An opening, or rupture, in the surface or crust of a planet that allows the hot magma, ash and gases to escape from beneath the surface is understood as a volcano. The term “volcano” has been derived from the Vulcano island of Sicily, which in turn has been named after the Roman God of fire, Vulcan. Usually, volcanoes are found at locations where the tectonic plates are diverging or converging. In a stark contrast, volcanoes are not generally created where the tectonic plates slide past each other. They can also form at locations where there is stretching and thinning of the crust of the earth. The African Rift Valley, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel volcanoes are the examples of such volcanoes.
What Causes Volcanic Eruptions
About 225 millions years ago, all the continents of the world were joined together into one entity, known as Pangaea, a supercontinent. With the movement in planets, the supercontinent got fragmented into seven plates. This process occurred due to the immense inner heat of the earth, which was able to force the planets apart from each other. According to the data available, the continents are believed to be moving at a rate of 2 cm in a year. Going by this rate, the continents will move 20 meters in a span of 1000 years. While the distance of 20 meters in 1000 years may not seem to be huge right now, but thinking in terms of millions of years, the continents will have moved far apart from each other.
This process is attributed to the rising of hot rock, as it is heated by the core of the earth. The rock spreads in two directions near the surface of the earth. As it goes sideways, it begins to lose heat. The crust of the earth is gradually dragged apart due to this and thereby, the continents are forced to move. Eventually, the rock that has cooled down to a greater degree sinks back down. This forms the basis of all volcanic eruptions, where gases and molten rock, in the form of lava, escapes from an opening in the earth’s surface. The magma pushes itself through the rock, thereby forcing the volcano to erupt. The intensity of the volcanic explosion depends on the thickness of the magma. Since the gases cannot escape easily from beneath the surface of the earth, they continue to accumulate inside till enough heat energy has been generated for an explosion.
Types of Volcanic Eruptions
Hawaiian eruptions are not explosive or destructive. The molten lava that is thrown out is low in gas content and flows down slowly. Sometimes, the volcano may also throw up a fountain of fire.
Strombolian eruptions are more explosive than Hawaiian ones, though they are not dangerous. There are small eruptions at regular intervals, where small amounts of lava are thrown into the air. This is accompanied by booming sounds.
Plinian Eruptions are the most explosive and dangerous eruptions, which can cause enormous destruction. The lava may be thrown out as much as 50 km in the air. The eruption may last for days.