Natural Hazards and Disasters

NATURAL HAZARDS AND DISASTERS: CAUSES, CONSEQUENCES AND MANAGEMENT

Introduction: Change and Disaster

**Change** is a continuous natural process occurring everywhere with varying magnitudes and intensities. Changes can be:

**Gradual/Slow**: Evolution of landforms and organisms (e.g., soil formation, species development)

**Sudden/Swift**: Volcanic eruptions, tsunamis, earthquakes, lightning

**Localized**: Hailstorms, tornadoes, dust storms occurring within seconds and small areas

**Global**: Global warming, ozone layer depletion affecting entire planet

From **nature's perspective**, changes are value-neutral (neither good nor bad). From **human perspective**, changes are value-loaded:

**Desirable changes**: Seasonal changes, fruit ripening, technological advancement

**Undesirable changes**: Earthquakes, floods, droughts, wars, human-made disasters

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DEFINITION AND DISTINCTION: DISASTER vs. NATURAL HAZARD

What is a Disaster?

**Disaster** (UNESCO-UNISDR definition): An undesirable occurrence resulting from forces largely outside human control that strikes quickly with little or no warning, causing or threatening serious disruption of life and property including death and injury to large numbers of people, and requiring mobilization of efforts exceeding normal statutory emergency services.

**Key characteristics**:

Sudden and unexpected

Large-scale destruction

Widespread death and injury

Disruption of social systems

Requires extraordinary relief efforts

Largely uncontrollable

Natural Hazards vs. Natural Disasters: Critical Distinction

**Natural Hazards** are elements or circumstances in the natural environment with **potential** to cause harm:

May be swift or permanent aspects (ocean currents, steep Himalayan slopes, extreme desert/glacial conditions)

Represent inherent dangers in an environment

Do not necessarily cause disasters

Example: Steep slopes in Himalayas are hazards; they become disasters when they trigger destructive landslides

**Natural Disasters** are relatively sudden events with **actual** large-scale destruction:

Large-scale, widespread death and property loss

Disturbance to social systems over which people have little control

Magnitude of destruction and damage is very high

Example: 2004 Indian Ocean Tsunami from earthquake in Sumatra caused disaster with 230,000+ deaths in Indian Ocean region

Key Insight: Disaster = Hazard × Vulnerability

A natural hazard becomes a disaster when it strikes areas of **high population density** and **low preparedness**. Same hazard in sparsely populated area = lower disaster impact.

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CAUSES OF DISASTERS: NATURAL AND HUMAN-INDUCED

Natural Disasters

Caused by natural forces and earth processes:

Tectonic earthquakes

Volcanic eruptions

Tsunamis

Cyclones

Floods

Droughts

Landslides

Human-Caused Disasters (Direct Human Actions)

Activities directly responsible for disasters:

**Bhopal Gas Tragedy** (1984): Chemical plant disaster, 4,000+ deaths

**Chernobyl Nuclear Disaster** (1986): Nuclear reactor explosion

**Release of CFCs**: Ozone layer depletion

**Greenhouse gas emissions**: Climate change acceleration

**Wars and conflicts**: Direct human violence

**Environmental pollution**: Noise, air, water, soil pollution

Indirectly Human-Induced Disasters (Human-Accelerated)

Human activities that intensify or accelerate natural disasters:

**Floods and landslides due to deforestation**: Removal of vegetation reduces infiltration and slope stability

**Floods due to unscientific land use**: Improper drainage systems, blocked waterways

**Construction in fragile areas**: Building on fault lines, flood plains, coastal zones without proper engineering

**Coastal development**: Mumbai and Chennai cities developed on flood plains and coastal areas, increasing vulnerability to cyclones and tsunamis

**Important observation**: Human-made disasters have increased in both numbers and magnitudes over decades. Prevention is possible for human-caused disasters, but prevention is nearly impossible for natural disasters; hence emphasis must be on **mitigation and management**.

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INTERNATIONAL FRAMEWORKS FOR DISASTER MANAGEMENT

Yokohama Strategy and Plan of Action (1994)

**World Conference on Disaster Reduction** held at Yokohama, Japan (May 23-27, 1994):

**Key Resolutions**:

Each country has **sovereign responsibility** to protect its citizens from natural disasters

**Priority to developing countries**: Least developed, landlocked, and small-island developing states need special attention

**Develop national capacities**: Strengthen disaster prevention, mitigation, preparedness through national legislation

**Mobilize NGOs and local communities**: Participation of grassroots organizations essential

**Promote international cooperation**: Sub-regional, regional, and international collaboration for disaster reduction

**Focus Areas**:

Human and institutional capacity-building

Technology sharing and dissemination of information

Resource mobilization

International Decade for Natural Disaster Reduction (IDNDR)

**Period**: 1990-2000

**Objective**: Coordinated global effort to reduce disaster losses

**Legacy**: Continued International Strategy for Disaster Reduction (ISDR) after 2000

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CLASSIFICATION OF NATURAL DISASTERS

Natural disasters broadly classified into **four major categories**:

| **Category** | **Examples** | **Characteristics** |

|---|---|---|

| **ATMOSPHERIC** | Blizzards, thunderstorms, lightning, tornadoes, tropical cyclones, drought, hailstorms, frost, heat waves (Loo), cold waves | Related to atmospheric conditions; can be localized or regional |

| **TERRESTRIAL** | Earthquakes, volcanic eruptions, landslides, avalanches, subsidence (mining areas), soil erosion | Related to earth's crust and land surface; often sudden |

| **AQUATIC** | Floods, tidal waves, storm surge, tsunami | Related to water bodies; often triggered by other disasters |

| **BIOLOGICAL** | Locust swarms, insect infestations, fungal/bacterial/viral diseases (bird flu, dengue, plague) | Related to plants and animals; can spread epidemically |

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NATURAL DISASTERS AND HAZARDS IN INDIA

India's Vulnerability

**Why is India highly vulnerable to natural disasters?**

**Vast geographical area**: Diverse physical and socio-cultural attributes

**Environmental diversities**: Multiple climate zones, physiographic regions, tectonic settings

**Large population**: High population density increases disaster impact

**Economic constraints**: Developing country with limited resources for disaster management

**Colonial legacy**: Poor infrastructure in many areas

**Social discriminations**: Marginalized populations most affected

India experiences **most types of natural disasters** mentioned in classification system and loses thousands of lives and millions of rupees in property annually.

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EARTHQUAKES IN INDIA

Definition and Types

**Earthquakes**: Sudden shaking of Earth's crust caused by sudden release of energy during tectonic activities.

**Types based on origin**:

**1. Tectonic Earthquakes** (Most devastating)

Caused by movement and collision of lithospheric plates

Large area of influence

Highest magnitude and damage

Example: 2004 Sumatra earthquake (9.1 magnitude), 2015 Nepal earthquake (7.8 magnitude)

**2. Volcanic Earthquakes**

Associated with volcanic eruptions

Limited area of influence

Lower magnitude than tectonic

**3. Other Earthquakes**

Rock falls

Landslides

Mine subsidence

Dam and reservoir impounding (induced earthquakes)

Limited destructive capacity

Tectonic Plate Movement in India: Primary Cause

**Key Mechanism**:

**Indian Plate movement**: Moving northward/northeastward at **1 cm per year**

**Collision with Eurasian Plate**: From north, plate movement is obstructed

**Result**: Plates are "locked" with each other

**Stress accumulation**: Over time, excessive energy builds up stress at locked points

**Energy release**: Sudden breaking of lock releases energy causing earthquakes along Himalayan arch

**Impact**: This explains **persistent earthquake activity in Himalayan region** (Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Northeast states).

Earthquakes in Peninsular India (Central-Western Region)

**Anomaly**: Peninsular India (Deccan Plateau) is part of oldest, most stable, mature landmass, yet experiences earthquakes.

**Examples of Central-Western Earthquakes**:

**Gujarat**: 1819, 1956 (Anjar), 2001 (Bhuj, 7.7 magnitude, 20,000+ deaths)

**Maharashtra**: 1967 (Koyna), 1993 (Killari near Latur, 6.3 magnitude, 768 deaths)

**Recent Theory**: Emergence of fault lines with energy build-up:

Fault line represented by **Bhima/Krishna River** near **Latur and Osmanabad** (Maharashtra)

Possible fracturing/breaking of Indian Plate

Scientists from National Geophysical Laboratory and Geological Survey of India investigating this phenomenon

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EARTHQUAKE HAZARD ZONES IN INDIA

Five-Zone Classification

Based on analysis of 1,200+ earthquakes by National Geophysical Laboratory, Geological Survey of India, Department of Meteorology, and National Institute of Disaster Management:

**1. VERY HIGH DAMAGE RISK ZONE**

(Most Vulnerable - Experienced devastating earthquakes)

**Northeast States**: Assam, Meghalaya, Mizoram, Manipur, Nagaland, Tripura, Arunachal Pradesh

**North-Central regions**: Areas north of Darbhanga and Araria along Indo-Nepal border (Bihar)

**Himalayan region**:

Uttarakhand (entire state)

Western Himachal Pradesh (around Dharamshala)

Kuchchh/Kutch region (Gujarat)

Kashmir Valley (Jammu & Kashmir)

**Reason**: Active tectonic boundaries, plate collision zones

**2. HIGH DAMAGE RISK ZONE**

(Very Vulnerable)

Remaining parts of Jammu & Kashmir

Ladakh

Himachal Pradesh (except western parts)

Northern Punjab

Eastern Haryana

Delhi

Western Uttar Pradesh

Northern Bihar

**Reason**: Near active tectonic zones but less intense

**3. MODERATE DAMAGE RISK ZONE**

Central and southern parts of country

Parts of Madhya Pradesh, Rajasthan, Andhra Pradesh

**4. LOW DAMAGE RISK ZONE**

Southern Deccan Plateau regions

**5. VERY LOW DAMAGE RISK ZONE**

**Deccan Plateau** (most stable, mature landmass)

Southern peninsula

**Reason**: Ancient, stable continental crust, away from plate boundaries

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SOCIO-ENVIRONMENTAL CONSEQUENCES OF EARTHQUAKES

Scale of Impact

Earthquakes are **most unpredictable and highly destructive** of all natural disasters:

Strike without warning

No discrimination in affected areas

Become calamities in densely populated regions

Spread disastrous effects suddenly and unpredictably

Comprehensive Effects of Earthquakes

**Table 6.2: Effects of Earthquakes by Category**

**ON GROUND**:

Fissures (cracks through which water/volatile materials gush out, inundating areas)

Ground cracking and displacement

Settlements and subsidence

Landslides (secondary hazard)

Liquefaction (soil loses strength, acts like liquid)

Possible chain-effects (triggering further disasters)

**ON MAN-MADE STRUCTURES**:

Structural collapse (buildings, bridges, dams)

Overturning of structures

Buckling of materials

Earth pressure on structures

Possible chain-effects (one collapse triggering others)

**ON WATER**:

Tsunami formation (seismic sea waves)

Hydrodynamic pressure changes

Possible chain-effects (secondary floods, etc.)

Environmental and Social Consequences

**Destruction of settlements**: Loss of homes, displacement of millions

**Infrastructure damage**: Transport and communication networks destroyed, hindering relief efforts

**Economic loss**: Damage to industries, developmental activities

**Property loss**: Loss of accumulated material wealth over generations

**Loss of socio-cultural heritage**: Destruction of historical structures, cultural sites

**Secondary disasters**:

Landslides blocking rivers, forming natural reservoirs

River course changes causing floods

Fissures releasing groundwater and volatile materials

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EARTHQUAKE HAZARD MITIGATION STRATEGIES

Since **prevention of earthquakes is impossible**, focus is on **preparedness and mitigation** rather than cure.

Mitigation Measures

**1. Earthquake Monitoring and Early Warning**

Establish **seismological centres** for continuous monitoring

Use **GPS (Geographical Positioning System)** for tracking tectonic plate movements

Fast dissemination of warning information to vulnerable areas

Real-time seismic data collection and analysis

**2. Vulnerability Assessment and Public Education**

Prepare **vulnerability maps** showing high-risk areas

Disseminate vulnerability information to public

Educate people about earthquake risks and safety measures

Community awareness programs on protective measures

**3. Building Code and Construction Modification**

Modify **house types and building designs** in vulnerable zones

Discourage construction of **high-rise buildings** in earthquake-prone areas

Restrict **large industrial establishments** in vulnerable regions

Prevent **big urban centres** from being established in very high-risk zones

Promote alternative land use in vulnerable areas

**4. Earthquake-Resistant Construction Standards**

Make **earthquake-resistant designs mandatory** in vulnerable areas

Use **light, flexible materials** instead of rigid materials

Flexible foundation designs

Reinforced concrete with proper mesh

Base isolation techniques

Damping systems to absorb seismic energy

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TSUNAMI: GENERATION, CHARACTERISTICS, AND IMPACTS

Definition

**Tsunami** (Japanese: "harbour wave" or seismic sea wave): A series of ocean waves caused by sudden, large-scale disturbances of water in the ocean.

**Causes**:

**Underwater earthquakes** (most common): Sudden vertical displacement of sea floor

**Submarine volcanic eruptions**: Explosive displacement of water

**Underwater landslides**: Mass movement causing water displacement

Generation Mechanism

**Step-by-step process**:

1. Earthquake or volcanic eruption causes **abrupt displacement of sea floor**

2. This sudden movement displaces entire water column above

3. Creates **one instantaneous vertical wave** (initial disturbance)

4. After initial wave, **series of afterwaves** (oscillations) are created

5. These waves oscillate between **high crest and low trough**

6. Oscillations continue until water level is restored to equilibrium

Wave Behavior and Speed Characteristics

**Speed dependence on water depth**:

**Speed in shallow water** > Speed in deep ocean

**Mathematical relationship**: Wave speed = √(gd) where g = gravity, d = water depth

In deep ocean (4-6 km): Speed ~600-800 km/hr

In shallow coastal waters: Speed reduces to ~20-50 km/hr

Wave height **increases as water depth decreases**

Why Tsunami Impact Varies

**Over deep ocean**:

Low wave height (1-2 meters)

Ships at sea minimally affected

Difficult to detect in deeper parts of sea

Long wavelength (100+ km)

Relatively small amplitude

**Near coast/shallow water**:

Wave height increases dramatically (up to 30+ meters in extreme cases)

**Maximum devastation occurs at coastline**

Short wavelength

High energy concentration

Destructive force concentrated

**Critical insight**: Tsunami is **dangerous near coast**, not in open ocean; hence coastal areas face severe hazard.

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CONTINUITY NOTE

*[The chapter text continues with sections on Tsunami impacts, damage, and mitigation; Floods and Droughts; Cyclones; and Landslides. Due to token limitations, these sections were not provided in the source text. They should be covered in subsequent comprehensive notes following the same format and depth.]*

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KEY EXAMINATION POINTS

**Map-based questions expected**:

Identify earthquake zones on India map (Very High Risk: Northeast, Himalayan arch, Kuchchh)

Locate tsunami-prone coastal areas

Mark flood-prone river basins

Identify cyclone-prone coastal regions

**Short-answer questions**:

Distinguish between natural hazard and disaster

Explain why Peninsular India experiences earthquakes despite being stable landmass

Describe earthquake mitigation strategies

Explain tsunami generation mechanism

Analyze human contribution to disaster intensity

**Long-answer questions**:

Discuss classification of natural disasters with Indian examples

Analyze socio-environmental consequences of major disasters

Evaluate effectiveness of Yokohama Strategy

Compare disaster vulnerability in developed vs. developing nations

**Numerical/analytical questions**:

Calculate probable earthquake impacts given magnitude and population density

Interpret seismic zone maps

Analyze disaster frequency trends in India

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**End of Natural Hazards and Disasters Chapter Notes**