Chapter 5 — Natural and Man-made Disasters

What is a disaster? A disaster is an event that causes serious damage, disruption and loss to people, property and the environment. It happens when a natural or human-made hazard interacts with vulnerable people or systems. A hazard is a potential threat, like an earthquake or flood, while a disaster is the realised consequence when many people or assets are affected.

Why study disasters? Studying disasters helps us reduce loss of life and suffering. Knowledge can guide safer building, better planning and quicker responses. It also helps communities prepare for likely events based on local geography and climate. Learning about disasters builds practical skills such as evacuation, first-aid and simple household readiness that save lives.

Components of disaster risk Risk is often described as: Risk = Hazard × Vulnerability ÷ Capacity. Hazard is the dangerous event; vulnerability is how susceptible people and structures are; capacity is the ability to cope and recover. Reducing vulnerability and increasing capacity are two ways to lower overall risk.

Classification of hazards Hazards are broadly natural or human-made. Natural hazards include geophysical events (earthquakes, volcanoes), hydrometeorological events (cyclones, floods), and biological events (disease outbreaks). Human-made hazards include industrial accidents, large fires and pollution incidents. Hazards may be sudden-onset, like a quake, or slow-onset, like drought, and each requires different responses.

Disaster cycle and phases The disaster cycle is useful for planning: mitigation (measures to reduce risk), preparedness (planning, training and early warning), response (immediate actions to save lives and deliver aid), and recovery (restoring infrastructure and livelihoods). Actions in each phase overlap: mitigation and preparedness done before events reduce the scale of response and length of recovery.

Role of people and institutions Governments, local authorities, NGOs, schools and communities share disaster management responsibilities. Local knowledge and participation improve plans. Simple community measures—keeping drains clear, marking evacuation routes, practising drills—are effective, inexpensive and save lives when a hazard becomes a disaster.

How earthquakes occur Earthquakes are sudden shaking of the ground caused by the release of energy in the Earth's crust. This release happens when stresses build up along faults — fractures in rock — and the rock snaps back into a new position. Most earthquakes in India occur along major plate boundaries or active fault lines such as the Himalaya region where the Indian plate meets the Eurasian plate.

Seismic waves Energy radiates from the focus (the point inside Earth) as seismic waves. The point on the surface above the focus is the epicentre. Seismographs record shaking and help to locate epicentres and measure magnitude. Different waves (P-waves, S-waves, surface waves) arrive at different times and cause different types of ground motion.

Measuring earthquakes Magnitude tells us how much energy was released. The Richter scale is a logarithmic scale once used to show magnitude. Intensity measures effects at a place and varies with distance from the epicentre, ground conditions and building quality. An earthquake can have a small magnitude but high local intensity if buildings are weak or the focus is shallow.

Effects Earthquakes can cause ground rupture, building collapse, fires from gas leaks, landslides in hilly areas and tsunamis if undersea. Impacts depend on time of day, population density, construction standards and preparedness. Poorly built structures face higher damage. Secondary hazards like landslides may block roads and hamper rescue. Water supply and communications are often interrupted, complicating relief.

Safety Drop, cover and hold on is the basic immediate action. After shaking stops, move to open areas away from damaged buildings. Awareness of local safe spots and earthquake drills reduce casualties. Retrofits and building codes, early warning through seismic networks and public education are important long-term measures to reduce losses.

Volcano basics Volcanoes are openings in the Earth's surface where molten rock (magma), ash and gases escape. They form where magma rises through the crust because of plate movements or hotspots. When magma reaches the surface it is called lava. Volcanoes may lie on land or under the sea. Their behaviour varies from gentle lava flows to highly explosive eruptions that send ash and gas high into the atmosphere.

Types of volcanoes There are several types: shield volcanoes have gentle slopes and produce fluid lava flows; stratovolcanoes (composite volcanoes) have steep sides and alternating layers of lava and ash and are prone to explosive eruptions; cinder cones are small and built from fragments of lava. Hotspot volcanoes can form islands in oceans, while subduction-zone volcanoes are common around plate margins.

Hazards from eruptions Direct hazards include lava flows that destroy buildings and vegetation, pyroclastic flows of hot gas and ash that move rapidly and are lethal, and ballistic projectiles. Ash fall can blanket large areas, collapsing roofs, contaminating water supplies and damaging crops. Volcanic gases, such as sulphur dioxide, can harm lungs and produce acid rain. Secondary hazards include lahars—fast-moving volcanic mudflows formed when ash mixes with water—that follow river valleys and can bury communities far from the eruption site.

Monitoring and warnings Volcanologists monitor seismic activity under volcanoes, measure ground deformation using GPS and satellites, and sample gas emissions to detect rising magma. These signs can give days to months of warning before major eruptions. Evacuation plans, exclusion zones and public education reduce casualty numbers when warnings are issued.

Environmental and economic effects Large eruptions can affect climate by injecting ash and sulphur into the stratosphere, reducing sunlight and cooling regions for months. Ash can damage machinery and block water systems, harming agriculture and transport. However, volcanic soils are often very fertile in the long term, so communities sometimes live close to volcanoes despite the risks.

What is a tsunami? A tsunami is a series of long ocean waves caused mainly by sudden underwater earthquakes, submarine landslides or volcanic eruptions. They are not ordinary wind waves; tsunamis have very long wavelengths and can travel across entire ocean basins at high speed, carrying huge amounts of energy.

How they form The most common cause is abrupt vertical movement of the sea floor during an underwater earthquake. This lifts or drops a large volume of water, setting off waves that radiate outward. Submarine landslides and volcanic eruptions can likewise displace water. In deep water tsunami waves have small height but long wavelength; as they approach shallow coastal waters their speed decreases and wave height increases, causing inundation.

Wave behaviour and coastal impact Tsunami waves often arrive as a series; the first may not be the largest. Coastal shape, slope and offshore depth influence wave height: bays and inlets can amplify waves, increasing damage. A tsunami can flood low-lying areas, destroy buildings and roads, erode beaches, and deposit debris and sediment inland. Ports and harbours may be damaged, and fishing communities are especially vulnerable.

Warning and preparedness Tsunami detection uses seismic networks, ocean buoys, tide gauges and modelling to estimate arrival time and wave height. Timely communication through sirens, radio, TV and SMS helps evacuation. Natural signs — strong shaking, sudden sea retreat, or unusual ocean noise — are also important warnings; people should move to higher ground immediately if these occur. Evacuation maps, marked routes and raised shelters reduce casualties significantly.

Mitigation and recovery Coastal protection such as mangrove belts and properly designed seawalls can reduce wave energy. Land-use planning discourages settlements in the most vulnerable zones. After an event, clearing debris, restoring water and sanitation, and rebuilding with safer designs are priorities. Education and regular drills keep communities ready for rare but high-impact tsunami events.

What is a flood? A flood occurs when water overflows onto land that is normally dry. Floods vary widely: slow-onset riverine floods when rivers overflow after sustained rains, flash floods from intense local storms, coastal floods due to storm surge, and urban floods caused by poor drainage and rapid runoff.

Causes Heavy or prolonged rainfall saturates soil and raises river levels; rapid snowmelt can add large water volumes; failure of dams or embankments causes sudden flooding; and human actions make matters worse. Cutting down trees reduces interception and increases runoff. Urbanisation creates impermeable surfaces such as roads and pavements, increasing surface runoff and overloading drainage systems.

Impacts Floods damage homes, crops and infrastructure, cause loss of life, and lead to outbreaks of waterborne diseases. They can displace people and disrupt education and livelihoods. Economic losses include damaged property, lost income for farmers and traders, and expensive repairs to roads, bridges and utilities. Environmental impacts include soil erosion and contamination of water bodies with debris, chemicals or sewage.

Management methods Structural measures include levees, embankments, reservoirs and flood retention basins that reduce flood peaks. Channel improvement and better drainage in towns also help. Non-structural measures are equally important: flood zoning to keep buildings out of high-risk areas, land-use planning that preserves wetlands which absorb floodwaters, and early-warning systems that give people time to move to safety.

Community actions and preparedness Simple household measures — keeping important documents in waterproof bags, having emergency kits, and knowing evacuation routes — reduce personal loss. Local authorities must maintain drains and rivers, clear silt, and enforce building regulations. After floods, providing clean water and sanitation, vector control and quick medical aid prevents disease outbreaks and speeds recovery.

Understanding drought Drought is an extended period of below-normal rainfall leading to water shortage for agriculture, domestic use and industry. It develops slowly and may persist for months or years, making its detection and response different from sudden disasters. Drought affects not only crop yields but also groundwater and surface water supplies.

Types of drought Meteorological drought means less than normal rainfall. Agricultural drought affects soil moisture and plant water stress. Hydrological drought occurs when rivers, reservoirs and groundwater are below normal levels. Socio-economic drought happens when water shortage limits supply for human needs or markets, even if some resources remain.

Causes Natural causes include seasonal changes and large climate patterns such as El Niño which can weaken monsoon rains. Human causes include over-extraction of groundwater, deforestation, poor irrigation practices and changes in land use that reduce the land’s ability to retain water. Climate change may increase the frequency and severity of droughts in some regions.

Effects Drought leads to crop failure, livestock losses and reduced incomes for farmers. It can force migration, increase food prices and strain social services. Environmental consequences include loss of vegetation, soil degradation and increased desertification. Municipal water restrictions and reduced hydroelectric power are other common impacts.

Coping and mitigation Short-term responses include water rationing, food aid and seed distribution. Long-term measures reduce vulnerability: rainwater harvesting, watershed management, recharge of groundwater, use of drought-resistant crops, mulching and improved irrigation like drip systems. Institutional actions include drought monitoring using rainfall and reservoir data, contingency planning, and providing support for alternative livelihoods. Community-based water management and local planning build resilience and reduce the social costs of drought.

What is a cyclone? A cyclone (also called a tropical cyclone, hurricane or typhoon in other regions) is a powerful rotating storm formed over warm ocean waters. It brings very strong winds, heavy rain and a storm surge — a rise in sea level caused by winds pushing water toward the shore. Cyclones form in regions where ocean temperatures are high enough to fuel intense convection.

Formation and structure Warm ocean water heats and moistens the lower atmosphere. Warm, rising air creates low pressure at the surface. As air rises and condenses, it releases latent heat which intensifies the low pressure. The Coriolis force causes the system to rotate, forming the characteristic eye, eye wall and spiral rain bands. The eye is a relatively calm centre surrounded by violent winds in the eye wall.

Hazards to coastal and inland areas The three major hazards are extreme winds, heavy rainfall and storm surge. High winds damage roofs, topple trees and disrupt power lines. Torrential rain causes inland flooding and landslides in nearby hills. Storm surge can inundate low-lying coasts, destroy crops and erode beaches. The combined effect frequently leads to displacement, loss of livelihoods, and infrastructure damage that can take months to repair.

Preparedness and warning Meteorological agencies use satellites, buoys and models to forecast cyclones and issue advisories on landfall location and timing. Effective preparedness requires reliable communication, evacuation plans, designated shelters and stockpiles of relief supplies. Natural barriers like mangrove forests and artificial measures such as properly designed seawalls reduce surge damage. Regular drills, community evacuation maps and securing loose objects in homes lessen the impacts of high winds.

Recovery and long-term measures After a cyclone, priorities include restoring power and water, clearing roads and providing medical care. Long-term measures include rebuilding with cyclone-resistant materials, relocating settlements from the most exposed locations, maintaining coastal vegetation, and integrating cyclone risk into local development plans. Community involvement in planning and maintaining early-warning systems increases their effectiveness and saves lives.

What causes landslides? Landslides are the movement of rock, soil and debris down slopes as a result of gravity. They occur when forces pushing material downslope (such as gravity and added water weight) exceed resisting forces (such as cohesion and friction). Triggers include heavy rainfall that saturates and weakens soils, earthquakes that shake and dislodge slope materials, rapid snowmelt, and human activities such as road cutting, mining and deforestation that disturb slope stability.

Types and behaviour Landslides take several forms. Slides move on a defined slip surface and can be rotational or translational. Flows behave like fluids and travel long distances, often carrying debris and trees. Topples involve forward rotation of a mass of rock or soil, and falls involve free-fall of rock from a cliff. Slope material type (clay, sand, rock), slope angle, vegetation cover and groundwater conditions determine the type and speed of movement.

Impacts on people and infrastructure Landslides can bury homes, cut roads and rail links, rupture pipelines, and dam rivers to create flood risk downstream. In hilly and mountainous regions repeated slope failure reduces available farmland, increases maintenance costs for infrastructure, and can isolate communities. Casualties often occur when landslides happen suddenly during storms or earthquakes, leaving little time for escape.

Risk reduction and mitigation Effective measures include slope stabilisation through engineering works such as retaining walls, rock bolts and proper drainage to remove excess water. Bioengineering — planting deep-rooted vegetation — helps bind soil. Terracing and benching slopes reduce steepness. Avoiding construction on unstable slopes and controlling road cuts are preventive strategies. Early warning systems using rainfall thresholds, ground movement sensors and community observation of warning signs (new cracks, tilted trees, unusual springs) help with timely evacuation.

Community action and planning Local land-use policies should designate high-risk zones where new construction is restricted. Regular maintenance of drains and slope protection structures is essential. Community training on recognising early signs and having evacuation routes reduces casualties. After a slide, safe clearing, restoring drainage and replanting help prevent further failures and begin recovery.

What is an avalanche? An avalanche is the sudden downhill movement of snow, ice and debris on steep mountain slopes. It results when a weak layer within the snowpack fails under the weight of overlying snow or an external trigger. Avalanches are common in high mountain zones with heavy snowfall, wind-deposited snow, and rapid temperature changes that create unstable layers.

Causes and triggers Natural triggers include new heavy snow, rain on snow, rapid warming, and earthquakes. Human triggers come from skiers, climbers, snowmobiles, or construction activities. Wind can redistribute snow and form slabs on leeward slopes; these slabs can sit on weak layers and are prone to sudden failure. Slope angle is critical — most avalanches start on slopes between about 30 and 45 degrees.

Types and effects Loose-snow avalanches begin at a point and fan out, carrying surface snow. Slab avalanches involve cohesive slabs breaking away from a weak layer and are often larger and more destructive. Avalanches can bury people and livestock, damage buildings and roads, and block access routes. Secondary hazards include rapid melting of buried snow causing floods and damaging infrastructure downstream.

Forecasting and mitigation Forecasting uses weather data, snowpack tests and knowledge of wind and temperature trends. Hazard maps identify avalanche paths with start zones, tracks and runout areas to keep infrastructure and buildings out of danger. Mitigation may include snow fences, deflection berms, controlled triggering (explosives) to release unstable snow safely, and afforestation on lower slopes to reduce runout energy. Structural protection such as galleries over roads shields them from avalanches.

Safety and rescue Individuals should carry transceivers, probes and shovels and be trained in companion rescue. In case of burial, rapid location and digging within minutes increases survival chances. Community-level preparedness, avalanche education for visitors and clear signage in mountain areas reduce casualties. Land-use planning avoids placing permanent settlements or critical infrastructure in runout zones.

Types and causes Human-made disasters include industrial accidents, chemical spills, large fires, transportation crashes and technological failures. Causes often combine equipment failure, poor maintenance, human error, inadequate training, lack of safety systems and weak regulation. Urban areas with dense housing and narrow lanes face greater fire risk because firefighting access is limited and houses may be made of flammable materials.

Industrial hazards Industries handling hazardous chemicals, fuels, or gases can cause large-scale accidents. A leak or explosion can release toxic gases or flammable vapours, contaminate air and water, and force mass evacuations. Nuclear or industrial accidents may have long-term environmental and health consequences. Poor storage, overpressure in vessels, corrosion and unsafe handling practices increase accident likelihood.

Fires in settlements Fires spread rapidly in crowded markets and slums with mixed residential and commercial use. Electrical short-circuits, unattended stoves, careless disposal of cigarette butts and illegal wiring are common causes. Fire load (amount of combustible material) and lack of fire exits increase fatalities. Smoke inhalation often causes more deaths than burns.

Prevention and safety systems Prevention requires strong regulations, regular inspection, worker safety training and emergency planning. Industrial sites should have containment bunds, automatic shut-off valves, gas detectors and fire suppression systems. Public buildings require clear exits, fire extinguishers, alarms and routine drills. Transport of hazardous materials must follow route and timing rules to reduce exposure to populated areas.

Response and recovery Rapid containment, evacuation, medical care for burns and poisoning, and environmental cleanup are priorities. Coordination between local fire services, police, medical teams and community volunteers ensures effective action. After an incident, long-term remediation of contaminated land and water, health monitoring and compensation help communities recover. Public awareness campaigns and strict enforcement of safety rules reduce future incidents.

Purpose of hazard mapping Hazard maps identify areas likely to be affected by specific hazards such as floods, earthquakes, landslides or coastal storm surges. These maps are tools for planners, emergency managers and communities to make safer choices about where to build, where to place critical infrastructure and how to plan evacuation routes. They reduce guesswork and make mitigation investments more effective.

Sources of data Creating hazard maps uses historical records of past events, geological and soil surveys, topographic maps, satellite imagery and hydrological data. For example, flood maps consider river height records, rainfall patterns and land slope; landslide maps use slope angle, soil type and land use; seismic hazard maps use fault lines and earthquake histories.

Assessing vulnerability Vulnerability assessment looks at how susceptible people and assets are to harm. Factors include population density, building types and materials, lifelines such as roads and power lines, socio-economic status, and access to health and emergency services. Vulnerability mapping highlights who would be most affected in a given hazard — for example, informal settlements on floodplains or schools in seismic zones.

Combining hazard and vulnerability When hazard maps are layered with vulnerability and exposure data, they produce risk maps that classify areas into low, medium and high risk. These maps guide land-use zoning, insurance schemes, emergency planning and prioritisation of mitigation funds. They also help communities understand local risk and plan evacuation or sheltering accordingly.

Participatory mapping and local use Engaging local people in mapping ensures the maps capture everyday knowledge — locations of previous floods, old landslide scars, or safe high ground. Simple community maps displayed in schools and panchayats with evacuation routes and shelter locations increase preparedness. Regular updating of maps with new development and environmental changes keeps planning relevant and effective.

Purpose of early warning Early warning systems give advance notice of an impending hazard so people can act to reduce harm. Effective systems detect hazards early, forecast impacts, communicate warnings clearly, and enable specific actions by the community. Timeliness, accuracy and public trust are key to saving lives.

Four essential elements A complete system has four parts: risk knowledge (understanding hazards and who is vulnerable), monitoring and forecasting (instruments and models to detect hazards), communication and dissemination (methods to send alerts to people quickly), and preparedness and response capabilities (plans and practised actions by authorities and communities). Failure in any element reduces the system's value.

Technologies used Different hazards need different tools. Seismometers, GPS and accelerometers detect earthquakes; tide gauges, deep-ocean buoys and tsunami models detect and forecast tsunamis; Doppler radars and weather satellites track cyclones and heavy rainfall; river gauges monitor flood levels. These instruments feed data into models that estimate timing and severity, producing advisories for authorities.

Communication channels Warnings are transmitted through many channels: sirens and public address systems, radio and television bulletins, SMS alerts, smartphone apps, social media and community radio. In areas with low connectivity, trained volunteers, loudspeakers and flag systems help spread messages. Messages must be simple, in local languages, and tell people what to do, where to go and how much time they have.

Human factors and testing False alarms and confusing messages reduce public trust. Regular testing, drills and clear standard operating procedures maintain reliability. Education programmes teach communities how to recognise natural warnings (such as sudden sea retreat before a tsunami) and to follow official instructions quickly. Combining scientific technology with local knowledge and community networks makes early warning systems effective even in remote areas.

Why preparedness matters Preparedness at home, school and community reduces panic and saves lives. Quick, simple actions such as knowing safe spots, having emergency supplies and rehearsed evacuation plans make a big difference during disasters. Well-prepared households and institutions reduce the burden on emergency services and speed recovery.

Household plan A household disaster plan lists meeting points, emergency contacts, and the location of utilities like gas shut-off and main water valves. An emergency kit should include drinking water, non-perishable food, torch with spare batteries, first-aid kit, essential medicines, cash, and copies of important documents in a waterproof bag. Families should assign roles, practise drills, and agree on how to reunite if separated. Pets and special needs of elderly or disabled members must be considered.

School safety Schools must have a disaster management plan covering roles for staff, marked evacuation routes, assembly areas and first-aid facilities. Regular drills familiarise students with procedures like Drop, Cover and Hold On for earthquakes, orderly evacuation for fires, or moving to higher ground for floods and tsunamis. Teachers should maintain class lists and emergency contact information for each student.

Community coordination Communities should prepare maps of hazards and safe zones, maintain lists of vulnerable people, and identify volunteers and local resources (boats, tractors, shelters). Local disaster committees coordinate with government agencies for training and supplies. Sharing knowledge across neighbourhoods ensures that vulnerable households receive help during evacuations.

Practical tips Keep important numbers posted, maintain a small emergency fund, have clothes and medicines ready, and store drinking water for a few days. Learn basic first-aid and fire extinguisher use. Simple, low-cost measures and routine practice greatly increase survival and reduce damage when a hazard strikes.

Immediate response goals After a disaster, the first goals are to save lives, meet basic needs and prevent further harm. Rapid needs assessment identifies affected areas, numbers of injured and displaced people, and damage to critical infrastructure such as hospitals, roads and water systems. Accurate assessments guide prioritisation of resources.

Search and rescue Trained teams perform search and rescue to locate and free trapped people after events like earthquakes and landslides. Equipment such as cutting tools, lifting gear, thermal imagers and trained dogs speeds rescue work. Local volunteers often provide the first response, so training and coordination with professional teams improve safety and effectiveness. Clear command and control structures reduce duplication and ensure needs are met where they are greatest.

Relief logistics Relief operations deliver food, water, shelter materials, blankets and medicines. Logistics include warehousing, transport, inventory control and fair distribution. Prioritisation systems ensure the most vulnerable — children, elderly, pregnant women and the injured — receive assistance first. Temporary camps must provide safe sanitation, potable water and health services to prevent disease outbreaks. Coordination between government, armed forces, NGOs and community groups ensures coverage and avoids duplication.

Health and psychosocial care Medical teams treat injuries, manage trauma and provide immunisations where needed. Psychosocial support helps survivors cope with shock and grief; community-based counselling and support groups are important for long-term mental health. Water purification, vector control, and sanitation are essential to prevent epidemics in relief camps.

Transition to recovery Short-term recovery restores essential services: clearing roads, repairing power lines and restoring water supply. Transparent record-keeping, needs-based targeting and community involvement in decision-making improve the fairness and effectiveness of relief. Early planning for reconstruction and ‘build back better’ principles ensures that recovery reduces future vulnerability and strengthens resilience for the affected population.

Recovery stages Recovery shifts from immediate relief to restoring communities and rebuilding infrastructure and livelihoods. Short-term recovery focuses on re-establishing essential services such as water, power and transport, while long-term recovery involves reconstruction of homes, schools and health facilities and revitalising the economy. Effective recovery balances speed with safety and future risk reduction.

Build back better Reconstruction is an opportunity to reduce future risks. Building back better means using improved designs, stronger materials and safer locations to make structures resistant to hazards. Examples include raising homes in flood-prone areas, retrofitting public buildings for earthquakes, and planting coastal vegetation to reduce storm surge effects. Applying updated building codes and enforcing construction standards are essential for resilient reconstruction.

Livelihood restoration Restoring income sources is critical. Support can include providing cash-for-work programs, microcredit for small businesses, replacement of tools and livestock, and distribution of seeds and fertilizer to farmers. Training in alternative livelihoods or value-added activities helps communities adapt where traditional livelihoods remain vulnerable to hazards.

Social and psychological recovery Mental health support, community reconciliation, and re-establishing schools and social services help people regain normalcy. Children’s education continuity and community-based psychosocial support reduce long-term trauma and improve social cohesion. Special attention is needed for the most vulnerable groups, including widows, elderly and persons with disabilities, to ensure inclusive recovery.

Institutional roles and planning Governments, local bodies, NGOs and international agencies co-ordinate recovery. Participatory planning that involves affected people in decisions increases legitimacy and effectiveness. Monitoring and evaluation of reconstruction projects, transparent use of funds, and learning from past events improve future disaster planning. Resilient recovery requires integrating hazard maps, land-use planning and economic strategies so communities are safer and better prepared for future events.