NATURAL DISASTERS A natural disaster is the effect of a natural

hazard(e.g flood, tornado, volcanoes, earthquake,landslide,hurricanes,forest

fire,cyclone,famine,tsunamis) that affects the environment, and leads to financial, environmental and/or human losses. The resulting loss depends on the capacity of

the population to support or resist the disaster, and 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.

An Earthquake is a sudden shake of the Earth's crust.The vibrations may vary in magnitude.The magnitude of an earthquake is measured on the

richter scale. The underground point of origin of the earthquake is called the "focus". The point directly above the focus on the surface is called

the"epicentre". Siesmologists are earthquake scientists,measure the strength of an earthquake by estimating the amount of energy released at the focus. Earthquakes by themselves rarely kill people or wildlife. It is usually the secondary events that they trigger, such as building collapse, fires, tsunamis (seismic sea waves) and volcanoes, that are actually the

human disaster. As many of these could be avoided by better construction, safety systems, early warning and evaluation planning.

Seismic waves are detected, recorded and measured by seismographs. Earthquakes are caused by the discharge of accumulated along geologic

faults.

Earthquake DisastersSome of the most significant earthquakes in recent times

include:- The 2004 Indian Ocean earthquake, the second largest

earthquake in recorded history, registering a moment magnitude of 9.3. The huge tsunamis triggered by this earthquake cost the lives of at least 229,000 people.

The 7.6-7.7 2005 Kashmir earthquake, which cost 79,000 lives in Pakistan.

The 7.7 magnitude July 2006 Java earthquake, which also triggered tsunamis.

The 7.9 magnitude May 12, 2008 Sichuan earthquake in Sichuan Province, China. Death toll at over 61,150 as of May 27, 2008

TORNADOTORNADO• Some of the most violent tornadoes develop from

supercell thunderstorms. A supercell thunderstorm is a long-lived thunderstorm possessing within its structure a continuously rotating updraft of air. These storms have the greatest tendency to produce tornadoes, some of the huge wedge shape. The supercell thunderstorm has a low-hanging, rotating layer of cloud known as a “wall cloud.” It looks somewhat like a layer of a layer cake that hangs below the broader cloud base. One side of the wall cloud is often rain-free, while the other is neighbored by dense shafts of rain. The rotating updraft of the supercell is seen on radar as a “mesocyclone.”

• The tornadoes that accompany supercell thunderstorms are more likely to remain in contact with the ground for long periods of time—an hour or more—than other tornadoes, and are more likely to be violent, with winds exceeding 200 mph.

LANDSLiDES A landslide or landslip 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.

CAUSES OF CAUSES OF LANDSLIDESLANDSLIDES

Landslides occur 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 of landslides include:-

groundwater (porewater) pressure acting to destabilize the slope Loss or absence of vertical vegetative structure, soil nutrients,

and soil structure (e.g. after a wildfire) 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 volcanic

eruptions

volcanoesA 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.

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 plates

pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not created where two

tectonic plates slide past one another.

Mount Bromo, East Java, Indonesia. Irazú Volcano, Costa Rica.

HOW VOLCANOES OCCUR?

As the magma chamber fills with the gas-filled magma, pressure builds up. Weight from the solid rock surrounding the area contributes to

the force of this pressure. When the magma pushes its way up to the surface, it breaks or weakens fractures in the surrounding solid rock. As the magma reaches the surface, gas is released and the magma blasts an opening through the earth's surface. The material that is pushed up helps to create the mountain that surrounds a volcano.

Not all the magma or materials that are pushed up the magma chamber are expelled from the opening. Instead of reaching the surface it may escape through channels or remain underground.

FLOODSFLOODSA flood is an overflow of water that

submerges land, producing measurable property damage or forcing evacuation of people and vital resources. Floods develop slowly as rivers swell during an

extended period of rain, or during a warming trend following a heavy

snow. Even a very small stream or dry creek bed can overflow and

create flooding.A flood occurs when water overflows

or inundates land that's normally dry. This can happen in a multitude

of ways. Most common is when rivers or streams overflow their

banks. Excessive rain, a ruptured dam or levee, rapid ice melting in

the mountains, or even an unfortunately placed beaver dam can overwhelm a river and send it spreading over the adjacent land,

called a floodplain. Coastal flooding occurs when a large storm or

tsunami causes the sea to surge inland.

DROUGHTDROUGHT

A A droughtdrought is an extended period of months or is an extended period of months or years when a region notes a deficiency in its years when a region notes a deficiency in its water supply. Generally, this occurs when a water supply. Generally, this occurs when a region receives consistently below average region receives consistently below average

precipitation. It can have a substantial impact precipitation. It can have a substantial impact on the ecosystem and agriculture of the on the ecosystem and agriculture of the affected region. Although droughts can affected region. Although droughts can persist for several years, even a short, persist for several years, even a short,

intense drought can cause significant damage intense drought can cause significant damage and harm the local economy.and harm the local economy.

EFFECTS OF DROUGHTEFFECTS OF DROUGHT Rise in TemperatureRise in Temperature

Droughts may be linked to a rise in temperature which Droughts may be linked to a rise in temperature which may bring insects like locusts and mosquitoes. may bring insects like locusts and mosquitoes.

Hunger and famineHunger and famineIn a drought there may be not enough water to grow In a drought there may be not enough water to grow crops, or enough grass and rich can buy. If there is no crops, or enough grass and rich can buy. If there is no food people go hungry, and grain to feed animals. Food food people go hungry, and grain to feed animals. Food prices will go up and only the if the drought goes for a prices will go up and only the if the drought goes for a long time there may be famine, when people die. long time there may be famine, when people die.

ThirstThirstHumans, animals and plants and trees all need water to Humans, animals and plants and trees all need water to survive. Humans can only live a few days without water. survive. Humans can only live a few days without water.

DiseaseDiseaseIf there is no water for drinking, bathing or even If there is no water for drinking, bathing or even flushing toilets, there can be a wide range of dangerous flushing toilets, there can be a wide range of dangerous diseases. diseases.

Land DegradationLand DegradationIf there is no water the plants holding down the soil will If there is no water the plants holding down the soil will die, and winds can quickly strip the land of topsoil. The die, and winds can quickly strip the land of topsoil. The natural habitat of native animals is damaged and some natural habitat of native animals is damaged and some may not survive. Wetlands and lakes may dry up.may not survive. Wetlands and lakes may dry up.

BushfiresBushfiresWhen there is no water everything dries up, including When there is no water everything dries up, including the forests and bush. Lightning strikes or carelessness the forests and bush. Lightning strikes or carelessness often starts huge bushfires that burn animals, houses often starts huge bushfires that burn animals, houses and property. Humans are also killed in bushfires. and property. Humans are also killed in bushfires.

HURRICANESHURRICANESA hurricane is a powerful, spiraling storm that begins over A hurricane is a powerful, spiraling storm that begins over

a warm sea, near the equator. A storm is classified as a a warm sea, near the equator. A storm is classified as a hurricane when the speed of wind reaches 74 miles (119 hurricane when the speed of wind reaches 74 miles (119

kilometers) per hour. Hurricane storms usually start kilometers) per hour. Hurricane storms usually start over warm sea (near the equator) and are accompanied over warm sea (near the equator) and are accompanied by fierce winds, flash floods, mudslides and huge waves.by fierce winds, flash floods, mudslides and huge waves.

Their source of energy is water vapor which is evaporated Their source of energy is water vapor which is evaporated from the ocean surface. Water vapor is the "fuel" for the from the ocean surface. Water vapor is the "fuel" for the

hurricanes because it releases the "latent heat of hurricanes because it releases the "latent heat of condensation" when it condenses to form clouds and condensation" when it condenses to form clouds and rain, warming the surrounding air. (This heat energy rain, warming the surrounding air. (This heat energy

was absorbed by the water vapor when it was evaporated was absorbed by the water vapor when it was evaporated from the warm ocean surface, cooling the ocean in the from the warm ocean surface, cooling the ocean in the

process.) Usually, the heat released in this way in process.) Usually, the heat released in this way in tropical thunderstorms is carried away by wind shear, tropical thunderstorms is carried away by wind shear, which blows the top off the thunderstorms. But when which blows the top off the thunderstorms. But when

there is little wind shear, this heat can build up, causing there is little wind shear, this heat can build up, causing low pressure to form. The low pressure causes wind to low pressure to form. The low pressure causes wind to

begin to spiral inward toward the center of the low. begin to spiral inward toward the center of the low. These winds help to evaporate even more water vapor These winds help to evaporate even more water vapor from the ocean, spiraling inward toward the center, from the ocean, spiraling inward toward the center,

feeding more showers and thunderstorms, and warming feeding more showers and thunderstorms, and warming the upper atmosphere still more. The showers and the upper atmosphere still more. The showers and

thunderstorms where all of this energy is released are thunderstorms where all of this energy is released are usually organized into bands (sometimes called "rain usually organized into bands (sometimes called "rain

bands" or "feeder bands"), as well as into an "eye wall" bands" or "feeder bands"), as well as into an "eye wall" encircling the center of the storm. The eye wall is where encircling the center of the storm. The eye wall is where the strongest winds occur, which encircle the warmest the strongest winds occur, which encircle the warmest air, in the eye of the hurricane. This warmth in the eye air, in the eye of the hurricane. This warmth in the eye is produced by sinking air, which sinks in response to is produced by sinking air, which sinks in response to rising air in the thunderstorms. The winds diminish rising air in the thunderstorms. The winds diminish rapidly moving from the eye wall to the inside of the rapidly moving from the eye wall to the inside of the relatively cloud-free eye, where calm winds can exist.relatively cloud-free eye, where calm winds can exist.

Famine has afflicted societies since the beginning of history. It may be defined as a persistent failure in food supplies over a

prolonged period. It is something experienced by society, whereas starvation is something that affects individuals.

During famines more people are likely to die of famine related diseases than from starvation. The causes are complex.

Adverse weather conditions (drought, excessive rain, intense cold) at crucial times, effects of war (scorched earth policies,

the provisioning of armies, disruption of trade), pestilence and disease: all these individually or in combination may be

to blame.

TSUNAMITSUNAMIA tsunami is a series of waves generated when a body of A tsunami is a series of waves generated when a body of

water, such as a lake or ocean is rapidly displaced on a water, such as a lake or ocean is rapidly displaced on a massive scale. Earthquakes, landslides, volcanic eruptions massive scale. Earthquakes, landslides, volcanic eruptions

and large meteorite impacts all have the potential to and large meteorite impacts all have the potential to generate a tsunami. The effects of a tsunami can range from generate a tsunami. The effects of a tsunami can range from

unnoticeable to devastating.unnoticeable to devastating.

DISASTER CAUSED BY TSUNAMIS-DISASTER CAUSED BY TSUNAMIS-

• The highest Tsunami was 85m on April 24th, 1771, Japan.The highest Tsunami was 85m on April 24th, 1771, Japan.• The 2004 Indian Ocean Earthquake ranks as the deadliest The 2004 Indian Ocean Earthquake ranks as the deadliest

tsunami in recorded historytsunami in recorded history• In 1964, an Alaskan earthquake generated a tsunami with In 1964, an Alaskan earthquake generated a tsunami with

waves between 10 and 20 feet high along parts of the waves between 10 and 20 feet high along parts of the California, Oregon and Washington coasts.California, Oregon and Washington coasts.

• In 1946, a tsunami with waves of 20 to 32 feet crashed into In 1946, a tsunami with waves of 20 to 32 feet crashed into Hilo, Hawaii, flooding the downtown area.Hilo, Hawaii, flooding the downtown area.

FOREST FIREForest fires are the uncontrolled

destruction of forested lands caused by natural or human-

made wild fire. The probability of a wildfire in any one locality on a particular day depends on fuel conditions, topography, the time of year, wind direction and

speed, the past and present weather conditions, and the

activities (debris burning, land clearing, camping, etc.) that are or will be taking place. Controlled burns are also

conducted because the fire cycle is an important aspect of

management for many ecosystems. These are not

considered hazards unless they were to get out of control.

CYCLONESCyclone, atmospheric pressure distribution in which there

is a low central pressure relative to the surrounding pressure. The resulting pressure gradient, combined

with the Coriolis effect, causes air to circulate about the core of lowest pressure in a counterclockwise direction

in the Northern Hemisphere and in a clockwise direction in the Southern Hemisphere. Near the surface of the

earth, the frictional drag on the air moving over land or water causes it to spiral gradually inward toward lower pressures. This inward movement of air is compensated for by rising currents near the center, which are cooled by expansion when they reach the lower pressures of higher altitudes. The cooling, in turn, greatly increases

the relative humidity of the air, so that "lows" are generally characterized by cloudiness and high

humidity; they are thus often referred to simply as storms.

FORMATION OF FORMATION OF CYCLONESCYCLONES

Cyclones form after the ocean water warms up Cyclones form after the ocean water warms up past 27 deg C (80 deg F). Warm water past 27 deg C (80 deg F). Warm water

evaporates faster than cold water, so the air evaporates faster than cold water, so the air above has high amounts of water vapor. Water above has high amounts of water vapor. Water vapor that condenses to form cloud droplets vapor that condenses to form cloud droplets

gives off heat into the air. This heat is added to gives off heat into the air. This heat is added to the tropical air that is already warm. This the tropical air that is already warm. This

causes a large pulse of heat to rise high into causes a large pulse of heat to rise high into the atmosphere. If surface winds and the atmosphere. If surface winds and

atmospheric winds are traveling in the same atmospheric winds are traveling in the same direction, the warm air is concentrated in one direction, the warm air is concentrated in one

spot, this then forms bands of spiraling spot, this then forms bands of spiraling thunderstorms. As they spin they blow inward thunderstorms. As they spin they blow inward toward the center, rain is very heavy in these toward the center, rain is very heavy in these

bands, but between the bands it is raining bands, but between the bands it is raining lightly or not at all. The most violent band with lightly or not at all. The most violent band with

the heaviest rain is the eyewall, which the heaviest rain is the eyewall, which surrounds the eye or center of the cyclone. The surrounds the eye or center of the cyclone. The

average size of the eye is about 24 km (15 average size of the eye is about 24 km (15 miles) in diameter. All the updrafts of the miles) in diameter. All the updrafts of the

thunderstorms spread out when they hit the thunderstorms spread out when they hit the stratosphere forming a continuous cloud shield stratosphere forming a continuous cloud shield

above the storm. Barometric pressure in the above the storm. Barometric pressure in the middle of the mass drops, causing the wind middle of the mass drops, causing the wind

speed to increase. This wind whips the ocean speed to increase. This wind whips the ocean into a spray, causing even further increase in into a spray, causing even further increase in

evaporation. Within a few days the heat, evaporation. Within a few days the heat, moisture, pressure and wind whip each other moisture, pressure and wind whip each other

into a full blown Cyclone.into a full blown Cyclone.