Natural Disasters

Natural disasters are extreme, sudden events caused by environmental factors that injure people and damage property. The Earth is surrounded by a blanket of air, which we call the atmosphere. The envelope of gas surrounding the Earth changes from the ground up. Four distinct layers have been identified using temperature changes, chemical composition, movement, and density. The hydrosphere is the liquid water component of the Earth. It includes the oceans, seas, lakes,

ponds, rivers and streams. The hydrosphere covers about 70% of the surface of the Earth and is the home for many plants and animals. The biosphere is simply "life on Earth"—the sum total, that is, of all living things on Earth.The lithosphere (geosphere) is the "solid" part of Earth. It has two parts, the crust and the upper mantle. Cyclones are large revolving tropical storms caused by winds blowing around a central area of low atmospheric pressure.

Cyclones develop over warm waters in the tropical regions of the oceans where areas of very low pressure are created by air being heated by the sun. This causes the air to rise very rapidly and becomes saturated with moisture that condenses into large thunderclouds. Cool air rushes in to fill the void and is bent inwards and spirals upwards with a great force of the earth spinning on its axis. The result of all this is - the winds begin to rotate faster and form a large rotating weather system, in some cases up to several thousand km in diameter.Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually some of the magma pushes through vents and fissures in the Earth's surface. A volcanic eruption occurs. Magma that has erupted is called lava.Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly; the rocks catch on each other. The rocks are still pushing against each other, but not moving. After

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a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs.The Richter scale is a mathematical measurement of the intensity of the ground shaking, as measured on a seismograph. It is actually a measurement of the height (amplitude) of the waves produced by the earthquake. The Richter scale is an absolute scale; wherever an earthquake is recorded, it will measure the same on the Richter scale.The Modified Mercalli scales measures how people feel and react to the shaking of an earthquake. It is a relative scale, because people experience different amounts of shaking in different places. It is based on a series of key responses such as people awakening, the movement of furniture, and damage to structures. In general, the further one is from the epicenter of an earthquake, the less shaking is experienced.

There is a significant difference to both of the scales. Richter scale measures with instruments and the measurement will always be the same. However, the Mercalli scale measures how people feel and what will be the reaction to the destruction. The Richter scale is mainly objective as it does not use variables whereas the Mercalli scale is Subjective as it changes and there are many variables to consider.

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