Class 11 Geography Notes Chapter 7 (Natural hazards and disasters) – India Physical Environment Book
Detailed Notes with MCQs of Chapter 7: Natural Hazards and Disasters from your 'India Physical Environment' book. This is a crucial chapter, not just for understanding our country's geography but also for various competitive exams. Pay close attention as we break down the key concepts.
Understanding Hazards and Disasters
- Natural Hazard: A natural process or phenomenon occurring in the environment (like an earthquake, flood, cyclone) that possesses the potential to cause harm to human life, property, or the environment. It's a threat.
- Natural Disaster: The realization of a natural hazard. It is the actual event where a hazard causes significant damage, destruction, loss of life, and disruption to society and economy, often exceeding the community's capacity to cope using its own resources.
- Key Difference: A hazard is a threat, while a disaster is the event and its consequences. An earthquake in an uninhabited desert is a hazard, but not a disaster. The same earthquake in a densely populated city becomes a disaster.
- India's Vulnerability: India's unique geo-climatic conditions (monsoon climate, Himalayan geology, long coastline) make it highly vulnerable to a wide range of natural hazards.
Classification of Natural Disasters
Natural disasters can be broadly classified based on their origin:
- Atmospheric: Related to weather and climate.
- Examples: Tropical Cyclones, Floods (often linked), Droughts, Thunderstorms, Hailstorms, Heat Waves, Cold Waves, Tornadoes (rare in India).
- Terrestrial (Geological/Geomorphic): Originating from processes within the Earth.
- Examples: Earthquakes, Volcanic Eruptions (India has dormant/extinct volcanoes, e.g., Barren Island - active), Landslides, Avalanches, Soil Erosion.
- Aquatic (Hydrological): Related to water bodies.
- Examples: Floods (riverine, coastal, flash), Tsunamis, Storm Surges (associated with cyclones).
- Biological: Caused by living organisms or biological processes.
- Examples: Pest attacks (like locust swarms), Epidemics (like influenza, cholera - often exacerbated by other disasters like floods).
Major Natural Hazards and Disasters in India: Detailed Look
1. Earthquakes
- Cause: Primarily caused by the movement of tectonic plates. The Indian plate is continuously moving northwards and colliding with the Eurasian plate, leading to immense stress accumulation in the Himalayan region. Release of this stress causes earthquakes. Faulting and volcanic activity can also trigger earthquakes.
- Measurement:
- Magnitude: Measured by the Richter Scale (logarithmic scale, measures energy released).
- Intensity: Measured by the Modified Mercalli Scale (measures the visible damage and impact caused).
- Seismic Zones of India: India is divided into seismic zones based on vulnerability:
- Zone V (Very High Risk): Parts of Kashmir, Western and Central Himalayas, North-East Indian region, Rann of Kutch, Andaman & Nicobar Islands.
- Zone IV (High Risk): Remaining parts of Jammu & Kashmir and Himachal Pradesh, Northern parts of Uttar Pradesh, Bihar, Delhi, Sikkim, Northern Punjab, Chandigarh, West Bengal, parts of Gujarat, and small portions of Maharashtra near the west coast.
- Zone III (Moderate Risk): Kerala, Goa, Lakshadweep islands, remaining parts of Uttar Pradesh, Gujarat, West Bengal, Punjab, Rajasthan, Madhya Pradesh, Bihar, Jharkhand, Chhattisgarh, Maharashtra, Odisha, Andhra Pradesh, Tamil Nadu, and Karnataka.
- Zone II (Low Risk): Remaining parts of the country.
- Effects: Ground shaking, differential ground settlement, liquefaction, landslides, ground lurching, avalanches, ground displacement, floods from dam/levee failures, fires, structural collapse, falling objects, tsunamis.
- Mitigation: Earthquake monitoring centres, preparing a vulnerability map, community preparedness, modifying building designs (earthquake-resistant structures), enforcing building codes.
2. Tsunamis
- Cause: Generated by sudden displacement of a large volume of water, typically caused by undersea earthquakes, volcanic eruptions, or landslides.
- Characteristics: Series of waves with very long wavelengths and periods. Travel fast in deep oceans (hundreds of km/hr) but slow down and increase dramatically in height near the coast.
- Impact: Massive coastal inundation, destruction of infrastructure, loss of life, saltwater intrusion into groundwater.
- Indian Context: The 2004 Indian Ocean Tsunami severely affected the Andaman and Nicobar Islands and the coastal areas of Tamil Nadu, Andhra Pradesh, Kerala, and Puducherry.
- Mitigation: Tsunami Warning Systems (like the Indian Tsunami Early Warning System - ITEWS in Hyderabad), coastal zone management, mangrove plantation, raising awareness, evacuation plans.
3. Tropical Cyclones
- Formation Conditions:
- Large, continuous warm sea surface (temperature > 27°C).
- Presence of Coriolis force (hence they don't form near the equator, 0°-5° N/S).
- Pre-existing weak low-pressure area or low-level cyclonic circulation.
- Upper divergence above the sea level system.
- Small variations in vertical wind speed.
- Regions Affected: Originate over the Bay of Bengal and the Arabian Sea. Bay of Bengal cyclones are generally more frequent and intense. Affect coastal states like Odisha, Andhra Pradesh, Tamil Nadu, West Bengal, Gujarat, Maharashtra.
- Structure: Eye (calm centre), Eyewall (most intense winds and rainfall), Spiral/Rain Bands.
- Impact: Strong winds (damage structures, uproot trees), Torrential rainfall (leading to floods), Storm surge (abnormal rise in sea level, causing coastal inundation - most destructive element).
- Monitoring & Warning: Indian Meteorological Department (IMD) monitors and issues warnings.
- Mitigation: Cyclone shelters, coastal embankments, mangrove belts, hazard mapping, land-use control, effective warning dissemination, community preparedness.
4. Floods
- Causes: Intense rainfall over short periods, prolonged heavy rainfall (monsoon), snowmelt (in Himalayan rivers), cyclones (storm surge and heavy rain), inadequate drainage, dam failures, landslides blocking river flow, changes in river course.
- Flood-Prone Areas: Vast plains of North India (Ganga, Brahmaputra basins), coastal areas (delta regions of Mahanadi, Godavari, Krishna, Cauvery), regions of flash floods (Rajasthan, Gujarat, Haryana - due to intense rain in short spells). Brahmaputra valley is particularly vulnerable due to high rainfall, sediment load, and tectonic activity.
- Impact: Damage to life and property, destruction of crops, soil erosion, contamination of water leading to diseases (cholera, gastroenteritis), disruption of transport and communication.
- Mitigation: Embankments/levees, flood walls, construction of reservoirs/dams, improving river channels, watershed management (afforestation), flood plain zoning (restricting construction in vulnerable areas), flood forecasting and warning systems, community awareness.
5. Droughts
- Definition: An extended period of abnormally low rainfall, leading to a shortage of water. It's a complex phenomenon with slow onset.
- Types:
- Meteorological Drought: Prolonged period of inadequate rainfall marked with mal-distribution of the same over time and space.
- Hydrological Drought: Depletion of surface water (rivers, lakes, reservoirs) and groundwater.
- Agricultural Drought: Insufficient soil moisture to meet the needs of crops (also called soil moisture drought).
- Socio-economic Drought: When water shortage affects people's social and economic lives (food, fodder, livelihood).
- Ecological Drought: When the productivity of a natural ecosystem fails due to water shortage.
- Drought-Prone Areas: Primarily arid and semi-arid regions: Rajasthan (especially western part), Kutch region of Gujarat, rain-shadow areas of Western Ghats (parts of Maharashtra, Karnataka, Tamil Nadu, Andhra Pradesh).
- Impact: Crop failure leading to food insecurity, fodder scarcity, water shortage (drinking and irrigation), malnutrition, health issues, land degradation, desertification, migration, economic losses.
- Mitigation: Water harvesting structures (check dams, tanks), interlinking of rivers (controversial), promoting water-efficient irrigation (drip, sprinkler), cultivating drought-resistant crops, afforestation, watershed management, promoting efficient water use, drought monitoring and early warning.
6. Landslides
- Definition: Rapid downward movement of rock, debris, or earth down a slope.
- Causes: Steep slopes, heavy rainfall (saturates soil), earthquakes (ground shaking), volcanic activity, human activities like deforestation, road construction, mining, improper land use on slopes.
- Vulnerable Regions: Himalayas (geologically young and unstable), North-eastern hill ranges, Western Ghats, Nilgiris.
- Impact: Blocking roads and railways, damage to settlements and infrastructure, loss of life, damage to agricultural land, river blockage (can lead to flash floods when the blockage breaks).
- Mitigation: Hazard mapping to identify vulnerable zones, restricting construction in high-risk areas, promoting afforestation and vegetation cover, constructing retaining walls, improving surface drainage control, terracing slopes, raising awareness.
Consequences of Disasters
Disasters have far-reaching consequences:
- Economic: Loss of infrastructure, crops, livestock, industrial production; disruption of trade and transport; cost of relief and rehabilitation.
- Environmental: Damage to ecosystems, loss of biodiversity, soil erosion, water pollution, land degradation, changes in landscape.
- Social: Loss of life, injuries, displacement of population, health epidemics, psychological trauma, social unrest, damage to cultural heritage.
Disaster Management
- Concept: A continuous and integrated process of planning, organising, coordinating, and implementing measures necessary for:
- Prevention of danger or threat of any disaster.
- Mitigation or reduction of risk of any disaster or its severity.
- Capacity-building.
- Preparedness to deal with any disaster.
- Prompt response to any threatening disaster situation or disaster.
- Assessing the severity or magnitude of effects of any disaster.
- Evacuation, rescue, and relief.
- Rehabilitation and reconstruction.
- Phases:
- Pre-disaster: Focuses on reducing vulnerability (Prevention, Mitigation, Preparedness).
- During disaster: Focuses on immediate relief (Response).
- Post-disaster: Focuses on long-term recovery (Recovery, Rehabilitation, Reconstruction).
- Institutional Framework in India:
- National Disaster Management Authority (NDMA): Apex body, chaired by the Prime Minister. Lays down policies, plans, and guidelines.
- State Disaster Management Authority (SDMA): Headed by the Chief Minister.
- District Disaster Management Authority (DDMA): Headed by the District Collector/Magistrate.
- National Institute of Disaster Management (NIDM): Responsible for training, capacity building, research.
- National Disaster Response Force (NDRF): Specialized force for disaster response.
- Key Elements: Community participation, awareness generation, education, use of technology (GIS, remote sensing for mapping and monitoring), mock drills.
Remember, understanding these hazards and the management strategies is vital for building a resilient nation. Now, let's test your understanding with some questions.
Multiple Choice Questions (MCQs)
-
Which of the following regions in India is classified under Seismic Zone V (Very High Risk Zone)?
(a) Deccan Plateau
(b) Indo-Gangetic Plains
(c) North-Eastern Region
(d) Coastal Plains of Tamil Nadu -
Tsunamis are primarily generated by:
(a) Strong winds during cyclones
(b) Heavy monsoon rainfall
(c) Undersea earthquakes or volcanic eruptions
(d) Melting of glaciers -
Which of the following conditions is NOT necessary for the formation of Tropical Cyclones?
(a) Warm sea surface temperature (> 27°C)
(b) Presence of strong vertical wind shear
(c) Presence of Coriolis force
(d) Pre-existing weak low-pressure area -
The Brahmaputra river basin is highly prone to floods mainly due to:
(a) Low rainfall in its catchment area
(b) High sediment load and tectonic instability
(c) Presence of numerous dams controlling its flow
(d) Its flow through arid regions -
Meteorological drought is defined as:
(a) Depletion of groundwater levels
(b) Insufficient soil moisture for crops
(c) A prolonged period of inadequate rainfall
(d) Impact of water shortage on the economy -
Landslides are most common in which of the following regions of India?
(a) Thar Desert
(b) The Himalayas and Western Ghats
(c) Lakshadweep Islands
(d) Rann of Kutch -
The apex body for Disaster Management in India is:
(a) National Institute of Disaster Management (NIDM)
(b) National Disaster Response Force (NDRF)
(c) National Disaster Management Authority (NDMA)
(d) Indian Meteorological Department (IMD) -
The most destructive element associated with Tropical Cyclones causing coastal inundation is:
(a) Heavy Rainfall
(b) Strong Winds
(c) Storm Surge
(d) Hailstorms -
Which scale measures the intensity of an earthquake based on visible damage?
(a) Richter Scale
(b) Modified Mercalli Scale
(c) Barometer Scale
(d) Beaufort Scale -
The phase of disaster management that focuses on reducing the risk and severity before a disaster occurs includes:
(a) Response and Relief
(b) Recovery and Rehabilitation
(c) Prevention and Mitigation
(d) Reconstruction and Evacuation
Answer Key:
- (c)
- (c)
- (b) [Strong vertical wind shear inhibits cyclone formation]
- (b)
- (c)
- (b)
- (c)
- (c)
- (b)
- (c)
Study these notes thoroughly. Understanding the causes, impacts, and management strategies for each hazard is essential. Good luck with your preparation!