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  • NATURAL DISASTERS

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 therichter 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 ".Siesmologistsare 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 andmeasured byseismographs . Earthquakes are caused by the discharge of accumulated along geologic faults. EARTHQUAKE Earthquake Disasters

  • 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

Tornado TORNADO

  • 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 timean hour or morethan other tornadoes, and are more likely to be violent, with winds exceeding 200mph .

LANDSLiDES

  • Alandslideorlandslipis 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
  • earthquakes adding loads to barely-stable slopes
  • earthquake-caused liquefaction destabilizing slopes volcanic eruptions

volcanoes

  • 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. Iraz Volcano, Costa Rica. HOWVOLCANOES 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.

FLOODS FLOODS

  • 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.

DROUGHT

  • Adroughtis 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.

HURRICANES

  • 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,