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Natural disasters A natural disaster is a change of the surface of the earth which has enormous effects on all creatures. These disasters are not caused by humans. When a humans release a disaster it is called "eco-catastrophe". There are several types of natural disasters. Today I want to point out storms, especially Hurricanes, earthquakes and Tsunamis, forest-fire, flood and avalanches. STORMS/HURRICANE First I tell you something about storms and Hurricanes.
A storm is a wind which has a speed of 75 km/h. But when the storm crosses this speed, it is called an Orkan. A storm is called a Hurricane when it crosses the speed of 118 km/h. It is a tropical cyclone. The diameter can be more than 100 kilometres. The Hurricane season runs from June through November.
The points of formation include the Caribbean Sea, the Atlantic Ocean and the Gulf of Mexico. The United States, Mexico, Central America, the Caribbean Islands, Bermuda and Canada are affected by storms in this basin. Hurricanes gather heat and energy through contact with warm ocean water. Evaporation from the seawater increases their power. A Hurricane is a large rotating system of clouds, winds and thunderstorm activity. When the sea surface temperatures are above 26.
5 degrees to at least to a depth of 50 metres a Hurricane can be formed. The steam of the evaporation rises up and big thunderclouds are formed. Hurricanes rotate in a counter-clockwise direction around an eye. It is the middle of the cyclone. Weather in the eye is normally calm and free of clouds. Once a Hurricane hits the shore, the heavy rain, strong winds and heavy waves can damage buildings, trees and cars.
EARTHQUAKES/TSUNAMI Now I want to tell you a little bit about earthquakes and Tsunamis. An earthquake is a sudden and sometimes catastrophic movement or vibration of the Earth's surface that follows a release of energy in the Earth's crust. This energy can be generated by a dislocation within the Earth's crust or by a volcanic eruption. The crust may first bend and then when the stress exceeds the strength of the rocks break and get to a new position. In the process of breaking vibrations are generated. They are called "seismic waves".
These waves travel outward from the source of the earthquake along the surface and through the Earth at different speeds depending on the mate-rial through which they move. A Tsunami is a series of waves generated when water in the sea is rapidly displaced. It can be generated by an displacement of large masses of water, such as an earth-quake, volcanic eruption, landslide and meteorite impact. Large vertical movements of the Earth's crust can occur at plate boundaries. They build up a big wave which is very dangerous for the people at the coast. In 2004 thousands of people died be-cause of a Tsunami in the Indian Ocean.
FOREST-FIRE A next big natural disaster is the forest-fire. At dry and warm places after a long hot period, the chance of a forest fire is very high. When fallen branches, leaves and other material dry out, they become highly flammable. Most fires occur when there is a period of drought and on days of strong winds. Often it is the guilt of an lightning stroke or of an arson. Wildfires cause damage to property, destroying many homes and causing death when they reach cities.
If heavy rains occur after such a fire, land-slides and flash floods are also dangerous. FLOOD Another very dangerous natural disaster is a flood. A flood is an overflow of water from the sea, lake or a river. In many regions, when it rains a lot, the ground's ability to absorb water stops. Floods from the sea may be caused by heavy storm, high tide or a Tsunami. Floods from the river may be caused when heavy rainfall or melting snow causes the river's depth to increase and the river overflows its bank.
The flood covers the land with water. A flood that rises and falls rapidly with no warning is called "flash flood". Hurricanes and earthquakes can also cause floods. Floods are the most frequent type of natural disasters worldwide. The water sub-merges streets and buildings. After being hit by a flood, most houses are uninhabitable.
AVALANCHE The last natural disaster I want to talk about is the avalanche. An avalanche is caused when a build up of snow or rock is released down a slope. It is a great danger in the mountains in winter. A large avalanche can run for miles and can create mas-sive destruction of forest or anything else lies in its way. In the past many people dies because of avalanches. Avalanches are created dependent on the wind, new snow, temperatures before, during and after snowfall, the ground and the snow cover.
The danger raises up, when the slope is very steep. The wind damages the snow crystals and so the snow cover is very unstable. In 1999 12 people were buried and killed by an avalanche, under 100.000 tons of snow.
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