Natural Disasters


A disaster is the impact of a natural or human-made hazard that negatively affects society or environment. The root of the word disaster ("bad star" in Greek) comes from an astrological idea that when the stars are in a bad position a bad event will happen.

In contemporary academia, disasters are seen as the consequence of inappropriately managed risk. These risks are the product of hazards and vulnerability. Hazards that strike in areas with low vulnerability are not considered a disaster, as is the case in uninhabited regions.

Developing countries suffer the greatest costs when a disaster hits – more than 95 percent of all deaths caused by disasters occur in developing countries, and losses due to natural disasters are 20 times greater (as a percentage of GDP) in developing countries than in industrialized countries.

A disaster can be defined as any tragic event that involves at least one victim of circumstance, such as an accident, fire, terrorist attack, or explosion.


For more than a century researchers have been studying disasters and for more than forty years disaster research has been institutionalized through the Disaster Research Center. Wisner et al reflect a common opinion when they argue that all disasters can be seen as being human-made, their reasoning being that human actions before the strike of the hazard can prevent it developing into a disaster. All disasters are hence the result of human failure to introduce appropriate disaster management measures. Hazards are routinely divided into natural or human-made, although complex disasters, where there is no single root cause, are more common in developing countries. A specific disaster may spawn a secondary disaster that increases the impact. A classic example is an earthquake that causes a tsunami, resulting in coastal flooding.

(1) Natural Disasters : A natural disaster is the consequence when a natural hazard (e.g., volcanic eruption or earthquake) affects humans. Human vulnerability, caused by the lack of appropriate emergency management, leads to financial, environmental, or human impact. The resulting loss depends on the capacity of the population to support or resist the disaster: their resilience. This understanding is concentrated in the formulation: "disasters occur when hazards meet vulnerability". A natural hazard will hence never result in a natural disaster in areas without vulnerability, e.g., strong earthquakes in uninhabited areas. The term natural has consequently been disputed because the events simply are not hazards or disasters without human involvement

(2) Man-made Disasters : Disasters caused by human action, negligence, error, or involving the failure of a system are called human-made disasters. Human-made disasters are in turn categorized as technological or sociological. Technological disasters are the results of failure of technology, such as engineering failures, transport disasters, or environmental disasters. Sociological disasters have a strong human motive, such as criminal acts, stampedes, riots, and war.


Various natural disasters are :


An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.


Tectonic earthquakes will occur anywhere within the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. In the case of transform or convergent type plate boundaries, which form the largest fault surfaces on earth, they will move past each other smoothly and aseismically only if there are no irregularities or asperities along the boundary that increase the frictional resistance. Most boundaries do have such asperities and this leads to a form of stick-slip behaviour. Once the boundary has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the Elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.


There are many effects of earthquakes including, but not limited to the following:

(1) Shaking and Ground Rapture : Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings or other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation. The ground-shaking is measured by ground acceleration.

Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the seismic motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the deposits.

Ground rupture is a visible breaking and displacement of the earth's surface along the trace of the fault, which may be of the order of few metres in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations and requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.

(2) Landslides and avalanches : Landslides are a major geologic hazard because they can happen at any place in the world, much like earthquakes. Severe storms, earthquakes, volcanic activity, coastal wave attack, and wildfires can all produce slope instability. Landslide danger may be possible even though emergency personnel are attempting rescue.

(3) Fires : Following an earthquake, fires can be generated by break of the electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started. For example, the deaths in the 1906 San Francisco Earthquake were caused more by the fires than by the earthquake itself.

(4) Solid Liquefaction : Solid Liquefaction occurs when, because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, as buildings or bridges, to tilt or sink into the liquefied deposits. This can be a devastating effect of earthquakes. For example, in the 1964 Alaska Earthquake, many buildings were sunk into the ground by soil liquefaction, eventually collapsing upon themselves.

(5) Tsunami : Tsunamis are long-wavelength, long-period sea waves produced by an sudden or abrupt movement of large volumes of water. In the open ocean, the distance between wave crests can surpass 100 kilometers, and the wave periods can vary from five minutes to one hour. Such tsunamis travel 600-800 kilometers per hour, depending on water depth. Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes. Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them.

Ordinarily, subduction earthquakes under magnitude 7.5 on the richter scale do not cause tsunamis. However, there have been recorded instances, yet most destructive tsunamis are caused by magnitude 7.5 plus earthquakes.

Tsunamis are distinct from tidal waves, because in a tsunami, water flows straight in stead of in a circle like the typical wave. Earthquake-triggered landslides into the sea can also cause tsunamis.

(6) Human Impacts : Earthquakes may result in disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse of buildings or destabilization of the base of buildings which may lead to collapse in future earthquakes. Earthquakes can also lead to volcanic eruptions, which cause further damages such as substantial crop damage, like in the "Year Without a Summer" (1816).

Most of civilization agrees that human death is the most significant human impact of earthquakes.


Today, there are ways to protect and prepare possible sites of earthquakes from severe damage, through the following processes: Earthquake engineering, Earthquake preparedness, Household seismic safety, Seismic retrofit (including special fasteners, materials, and techniques), Seismic hazard, Mitigation of seismic motion, and Earthquake prediction.


A flood is an overflow of an expanse of water that submerges land, a deluge. In the sense of "flowing water", the word may also be applied to the inflow of the tide.

Flooding may result from the volume of water within a body of water, such as a river or lake, exceeding the total capacity of its bounds, with the result that some of the water flows or sits outside of the normal perimeter of the body. It can also occur in rivers, when the strength of the river is so high it flows right out of the river channel, particularly at corners or meanders.


There are many causes of flooding including, but not limited to the following :

(1) Tropical Storms : In 1969, a tropical storm caused extensive floods in Virginia. Hurricane Camille had spent most of its initial energy over the Gulf of Mexico. As it neared Virginia, it met a line of large thunderstorms coming down from the north. The warm, moist air carried by Hurricane Camille clashed with the cold northern storms, meeting over the Tye and Rockfish river valleys. Together, the two weather systems caused huge sheets of rainfall.

Camille was an example of one of the most common causes of floods - heavy rains that come with tropical storms. Such storms form over the warm waters of the tropics, so they are full of moisture. When the right conditions form, bringing these giant storms toward land, many inches of rain usually fall. The heavy precipitation is too much for the streams and rivers to handle, causing water to overflow and produce inland floods. Many of these tropical storms form over the Gulf of Mexico.

(2) Seasonal Flooding : According to some scientists, the record floods of 1990 were caused by global warming, the theory that the earth's atmosphere traps heat near the earth, slowly warming the earth. This greenhouse effect may have heated the water in the Gulf of Mexico, causing it to evaporate faster. With more water vapor in the lower atmosphere, small storms escalated into large systems with lots of moisture. These storms moved over the southern United States and released a torrent of rain that led to massive flooding. If the global warming theory is correct, sea levels will rise three to five feet in 60 years. Coastal areas may be partially submerged underwater or easily flooded.

The next winter brought another heavy snowfall. Now that they were prepared for what was to come, residents filled over one million sandbags and placed them on riverbanks to keep them from overflowing in the spring. In May, a heavy thunderstorm hit, starting a new series of floods.

The water swelled the Great Salt Lake, bursting through dikes and flooding wetlands, marshes, roads, parks, and homes. Fortunately, very few people or livestock died because of the warning people had beforehand. The flood had also built slowly, giving people lots of time to prepare.

(3) Coastal Flooding : The earth has seven oceans that cover almost three-fourths of its surface. Naturally, wind and other events caused ocean water to sometimes overflow. When this happens, flooding on the shores occurs. Ocean storms can dump lots of water on a coast, raising the sea level in that area. These are known as storm surges, and cause coastal flooding.

Coastal flooding usually occurs as a result of severe storms, either tropical or winter storms. Ocean waves intensify on the open ocean, and these storms make surface water much choppier and fierce than normal. Raging winds can create huge waves that crash on unprotected beaches.

In the winter of 1978, the northeastern United States coast saw severe flooding that resulted from high winds, high tides, and a storm surge. High winds coincided with unusually high waves. South of Boston, Massachusetts, waves came over a seawall built to protect houses in the region. These wild waves destroyed the houses into rubble. Low-lying towns were also flooded with ocean water and ice.


Primary effects :

· Physical damage- Can range anywhere from bridges, cars, buildings, sewer systems, roadways, canals and any other type of structure.

· Casualties- People and livestock die due to drowning. It can also lead to epidemics and diseases.

Secondary effects :

· Water supplies- Contamination of water. Clean drinking water becomes scarce.

· Diseases- Unhygienic conditions. Spread of water-borne diseases

· Crops and food supplies- Shortage of food crops can be caused due to loss of entire harvest.

· Trees - Non-tolerant species can die from suffocation

Tertiary/long-term effects :

· Economic- Economic hardship, due to: temporary decline in tourism, rebuilding costs, food shortage leading to price increase etc


There are ways to prevent or minimise the damage caused by floods. People can protect their property by insurance. The insurance money will pay for repair and replacement of damaged items. But this doesn't stop a flood from happening, or prevent the damage to property.

People can put sand bags around their houses, and by cracks in doors and conservatories. Windows can also be boarded up to stop water from coming into the house.

(1) Sandbags to protect property : If flood water does get into the house, people can use a pump to remove this water. But this takes a lot of time, and damage can still be done.

People can evacuate their houses, if there is time. They may take precious belongings, pets and essential items such as clothes, food and money. They will have to stay somewhere else during the flood. But damage is still done to the property and has to be dealt with when the owners return.

Governments can spend money to make river banks higher. Soil or concrete can be used to make the river banks higher. This is called a levee. When there is more water in the river, it should stay in the channel as the banks are higher.

(2) Raising banks before a flood :Sometimes a flood wall can be built by the river bank to protect the town from floods. If the river bursts its banks, the water should stay in front of the flood wall. The water will not reach the town as it is trapped between the river bank and the flood wall. Flood walls are usually white.

(3) Dams : Dams are also used to control floods. In times of really heavy rainfall, more holes can be opened to allow more water to flow into the river downstream. The water can be released quickly before it has a chance to build up.

Floodways are artificial river channels which can be built to divert the flow of extra water in rivers. The water then has two channels to flow through in times of heavy rainfall, meaning that the river banks shouldn't burst.

(4) Floodways :Flood barriers can be built across rivers. These are like walls and are similar to dams. They are usually built near the mouth of a river. Flood barriers protect against floods caused by high tides or strong winds. The flood gate is closed to keep the water out of the river. In times of normal water level, the gates are kept open to allow ships to pass through. The Thames Flood Barrier is an example.


A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm the local economy. According to the UN, an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation and climate instability.


Generally, rainfall is related to the amount of water vapour in the atmosphere, combined with the upward forcing of the air mass containing that water vapour. If either of these are reduced,the result is a drought. Factors include:

· Above average prevalence of high pressure systems;

· Winds carrying continental, rather than oceanic air masses (ie. reduced water content);

· Ridges of high pressure areas form with behaviors which prevent or restrict the developing of thunderstorm activity or rainfall over one certain region;

· El Nino, La Nina (and other oceanic and atmospheric temperature cycles) and global warming;

· Deforestation and erosion adversly impacting the ability of the land to capture water;

· Climate change has a substantial impact on agriculture throughout the world, and especially in developing nations


Periods of drought can have significant environmental, agricultural, health, economic and social consequences. Examples include:

· Death of livestock.

· Reduced crop yields.

· Wildfires, such as Australianbushfires, are more common during times of drought.

· Shortages of water for industrial users.

· Dust storms, when drought hits an area suffering from desertification and erosion

· Malnutrition, dehydration and related diseases.

· Famine due to lack of water for irrigation.

· Social unrest.

· Substandard or highly limited crop growth or yield productions.

· Mass migration, resulting in internal displacement and international refugees.

· War over natural resources, including water and food.

· Reduced electricity production due to insufficient available coolant for power stations and reduced water flow through hydroelectricdams.

· Snakes have been known to emerge and snakebites become more common.

· Creates windblown dust bowls which erodes the landscape, damages terrestrial and aquatic wildlife habitat

The effect varies according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food sources. Areas with populations that depend on subsistence farming as a major food source are more vulnerable to drought-triggered famine. Drought is rarely if ever the sole cause of famine; socio-political factors such as extreme widespread poverty play a major role. Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase contamination of remaining water sources.


· Desalination of sea water for irrigation or consumption.

· Drought monitoring - Continuous observation of rainfall levels and comparisons with current usage levels can help prevent man-made drought. For instance, analysis of water usage in Yemen has revealed that their water table (underground water level) is put at grave risk by over-use to fertilize their Khat crop. Careful monitoring of moisture levels can also help predict increased risk for wildfires, using such metrics as the Keetch-Byram Drought Index or Palmer Drought Index.

· Land use - Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependent crops in drier years.

· Rainwater harvesting - Collection and storage of rainwater from roofs or other suitable catchments.

· Recycled water - Former wastewater (sewage) that has been treated and purified for reuse.

· Transvasement - Building canals or redirecting rivers as massive attempts at irrigation in drought-prone areas.

· Water restrictions - Water use may be regulated (particularly outdoors). This may involve regulating the use of sprinklers, hoses or buckets on outdoor plants, the washing of motor vehicles or other outdoor hard surfaces (including roofs and paths), topping up of swimming pools, and also the fitting of water conservation devices inside the home (including shower heads, taps and dual flush toilets).

· Cloud seeding - an artificial technique to induce rainfall.


A landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide to occur, there are other contributing factors affecting the original slope stability. Typically, pre-conditional factors build up specific sub-surface conditions that make the area/slope prone to failure, whereas the actual landslide often requires a trigger before being released.


Landslides are caused when the stability of a slope changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, acting together or alone:

Natural causes:

· groundwater pressure acting to destabilize the slope

· Loss or absence of vertical vegetative structure, soil nutrients, and soil structure.

· erosion of the toe of a slope by rivers or ocean waves

· weakening of a slope through saturation by snowmelt, glaciers melting, or heavy rains

· earthquakes adding loads to barely-stable slopes

· earthquake-caused liquefaction destabilizing slopes (see Hope Slide)

· volcanic eruptions

Human causes:

· vibrations from machinery or traffic

· blasting

· earthwork which alters the shape of a slope, or which imposes new loads on an existing slope

· in shallow soils, the removal of deep-rootedvegetation that binds colluvium to bedrock

· Construction, agricultural, or forestry activities which change the amount of water which infiltrates into the soil.


They may destroy human habitat, block roads, bury buildings , destroy plantations and consequently cause great economic loss.

Landslides can also threaten ‘life line' services such as water, power , telecommunication and transportation network.


Though landslide is a natural process , human activities work as a catalyst for them. Industrialization by cutting forests in the mountains, cutting trees for establishing railway tracks and for making place for human habitat all can cause landslide. So, this must be maintained in hilly regions. Buildings must not be constructed on steep slopes. Strict enforcement of the existing rules must be made.


Most of the world's worst disasters occur in tropical regions, where most of the developing countries are situated. Because of the increasing frequency of disasters, these countries are facing repeated setbacks to progress. Disaster can be a strong aggravating factor. In the differences between wealthy nations and poor nations. Unless disasters can be mitigated and managed to the optimum level, it will continue to have a debating effect in future. The most significant global effort made in recent times to mitigate the effects of disasters was the launching of International Decade for Natural Disaster Reduction by UNO. Its major conference held in Japan, in May, 1994 evolved a plan of action known as Yokahama Strategies. The plan of action was based on the points like disaster reduction, adoption of a policy, efficient use of resources, community participation, broader monitoring, timely assessment, forecast and warning etc.


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  2. We are one of the leading publishers of educational books in the country.

    We specialize in Text books, Guides, Question Banks, Model Specimen Papers and Ten Years Solved Papers for the students appearing for I.C.S.E. and I.S.C. examinations.

    Anyone interested or want to purchase.

    Contact us:

    Oswal Printers & Publishers Pvt. Ltd.
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    Email id:
    Call us: +91-562-2527771-72-73-74