They are also called twisters or cyclones. Even though they are often limited by size, not being more than one kilometer wide at most, they leave vast areas of destruction and death behind them. Tornadoes are characterized by violent winds that swirl in a counter clockwise direction north of the equator and clockwise south of the equator. The speed ofthe wind is the primary cause of deaths and destruction of property. Many people are killed by flying objects and debris. Australia, the Midwestern and Southern US are more prone to have tornadoes. They also occur more frequently in the spring and summer months. Tornadoes usually occur as part of a severe thunderstorm and often come in advance of cold fronts; however, they can also occur ahead ofwarm fronts, and even behind cold fronts.
"Tsunami" is the Japanese word meaning tidal wave. A tidal wave is a large sea wave caused by a submarine earthquake or volcanic explosion. When the ocean floor is tilted or offset during an earthquake, a set of waves is created. These waves are similar to the concentric waves generated by an object dropped into the water.Usually tsunamis move entirely across an ocean to the shore. A tsunami can have wavelengths of 60 to 120 mi and may reach speeds of 800 km/h. Most deaths during a tsunami are a result of drowning. Associated risks include flooding, polluted water supplies, and damaged gas lines.
An earthquake is a shaking of the ground caused by the sudden dislocation of material withinthe earth's outer layer, or crust. When forces pushing on a mass of rock overcome the friction holding the rock in place and blocks of rock slip against each other a earthquake may occur. Some earthquakes are so slight, and some occur in such remote areas, that they are barely felt. Others are so violent that they cause extensive damage.
A Volcano is a vent in the earththrough which hot gases and molten rock rise to the surface. A coneshaped mountain of erupted material around such a vent is also called a volcano. The name is taken from Vulcano, an island north of Sicily in the Mediterranean Sea. Volcano consists of a fissure in the earth's crust, above which a cone of volcanic material has accumulated. At the top of the cone is a bowl-shaped vent called acrater. The cone is formed by the deposition of molten or solid matter that flows or is ejected through the vent from the interior of the earth. In successive eruptions, the solid materials fall around the vent on the slopes of the cone, while lava streams issue from the vent and from fissures on the flanks of the cone. Thus, the cone is built up of layers of fragmental materials and flows of lava, allinclined outward away from the vent. Some enormous, craterlike basins, called calderas, at the top of long-dormant or extinct volcanoes, are eventually occupied by deep lakes.
Lightning is characterized by the discharge of electricity between rain clouds or between a rain cloud and the earth. It is usually seen as an arc of extremely bright light which can be manykilometers in length, however, there are other forms as well. Accompanying the lightning is the giant roar of thunder. The thunder is caused by the expansion of air that has been heated by the lightning which then collides with cooler air, creating the sound of an explosion. Thunderstorms are the most common types of storms, and thunder itself, although frightening, is not dangerous. It is thelightning that causes the problems. Lightning and thunder occur together, however we hear the thunder after we see the lightning. Sound waves travel about one mile in five seconds, while light travels at more than 186,000 miles per second. Therefore, lightning is seen immediately when it occurs, and thunder is heard a little later.
Drought is a period or condition of unusually dry...