A disaster is the tragedy of a natural or human-made hazard (a hazard is a situation which poses a level of threat to life, health, property, or environment) that negatively affects society or environment.

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 with great loss stemming from events such as earthquakes, floods, catastrophic accidents, fires, or explosions.

NATURAL DISASTER- A natural disaster is a 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.

MAN-MADE DISASTER- Disasters caused by human action, negligence, error, or involving the failure of a system are called man-made disasters. Man-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.

Emergency management (or disaster management) is the discipline of dealing with and avoiding risks. It is a discipline that involves preparing for disaster before it occurs, disaster response (e.g. emergency evacuation, quarantine, mass decontamination, etc.), as well as supporting, and rebuilding society   after natural   or human-made disasters have occurred. In general, any Emergency management is the continuous process by which all individuals, groups, and communities manage hazards in an effort to avoid or ameliorate the impact of disasters resulting from the hazards. Actions taken depend in part on perceptions of risk   of those exposed.[2] Effective emergency management relies on thorough integration of emergency plans at all levels of government and non-government involvement. Activities at each level (individual, group, community) affect the other levels. It is common to place the responsibility for governmental emergency management with the institutions for civil defence or within the conventional structure of the emergency services. In the private sector, emergency management is sometimes referred to as business continuity planning.

  

  TYPES OF NATURAL DISASTERS

1. EARTHQUAKES- Caused due to discharge of accumulated force along geologic faults.

2. AVALANCHES- Caused mainly due to release of excess stress on the snow pack of glaciers.

3. TSUNAMIS- Caused when a large volume of a body of water, such as an ocean, is rapidly displaced.

4. FOREST FIRES- Caused mainly due to lightning, volcanic eruption, sparks from rock falls.

5. FLOODS- Caused due to overflow of volume of water from a body of water towards the land.

6. VOLCANOS- Caused by divergent tectonic plates   pulling apart or convergent tectonic plates   coming together.

7. TROPICAL CYCLONES- Caused generally when a great deal of moisture in the atmosphere.

EARTHQUAKES

An Earthquake is a sudden shake of the Earth's crust. The vibrations may vary in magnitude. The earthquake has point of origin underground called the "focus". The point directly above the focus on the surface is called the"epicentre". Earthquakes by themselves rarely kill people or wildlife. It is usually the secondary events that they trigger, such as building collapse, fires, tsunamis and volcanoes, that are actually the human disaster. Earthquakes are caused by the discharge of accumulated force along geologic faults.

Naturally occurring earthquakes

Tectonic earthquakes will occur anywhere within the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. 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.

  Earthquake fault types

There are three main types of fault that may cause an earthquake: normal, reverse (thrust) and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component. Normal faults occur mainly in areas where the crust is being extended   such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other .

Shallow-focus and deep-focus earthquakes

The majority of tectonic earthquakes originate at the ring of fire in depths not exceeding tens of kilometers. Earthquakes occurring at a depth of less than 70 km are classified as 'shallow-focus' earthquakes, while those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes.

Earthquakes and volcanic activity

Earthquakes often occur in volcanic regions and are caused there, both by tectonic faults and the movement of magma in volcanoes. Such earthquakes can serve as an early warning of volcanic eruptions, like during the Mount St. Helens eruption of 1980.

Earthquake clusters

Most earthquakes form part of a sequence, related to each other in terms of location and time.[8] Most earthquake clusters consist of small tremors which cause little to no damage, but there is a theory that earthquakes repeat themselves.

Aftershocks

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the main shock.[8]

Earthquake storms

Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks   but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones.

Size and frequency of occurrence

Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in Guatemala. Chile, Peru, Indonesia, Iran, Pakistan, New Zealand, Greece, Italy, and Japan, but earthquakes can occur almost anywhere, including New York City, London, and Australia. Larger earthquakes occur less frequently, the relationship being exponential. The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past, but this is because of the vast improvement in instrumentation, rather than an increase in the number of earthquakes. The USGS estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0-7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable.Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate. 

Seismology

Seismology is the scientific study of earthquakes   and the propagation of elastic waves   through the Earth. The field also includes studies of earthquake effects, such as tsunamis   as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions).

 Earthquake prediction

Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction. Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give significant warning of impending seismic events.

How to measure and locate an earthquake

Earthquakes can be recorded by seismometers up to great distances, because seismic waves   travel through the whole Earth's interior. The absolute magnitude of a quake is conventionally reported by numbers on the Moment magnitude scale   (formerly Richter scale, magnitude 7 causing serious damage over large areas), whereas the felt magnitude is reported using the modified Mercalli scale (intensity II-XII).Every tremor produces different types of seismic waves which travel through rock with different velocities: the longitudinal P-waves   (shock- or pressure waves), the transverse S-waves   (both body waves) and several surface waves   (Rayleigh   and Love   waves). The differences in travel time   from the epicentre   to the observatory are a measure of the distance and can be used to image both sources of quakes and structures within the Earth. Also the depth of the hypocenter   can be computed roughly.

Effects/impacts of earthquakes

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

Shaking and ground rupture

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.

Landslides and avalanches Landslides are a major geologic hazard because they can happen at any place in the world,

much like earthquakes.

Tsunami Tsunamis are long-wavelength, long-period sea waves produced by a sudden or abrupt

movement of large volumes of water. Tsunamis can also travel thousands of kilometres across open ocean and wreak destruction on far shores hours after the earthquake that generated them.

Fires Following an earthquake, fires   can be generated by break of the electrical power   or gas lines.

Soil liquefaction Soil 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.. This can be a devastating effect of earthquakes.

Floods A flood is an overflow of any amount of water that reaches land. However, floods may be

secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which then collapse and cause floods.

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; this may lead to collapse in future earthquakes.

Preparation  For  Earthquakes

In order to determine the likelihood for future seismic activity, geologists   and other scientists examine the rock of an area to determine if the rock appears to be "strained". Studying the faults   of an area to study the build-up time it takes for the fault to build up stress sufficient for an earthquake also serves as an effective predicition technique. Measurements of the amount of pressure which collocates on the fault line each year, time passed since the last major temblor, and the energy and power of the last earthquake are made.

South Asia earthquakes list

 Date Time Place Lat. Long. Fatalities Comments Magnitude

October 8,2005

03:50:38 UTC, 08:50:38 Local Time October 8

Kashmir   Pakistan   India  see 2005 Kashmir earthquake

34.43°N 73.54°E >80,000 95km (59 miles) NE of Islamabad, Pakistan, 125 km (75 miles) WNW of Srinagar, Kashmir   (pop 894,000)

7.6

December 26, 2004

00:58:53 UTC, 07:58:53 Local Time December 26

off west coast northern Sumatra India   Srilanka Maldives see 2004 Indian Ocean earthquake

3.30°N 95.87°E 283,106 second largest earthquake ever recorded

9.0 to 9.3

Richter magnitude scale

The Richter magnitude scale, also known as the local magnitude (ML) scale, assigns a single number to quantify the amount of seismic energy   released by an earthquake. It is a base-10 logarithmic scale   obtained by calculating the logarithm of the combined horizontal amplitude   of the largest displacement from zero on a Wood–Anderson torsion seismometer output. The effective limit of measurement for local magnitude ML is about 6.8.

             

     

  AVALANCHES

  Avalanche is a rapid flow of snow down a slope, from either natural triggers or human activity. Typically occurring in mountainous terrain, an avalanche can mix air and water with the descending snow. Powerful avalanches have the capability to entrain ice, rocks, trees, and other material on the slope; however avalanches are always initiated in snow, are primarily composed of flowing snow, and are distinct from mudslides, rock slides, rock avalanches, and serac collapses from an icefall. In mountainous terrain avalanches are among the most serious objective hazards to life and property, with their destructive capability resulting from their potential to carry an enormous mass of snow rapidly over large distances.

Avalanches are classified by their morphological characteristics, and are rated by either their destructive potential, or the mass of the downward flowing snow. Some of the morphological characteristics used to classify avalanches include the type of snow involved, the nature of the failure, the sliding surface, the propagation mechanism of the failure, the trigger of the avalanche, the slope angle, direction, and elevation. Avalanche size, mass, and destructive potential are rated on logarithmic magnitude scales, typically made up of 4 to 7 categories, with the precise definition of the categories depending on the observation system or forecast region.

Avalanches only occur when the stress on the snow exceeds the shear, ductile, and tensile strength either within the snow pack or at the contact of the base of the snow pack with the ground or rock surface. A number of the forces acting on a snow pack can be readily determined, for example the weight of the snow is straightforward to calculate, however it is very difficult to know the shear, ductile, and tensile strength within the snow pack or with the ground.The thermo-mechanical properties of the snow crystals in turn depend on the local conditions they have experienced such as temperature and humidity.

Classification and Terminology

All avalanches share common elements: a trigger which causes the avalanche, a start zone from which the avalanche originates, a slide path along which the avalanche flows, a run out where the avalanche comes to rest, and a debris deposit which is the accumulated mass of the avalanched snow once it has come to rest. Additionally slab avalanches have a crown fracture at the top of the start zone, flank fractures on the sides of the start zones, and a shallow staunch fracture at the bottom of the start zone.

The nature of the failure of the snow pack is used to morphologically classify the avalanche.

Loose snow avalanches occur in freshly fallen snow that has a lower density and are most common on steeper terrain. In fresh, loose snow the release is usually at a point and the avalanche then gradually widens down the slope as more snow is entrained, usually forming a teardrop appearance. This is in contrast to a slab avalanche.

Slab avalanches account for around 90% of avalanche-related fatalities, and occur when there is a strong, cohesive layer of snow known as a slab. These are usually formed when falling snow is deposited by the wind on a lee slope.

Wet snow avalanche or isothermal avalanche, which occurs when the snow pack becomes saturated by water.. When the percentage of water is very high they are known as slush flows and they can move on very shallow slopes.

Among the largest and most powerful of avalanches, powder snow avalanches can exceed speeds of 300 km/h, and masses of 10,000,000 tonnes; their flows can travel long distances along flat valley bottoms and even up hill for short distances. A powder snow avalanches is a powder cloud that forms when an avalanche accelerates over an abrupt change in slope, such as a cliff band, causing the snow to mix with air.

 

Terrain

Terrain affects avalanche occurrence and development through three factors:

First, terrain affects the evolution of the snow pack by determining the meteorological exposure of the snow pack.

Second, terrain affects the stability of the snow pack, through the geometry and ground composition of the slope.

Third, the down slope features of the terrain affects the path and consequences of a flowing avalanche.

Snow structure and characteristics

The snow pack is composed of deposition layers of snow that are accumulated over time. The deposition layers are stratified parallel to the ground surface on which the snow falls. Each deposition layer indicates a distinct meteorological condition during which the snow was accumulated. Once deposited a snow layer will continue to evolve and develop under the influence of the meteorological conditions that prevail after deposition.

For an avalanche to occur, it is necessary that a snow pack have a weak layer (or instability) below a slab of cohesive snow. These results in two principal sources of uncertainty in determining snow pack stability based on snow structure:

First, both the factors influencing snow stability and the specific characteristics of the snow pack vary widely within small areas and time scales, resulting in an inability to extrapolate point observations of snow layers. Second, the understanding of the relationship between the readily observable snow pack characteristics and the snow pack's critical mechanical properties has not been completely developed.

Weather

Avalanches can only occur in a standing snow pack. Typically winter seasons and high altitudes have weather that is sufficiently unsettled and cold enough for precipitated snow to accumulate into a snow pack. Among the critical factors controlling snow pack evolution are: heating by the sun, radiational cooling, vertical temperature gradients in standing snow, snowfall amounts, and snow types. Persistent cold temperatures can either prevent the snow from stabilizing or destabilize a snow pack. Cold air temperatures on the snow surface produce a temperature gradient in the snow,

because the ground temperature at the base of the snow pack is close to freezing; in which case the temperature at the base of the snow pack can be significantly below freezing.

Triggers

Avalanches are always caused by an external stress on the snow pack, they are not random or spontaneous events. Natural triggers of avalanches include additional precipitation, radioactive and convective heating, rock fall, ice fall, and other sudden impacts; however, even a snow pack held at a constant temperature, pressure, and humidity will evolve over time and develop stresses, often from the down slope creep of the snow pack. Human triggers of avalanches include skiers, snowmobiles, and controlled explosive work. The triggering stress load can be either localized to the failure point, or remote. Localized triggers of avalanches are typified by point releases from solar heated rocks.

Prevention

There are several ways to prevent avalanches and minimize their power and destruction. They are employed in areas where avalanches pose a significant threat to people, such as ski resorts and mountain towns, roads and railways. Explosive are used extensively to prevent avalanches, especially at ski resorts where other methods are often impractical. Explosive charges are used to trigger small avalanches before enough snow can build up to cause a large avalanche. Snow fences and light walls can be used to direct the placement of snow.

Safety in avalanche terrain

Terrain management - Terrain management involves reducing the exposure of an individual to the risks of travelling in avalanche terrain by carefully selecting what areas of slopes to travel on.

Group management - Group management is the practice of reducing the risk of having a member of a group, or a whole group involved in an avalanche. Most important of all practice good communication with in a group including clearly communicating the decisions about safe locations, escape routes, and slope choices, and having a clear understanding of every members skills in snow travel, avalanche rescue, and route finding.

Risk Factor Awareness - Risk factor awareness in avalanche safety requires gathering and accounting for a wide range of information such as the meteorological history of the area, the current weather and snow conditions, and equally important the social and physical indicators of the group.

Leadership - Leadership in avalanche terrain requires well defined decision making protocols that use the observed risk factors. Fundamental to leadership in avalanche terrain is honestly assessing and estimating the information that was ignored or overlooked.

         

  

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 kilometres, and the wave periods can vary from five minutes to one hour. Such tsunamis travel 600-800 kilometres 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 kilometres across open ocean and wreak destruction on far shores hours after the earthquake that generated them.

Ordinarily, sub duct ion earthquakes under magnitude 7.5 on the Richter scale do not cause tsunamis, although some instances of this have been recorded. Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.

Earthquakes, volcanic eruptions   and other underwater explosions   (detonations of nuclear devices   at sea), landslides   and other mass movements, bolides impacts, and other disturbances above or below water all have the potential to generate a tsunami. Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating.

The Greek   historian Thucydides   was the first to relate tsunami to submarine quakes, but understanding of the nature of tsunami remained slim until the 20th century and is the subject of ongoing research.

Many early geological, geographical, and oceanographic   texts refer to tsunamis as "seismic sea waves."

Terminology

The term tsunami comes from the Japanese, meaning "harbour" (tusk, 津) and "wave"

(name, 波). (For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in the Japanese.) Tsunami are common throughout Japanese history; approximately 195 events in Japan have been recorded

Tsunamis are sometimes referred to as tidal waves. In recent years, this term has fallen out of favour, especially in the scientific community, because tsunami actually have nothing to do with tides. Tsunami and tides both produce waves of water that move inland, but in the case of tsunami the inland movement of water is much greater and lasts for a longer period, giving the impression of an incredibly high tide.

Causes

A tsunami can be generated when convergent   or destructive plate boundaries   abruptly move and vertically displace the overlying water.

Tsunamis have a small amplitude   (wave height) offshore, and a very long wavelength   (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 mm above the normal sea surface...

Tsunami caused by these mechanisms, unlike the trans-oceanic tsunami   caused by some earthquakes, may dissipate quickly and rarely affect coastlines distant from the source due to the small area of sea affected.

Characteristics

While everyday wind waves have a wavelength (from crest to crest) of about 100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in the deep ocean has a wavelength of about 200 kilometres (120 mi). This wave travels at well over 800 kilometres per hour (500 mph), but due to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre (3.3 ft). This makes tsunamis difficult to detect over deep water. As the tsunami approaches the coast and the waters become shallow, the wave is compressed due to wave shoaling   and its forward travel slows below 80 kilometres per hour (50 mph). Its wavelength diminishes to less than 20 kilometres (12 mi) and its amplitude grows enormously, producing a distinctly visible wave.

Signs of an approaching tsunami

There is often no advance warning of an approaching tsunami. However, since earthquakes are often causes of tsunami, any earthquake occurring near a body of water may generate a tsunami if it occurs at shallow depth, is of moderate or high magnitude, and the water volume and depth is sufficient,If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run.

Warnings and prevention

A tsunami cannot be prevented or precisely predicted—even if the right magnitude of an earthquake occurs in the right location. Geologists, oceanographers, and seismologists   analyse each earthquake and based upon many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunami. One of the most important systems that is used and constantly monitored are bottom pressure sensors.

                  

         

WILDFIRES/FOREST FIRES

A wildfire is any uncontrolled fire   that occurs in the countryside or a wilderness   area. Reflecting the type of vegetation or fuel, other names such as brush fire, bushfire, forest fire, grass fire, hill fire, peat fire, vegetation fire, and wild land fire may be used to describe the same phenomenon. A wildfire differs from other fires by its extensive size, the speed at which it can spread out from its original source, and its ability to change direction unexpectedly and to jump gaps, such as roads, rivers and fire breaks. Wildfires are characterized in terms of their physical properties such as speed of propagation; the combustible material present; the effect of weather on the fire; and the cause of ignition.

Wildfires occur on every continent except Antarctica. Fossil records and human history contain accounts of wildfires, which can be cyclical eventsWildfires can cause extensive damage, both to property and human life, but they also have various beneficial effects on wilderness areas. Some plant species depend on the effects of fire for growth and reproduction, although large wildfires may have negative ecological effects.

Distinction from other fires

The name forest fire   was once a synonym for Greek fire   as well as a word for any furious or destructive conflagration. Forest fires differ from other fires in that they take place outdoors in areas of grassland, woodlands, bush land, scrubland, peat land, and other woody materials that act as a source of fuel, or combustible material. Buildings are not usually involved unless the fire spreads to adjacent communities and threaten these structures.

Wildfires have a rapid forward rate of spread (FROS) when fueled by dense uninterrupted vegetation, particularly in wooded areas with canopies.  The ability of a wildfire's burning front to change direction unexpectedly and jump across fire breaks is another identifying characteristic. Intense heat and smoke can lead to disorientation and loss of appreciation of the direction of the fire.

Physical properties

Wildfires occur when the necessary elements of a fire triangle   intersect: an ignition source is brought into contact with a combustible material such as vegetation, that is subjected to sufficient heat and has an adequate supply of oxygen from the ambient air. A high moisture content usually prevents ignition and slows propagation, because higher temperatures are required to evaporate any water within the material and heat the material to its fire point. . Less dense material such as grasses and leaves are easier to ignite because they contain less water than denser material such as branches and trunks. Plants continuously lose water by evapo-transpiration, but water loss is usually balanced by

water absorbed from the soil, humidity, or rain.  When this balance is not maintained, plants dry out

and are therefore more flammable, often a consequence of a long, hot, dry periods.

Fuel type

The spread of wildfires varies based on the flammable material present and its vertical arrangement. Fuel density is governed by topography, as land shape determines factors such as available sunlight and water for plant growth. Overall, fire types can be generally characterized by their fuel: Ground fires are fed by subterranean roots, duff   and other buried organic matter. This fuel type is especially susceptible to ignition due to spotting.

Crawling or surface fires are fueled by low-lying vegetation such as leaf and timber litter, debris, grass, and low-lying shrubbery.

Ladder fires consume material between low-level vegetation and tree canopies, such as small trees, downed logs, and vines. 

Crown, canopy, or aerial fires devour suspended material at the canopy level, such as tall trees, vines, and mosses.

Effect of weather

Heat waves, droughts, cyclical climate changes   such as El Niño, and other weather patterns can also increase the risk and alter the behaviour of wildfires dramatically. Years of precipitation followed by warm periods have encouraged more widespread fires and longer fire seasons.

Fire intensity also increases during daytime hours. Burn rates of smouldering  logs are up to five times greater during the day due to lower humidity, increased temperatures, and increased wind speeds. Sunlight warms the ground during the day and causes air currents to travel uphill, and downhill during the night as the land cools.

Causes

The four major natural causes of wildfire ignitions are lightning, volcanic eruption, sparks from rock falls, and spontaneous combustion. The thousands of coal seam fires   that are burning around the world can also flare up and ignite nearby flammable material such as those in Centralia, Pennsylvania, Burning Mountain, Australia. However, many wildfires are attributed to human sources such as arson, discarded cigarettes, and sparks from equipment and power line arcs   (detected by arc mapping). Forested areas cleared by logging encourage the dominance of flammable grasses, and abandoned logging roads   overgrown by vegetation may act as fire corridors.

Plant adaptations

Some wilderness areas are now considered fire-dependent, especially those in North America. Previous policies of complete suppression   are believed to have upset natural cycles and increased fuel loads and the amount of fire-intolerant vegetation. In the absence of human intervention, certain organisms in these ecosystems   survive through adaptations to fire regimes. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate competition.

Atmospheric effects

Most of the Earth's weather and air pollution reside in the troposphere, the part of the atmosphere that extends from the surface of the planet to a height of between 8 and 13 kilometres Previously, prevailing scientific theory held that most particles in the stratosphere came from volcanoes, but smoke and other wildfire emissions have been detected from the lower stratosphere. With an increase in fire byproducts in the stratosphere, ozone   concentration was three times more likely to exceed health standards.  Wildfires can affect climate and weather and have major impacts on regional and global pollution. Wildfire emissions   contain greenhouse gases and a number of criteria pollutants which can have a substantial impact on human health and welfare.

Human involvement

Wildfires have been mentioned in human history, from minor allusions in the Bible   to classical writers such as Homer, although less focus was placed on uncultivated lands where wildfires occurred.[103][104] Wildfires were also used in battles throughout human history as early thermal weapons. From the Middle ages, accounts were written of occupational burning as well as customs and laws that governed the use of fire. In 14th century Sardinia, firebreaks were used for wildfire protection. In the Atlantic Ocean on the island of Madeira, fire was used to clear the land of Laurisilva   (laurel forest) in 1419.[105] In Spain during the 1550s, sheep husbandry   was discouraged in certain provinces by Phillip II   due to the harmful effects of fires used in transhumance.[103][104] In the countries bordering the Baltic Sea, fire in land use   systems was typical during the Neolithic   period until World War II.[106] As early as the 1600s, Native Americans were observed using fire   for many purposes including cultivation, signalling, and warfare. Scottish botanist David Douglas   noted the native use of fire for tobacco cultivation, to encourage deer into smaller areas for hunting purposes, and to improve foraging for honey and grasshoppers. Wildfires typically occurred during periods of increased temperature and drought. However, human influence caused an increase in fire frequency.  This period was followed by an overall decrease in burning in the 20th century, linked to the expansion of agriculture, increased livestock grazing, and fire prevention efforts.

Prevention

Wildfire prevention refers to the pre-emptive methods of reducing the risk of fires as well as lessening its severity and spread. Effective prevention techniques allow supervising agencies to manage air quality, maintain ecological balances, protect resources, and to limit the effects of future uncontrolled fires. However, prevention policies must consider the role that humans play in wildfires. Wildfire prevention programs around the world may employ techniques such as wild land fire use and prescribed or controlled burns. Wild land fire use refers to any fire of natural causes that is monitored but allowed to burn. Controlled burns are fires ignited by government agencies under less dangerous weather conditions.. Multiple fuel treatments are often needed to influence future fire risks, and wildfire models may be used to predict and compare the benefits of different fuel treatments on future wildfire spread. Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a defensible space   be maintained by clearing flammable materials within a prescribed distance from the edifice.

Detection

Fast and effective detection is a key factor in wildfire fighting. Early detection efforts were focused on early response, accurate day and night time use, the ability to prioritize fire danger, and fire size and location in relation to topography. Aerial and land photography using instant cameras   were used in the 1950s until infrared scanning   was developed for fire detection in the 1960s.Nowdays,Electronic systems have gained popularity in recent years as a possible resolution to human operator error. An integrated approach of multiple systems can be used to merge satellite data, aerial imagery, and personnel position via GPS into a collective whole for near-real time use by wireless Incident

Command Centres Satellite and aerial monitoring can provide a wider view and may be sufficient to monitor very large, low risk areas. These more sophisticated systems employ GPS   and aircraft-mounted infrared or high-resolution visible cameras to identify and target wildfires.

  Suppression

Wildfire suppression may include a variety of tools and technologies, including throwing sand and beating fires with sticks and palm fronds in rural Thailand, using silver iodide   to encourage snow fall in China, and full-scale aerial assaults   by ALTUS II   unmanned aerial vehicles , planes, and helicopters   using drops of water and fire retardants.. Fuel build up can   result in costly, devastating fires as new homes, ranches, and other development are built adjacent to wilderness areas. Continued growth in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism. Smoke is an irritant and attempts to thin out the fuel load is met with opposition due to desirability of forested areas, in addition to other wilderness goals such as endangered species protection and habitat preservation. The ecological benefits of fire is often overridden by the economic benefits of protecting structures and lives. additionally, government policies that cover the wilderness usually differs from local and state policies that govern urban lands.

SOME OF MAJOR FOREST FIRES OF AUSTRALIA:

Black Christmas (bushfires)   2001-2002 Canberra bushfires of 2003 Black Tuesday bushfires   of 2005 (Eyre Peninsula South Australia) Mount Lumbar bushfire   of 2006 Black Saturday bushfires   of 2009, the deadliest bushfire event ever recorded in Australian

history

                     

    

FLOODS

A flood is an overflow or accumulation of an expanse of water that submerges land. 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, which overflows or breaks levees, with the result that some of the water escapes its normal boundaries. Floods can also occur in rivers, when the strength of the river is so high it flows out of the river channel, particularly at bends or meanders and causes damage to homes and businesses along such rivers. That humans continue to inhabit areas threatened by flood damage is evidence that the perceived value of living near the water exceeds the cost of repeated periodic flooding.

Principal types of flood

Riverine floods

Slow kinds: Runoff from sustained rainfall or rapid snow melt exceeding the capacity of a river's channel..

Fast kinds: include flash floods resulting from convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind

a dam, landslide, or glacier. 

  Estuarine floods

Commonly caused by a combination of sea tidal surges caused by storm-force winds. either a tropical cyclone   or an extra tropical cyclone, falls within this category.

Coastal floods

Caused by severe sea storms, or as a result of another hazard (e.g. tsunami   or hurricane).

Catastrophic floods

Caused by a significant and unexpected event e.g. dam   breakage, or as a result of another hazard (e.g. earthquake   or volcanic eruption).

Muddy floods

A muddy flood   is generated by run off on crop land.. Muddy floods are  a hillslope process, and confusion with mudflows produced by mass movements should be avoided.  

Effects

Primary effects

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

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.

Flood control

In many countries across the world, rivers prone to floods are often carefully managed. Defences such as levees,[5]   bunds , reservoirs, and weirs   are used to prevent rivers from bursting their banks. When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used. Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands.

Benefits of flooding

There are many disruptive effects of flooding on human settlements and economic activities. However, floods (in particular the more frequent/smaller floods) can bring many benefits, such as recharging ground water, making soil more fertile and providing nutrients in which it is deficient. Flood waters provide much needed water resources in particular in arid and semi-arid regions where precipitation events can be very unevenly distributed throughout the year. 

Deadliest floods

Below is a list of the deadliest floods worldwide, showing events with death toll:

Death Toll   Event   Location   Date  

2,500,000–3,700,000[18] 1931 China floods China 1931

900,000–2,000,000 1887 Yellow River (Huang He) flood China 1887

500,000–700,000 1938 Yellow River (Huang He) flood China 1938

 

VOLCANO

A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash   and gases to escape from below the surface. The word volcano is derived from the name of Vulcano   island off Sicily   which in turn, was named after Vulcan, the Roman   god of fire.[1]

Volcanoes are generally found where tectonic plates   are diverging   or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by divergent tectonic plate                   pulling apart; the Pacific Ring of Fire   has examples of volcanoes caused by convergent tectonic plates   coming together. These so-called hotspots, for example at Hawaii, can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the solar system, especially on rocky planets and moons.

An Eruption may in itself be a disaster due to the explosion of the volcano or the fall of rock but there are several effects that may happen after an eruption that are also hazardous to human life.

Lava   may be produced during the eruption of a volcano a material consisting of superheated rock. There are several different forms which may be either crumbly or gluey. Leaving the volcano this destroys any buildings and plants it encounters.

Volcanic ash   - generally meaning the cooled ash - may form a cloud, and settle thickly in nearby locations. When mixed with water this forms a concrete like material. In sufficient quantity ash may cause roofs to collapse under its weight but even small quantities will cause ill health if inhaled. Since the ash has the consistency of ground glass it causes abrasion damage to moving parts such as engines.

Supervolcanos   : According to the Toba catastrophe theory   70 to 75 thousand years ago a super volcanic event at Lake Toba reduced the human population to 10,000 or even 1,000 breeding pairs creating a bottleneck in human evolution. It also killed three quarters of all plant life in the northern hemisphere. The main danger from a supervolcano is the immense cloud of ash which has a disastrous global effect on climate and temperature for many years.

Divergent plate boundaries

At the mid-oceanic ridges, two tectonic plates   diverge from one another. New oceanic crust   is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. Most divergent plate boundaries   are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers   or deep sea vents are an example of this kind of volcanic activity.

Convergent plate boundaries

Subduction zones   are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Typical examples for this kind of volcano are Mount Etna   and the volcanoes in the Pacific Ring of Fire.

Hotspots

Hotspots   are not usually located on the ridges of tectonic plates, but above mantle plumes, where the convection   of the Earth's mantle   creates a column of hot material that rises until it reaches the crust, which tends to be thinner than in other areas of the Earth. Because the tectonic plates move whereas the mantle plume remains in the same place, each volcano becomes dormant after a while and a new volcano is then formed as the plate shifts over the hotspot.

Volcanic features

The most common perception of a volcano is of a conical   mountain, spewing lava   and poisonous gases   from a craterat its summit. This describes just one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes   rather than a summit crater, whereas others present landscape   features such as massive plateaus. Vents that issue volcanic material (lava, which is what magma is called once it has escaped to the surface, and ash) and gases (mainly steam and magmatic gases) can be located anywhere on the landform. Many of these vents give rise to smaller cones such as Puʻu   ʻŌʻō   on a flank of Hawaii's Kilauea.

Other types of volcano include cryovolcanoes   (or ice volcanoes), particularly on some moons of Jupiter, Saturn   and Neptune; and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous   volcanoes, except when a mud volcano is actually a vent of an igneous volcano.

Fissure vents

Volcanic fissure vents are flat, linear cracks through which lava   emerges.

Shield volcanoes

Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent, but not generally explode catastrophically. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings.

Lava domes are built by slow eruptions of highly viscous lavas. They are sometimes formed within the crater of a previous volcanic eruption (as inMount Saint Helens), but can also form independently, as in the case of Lassen Peak. Like stratovolcanoes, they can produce violent, explosive eruptions, but their lavas generally do not flow far from the originating vent.

Crypto domes are formed when viscous lava forces its way up and causes a bulge. The 1980 eruption of Mount St. Helens   was an example. Lava was under great pressure and forced a bulge in the mountain, which was unstable and slid down the North side.

Volcanic cones or cinder cones are the result from eruptions that erupt mostly small pieces of scoria   and pyroclastics   that build up around the vent. Cinder cones may form as flank vents   on larger volcanoes, or occur on their own.Parícutin   in Mexico   and Sunset Crater   in Arizona   are examples of cinder cones.

Strato volcanoes (composite volcanoes)

Strato volcanoes or composite volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata   that give rise to the name. Stratovolcanoes are also known as composite volcanoes, created from several structures during different kinds of eruptions. Strato/composite volcanoes are made of cinders, ash and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process begins again. Classic examples include Mt. Fuji   in Japan, Mayon Volcano   in the Philippines, and Mount Vesuviusand Stromboli   in Italy. I

  Super volcanoes

A super volcano is a large volcano that usually has a large caldera   and can potentially produce devastation on an enormous, sometimes continental. They are the most dangerous type of volcano. Examples include Yellowstone Caldera   in Yellowstone National Park   .

Submarine volcanoes are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases. Pillow lava   is a common eruptive product of submarine volcanoes.

Subglacial volcanoes develop underneath icecaps. They are made up of flat lava   which flows at the top of extensive pillow lavas and palagonite. When the icecap melts, the lavas on the top collapse leaving a flat-topped mountain..

Mud volcanoes or mud domes are formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity.

Erupted material

Lava composition Another way of classifying volcanoes is by the composition of material erupted (lava), since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions:

If the erupted magma   contains a high percentage (>63%) of silica, the lava is called Felsic. o Felsic lavas (dacites   or rhyolites) tend to be highly viscous   (not very fluid) and are

erupted as domes or short, stubby flows. Viscous lavas tend to form stratovolcanoes   or lava domes. Lassen Peak   in California   is an example of a volcano formed from felsic lava and is actually a large lava dome.

If the erupted magma contains 52–63% silica, the lava is of Intermediate composition. o Andesitic lava is typically formed at convergent boundary   margins of tectonic

plates, by several processes: Hydration melting of peridotite and fractional crystallization Melting of subducted slab containing sediments Magma mixing between felsic rhyolitic and mafic basaltic magmas in an

intermediate reservoir prior to emplacement or lava flow. o At mid-ocean ridges, where two oceanic plates   are pulling apart, basaltic lava erupts

as pillows   to fill the gap; o Shield volcanoes   (e.g. the Hawaiian Islands, including Mauna Loa   and Kilauea), on

both oceanic   and continental crust

Volcanic activity

Scientific classification of volcanoes

Philippine Institute of Volcanology and Seismology   provides a scientific classification system for volcanoes.[2]

Active - Eruption in historic times - Historical record - 500 years - C14 dating - 10,000 years - Local seismic activity - Oral / folkloric history

Potentially Active - Solfataras / Fumaroles - Geologically young (possibly erupted < 10,000 years and for calderas and large systems - possibly < 25,000 years). - Young-looking geomorphology (thin soil

cover/sparse vegetation; low degree of erosion and dissection; young vent featuresl; +/- vegetation cover). - Suspected seismic activity.

Inactive No record of eruption and its form is beginning to change by the agents of weathering and erosion via formation of deep and long gullies

Popular classification of volcanoes

Active

A popular way of classifying magmatic volcanoes is by their frequency of eruption, with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant, and those that have not erupted in historical times called extinct. There is no real consensus among volcanologists on how to define an "active" volcano. Scientists usually consider a volcano to be erupting or likely to erupt if it is currently erupting, or showing signs of unrest such as unusual earthquake activity or significant new gas emissions.

Extinct

Extinct volcanoes are those that scientists consider unlikely to erupt again, because the volcano no longer has a lava supply. Examples of extinct volcanoes are many volcanoes on the Hawaiian Islands   in the U.S. (extinct because the Hawaii hotspot   is centred near the Big Island), and Paricutin, which is monogenetic.

Dormant

It is difficult to distinguish an extinct volcano from a dormant one. Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless volcanoes may remain dormant for a long period of time, and it is not uncommon for a so-called "extinct" volcano to erupt again.

SOME  LAST DECADE VOLCANOS:

o Avachinsky -Koryaksky, K

amchatka, Russia o Nevado  

Colima, Jalisco   and Colima, Mexico o Mount Etna , Sicily, Italy o Galeras , Nariño, Colombia

o Mauna Loa , Hawaii, USA

o Sakurajima , Kagoshima Prefecture,

Japan o Santamaria/Santiaguito , Guatemala

o Santorini , Cyclades, Greece o Taal Volcano , Luzon, Philippines

o Teide , Canary Islands, Spain

CONSEQUENCES OF   VOLCANIC   ERRUPTIONS

The concentrations of different volcanic gases   can vary considerably from one volcano to the next. Water vapour   is typically the most abundant volcanic gas, followed by carbon dioxide   and sulphur dioxide. Other principal volcanic gases include hydrogen sulphide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, Large, explosive volcanic eruptions inject water vapour (H2O), carbon dioxide (CO2), sulphur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere   to heights of 16–32 kilometres (10–20 mi) above the Earth's surface. The most significant impacts from these

injections come from the conversion of sulphur dioxide to sulphuric (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate   aerosols . The sulfate aerosols also promote complex chemical   reactions on their surfaces that alter chlorine and nitrogen   chemical species in the stratosphere. This effect, together with increased stratospheric chlorine   levels from chlorofluorocarbon   pollution, generates chlorine monoxide (ClO), which destroys ozone   (O3). Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon   for biogeochemical cycles.

 

After completing this assignment, I conclude the topic in following points:

Disasters mainly occur due to hazards and vulnerability.

Hazards and vulnerability result in risks for the human being to suffer the consequences of disasters.

Disasters, whether it be a natural or manmade disasters both are due to unmanaged risks.

Finally, we can avoid manmade disasters by taking necessary precautions; but we can take preventive measures for natural disasters.

  

 

Britannica Encyclopaedia- Natural disasters:

VOLUME NO: 1 VOLUME NO: 2

VOLUME NO: 3

VOLUME NO: 4

VOLUME NO: 5

WIKIPEDIA-NATURAL DISASTERS