Why Do Volcanoes Erupt in Different Ways

“Why do volcanoes erupt in different ways” is an interesting question. There are seven types of volcanic eruptions. These are the Strombolian, Vulcanian, Vesuvian, Pelean, Hawaiian, Phreatic, and Plinian types. Many of these names come from the names of famous volcanoes that exemplified certain type of eruption. For example, the eruption of Mount Vesuvius in Italy in the year 79 AD has the typical characteristics of all eruptions now called Vesuvian.

Different Types of Eruption

• The most violent type of eruption is the Plinian one. It is explosive and very powerful. It is also very destructive, especially if the volcano is located in or near a place where people live. An example of a Plinian eruption is what took place in 1991 in Mount Pinatubo, Philippines.

• In contrast, Hawaiian eruptions are relatively calm and peaceful. These eruptions look like this: lava is slowly pouring down the volcano’s slopes. There is very little gas or volcanic ash. This activity may go on for years without causing any damage. In fact, in the case of the Hawaiian volcano Mauna Loa, people can watch these peaceful eruptions. It is so safe and very educational that it has become something like a tourist attraction.

• There are other ways of classifying volcanic eruptions. According to some classifications, there are just two types of volcanic eruptions: effusive and explosive. Hawaiian volcanoes are the effusive and gentle types, while Plinian eruptions exemplify very violent and explosive ejections of ashes and pyroclastic materials into the air.

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How Are Volcanoes Formed

• What causes a volcano to erupt gently and harmlessly, or to blow up and cause terrible upheaval and damage to its surroundings? The answer lies in the viscosity of magma under the volcano. Magma is a very hot liquid under the earth’s surface that comes out as lava during a volcanic eruption. If the magma is viscous and thick, the eruption is likely to be explosive. Also, if the temperature of magma is higher, the possibility for an explosive eruption is higher. But if magma has a lower viscosity and crystal content, as well as lower temperatures, the eruption will be less violent and less powerful. The presence of gases also contributes to the intensity of a volcanic eruption. If there are trapped gases that cannot “escape” easily, there may be a very strong and explosive eruption.

• An interesting fact is that one volcano can have various types of eruptions. For example, a volcano known to have a history of very violent pyroclastic eruptions may erupt calmly, too. In the same manner, an effusive or gentle-type volcano may become more explosive in its next eruption. Changes in magma can partly explain the altered quality of these eruptions.


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