Natural Disasters ppt
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Joined: Sep 2010
27-01-2011, 03:38 PM
naturaldisasters.ppt (Size: 572 KB / Downloads: 536)
What are Natural Disasters?
Cyclone or Hurricane
Forest fire or Bushfire
A volcanic eruption is the spurting out of gases and hot lava from an opening in the Earth’s crust.
Pressure from deep inside the Earth forces ash, gas and molten rock to the surface.
An earthquake is a violent shaking of the ground. Sometimes it is so strong that the ground splits apart.
When parts of the earth, called plates, move against each other giant shock waves move upwards towards the surface causing the earthquake.
Cyclone, Hurricane, Tornado or Typhoon
A Cyclone is a fierce storm with storm winds that spin around it in a giant circle. During a cyclone trees can be uprooted, buildings can be destroyed and cars can be overturned.
An Avalanche is a movement of snow, ice and rock down a mountainside. Avalanches happen very suddenly and can move as fast as a racing car up to 124mph.
Avalanches can be caused by –
snow melting quickly
snow freezing, melting then freezing again
a loud noise or an earth tremor
A flood is caused by an overflow of water which covers the land that is usually dry.
Floods are caused by heavy rain or by snow melting and the rivers burst their banks and overflow.
Costal floods are caused by high tides, a rise in sea level, storm waves or tsunami (earthquakes under the sea).
A drought is the lack of rain for a long time.
In 1968 a drought began in Africa. Children born during this year were five years old before rain fell again.
Forest Fire or Bushfire
Fires can burn out of control in areas of forest or bush land. Fires are caused by lightning, sparks of electricity or careless people. Wind may blow a bushfire to areas where people live.
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Joined: May 2012
18-05-2012, 10:56 AM
This is one of the most in demand topics for seminar and presentations. Natural disasters are occurring everywhere. People should be informed.
Joined: Apr 2012
27-08-2012, 01:20 PM
disasters.ppt (Size: 1.65 MB / Downloads: 163)
In strict meteorological terminology, an
area of low atmospheric pressure surrounded
by a wind system blowing, in the
northern hemisphere, in a counterclockwise direction.
A corresponding high-pressure area with clockwise winds is known as an anticyclone. In the southern hemisphere these wind directions are reversed. Cyclones are commonly called lows and anticyclones highs. The term cyclone has often been more loosely applied to a storm and disturbance attending such pressure systems, particularly the violent tropical hurricane and the typhoon, which center on areas of unusually low pressure.
Hurricane, name applied to migratory tropical cyclones that originate over oceans in certain regions near the equator, and particularly to those arising in the West Indian region, including the Caribbean Sea and the Gulf of Mexico.
Hurricane-type cyclones in the western Pacific are known as typhoons.
Tornado-violently rotating column of air extending from within a thundercloud down to ground level. The strongest tornadoes may sweep houses from their foundations, destroy brick buildings, toss cars and school buses through the air, and even lift railroad cars from their tracks. Tornadoes vary in diameter from tens of meters to nearly 2 km (1 mi), with an average diameter of about 50 m (160 ft). Most tornadoes in the northern hemisphere create winds that blow counterclockwise around a center of extremely low atmospheric pressure. In the southern hemisphere the winds generally blow clockwise. Peak wind speeds can range from near 120 km/h (75 mph) to almost 500 km/h (300 mph). The forward motion of a tornado can range from a near standstill to almost 110 km/h (70 mph).
When it rains or snows, some of the water is retained by the soil, some is absorbed by vegetation, some evaporates, and the remainder, which reaches stream channels, is called runoff.
Floods occur when soil and vegetation cannot absorb all the water; water then runs off the land in quantities that cannot be carried in stream channels or retained in natural ponds and constructed reservoirs.
CONTROL OF FLOODS
The basic methods of flood control have been practiced since ancient times. These methods include reforestation and the construction of levees, dams, reservoirs, and floodways (artificial channels that divert floodwater).
Although dams have been used for many centuries, their primary purposes were to build up water reservoirs for irrigation and other domestic uses and to create power
An effective method of controlling floodwaters is to construct coordinated groups of dams and reservoirs on the headwaters of the streams that lead into the main rivers, so that water can be stored during periods of heavy runoff and released gradually during dry seasons (see Water Supply and Waterworks).
The sudden movement of rocks along a fault causes vibrations that transmit energy through the Earth in the form of waves.
Waves that travel in the rocks below the surface of the Earth are called body waves, and there are two types of body waves: primary, or P, waves, and secondary, or S, waves.
The S waves, also known as shearing waves, move the ground.
Earthquakes cannot be prevented, but the damage they cause can be greatly reduced with communication strategies, proper structural design, emergency preparedness planning, education, and safer building standards.
Engineers minimize earthquake damage to buildings by using flexible, reinforced materials that can withstand shaking in buildings
Since the 1960s, scientists and engineers have greatly improved earthquake-resistant designs for buildings that are compatible with modern architecture and building materials.
In urban areas of the world, the seismic risk is greater in non-reinforced buildings made of brick, stone, or concrete blocks because they cannot resist the horizontal forces produced by large seismic waves.
Fortunately, single-family timber-frame homes built under modern construction codes resist strong earthquake shaking very well.
Such houses have laterally braced frames bolted to their foundations to prevent separation.
Although they may suffer some damage, they are unlikely to collapse because the strength of the strongly jointed timber-frame can easily support the light loads of the roof and the upper stories even in the event of strong vertical and horizontal ground motions.
Joined: Apr 2012
14-09-2012, 11:21 AM
Natural Hazards.ppt (Size: 653.5 KB / Downloads: 226)
Natural Disasters are disasters that occur in this world naturally.
Natural disasters can happen at any location at any time throughout the universe.
Natural disasters can destroy cities, or sometimes a whole country if it is that severe.
They can occur on land, in the water, and with the weather.
The Nature of the Hazard
a. Rapid Onset vs. Slow Onset
At one extreme earthquakes, landslides, and flash floods give virtually no warning. Less extreme are tsunamis, which typically have warning periods of minutes or hours, and hurricanes and floods, where the likelihood of occurrence is known for several hours or days in advance. Volcanoes can erupt suddenly and surprisingly where as hazards such as drought, desertification, and subsidence act slowly over a period of months or years.
b. Controllable Events vs. Immutable Events
For some types of hazards the actual dimensions of the occurrence may be altered if appropriate measures are taken(Eg floods). For others, no known technology can effectively alter the occurrence itself(Eg earthquakes,volcanoes,etc.).
c. Frequency vs. Severity
Some hazards like floods occurs every year or every few years, the hazard becomes part of the landscape, and project and implimentations are sited and designed with this constraint in mind. Unlike tsunami which may strike any time in 50 or 100 years, it is difficult to take up mitigation measure..
d. Mitigation Measures to Withstand Impact vs. Mitigation Measures to Avoid Impact
Earthquake-resistant construction and flood proofing of buildings are examples of measures that can increase the capacity of facilities to withstand the impact of a natural hazard. Measures such as zoning ordinances, insurance, and tax incentives, which direct uses away from hazard-prone areas, lead to impact avoidance
Fundamental Concepts Related To Natural Hazards
Natural process have service functions.
Hazards are predictable.
Linkages exist between hazards and physical and biological environment.
Hazards that previously produced disasters are now producing catastrophes
Risks from hazards can be estimated.
Adverse effects can be minimized.
Kinds Of Floods
Flooding can also be divided into different categories according to their location:
Coastal Floods usually occur along coastal areas. When there are hurricanes and tropical storms which will produce heavy rains, or giant tidal waves created by volcanoes or earthquakes, ocean water may be driven onto the coastal areas and cause coastal floods.
This is the most common type of flooding. When the actual amount of river flow is larger than the amount that the channel can hold, river will overflow its banks and flood the areas alongside the river. And this may cause by reasons like snow melt or heavy spring rain.
In most of the urban area, roads are usually paved. With heavy rain, the large amount of rain water cannot be absorbed into the ground and leads to urban floods.
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. Freshwater floods in particular play an important role in maintaining ecosystems in river corridors and are a key factor in maintaining floodplain biodiversity
Education and Training Activities
Education and training, both formal and informal, prepare people at all levels to participate in hazard management. Universities, research centers, and international development assistance agencies play the leading formal role in preparing individuals to face natural hazards. These activities are also carried out by operational entities such as ministries of agriculture, transportation, public works, and defense.