A natural disaster is unforeseen, severe and immediate. Pollution, ozone depletion in the stratosphere and global warming come in this category. The destructive potential of any natural hazard is estimated basically by its spatial extent and severity.
Spatial extent upto which the effect of a disastrous event could be felt may easily be classified into small, medium and large scales.
The phenomenon extending from a few kilometers to a few tens of kilometers are termed as small scale. Growing industrialisation and unjustified exploitation of natural resources have brought our echo system to a verge of non-reversibility and imbalance. This has led to a threat from a set of natural hazards like pollution, global warming and ozone depletion on large or global scale.
The management aspect of disaster may be classified as: The most important is the early warning systems. Unless sufficient advance notice is available, evacuation of the population likely to be affected cannot be undertaken. There are two aspects of early warning system. One is the availability of an effective technique to forecast the disaster with its extent and the other is effective communication of the same to the civil authority responsible for rescue operations.
In some phenomena, such as cyclones, flood, etc. Hence early warning, communication, and rescue operations are possible. But, in a few cases like flash floods, microburst, etc.
On the contrary, in earthquakes no proven methods has yet been evolved to give any prior warning and so post-hazard mitigation is the only alternative.
Role of Communication For a developing country like India, the role of communication in disaster mitigation is extremely critical. These can neither be provided in a short span of time available for mitigation nor are there resources to do so. We have to depend on existing links, many of which completely break down during the disaster. The various types available for dissemination of disaster warning as well as arranging mitigation are: This assumes that the earth stations at the two ends are suitably located to remain unaffected.
Experience has shown that it remains completely unaffected under the severest cyclonic condition. However, the system is limited to one way communication only. The only addition required is the missing link between the nearest earth station to police headquarters. This would be a cost effective and reliable communication system for disaster warning and mitigation. The theory of plate tectonics offers a comprehensive explanation for several geological phenomena — continental drift, mountain building and volcanism, and, of course, earthquake.
According to this theory, when the molten mass that was the earth billions of years ago cooled down, the crust that was formed was not one homogenous piece but broken into about a dozen large plates and several smaller ones with their thickness ranging from 30 km down to the lithosphere at depth of about km or so.
The plates are in incessant motion, with speeds of about 1 cm to 5 cm a year. Where two places converge or collide, a deep trench forms and one plate is deflected downwards into the asthenosphere which lies below the crust and the lithosphere.
When two thick continential plates collide, rocks on the land are relatively light and too buoyant to descend into the asthenosphere. The result is a huge zone of crushing, with rocks and other materials being folded. And this is how the Himalayas have emerged or, in fact, are continuing to emerge.
As the deformation of the plate margins goes on, energy builds up in rocks in the form of elastic strain which continues till it exceeds their elastic limits and the rocks give way. The sudden release of stored elastic energy causes earthquakes. Earthquakes in India are caused by the release of elastic strain energy created and replenished by the stresses from the collision between the Indian plate and the Eurasian plate. The most intense earthquakes occur on the boundaries of the Indian plate to the east, north and west.
In the Indian plate, faults are created when this rubs against the Eurasian plate. When an earthquake occurs along a fault line within the plate, it is called an intra-plate earthquake. The majority of the earthquakes occur along plate boundaries. Earthquakes are also caused by volcanic activity. Construction of large water reservoirs may also cause earthquakes—these are called reservoir-induced earthquakes.
The movement of the plates and occurrence of earthquakes seem to be concentrated in certain areas or zones of the earth. Based on intensity and frequency of occurrence, world map is divided into the following earthquake zones or belts—. These represent the eastern and western margins of the Pacific Ocean respectively.
The occurrence of maximum number of earthquakes in this region is due to four ideal conditions—. Also called the Mediterranean Belt or Alpine-Himalayan Belt, it accounts for about 21 per cent of the total seismic shocks. The epicentres of this region are along the mid-Atlantic Ridge and the islands near the ridge.
This belt represents the zone of moderate and shallow focus earthquakes—the reason for this being the creation of transform faults and fractures because of splitting of plates followed by their movement in the opposite direction. Based on seismic data and different geological and geophysical parameters, the Bureau of Indian Standards BIS had initially divided the country into five seismic zones.
There is thus no part of the country that can be termed earthquake free. Of the five seismic zones, zone V is the most active region and zone I shows least seismic activity. The entire north-eastern region falls in zone V. One of the reasons for this region being prone to earthquake is the presence of the young-fold Himalayan Mountains here which have frequent tectonic movements.
Zone IV which is the next most active region of seismic activity covers Sikkim, Delhi, remaining parts of Jammu and Kashmir, Himachal Pradesh, Bihar, northern parts of Uttar Pradesh and West Bengal, parts of Gujarat and small portions of Maharashtra near the west coast.
The remaining states with lesser known activity fall in zone II. The high seismicity of the Indian subcontinent arises from the tectonic disturbances associated with the northward movement of the Indian plate, which is underthrasting the Eurasian plate. The Himalayan region has been the site for great earthquakes of the world of magnitude greater than 8. The high seismicity region extends from Hindukush in the west to Sadiya in the northeast which further extends down to the Andaman and Nicobar Islands.
Different institutions including the Indian Meteorogical Department and the Indian School of Mines, have after a study of mechanics of several earthquakes in the north- eastern region found that the thrust faulting was generally indicated along with Dawki fault and the Indo-Burma border.
Teiedemann, a member of the Earthquake Engineering Research Institute of the Seismological Society of America, said in that the increased interplay activity near the north-eastern boundary in the Indian plate coupled with thrusting of the Himalayan Burmese sector pointed to the danger of earthquakes in the region. There are three kinds of seismic waves. Waves that move the fastest are called primary, or P, waves.
These waves, like sound waves, travel longitudinally by alternate compression and expansion of the medium, like the movement of the bellows of an accordion. Somewhat slower are the secondary, or S, waves which propagate transversely in the form of snakelike wriggles at right angle to the directions of travel. These cannot travel through liquids or gases. They rise to feet or more and cause damage when they break on habitated coasts. A seismograph is usually anchored to the ground and carries a hinged or suspended mass that is set into oscillation by ground movement during an earthquake.
The instrument can record both horizontal and vertical ground movement in the form of wavy lines on paper or film. From the record, called a seismogram, it is possible to find out how strong the quake was, where it began and how long it lasted. The location of the epicentre of a quake is determined from the time of arrival of the P and S waves at the seismographic station. Since P waves travel at a speed of about 8 km per second and S waves at 5 km per second, it is possible to compute the distance of their origin from the seismic record.
If the distance from three stations are computed, the exact location can be pin pointed. A circle of appropriate radius is drawn around each station.
The epicentre lies where the circles intersect. The magnitude is a measure that depends on the seismic energy radiated by the quake as recorded on seismographs. The intensity, in turn, is a measure that depends on the damage caused by the quake.
It does not have a mathematical basis but is based on observed effects. Devised by the American seismologist, Charles Francis Richter, in , the Richter scale is not a physical device but a logarithmic scale based on recordings of seismographs, instruments which automatically detect and record the intensity, direction and duration of a movement on the ground.
The scale starts at one and has no upper limit. On this scale, the smallest quake felt by humans is about 3. The strongest quake ever recorded had a magnitude of 8. Richter magnitude effects are confined to the vicinity of the epicentre. The Richter scale has been immensely modified and upgraded since it was introduced.
It remains the most widely known and used scale for measuring the magnitude of an earthquake. For measurement of the intensity of an earthquake, the Modified Mercalli Intensity Scale is used. The point Mercalli scale measures the intensity of shaking during an earthquake and is assessed by inspecting the damage and interviewing survivors of the earthquake.
As such, it is extremely subjective. Furthermore, because the intensity of shaking varies from one place to another during an earthquake, different Mercalli ratings can be given for the same earthquake. Unlike the Mercalli scale, the Richter scale measures the magnitude of an earthquake at its epicentre. Aftershocks are earthquakes that often occur during the days and months that follow some larger quake. Aftershocks occur in the same general region as the main shock and are believed to be the result of minor readjustment of stress at place in the fault zones.
Generally, major quakes are followed by a larger number of aftershocks, decreasing in frequency with time. Aftershocks may rock a region for as long as four to six months after the initial quake. However, strong ones last only a few days. Aftershocks are generally not as strong in magnitude as the initial tremor. But a small chance of them being stronger in magnitude cannot be ruled out, in which case the first and aftershocks become known as foreshocks.
Earthquakes occur every day around the world. Each day there are about 1, very small earthquakes measuring 1 to 2 on the Richter scale. Approximately, there is one every 87 seconds. Annually, on an average, there are quakes capable of causing damage with a magnitude of The science of earthquake prediction is at its infancy at present, even though several intensive attempts in this direction have been going on for the last two to three decades in the USA, Russia, Japan, China and India.
In spite of some breakthroughs— the notable example being the prediction of the Haicheng earthquake of China 7.
For, just a year later in , the seismologists could not predict the Tangshan earthquake. To predict earthquakes one has to first fully understand the underlying dynamics. For example, even though it is known that this intense seismic activity is a result of the north-northeastern movement and under thrusting of the Indian plate, it is not known what fraction of the strain energy is being released by earthquakes along the belt.
Aside from such dynamic imputs, an empirical basis of prediction can be founded by recognising, monitoring and interpreting observable and decipherable precursory phenomena. Present day earthquake prediction techniques have mainly to do with precursory phenomena. The parameters that are normally looked at include electrical resistivities, geomagnetic properties, variation in the ratio of compressional to shear wave velocities, etc.
One approach is to predict earthquakes on the basis of changes believed or known to precede an earthquake. Such earthquake precursors include abnormal tilting of ground, change in strain in rock, dilatancy of rocks which could be measured by a change in velocities, ground and water levels, sharp changes in pressure, and unusual lights in the sky. The behaviour of some animals is also believed to undergo a distinct change prior to an earthquake. Some lower creatures are perhaps more sensitive to sound and vibrations than humans; or endowed with what one may call prescience.
Another approach is to estimate the probabilistic occurrence of an earthquake statistically by relating the past occurrences to weather conditions, volcanic activity and tidal forces. There have been some notable Indian efforts too in developing prediction models in the Himalayan-belt context.
One relates to the so- called seismic gaps, which postulates that great earthquakes rupture the Himalayan arc whose total length is about km. Proponents of this model have postulated that the entire Himalayan detachment would rupture in years, the rupture being caused by a 8.
This hypothesis forms the basis for the apprehension of the Tehri dam being subjected to earthquakes of this magnitude. Some scientists have noted that certain cycles of low and high seismicity characterise the Alpide belt. For example, after an extremely active cycle from to , with 14 earthquakes of magnitude greater than 7.
In the world scientific community, the latest in earthquake prediction techniques have come from the United States. One method developed by the Americans involves the use of laser beams. These beams are shot from an observatory to a geostationary satellite in space. On hitting the satellite, the waves are reflected back to the observatory. A substantial difference in the time taken by the laser beams to travel between the two points is an indication of considerable tectonic plate movement, and perhaps an imminent earthquake.
A recent study of Indonesian reefs showed that corals record cyclical environmental events and could predict a massive earthquake in the eastern Indian Ocean within the next 20 years.
Scientists said the earthquake could be similar to the magnitude 9. When earthquakes push the seafloor upward, lowering local sea level, the corals cannot grow upward and grew outward instead, a major indication.
An area off Sumatra that has been the source of disastrous earthquakes, still carries a lot of pent-up pressure that could result in another strong quake, noted the study reported in the journal Nature.
It is not, however, clear as of now whether a precise earthquake prediction and warning system can be developed and put to any effective use. The greatest damage in an earthquake is caused by the destruction of buildings and resultant loss of life and property and destruction of infrastructure. The earthquakes having the same magnitude on the Richter scale may vary in damage from place to place. The extent of damage that an earthquake can cause may depend on more than one factor.
The depth of the focus may be one factor. Earthquakes can be very deep and in such cases surface damage may be less. The extent of damage also depends on how populated and developed an area is. The National Buildings Organisation of India lists weaknesses in burnt brick buildings as follows: Large openings placed too close to the corners. Long rooms having long walls unsupported by cross-walls. Some measures to prevent building collapse during the earthquake are: The last one is the one feature that is most effective in ensuring the integrity of enclosures like a rigid box.
For masonry construction, the BIS has specified that materials to be used should be well-burnt bricks and not sun-dried bricks. The use of arches to span over openings is a source of weakness and should be avoided unless steel ties are provided. Scientists have suggested designing buildings to counter quake movement by shifting the centre of gravity with the help of a steel weight placed on the top of the buildings. In this technique, thick, columns of concrete and steel are inserted metre deep into the soil beneath the regular foundation.
In case of earthquakes, these pillars provide extra strength and prevent the buildings from collapsing. During a quake, the rubber absorbs the shocks. In high-rises, enlarged structures on the top floors should be avoided. Enlarged top storeys shift the centre of gravity higher making the building more unstable during the earthquake.
In cities, many buildings stand on columns. The ground floor is generally used for parking and walls start from the first floor. These buildings collapse quickly during an earthquake. It is associated with fierce wind and heavy rainfall. Horizontally it extends from to km and vertically from the surface to about 14 km. Severe tropical cyclones cause considerable damage to property and agricultural crops.
The principal dangers posed are: Rainfall up to 20 to 30 cm a day is common. The highest ever sustained winds recorded in the case of tropical cyclones are kmph.
Storm surge rise of sea level of four metres are common. The highest sea level elevation in the world due to continued effect of storm surge and astronomical high tide occurred in near Bakerganj, where the sea level rose by about 12 metres above the mean sea level on that occasion. Tropical cyclones over the Bay of Bengal occur in two district seasons, the pre-monsoon months of April-May and the post-monsoon months of October-November.
On an average, in fact, almost half a dozen tropical cyclones form in the Bay of Bengal and the Arabian Sea every year, out of which two or three may be severe. Out of these, the stormiest months are May-June, October and November. Compared to the pre- monsoon season of May, June, when severe storms are rare, the months of October and November are known for severe cyclones. The IMD has published the tracks of the cyclones since and updates them every year in its quarterly scientific journal, Mausam.
As 90 per cent of the deaths in severe cyclones all over the world occur in high storm surges accompanying them, the only feasible method to save the lives of human beings and animals is to evacuate them to safe inland cyclone shelters as early as possible after the receipt of advance cyclone warnings from the IMD.
The evacuation of people is difficult in flat coastal districts as in Bangladesh where the tides of six to 10 metres above the sea level submerges offshore islands and travels inland for considerable distances.
This is a narrow belt at the equator, where the trade winds of the two hemispheres meet. It is a region of high radiation energy which supplies the necessary heat for the vaporisation of sea water into the air. This moist unstable air rises, generates convective clouds and leads to an atmospheric disturbance with a fall in surface atmospheric pressure.
This causes a convergence of surrounding air towards this region of low pressure. The converging mass of air gains a rotary motion because of what is known as the Coriolis force caused by the rotation of the Earth. However, under favourable circumstances, such as high sea-surface temperatures, this low pressure area can get accentuated.
The convective instability builds up into an organised system with high-speed winds circulating around the low pressure interior. The eye has an average radius of 20 to 30 km. It can even be as much as 50 km. Given the existing scientific knowledge about cyclones, it is not yet possible to physically dissipate the buildup of a massive cyclone. Cures are generally worse than the disease.
For example, while seeding by sodium iodide crystals has been attempted in some parts of the world— with marginal success—a more effective prescription proposed sometimes is a nuclear explosion. Obviously, that would be trading one disaster for an even greater one.
Accepted technology, therefore, only provides the capability to detect and track cyclones with sophisticated satellite imagery and ground- based radar systems. With climate change causing increasingly chaotic weather patterns, natural disasters are becoming more common across the world.
A natural disaster is anything ranging from a volcanic eruption to a tropical storm. This is regardless of whether the natural disaster was indirectly caused by mankind, like those caused as a result of global warming. The distance is a major factor in the effects of a natural disaster.
A major forest fire in the wilds of California, as has happened frequently in the late s, impacts a minimal number of people because there are few people who live here. During these fires, large swathes of forest were wiped out. It reduces the chance of another natural disaster in future, but it also sends large numbers of animals away from the area.
This leaves California less naturally diverse and might deter some nature tourists, which impacts the economy. The human cost is the main effect of a natural disaster when it occurs closer to densely populated areas. Mount Vesuvius is the most dangerous volcano in Europe and is the only European mainland volcano to erupt in the last years. The number of deaths impacts society because it wipes part of the population away.
This leaves survivors traumatised and family members impacted emotionally. In the context of a nation, a natural disaster in a populated area could easily cause an economic slump.
Mar 11, · A natural disaster is an event caused by natural destructive factors, which can be further divided into either climatic disasters such as floods and tornados, or geological disasters such as earthquakes, which consequently lead to great physical damage or life loss (Bankoff, , 56).
Natural disasters happen all over the world, and they can be utterly devastating for people’s lives and the environments in which they live.
This essay seeks to provide an overview of insurance specifically on assessment, measurement and management of both man-made risks and natural disaster risks. The essay further highlights the formulas adopted in measuring man-made risks. There have been natural disasters that have occurred in every country on every continent in the world that you could write about for your natural disasters essay. Your summary should sum up all of these disasters and you should then make some personal comments about how we could prevent harm from some of these in the future or even suggest disasters that may have a bigger impact on us in the future.5/5.
A natural disaster is unforeseen, severe and immediate. Pollution, ozone depletion in the stratosphere and global warming come in this category. Natural disasters include cyclones, earthquakes, floods, drought (though these two are now being increasingly considered ‘man- made’ disasters) heat and cold waves, landslides, avalanches, flash floods, severe thunderstorms, hail, low level wind shears, and . Natural Disaster Management (Argumentative Essay Sample) May 16, by admin Essay Samples, Free Essay Samples Facebook 0 Twitter 0 Google+ 0 Viber WhatsApp.