Lightning put simply, is a bright flash of electricity, caused during a thunderstorm. Besides thunderstorm, lightning can also be observed during volcanic eruptions, surface nuclear explosions and forest fires. It travels up to a speed of 60,000 meters per second and has the power to kill more people each year than a hurricane or a tornado. Over a hundred people die and over 250 people are injured from lightning each year in the United States. Florida in the US, has the maximum number of lightning strikes each year than any other part of the US. This natural phenomenon which occurs in the form of a luminous zigzag pattern in the sky is something that has interested people for generations. What Causes Lightning? There are several theories stating how lightning is formed, and these theories have generated scores of controversies as well. Scientists have still not succeeded in figuring out this phenomenon completely. However, the polarization mechanism in clouds is the theory which is widely accepted across the globe. Formation of Cumulonimbus Clouds (Thunder Clouds) Water from the lakes, rivers, ponds, oceans and all other water bodies on the surface of the Earth evaporates and rises into the Earth's atmosphere in the form of gas by a process called convection. Water evaporated from the aerial parts of plants by the process of transpiration also rises into the atmosphere. As this warm, evaporated water rises into the atmosphere, it is encountered by cold air, which causes the warm air to rise even more rapidly and form large, dense and tall cumulonimbus clouds (thunder clouds) at a height of 15000-25000 feet above sea level. At such a height some of the water particles in the clouds are converted into ice or snow particles. Electric Charge Formation and Ionization During thunderstorms, what happens is that strong air currents cause the water and ice particles inside the cumulonimbus clouds to collide against each other. Scientists believe that these collisions in the clouds create an electric charge: positive and negative. Further, the positive and negative charges separate from one another, wherein the negative charges move towards the bottom of the cloud and the positive charges dwell in the upper and middle regions of the cloud. The negative charges cause positive charges to develop in the area surrounding the cloud and on the ground below. The electric charges get stronger and make the cloud negatively charged and the surface of the Earth positively charged. The electric charge caused between the Earth and the cloud serves as the perfect platform for the occurrence of lightning. Lightning Formation When the difference in electric charge is large enough, the huge charges inside the cloud ionize the air and make it a good conductor of electricity. The air acts as the bridge between the ground and the cloud and thus a path is formed. Further, a giant spark is generated which causes electricity to flow through the air to another point of opposite charge. This flow of electricity between regions of opposite charges is called a leader stroke and can occur between two clouds (cloud to cloud lightning), from the cloud to the ground (cloud to ground lightning) or from one part of the cloud to another part of the same cloud (in-cloud lightning). Thus, for better understanding, scientists have classified the different types of lightning based on their physical and visual characteristics. Once the connection between the opposite charges are formed and the path is set, the positive charges leap upwards in the path to meet the negatively charged particles, thereby causing the zigzag path of the negative charges to light up. Often people think that lightning comes from the clouds, on the contrary the path of lightning is from the ground to the cloud. This is called the production of a main stroke of lightning. The zigzag pattern of lightning appearing to us is because of the uneven ionization of the air in all directions. All this occurs in less than a millionth of a second. Lightning bolts have temperatures ranging from 30,000 to 50,000° F, which is extremely hot, even hotter than the surface of the Sun. Once the air, the Earth and the cloud have been neutralized by the lightning, it will not strike again. However, at times more than one strike is required for neutralization and this is known as a lightning storm. What Causes Lightning When Volcanoes Erupt? Volcanic eruptions are frequently accompanied by sensational lightning storm displays. The eruption of Mount St. Helens in Washington state in 1980, known for producing one lightning bolt per second has been one of the most studied eruptions till date. However, why is lightning seen during a volcanic eruption? Is volcanic lightning formed in the same manner as lightning during a thunderstorm? Well, once again, volcanologists are not exactly aware as to how lightning generation takes place during volcanic eruption. Thus, the theory most accepted is placed before you here. Lightning takes place when there is a flow of electricity between positive and negative charges. In the case of lightning during thunderstorms, lightning is produced as a result of collision between water particles, however, in case of lightning during volcanic eruptions, collisions between ash and dust particles result in lightning. When a volcano erupts, the volcano comprises hot ash particles, steam and gas. As the volcanic dust particles collide with one another, charge separation takes place by a process called aerodynamic sorting. Separation of positively and negatively charged particles occurs in the volcanic cloud, which causes the cloud to be positively charged at one particular end and negatively charged at the other end. This charge separation goes on increasing until a point when it is beyond resistance and electricity begins to flow between the opposite charges. Thus, lightning display occurs during an eruption. Lightning is not restricted to thunderstorms and can occur independently. This unpredictable nature of lightning is what makes it so dangerous. Nobody knows when, where and with which intensity it will strike. Which is why it is one of nature's wonders that still eludes humans!