harbour waves, seismic sea waves): earthquakes and volcanic eruptions move the sea floor abruptly, suddenly displacing water as high vertical waves; after the first wave, a series of after-waves oscillate to restore the level.

• Wave speed depends on depth; impact is less over the deep ocean and more near the coast. Over deep water a tsunami has a very long wavelength and small height, lifting a ship only a metre or two over several minutes. In shallow water the wavelength shortens while the period stays the same, so height increases, sometimes to 15 m or more: hence 'shallow water waves'.
• Frequent along the Pacific Ring of Fire: Alaska, Japan, the Philippines, South-east Asian islands, Indonesia, Malaysia, Myanmar, Sri Lanka and India.
• Losses are high because coasts are densely populated; mitigation is beyond one country, so international cooperation is needed. The 26 December 2004 tsunami killed more than 300,000 people; India then volunteered to join the International Tsunami Warning System.

Tropical cyclones: intense lows between 30°N and 30°S, with high-velocity winds; 500-1,000 km across and 12-14 km high; a heat engine powered by latent heat of condensation of moisture gathered over the seas.

• Initial conditions: (i) large, continuous supply of warm, moist air; (ii) strong Coriolis force to stop the centre filling (none between 0° and 5°); (iii) unstable troposphere creating local disturbances; (iv) absence of strong vertical wind shear.
• India: cyclones arise in the Bay of Bengal and Arabian Sea; most originate between 10° and 15°N in the monsoon season; in the Bay, mostly in October-November, between 16°-2°N (as printed) and west of 92°E; by July the origin shifts to about 18°N, west of 90°E, near the Sunderbans delta.
• Consequences: force decreases inland, so coasts are hit hardest, with average velocities of about 180 km/h; abnormal sea-level rise: the storm surge, from the interaction of air, sea and land, flooding settlements and fields.

Worked example

Why does a ship in the open ocean hardly notice a tsunami that devastates the coast? (2 marks)

Try it first, then show the solutionSolution

1. Over deep water a tsunami has a very long wavelength and limited height, raising a ship only a metre or two over several minutes.
2. Near the coast, in shallow water, the wavelength shortens while the period stays the same, so the height grows, sometimes to 15 m or more.

Answer: Low and long at sea; tall and destructive in shallow coastal water.

Floods and droughts

NCERT section Natural Disasters and Hazards in India

Floods: inundation of land and settlements as water rises in channels and spills over. Unlike other disasters, causes are well established; floods are relatively slow, in known regions and at expected times.

• Causes: runoff exceeding channel capacity; storm surge (coasts); long, intense rain; melting snow and ice; reduced infiltration; eroded material in water. Common and disastrous in China, India and Bangladesh.
• Human role: deforestation, unscientific farming, disturbing natural drainage, colonising floodplains and river beds.
• India: the Rashtriya Barh Ayog identified 40 million ha as flood-prone; Assam, West Bengal, Bihar are high flood-prone; rivers of Punjab and UP flood occasionally; flash floods in Rajasthan, Gujarat, Haryana, Punjab in recent decades; Tamil Nadu may flood in November-January (retreating monsoon).
• Consequences: crops, roads, rails, bridges and homes destroyed; people and cattle washed away; cholera, gastro-enteritis, hepatitis. Small benefit: fertile silt (e.g. good paddy on Majuli, the world's largest riverine island, in the Brahmaputra).
• Control: embankments, dams, afforestation, discouraging construction in upper reaches, removing encroachments, depopulating floodplains (especially for flash floods); cyclone centres for storm-surge coasts.

Droughts: an extended period of water shortage due to inadequate rain, excessive evaporation and over-use of stored and ground water; involves rainfall, evaporation, soil moisture, runoff, crops and socio-economic practices.

Type	Meaning
Meteorological	Prolonged inadequate, mal-distributed rainfall
Agricultural (soil moisture)	Low soil moisture causing crop failure; areas with > 30 per cent of gross cropped area irrigated are excluded from drought-prone category
Hydrological	Water in aquifers, lakes, reservoirs falls below what rain can replenish
Ecological	Natural ecosystem productivity fails from water shortage

• Extent: about 19 per cent of area and 12 per cent of population suffer each year; about 30 per cent of area is drought-prone, affecting about 50 million people; floods and droughts can occur at the same time in different regions because of monsoon variability.
• Zones: extreme: Rajasthan west of the Aravalis (Marusthali) and Kachchh, Jaisalmer and Barmer (under 90 mm); severe: eastern Rajasthan, most of MP, eastern Maharashtra, interior Andhra Pradesh and Karnataka plateau, north interior Tamil Nadu, south Jharkhand, interior Odisha; moderate: north Rajasthan, Haryana, south UP, rest of Gujarat, Maharashtra except Konkan, Jharkhand, Coimbatore plateau, interior Karnataka.
• Consequences: akal (food scarcity), trinkal (fodder), jalkal (water); trikal (all three) is worst; cattle deaths, migration, waterborne diseases.
• Measures: immediate: safe drinking water, medicines, fodder and water for cattle, shifting people and livestock; long-term: identifying aquifers, transferring surplus water, inter-linking rivers, reservoirs and dams, remote sensing, drought-resistant crops, rainwater harvesting.

Worked example

In the same monsoon, the Brahmaputra stays above danger level for weeks in Assam, while a town in Rajasthan is swamped for a few hours after one heavy downpour. Explain the difference in the two kinds of flood. (2 marks)

Try it first, then show the solutionSolution

1. Eastern India (Assam, West Bengal, Bihar, eastern Uttar Pradesh) has recurrent floods as large rivers spill over their banks during the monsoon.
2. Western and north-western India (Rajasthan, Gujarat, Haryana, Punjab) increasingly face sudden flash floods, partly from the monsoon pattern and partly because streams and channels are blocked by human activity.

Answer: Assam: recurrent, long river floods; Rajasthan: short flash floods worsened by blocked channels.

Landslides and disaster management

NCERT section Disaster Management

Landslides: rapid sliding of large masses of bedrock (e.g. roads to Srinagar blocked; stones on the Konkan Railway). Less dramatic than earthquakes or cyclones but as harmful to environment and economy. Controlled by highly localised factors (geology, geomorphic agents, slope, land use, vegetation, human activity), so monitoring is difficult and costly.

Zone	Areas
Very high vulnerability	Young, unstable mountains of the Himalayas and Andaman and Nicobar; steep, rainy Western Ghats and Nilgiris; the north-east; areas with frequent earthquakes; areas of intense road and dam construction
High vulnerability	Similar conditions with a different combination and intensity: all Himalayan states and north-eastern states except the plains of Assam
Moderate to low	Low-rainfall Trans-Himalaya (Ladakh, Spiti), the Aravali, rain-shadow parts of the Western and Eastern Ghats and the Deccan; mining and subsidence landslides in Jharkhand, Odisha, Chhattisgarh, MP, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa, Kerala
Other (safe)	Rajasthan, Haryana, UP, Bihar, West Bengal (except Darjiling), Assam (except Karbi Anglong), coastal southern states

• Consequences: localised direct impact, but roadblocks, broken railway lines, blocked channels, diverted rivers causing floods; spatial interaction becomes risky and costly, hurting development.
• Mitigation: area-specific: restrict construction of roads and dams, limit farming to valleys and moderate slopes, control large settlements in high-risk zones; large-scale afforestation, bunds to slow water; terrace farming in north-eastern hill states where jhumming (shifting cultivation) persists.

Disaster management: cyclones are more predictable than earthquakes or tsunamis; monitoring allows cyclone shelters, embankments, dykes, reservoirs and afforestation (to reduce wind speed). Rising losses in India, Bangladesh and Myanmar are due to the high vulnerability of coastal populations.

• Disaster Management Bill, 2005: defines a disaster as a catastrophe, mishap, calamity or grave occurrence from natural or human-made causes, accident or negligence, causing substantial loss of life, suffering or environmental damage beyond the coping capacity of the affected community.
• Three stages: (i) pre-disaster: data and information, vulnerability zoning maps, awareness, planning, preparedness and prevention; (ii) during disaster: rescue and relief, evacuation, shelters and relief camps, water, food, clothing, medical aid; (iii) post-disaster: rehabilitation, recovery and capacity-building.
• India has about two-thirds of its area and population vulnerable to disasters; the Disaster Management Bill 2005 and the National Institute of Disaster Management are positive steps. Conclusion: not every hazard becomes a disaster; since natural disasters cannot be eliminated, mitigation and preparedness are the best options.

Worked example

Name the three stages of disaster management and one action in each. (3 marks)

Try it first, then show the solutionSolution

1. Pre-disaster: prepare vulnerability zoning maps and spread awareness.
2. During disaster: rescue and relief such as evacuation and relief camps.
3. Post-disaster: rehabilitation, recovery and capacity-building for future disasters.

Answer: Pre-disaster (maps, awareness), during (rescue, relief), post-disaster (rehabilitation, capacity-building).

Natural Hazards and Disasters in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Hazard, Disaster and Vulnerability, Classification of Disasters and Earthquakes in India
• Tsunami, Tropical Cyclones, Floods, Droughts, Landslides and Disaster Management in India

Natural Hazards and Disasters: key facts

Classification

$Atmospheric|terrestrial|aquatic|biological$

Blizzards = atmospheric; tsunami = aquatic; locusts = biological.

Earthquake zones

Very high, high, moderate, low, very low damage risk

From over 1,200 earthquakes analysed.

Plate movement

Indian plate about 1 cm/year north and north-east

Locked against the Eurasian plate.

Tsunami height

Deep water: long wavelength, 1-2 m; shallow water: shorter wavelength, same period, up to 15 m or more

'Shallow water waves'.

Tropical cyclone

30°N-30°S; 500-1,000 km wide; 12-14 km high; coastal winds about 180 km/h

No formation between 0° and 5°.

Flood and drought figures

40 million ha flood-prone; drought: 19% area and 12% people yearly; 30% area drought-prone, 50 million people

Agricultural drought excludes > 30% irrigated areas.

Drought types

$Meteorological,agricultural,hydrological,ecological$

Akal, trinkal, jalkal, trikal.

Management stages

1. 1.Pre-disaster
2. 2.during disaster
3. 3.post-disaster

Disaster Management Bill 2005; NIDM.

International steps

1. 1.UN General Assembly 1989
2. 2.Yokohama Strategy, May 1994
3. 3.IDNDR 1990-2000

Earth Summit, Rio (cited by NCERT here).

Natural Hazards and Disasters: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

Tricks to remember Natural Hazards and Disasters

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Classification

  'All Teachers Are Brilliant': Atmospheric, Terrestrial, Aquatic, Biological.

  Use it when: Table 6.1.

• Drought types

  'My Aunt Has Eggs': Meteorological, Agricultural, Hydrological, Ecological.

  Use it when: Types of drought.

• Drought scarcities

  'Akal food, Trinkal fodder, Jalkal water, Trikal all three'.

  Use it when: Consequences of drought.

• Management stages

  'Before, During, After': prepare, rescue, rebuild.

  Use it when: Disaster management.

Where students lose marks in Natural Hazards and Disasters

The slips examiners see most often, and what to write instead.

• ✗Mistake: Using hazard and disaster as the same thing

  They are related and often used interchangeably.

  Wrong working

  Steep slopes are a disaster.

  Right working

  Steep, unstable slopes are a hazard (potential harm); a large landslide that kills people is a disaster.

  ✓Do this: Hazard = potential; disaster = realised damage.

  Usually costs: Accuracy in the project and viva.

• ✗Mistake: Classifying drought as terrestrial

  Drought affects land.

  Wrong working

  Drought is a terrestrial disaster.

  Right working

  Table 6.1 lists drought under atmospheric disasters.

  ✓Do this: Learn Table 6.1 as printed.

  Usually costs: Accuracy in the viva.

• ✗Mistake: Thinking tsunamis are huge in the open ocean

  Images show giant waves at the coast.

  Wrong working

  Ships at sea are destroyed by tsunami waves.

  Right working

  At sea the wave is only 1-2 m high with a long wavelength; it grows in shallow water.

  ✓Do this: Tsunamis grow as water shallows.

  Usually costs: Accuracy in the project.

• ✗Mistake: Calling all of India drought-prone

  Over-generalisation.

  Wrong working

  All of India is drought-prone.

  Right working

  About 30 per cent of the area is drought-prone; zones range from extreme (west of the Aravalis, Kachchh) to moderate.

  ✓Do this: Use the zone names and figures.

  Usually costs: Accuracy in the project.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What did the Yokohama conference of May 1994 adopt?Show answer

   The Yokohama Strategy and Plan of Action for a Safer World.

2. 2.Which decade was declared the IDNDR?Show answer

   1990-2000.

3. 3.Into how many earthquake zones is India divided?Show answer

   Five.

4. 4.Why are tsunamis called shallow water waves?Show answer

   Because they gain great height when they enter shallow water near coasts.

5. 5.How much land did the Rashtriya Barh Ayog identify as flood-prone?Show answer

   40 million hectares.

6. 6.Which is the world's largest riverine island?Show answer

   Majuli, in the Brahmaputra (Assam).

7. 7.What is trikal?Show answer

   Scarcity of food grains, fodder and water together.

8. 8.What share of India is vulnerable to disasters?Show answer

   About two-thirds of its area and population.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Assessed only through a project and presentation in 2026-27.
• ☐Disaster: sudden, largely uncontrollable, serious disruption beyond normal services; natural or human-made.
• ☐Hazard = potential harm; disaster = realised large-scale damage; vulnerability rises as people settle in hazard zones.
• ☐Yokohama Strategy 1994; IDNDR 1990-2000.
• ☐Classification: atmospheric, terrestrial, aquatic, biological.
• ☐Earthquakes: Indian plate locked with Eurasian; five zones; mitigation by monitoring, maps, design.
• ☐Tsunami: grows in shallow water up to 15 m; 2004 tsunami over 300,000 deaths.
• ☐Cyclones: 30°N-30°S; conditions: warm moist air, Coriolis, instability, low wind shear; storm surge.
• ☐Floods: 40 million ha prone; Assam, West Bengal, Bihar; flash floods in the west.
• ☐Droughts: four types; 30% area prone; extreme in western Rajasthan and Kachchh.
• ☐Landslides: very high in Himalayas, A&N, Western Ghats, Nilgiris, north-east.
• ☐Management: pre, during, post; Disaster Management Bill 2005; NIDM.

Natural Hazards and Disasters: frequently asked questions