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
Some 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
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 .
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 LANDSLIDES
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
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.
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.
A 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.
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm the local economy.
EFFECTS OF DROUGHT
Rise in Temperature Droughts may be linked to a rise in temperature which may bring insects like locusts and mosquitoes.
Hunger and famine In a drought there may be not enough water to grow crops, or enough grass and rich can buy. If there is no food people go hungry, and grain to feed animals. Food prices will go up and only the if the drought goes for a long time there may be famine, when people die.
Thirst Humans, animals and plants and trees all need water to survive. Humans can only live a few days without water.
Disease If there is no water for drinking, bathing or even flushing toilets, there can be a wide range of dangerous diseases.
Land Degradation If there is no water the plants holding down the soil will die, and winds can quickly strip the land of topsoil. The natural habitat of native animals is damaged and some may not survive. Wetlands and lakes may dry up.
Bushfires When there is no water everything dries up, including the forests and bush. Lightning strikes or carelessness often starts huge bushfires that burn animals, houses and property. Humans are also killed in bushfires.
A hurricane is a powerful, spiraling storm that begins over a warm sea, near the equator. A storm is classified as a hurricane when the speed of wind reaches 74 miles (119 kilometers) per hour. Hurricane storms usually start over warm sea (near the equator) and are accompanied by fierce winds, flash floods, mudslides and huge waves.
Their source of energy is water vapor which is evaporated from the ocean surface. Water vapor is the "fuel" for the hurricanes because it releases the "latent heat of condensation" when it condenses to form clouds and rain, warming the surrounding air. (This heat energy was absorbed by the water vapor when it was evaporated from the warm ocean surface, cooling the ocean in the process.) Usually, the heat released in this way in tropical thunderstorms is carried away by wind shear, which blows the top off the thunderstorms. But when there is little wind shear, this heat can build up, causing low pressure to form. The low pressure causes wind to begin to spiral inward toward the center of the low. These winds help to evaporate even more water vapor from the ocean, spiraling inward toward the center, feeding more showers and thunderstorms, and warming the upper atmosphere still more. The showers and thunderstorms where all of this energy is released are usually organized into bands (sometimes called "rain bands" or "feeder bands"), as well as into an "eye wall" encircling the center of the storm. The eye wall is where the strongest winds occur, which encircle the warmest air, in the eye of the hurricane. This warmth in the eye is produced by sinking air, which sinks in response to rising air in the thunderstorms. The winds diminish rapidly moving from the eye wall to the inside of the 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.
A tsunami is a series of waves generated when a body of water, such as a lake or ocean is rapidly displaced on a massive scale. Earthquakes, landslides, volcanic eruptions and large meteorite impacts all have the potential to generate a tsunami. The effects of a tsunami can range from unnoticeable to devastating.
DISASTER CAUSED BY TSUNAMIS-
The highest Tsunami was 85m on April 24th, 1771, Japan.
The 2004 Indian Ocean Earthquake ranks as the deadliest tsunami in recorded history
In 1964, an Alaskan earthquake generated a tsunami with waves between 10 and 20 feet high along parts of the California, Oregon and Washington coasts.
In 1946, a tsunami with waves of 20 to 32 feet crashed into Hilo, Hawaii, flooding the downtown area.
Forest 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.
Cyclone, 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 CYCLONES
Cyclones form after the ocean water warms up past 27 deg C (80 deg F). Warm water evaporates faster than cold water, so the air above has high amounts of water vapor. Water vapor that condenses to form cloud droplets gives off heat into the air. This heat is added to the tropical air that is already warm. This causes a large pulse of heat to rise high into the atmosphere. If surface winds and atmospheric winds are traveling in the same direction, the warm air is concentrated in one spot, this then forms bands of spiraling thunderstorms. As they spin they blow inward toward the center, rain is very heavy in these bands, but between the bands it is raining lightly or not at all. The most violent band with the heaviest rain is the eyewall, which surrounds the eye or center of the cyclone. The average size of the eye is about 24 km (15 miles) in diameter. All the updrafts of the thunderstorms spread out when they hit the stratosphere forming a continuous cloud shield above the storm. Barometric pressure in the middle of the mass drops, causing the wind speed to increase. This wind whips the ocean into a spray, causing even further increase in evaporation. Within a few days the heat, moisture, pressure and wind whip each other into a full blown Cyclone.